Anne-Marie Desaulty
email: am.desaulty@brgm.fr

Petelet-Giraud Emmanuelle

Zinc isotope composition as a tool for tracing sources and fate of metal contaminants in rivers A review

Keywords: Zinc isotopes, metals, contamination, source tracer, catchment

Zinc is a ubiquitous metal, acting both as an essential and a toxic element to organisms depending on its concentration and speciation in solution. Human activities mobilize and spread large quantities of zinc broadly in the environment. Discriminating the natural and various anthropogenic zinc sources in the environment and understanding zinc's fate at a catchment scale are key challenges in preserving the environment. This review presents the state of the art in zinc isotope studies applied to environmental purposes at a river-basin scale. Even though the study of zinc isotopes remains less developed than more "traditional" lead isotopes, we can assess their potential for being a relevant tracer of zinc in the environment. We present the principles of zinc isotope measurements from collecting samples to mass spectrometry analysis. To understand the fate of zinc released in the environment by anthropogenic activities, we summarize the main processes governing zinc distribution between the dissolved and solid phases, with a focus on the isotope fractionation effects that can modify the initial signature of the various zinc sources. The signatures of zinc isotopes are defined for the main natural sources of zinc in the environment: bulk silicate earth (BSE), zinc sulfide ore deposits, and coal signatures. Rivers draining natural environments define the "geological background for surface water", which is close to the BSE value. We present the main anthropogenic sources (metallurgical waste, effluents, fertilizers, etc.) with their respective isotope signatures and the main processes leading to these specific isotope characteristics. We discuss the impact of the various anthropogenic zinc

Introduction

Zinc (Zn) is ubiquitous, being present in soils, plants and biota, acting both as an essential and a toxic element to organisms depending on its concentration and speciation in solution (e.g. [START_REF] Campbell | Interactions between trace metals and aquatic organisms: a critique of the free-ion activity model[END_REF][START_REF] Whitton | Toxicity of heavy metals to freshwater algae: a review[END_REF]. For instance, zinc depletion produces nutrient limitation in the sea, whereas excess zinc can cause a range of reproductive, developmental, behavioral, and toxic responses in a variety of aquatic organisms and insects (e.g. [START_REF] Muyssen | Mechanisms of chronic waterborne Zn toxicity in Daphnia magna[END_REF][START_REF] Schmidt | Critical tissue residue approach linking accumulated metals in aquatic insects to population and community-level effects[END_REF]. Concerning human health, a surplus of zinc is associated with oxidative stress and is a contributing factor in many chronic diseases (e.g. [START_REF] Walsh | Zinc: Health effects and research priorities for the 1990s[END_REF]. Many human activities make and mobilize widespread large quantities of zinc in the environment. Industries and wastewater treatment plants expel their zinc-rich liquid effluents directly into rivers. Emissions from metal processing (mining and smelting) are a major source of zinc in the atmosphere and soil [START_REF] Nriagu | Quantitative assessment of worldwide contamination of air, water and soils by trace metals[END_REF]. Coating steel by "hot dip" galvanization or zinc electroplating (also called "electrogalvanization") is a common use of zinc, and zinc in these products may be easily released into the environment through corrosion. Other sources of zinc contamination include the disposal of fertilizers and crop protection treatments in cultivated areas [START_REF] Eriksson | Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops[END_REF]. Zinc is also transferred to the atmosphere and soil through coal combustion and waste incineration [START_REF] Abanades | Fate of heavy metals during municipal solid waste incineration[END_REF][START_REF] Xu | Status of trace element emission in a coal combustion process: A review[END_REF]. Non-combustion traffic emissions relative to vehicles (tires and brakes) and road furniture (galvanized parts and railings) also spread this metal into the environment [START_REF] Councell | Tire-wear particles as a source of zinc to the environment[END_REF][START_REF] Legret | Evaluation of pollutant loadings in the runoff waters from a major rural highway[END_REF][START_REF] Zarcinas | Copper, lead and zinc mobility and bioavailability in a river sediment contaminated with paint stripping residue[END_REF]. These various zinc contributions, deposited in the environment in particulate form or in larger deposits, are leached by rainfall, forming water runoff with high Zn concentrations. These releases then join rivers, polluting riverbed sediments and the water itself. River basins play a key role in the water cycle, capturing and storing enormous quantities of water, which ultimately supply a large part of the available freshwater on Earth. Thus, controlling Zn concentrations in surface water is a major environmental and public health issue.

The European Union (EU) Water Framework Directive (2000/60/EC) aims to deliver integrated river basin management for the whole of Europe. The member states of the EU are required to prepare a list of specific pollutants and their environmental quality standards (EQS) in the aquatic environment for evaluating the ecological status of water. Metal zinc, regulated by 22 EU member states, is the river basin-specific pollutant most often monitored in the EU [START_REF] Arle | Monitoring of Surface Waters in Germany under the Water Framework Directive-A Review of Approaches[END_REF]. The predicted no-effect concentration (PNEC) from the EU Risk Assessment Reports varies depending on the water hardness, with the lowest EQS at 7.8 µg/L [START_REF] Kos Durjava | Water Framework Directive and Specific Pollutants in Surface Waters in Slovenia[END_REF]. In France, an acceptable ecological status for a water body is reached, without a hardness condition, when the bioaccessible zinc content is below 7.8 µg/L (Statute of 27 July 2015, https://substances.ineris.fr/fr/page/9). In the USA, the water quality criterion recommended by the United States Environmental Protection Agency, below which significant risks to the majority of species in a given environment are not expected, is 66.6 µg/L at a hardness of 50 mg/L (United States Environmental Protection Agency, 1996). For good management of water bodies, defining numerical limits for zinc in the environment below which unacceptable effects are not expected is not enough. Indeed, the multiplicity of pollution sources, the presence of variable "naturally" occurring background concentrations, the existence of a number of chemical species with various toxicity, and how the abundance of those species changes in response to changes of the water's physical and chemical conditions must be considered.

Within the last twenty years, developments in mass spectrometry (TIMS, thermal ionization mass spectrometry and MC-ICP-MS, multicollector-inductively coupled plasma-mass spectrometry) have allowed the high-precision measurement of isotope compositions of transition metals and post-transition metals such as zinc (e.g. [START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF][START_REF] Schoenberg | An assessment of the accuracy of stable Fe isotope ratio measurements on samples with organic and inorganic matrices by highresolution multicollector ICP-MS[END_REF][START_REF] Schönbächler | High precision Ag isotope measurements in geologic materials by multiple-collector ICPMS: An evaluation of dry versus wet plasma[END_REF]. Zinc has five stable isotopes, 64 Zn, 66 Zn, 67 Zn, 68 Zn, and 70 Zn, with natural abundances of 49.2, 27.8, 4.0, 18.4, and 0.6% respectively. Since the pioneering work of [START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF], the application of Zn isotope biogeochemistry has rapidly expanded, and Zn isotope compositions have been used in various domains and already discussed in review papers [START_REF] Albarède | The stable isotope geochemistry of copper and zinc[END_REF][START_REF] Cloquet | Variation in the isotopic composition of zinc in the natural environment and the use of zinc isotopes in biogeosciences: A review[END_REF][START_REF] Moynier | The Isotope Geochemistry of Zinc and Copper[END_REF][START_REF] Yin | Application of Zn isotopes in environmental impact assessment of Zn-Pb metallurgical industries: A mini review[END_REF]. This review is specifically dedicated to the use of Zn isotopes as tracers to determine the sources of anthropogenic pollution and how they were transported into rivers. This review compiles and discusses currently available data from these previous studies, together with unpublished data from the Loire River Basin (France). From this compilation we have evaluated the ability of Zn isotope compositions to trace metal sources at the catchment scale, in both dissolved and solid phases.

Materials and methods

The mass of zinc typically required for mass spectrometry analysis (at least 4 replicates) is 1 µg (e.g. Chen et al., 2009a;[START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF]. Several steps (i.e. collection, preparation and measurement) are necessary to acquire the isotope composition of natural sample. Because metals are everywhere in field and laboratory equipment, costly and timeconsuming procedures are required to minimize zinc contaminations during these steps. All reagents are prepared with 18.2 MΩ.cm (at 25 °C) water and commercial acid purified in laboratory by sub-boiling distillation (e.g. Araújo et al., 2017a;[START_REF] Bermin | The determination of the isotopic composition of Cu and Zn in seawater[END_REF]. All materials, including PFA vessels, pipette tips, columns, and bottles, are previously cleaned in a laboratory with nitric and/or hydrochloric acid and then rinsed thoroughly with 18.2 MΩ.cm water prior to use (e.g. [START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Bryan | Zinc isotope fractionation during adsorption onto Mn oxyhydroxide at low and high ionic strength[END_REF]. According to previous studies [START_REF] Bryan | Zinc isotope fractionation during adsorption onto Mn oxyhydroxide at low and high ionic strength[END_REF][START_REF] Nelson | Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces[END_REF], polyvinyl gloves, which are commonly manufactured using zinc stearate as a mold release compound, must not be used when handling samples and hardware. Total procedural blanks (from field to mass spectrometry analysis) must be regularly measured to verify the cleaning procedure. Procedural blanks are generally lower than 10 ng, which represented less than 1% of the mass of zinc analyzed (e.g. Chen et al., 2009a;[START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF].

Sampling requirements for zinc isotope analyses in water and sediments

We have seen that all materials used in the field to collect samples must be previously cleaned in the laboratory. To determine Zn isotope compositions in solution in liquid samples (surface water, effluent, etc.) the sample volume taken in the field varies between a few tens of milliliters to several liters according to the concentration of the medium. Samples are taken using plastic containers, then generally filtered at 0.20 µm or 0.45 µm and placed in plastic bottles rinsed several times with water filtered from the sample (e.g. [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Borrok | Isotopic variations of dissolved copper and zinc in stream waters affected by historical mining[END_REF][START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Szynkiewicz | Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF]. Water samples are preserved with sub-boiled concentrated nitric or hydrochloric acid to a pH of approximately 2 (e.g. [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Chen | Zn isotope compositions of the thermal spring waters of La Soufrière volcano, Guadeloupe island[END_REF].

Recently, passive diffusive gradients in thin film samplers (DGT samplers) have been also used successfully for Zn isotope measurements in surface water (Desaulty et al., 2017;Desaulty and Millot, 2017). DGT can pre-concentrate metals in situ and provide an isotope composition of water integrated over time.

For solid samples, the quantity of materials sampled is not governed by the concentration of solid metals (generally a few hundred mg/kg), which is high compared with the quantity necessary for isotope analysis (1 µg of Zn), but usually considers the need for representative samples. Stream sediments are sampled from the middle of water courses with sampling media (shovels, augers, etc.) not containing zinc and not coated with painted surfaces that contain metal-based pigments [START_REF] Bullen | Stable isotopes of transition and post-transition metals as tracers in environmental studies[END_REF]. The sediment cores are generally taken using acrylic tubes (Araújo et al., 2017a;[START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF]. To obtain the required mass of suspended particulate matter (SPM) for isotope and chemical analyses (>50 mg) a large volume of water is collected (often more than 1 L) and then filtered or centrifuged to recover all SPM (Araújo et al., 2017b;Chen et al., 2009b;[START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF].

Chemical separation and analysis of zinc isotopes

Prior to isotope analyses, preparation (e.g. solid dissolution) and chemical purification are necessary to separate zinc from coexisting matrix elements. Sample preparation takes place in a cleanroom under positive pressure of filtered air, under a laminar airflow, allowing all phases of sample preparation to be performed under clean conditions (e.g. [START_REF] Borrok | Isotopic variations of dissolved copper and zinc in stream waters affected by historical mining[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF]. The chemical purification is generally performed with anionexchange chromatography in concentrated HCl on macro-porous, pre-cleaned resin (AG-MP1, BioRad®) (e.g. [START_REF] Borrok | Separation of copper, iron, and zinc from complex aqueous solutions for isotopic measurement[END_REF][START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF].

While Zn isotope compositions were initially measured by TIMS (Thermal-ionization mass spectrometry) [START_REF] Rosman | A survey of the isotopic and elemental abundance of zinc[END_REF], it is high-precision measurement by MC-ICP-MS [START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF]) that led to the rapid expansion of Zn isotopes into a variety of environmental applications. Several methods are used for correcting isotope discrimination in the instrument during analysis. Zn isotope data can be acquired by MC-ICP-MS, either by standard-sample bracketing or by the double-spike method. Standard-sample bracketing involves analyzing a standard solution directly before and after a sample. This method is often associated with external normalization, which consists, prior to the analysis, of adding to the sample another element having an atomic mass close to that of the element of interest. Zinc data are generally externally normalized to copper (Cu) using an exponential mass-fractionation law (Archer and Vance, 2004;[START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF]. Standard-sample bracketing needs complete recovery of the element during chemical preparation to avoid mass discrimination leading to analysis that would not be representative of the bulk sample. In the double-spike method, before chemical preparation, a mixture of two isotopes of the element (generally 64 Zn-67 Zn) with a non-natural isotopic composition are added (Arnold et al., 2010a;[START_REF] Bermin | The determination of the isotopic composition of Cu and Zn in seawater[END_REF]. The advantage of using a double-spike method is that the complete recovery of the element during chemical preparation is not necessary. Moreover, since the mass bias is corrected using an isotope ratio of the analyte element, this method is little affected by matrixinduced mass bias effects. The double-spike method is particularly well adapted for samples that only contain small amounts of zinc (a few µg/L) in a matrix with much higher concentrations of other elements such as seawater and biological materials (e.g. [START_REF] Arnold | Iron and zinc isotope fractionation during uptake and translocation in rice (Oryza sativa) grown in oxic and anoxic soils[END_REF][START_REF] Zhao | Biogeochemical cycling of zinc and its isotopes in the Southern Ocean[END_REF]. In spite of the advantages of the double-spike method, due to its straightforward approach the standard-sample bracketing method is still in widespread use in recent MC-ICP-MS Zn isotope studies (e.g. [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF][START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF].

Zn isotope compositions are reported as a classical δ-notation (parts per thousand, ‰) with the 66 Zn/ 64 Zn ratio relative to zinc standard:

After the standard used in the original work by [START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF] i.e. JMC 3-0749C (usually called JMC-Lyon) a number of different reference standards have been developed and used in a routine manner in different laboratories (SRM NIST 683, IMC 12053, PCIGR-1, IRMM-3702, Imperial) (e.g. [START_REF] Moeller | Calibration of the New Certified Reference Materials ERM-AE633 and ERM-AE647 for Copper and IRMM-3702 for Zinc Isotope Amount Ratio Determinations[END_REF][START_REF] Yang | Calibrating NIST SRM 683 as a new international reference standard for Zn isotopes[END_REF]. Despite JMC-Lyon having not been available for many years, data are generally normalized to this standard. All data presented in this review were recalculated referring to JMC-Lyon for easy comparison.

The precision of Zn isotopic measurements depends on the quality of the chemical preparation (total procedural blanks relative to content in sample, quantitative recovery of the element) and on the operating parameters and corrections applied during MC-ICP-MS measures. In recent studies, typical analytical precision for δ 66/64 Zn measurements verified by repeated runs of samples and standards is generally around ± 0.05‰ (2σ) for environmental samples regardless of the method used to correct the instrumental bias (e.g. [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF][START_REF] Vance | The behaviour of Cu and Zn isotopes during soil development: Controls on the dissolved load of rivers[END_REF] .

Additional data from the Loire River Basin

The corpus of samples coming from the Loire River Basin was composed of liquid and solid samples described in supplementary Tables S1,S2, and S3. Liquid effluents coming from various industries and wastewater treatment plants (WWTP) that are usually directly discharged into the Loire river were analyzed (Table S1). Other samples containing high Zn contents were also analyzed (organic fertilizers and brake pads) (Table S1). Pig slurry and manure samples were sampled in Brittany and Pays de la Loire (France) and brake pad linings commercially available in France were purchased (Valeo®). Dissolved loads were sampled from the Loire River Basin in an upstream/downstream transect, as well as the Furan River draining various sulfide mineralizations (Table S2). SPM was collected in the Loire River before the estuary (Montjean-sur-Loire) (Table S3). SPM and sediments were collected in the watershed mainly occupied by intensive farming (Argos, Vilaine, Couesnon) (AELB, 2013) (Table S3). The sampling and analysis protocols were in line with these described above (sections 2.1. and 2.2.) and detailed in supplementary materials.

Impact of natural physical and chemical processes on zinc isotope compositions

Various processes control metal distribution between the dissolved and particulate phases in surface water. The main mechanisms causing a new Zn isotope distribution between the phases (i.e. isotope fractionation) are equilibrium isotope distribution between dissolved aqueous species and equilibrium and kinetic effects due to the interactions between minerals or live organisms and aqueous solutions (adsorption, precipitation, uptake, etc.). The goal of this article is not to make an exhaustive study of the fractionation that affects Zn isotope compositions in the environment, but to highlight the main processes that govern zinc distribution between dissolved and particulate phases and to evaluate how they affect the initial δ 66/64 Zn signatures of anthropogenic zinc sources. Isotope fractionation between zinc bound, fixed or adsorbed on a solid organic or inorganic phase and zinc in solution is defined as follows:

∆ 66/64 Znsolid-dissolved=δ 66/64 Znsolid-δ 66/64 Zndissolved Laboratory experimental studies investigated the mechanisms that potentially fractionate Zn isotopes [START_REF] Fernandez | Fractionation of Cu, Fe, and Zn isotopes during the oxidative weathering of sulfide-rich rocks[END_REF][START_REF] Guinoiseau | Zn isotope fractionation during sorption onto kaolinite[END_REF][START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF].

These various mechanisms (adsorption, dissolution, precipitation etc.) and their impact on isotope signatures as described in the literature are summarized in Fig. 1. These experiments can be also coupled with X-ray absorption spectroscopy, which provides the metal's local structural information (i.e., coordination number, bond distance) allowing to make the link between changes in crystal-chemical parameters and the isotope fractionations. This technique is mainly used to study the chemical environment of zinc during adsorption onto several minerals [START_REF] Gou | Zinc Isotope Fractionation during Sorption onto Al Oxides: Atomic Level Understanding from EXAFS[END_REF][START_REF] Juillot | Zn isotopic fractionation caused by sorption on goethite and 2-Lines ferrihydrite[END_REF][START_REF] Nelson | Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces[END_REF].

Several theoretical studies used ab initio and density functional methods to determine equilibrium stable isotope partitioning between various zinc species by calculating their reduced partition function ratios (RPFR or β). The fractionation between two species A and B is then defined as the ratio of their β-factors α 66/64 A-B=β 66/64 A/β 66/64 B and a simple relation allows the comparison of these theoretical equilibrium isotopic fractionations and δ 66/64 Zn values, which are commonly reported on natural samples: 10 3 ln α 66/64 A-B ~ ∆ 66/64 ZnA-B = δ 66/64 ZnA-δ 66/64 ZnB By calculating β-factors we identify some of the crystal-chemical parameters controlling isotopic properties. In particular, the proprieties of bonds between zinc and its neighbors is an important crystal-chemical parameter controlling isotopic fractionation between phases.

General theoretical considerations suggest that the lower coordination states and bond lengths should prefer the heavy isotope [START_REF] Schauble | Applying stable isotope fractionation theory to new systems[END_REF]. Equilibrium stable isotope partitioning between aqueous zinc complexes including aqueous sulfate, chloride, and carbonate species are determined by previous studies [START_REF] Black | Calculation of equilibrium stable isotope partition function ratios for aqueous zinc complexes and metallic zinc[END_REF][START_REF] Fujii | Density functional theory estimation of isotope fractionation of Fe, Ni, Cu, and Zn among species relevant to geochemical and biological environments[END_REF][START_REF] Fujii | The origin of Zn isotope fractionation in sulfides[END_REF][START_REF] Fujii | Experimental and theoretical investigation of isotope fractionation of zinc between aqua, chloro, and macrocyclic complexes[END_REF]. Zinc complexes (Zn phosphates, citrates and malates) were also modeled to discuss the Zn isotope fractionation in roots and leaves of plants [START_REF] Fujii | Ab initio calculation of the Zn isotope effect in phosphates, citrates, and malates and applications to plants and soil[END_REF].

In their review study, [START_REF] Moynier | The Isotope Geochemistry of Zinc and Copper[END_REF] summarized the calculated β-factors available in the literature for aqueous solutions and molecules relevant for zinc in biogeochemistry. Their study also provides unpublished data for various molecules (e.g. oxalate species). [START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF][START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF] used also ab initio calculations to determine equilibrium Zn isotope fractionation factors in Zn-bearing minerals (e.g. sphalerite, hydrozincite) and between hexaaquo zinc complexes and minerals. Although a straightforward comparison between the various theoretical data available in the literature is difficult since the β-factors have been determined with different types of input data and methods [START_REF] Black | Calculation of equilibrium stable isotope partition function ratios for aqueous zinc complexes and metallic zinc[END_REF][START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF][START_REF] Fujii | Experimental and theoretical investigation of isotope fractionation of zinc between aqua, chloro, and macrocyclic complexes[END_REF], these data provide a theoretical basis for the interpretation of Zn isotopic measurements. The β-factors for various dissolved species, organic ligands, Znbearing minerals and zinc metal are represented in supplementary Fig. S1 [START_REF] Black | Calculation of equilibrium stable isotope partition function ratios for aqueous zinc complexes and metallic zinc[END_REF][START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF][START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF][START_REF] Fujii | Density functional theory estimation of isotope fractionation of Fe, Ni, Cu, and Zn among species relevant to geochemical and biological environments[END_REF][START_REF] Fujii | Ab initio calculation of the Zn isotope effect in phosphates, citrates, and malates and applications to plants and soil[END_REF][START_REF] Moynier | The Isotope Geochemistry of Zinc and Copper[END_REF]. To compare the β-factors and evaluate the isotope fractionation between phases, in this publication we considered an ambient temperature of 25°C.

Distribution between dissolved aqueous species. In aqueous solutions, stable Zn complexes depend on the dominant ligands [START_REF] Albarède | The stable isotope geochemistry of copper and zinc[END_REF]. At increasing chlorine and sulfate concentrations, the hexaaquo zinc complex Zn(H2O)6 2+ gives zinc-chloro complexes (e.g. ZnCl(H2O)5) + , ZnCl2(H2O)4) and zinc-sulphato complexes (e.g. ZnSO4(H2O)6, ZnSO4(H2O)5). Ab initio calculations showed that aquo-ion and zinc chloride complexes have close isotope signatures [START_REF] Fujii | Density functional theory estimation of isotope fractionation of Fe, Ni, Cu, and Zn among species relevant to geochemical and biological environments[END_REF], whereas zinc sulfates are enriched in 66 Zn with a value of ∆ 66/64 Zn ~+0.5‰ relative to aquo-ions [START_REF] Moynier | The Isotope Geochemistry of Zinc and Copper[END_REF] (Fig. S1). With increasing pH, carbonate (ZnCO3(H2O)3) and hydroxide (Zn(OH)2(H2O)4) become the dominant species with ∆ 66/64 Zn enrichment until +1‰ for zinc carbonates relative to aqua-ion [START_REF] Fujii | Density functional theory estimation of isotope fractionation of Fe, Ni, Cu, and Zn among species relevant to geochemical and biological environments[END_REF].

Organic complexation.

A major part of "dissolved" zinc in rivers is organically complexed rather than free and inorganically complexed; this part of organically complexed Zn increases greatly in estuary zones (e.g. [START_REF] Montgomery | Zinc and copper in "particulate" forms and "soluble" complexes with inorganic or organic ligands in the guanajibo river and coastal zone, Puerto Rico[END_REF][START_REF] Van Den Berg | Organic complexation of zinc in estuarine interstitial and surface water samples[END_REF]. Experiments dedicated to complexation on organic compounds' humic acid (an organic matter analog) showed that below pH 6 isotope fractionation is not measurable, while at higher pH the complexed organic Zn is heavier than free Zn 2+ (∆ 66/64 Zn =+0.24‰) [START_REF] Jouvin | Zinc Isotopic Fractionation: Why Organic Matters[END_REF]. The authors explained this difference by changes in Zn speciation with pH, with higher complexation constants and shorter bond lengths for organic complexed Zn compared to the free Zn 2+ . [START_REF] Ban | Zinc Isotope Separation by Ligand Exchange Chromatography Using Cation Exchange Resin[END_REF] measured similar fractionation (∆ 66/64 Zn= +0.20‰) between EDTA complexed Zn and Zn 2+ . Theoretical equilibrium isotopic factors seem to confirm these experimental results. β-factor for citrate, another analog for humic acids, showed that the predominant species present in solutions at pH between 4 and 8, Zn(cit)(H2O)3 -, is enriched in 66 Zn compared to the hexaaquo zinc complex with ∆ 66/64 Zn=+0.16‰ [START_REF] Fujii | Density functional theory estimation of isotope fractionation of Fe, Ni, Cu, and Zn among species relevant to geochemical and biological environments[END_REF][START_REF] Fujii | Ab initio calculation of the Zn isotope effect in phosphates, citrates, and malates and applications to plants and soil[END_REF]) (Fig. S1).

Adsorption onto mineral particles. Adsorption of zinc onto mineral particles (oxides, oxidehydroxides, clay, carbonate and silicates) causes a drop in the δ 66/64 Zndissolved value with ∆ 66/64 Zn fractionation around +0.30‰. This depends on the nature of the mineral and the solution conditions (pH, ionic strength) [START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Bryan | Zinc isotope fractionation during adsorption onto Mn oxyhydroxide at low and high ionic strength[END_REF][START_REF] Dong | Zinc isotope fractionation during adsorption to calcite at high and low ionic strength[END_REF][START_REF] Gou | Zinc Isotope Fractionation during Sorption onto Al Oxides: Atomic Level Understanding from EXAFS[END_REF][START_REF] Guinoiseau | Zn isotope fractionation during sorption onto kaolinite[END_REF][START_REF] Juillot | Zn isotopic fractionation caused by sorption on goethite and 2-Lines ferrihydrite[END_REF][START_REF] Nelson | Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces[END_REF][START_REF] Pokrovsky | Zinc stable isotope fractionation during its adsorption on oxides and hydroxides[END_REF]. In most cases, the fractionation is driven by a decrease of coordination number and bond lengths between aqueous Zn (six-coordinate octahedral) and adsorbed Zn (four-coordinate tetrahedral) complexes.

Precipitation. While synthetic hydrozincites (Zn5(CO3)2(OH)6) produced by Wanty et al., 2013 have δ 66/64 Zn identical to the dissolved Zn, [START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF] showed that hydrozincite and hopeite (Zn3(PO4)2.4H2O) precipitation tends to reduce the δ 66/64 Zndissolved value (∆ 66/64 Zn = +0.18‰ and +0.25‰ respectively). The δ 66/64 Zndissolved value in a river draining a Zn-Pb mining district in Sardinia and containing a consortium of a microalga and a cyanobacterium, which facilities the biomineralization of hydrozincite, is also significantly depleted in heavy isotopes compared to hydrozincite (∆ 66/64 Zn= +0.35‰) [START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF]. Data obtained by [START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF] (and also [START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF] for natural samples) are in agreement with the theoretical fractionation value calculated by [START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF] between hydrozincite precipitate and hexaaquo zinc complex (∆ 66/64 Zn ~ +0.30‰, Fig.

S1).

Laboratory experiments with and without bacteria showed that sphalerite (ZnS) precipitation increases δ 66/64 Zndissolved relative to the precipitate (∆ 66/64 Zn fractionation of -0.30‰) (Archer et al., 2004;[START_REF] Jamieson-Hanes | Evaluating zinc isotope fractionation under sulfate reducing conditions using a flow-through cell and in situ XAS analysis[END_REF][START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF]. This isotope fractionation is consistent with ab initio calculations that predict a fractionation of -0.50‰ between sphalerite precipitate and hexaaquo zinc complex [START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF] (Fig. S1).

Dissolution. Using the same calculation, sphalerite dissolution should lead to fractionation between solid and aqueous Zn of ∆ 66/64 Zn ~ -0.50‰, whereas during oxidative weathering experiments of sphalerite-rich rocks [START_REF] Fernandez | Fractionation of Cu, Fe, and Zn isotopes during the oxidative weathering of sulfide-rich rocks[END_REF] measured only a little initial fractionation (∆ 66/64 Zn = -0.20‰) that quickly dissipated to give a δ 66/64 Zndissolved close to sphalerite (∆ 66/64 Zn = 0.0‰). The initial fractionation can be explained by the transient formation of a surface coating on sphalerite composed of Zn sulfates [START_REF] Fernandez | Fractionation of Cu, Fe, and Zn isotopes during the oxidative weathering of sulfide-rich rocks[END_REF]. The theoretical β-factor for Gunningite (ZnSO4. H2O) showed that this phase preferentially incorporates the heavier Zn isotopes compared to sphalerite (∆ 66/64 Zn ~ +0.30‰) and is weakly deleted in heavy isotope compared to Zn 2+ (∆ 66/64 Zn ~ -0.20‰, [START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF] (Fig. S1).

According to the β-factor values, the dissolution of metallic zinc leads to an enrichment in 66 Zn for hexaaquo zinc complex with ∆ 66/64 Zn ~ -1.5‰ [START_REF] Black | Calculation of equilibrium stable isotope partition function ratios for aqueous zinc complexes and metallic zinc[END_REF] (Fig. S1).

Adsorption onto biological surfaces. Adsorption of zinc onto microorganisms (bacteria, diatoms, plankton, phototrophic biofilm) generally increases the δ 66/64 Znadsorbed value with ∆ 66/64 Zn fractionation between +0.30 and +1.20‰ that depends on the nature of microorganisms and the solution conditions (pH, ionic strength) [START_REF] Coutaud | Zn isotope fractionation during interaction with phototrophic biofilm[END_REF][START_REF] Gélabert | Interaction between zinc and freshwater and marine diatom species: Surface complexation and Zn isotope fractionation[END_REF][START_REF] John | A role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes[END_REF][START_REF] Kafantaris | Zinc isotope fractionation during surface adsorption and intracellular incorporation by bacteria[END_REF]. In most cases, the fractionation seems driven by a mechanism similar to a Zn complexation to organic functional groups on organisms' external surfaces.

Biological uptake. The uptake by plants (rice, tomato, etc.) and microorganisms (diatom, bacteria, plankton, phytoplankton) may increase or decrease the δ 66/64 Zndissolved value according the uptake process involved (high or low affinity pathway), which depends on the concentration of free ions in the nutrient solution [START_REF] Arnold | Iron and zinc isotope fractionation during uptake and translocation in rice (Oryza sativa) grown in oxic and anoxic soils[END_REF](Arnold et al., , 2010b;;[START_REF] Aucour | Dynamics of Zn in an urban wetland soil-plant system: Coupling isotopic and EXAFS approaches[END_REF][START_REF] Aucour | Fractionation of stable zinc isotopes in the zinc hyperaccumulator arabidopsis halleri and nonaccumulator arabidopsis petraea[END_REF][START_REF] Caldelas | Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc[END_REF][START_REF] Couder | Transpiration flow controls Zn transport in Brassica napus and Lolium multiflorum under toxic levels as evidenced from isotopic fractionation[END_REF][START_REF] Coutaud | Zn isotope fractionation during interaction with phototrophic biofilm[END_REF][START_REF] Gélabert | Interaction between zinc and freshwater and marine diatom species: Surface complexation and Zn isotope fractionation[END_REF][START_REF] Houben | Impact of root-induced mobilization of zinc on stable Zn isotope variation in the soil-plant system[END_REF]John et al., 2007a;[START_REF] Jouvin | Stable isotopes of Cu and Zn in higher plants: Evidence for Cu reduction at the root surface and two conceptual models for isotopic fractionation processes[END_REF][START_REF] Kafantaris | Zinc isotope fractionation during surface adsorption and intracellular incorporation by bacteria[END_REF][START_REF] Samanta | Zinc isotope fractionation by Emiliania huxleyi cultured across a range of free zinc ion concentrations[END_REF][START_REF] Smolders | Isotopic fractionation of Zn in tomato plants suggests the role of root exudates on Zn uptake[END_REF][START_REF] Tang | Zinc Isotope Fractionation in the Hyperaccumulator Noccaea caerulescens and the Nonaccumulating Plant Thlaspi arvense at Low and High Zn Supply[END_REF][START_REF] Viers | Evidence of Zn isotopic fractionation in a soil-plant system of a pristine tropical watershed (Nsimi, Cameroon)[END_REF][START_REF] Weiss | Isotopic discrimination of zinc in higher plants[END_REF]. The uptake of heavy isotopes by microorganisms and plants is favored in low Zn concentration media (~1-10 µg/L). The mechanism is the active uptake by a membrane transport protein Zn-ion-permease or by a chelating organic complex Znphytosiderophore (high affinity uptake) (e.g. Arnold et al., 2010b;[START_REF] Tang | Zinc Isotope Fractionation in the Hyperaccumulator Noccaea caerulescens and the Nonaccumulating Plant Thlaspi arvense at Low and High Zn Supply[END_REF].

Microorganisms and plants preferentially take up the lighter isotopes of zinc when the mechanism is diffusive transport across the cell membrane and through the boundary layer of the root (low affinity uptake) (e.g. John et al., 2007a;[START_REF] Jouvin | Stable isotopes of Cu and Zn in higher plants: Evidence for Cu reduction at the root surface and two conceptual models for isotopic fractionation processes[END_REF]. For plants, we do generally see a higher δ 66/64 Zn value in roots than in the nutrient medium with a preferential translocation of light isotopes into the upper parts (Fig. 3). [START_REF] Fujii | Ab initio calculation of the Zn isotope effect in phosphates, citrates, and malates and applications to plants and soil[END_REF] explained these results using ab initio calculations and proposed that the fractionation is driven by the difference in Zn speciation between the root system (isotopically heavy Zn phosphates) and the upper parts, rich in isotopically light citrates and malates (Fig. S1).

Isotope composition of natural zinc sources

The Upper Continental Crust

The average Zn content in the upper continental crust calculated by [START_REF] Taylor | The continental crust: its composition and evolution[END_REF] is 71 mg/kg. For rocks in the continental crust, analysis of Zn isotope compositions (δ 66/64 Zn) in granite shows values between +0.21 and +0.47‰ (n=4, Araújo et al., 2017a;Chen et al., 2009b;[START_REF] Chen | Zinc Isotopic Compositions of NIST SRM 683 and Whole-Rock Reference Materials[END_REF][START_REF] Viers | Evidence of Zn isotopic fractionation in a soil-plant system of a pristine tropical watershed (Nsimi, Cameroon)[END_REF]. Based on basaltic and ultramafic sample analyses from different geologic settings, [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF] estimated the average Zn isotope composition of bulk silicate earth (BSE) to be δ 66/64 Zn = +0.28 ± 0.05‰ (2σ).

Sulfide and non-sulfide ore deposits

The main zinc ore exploited is sphalerite or blende (ZnS). It represents 90% of current world zinc production [START_REF] Gordon | The characterization of technological zinc cycles[END_REF]; various zinc minerals such as smithsonite (ZnCO3) also called calamine, account for the rest [START_REF] Gordon | The characterization of technological zinc cycles[END_REF]. Since zinc is present in ores in only a single oxidation state (+II), the variety of isotope compositions in the various mineralizations is limited compared to other metal elements like copper (between -3 and +7‰ e.g. [START_REF] Braxton | Exploration applications of copper isotopes in the supergene environment: A case study of the bayugo porphyry copper-gold deposit, Southern Philippines[END_REF][START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF] (Fig. 2). However, the fact that zinc is in various crystallographic environments and coordination numbers (ranging from 4 to 6) in Zn-bearing minerals lead to a significant theoretical fractionation between ores until ∆ 66/64 Zn ~ +1.5‰ [START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF] (Fig. S1). For silicate and carbonate minerals, in accordance with the general rule of short bonds concentrating heavy isotopes [START_REF] Schauble | Applying stable isotope fractionation theory to new systems[END_REF], a general decrease in β-factors is observed when the bond lengths and coordination numbers increase [START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF]. The highest β-factor value is found for hemimorphite (Zn4Si2O7(OH)2.H2O) where Zn atoms are four-fold coordinate with O atoms. The β-factor for willemite (Zn2SiO4) is not calculated by [START_REF] Ducher | Equilibrium zinc isotope fractionation in Znbearing minerals from first-principles calculations[END_REF]. However, Zn being tetrahedrally coordinated with oxygen in willemite like in hemimorphite, it is likely that the β-factors for these phases would be comparable [START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF]. In hydrozincite (Zn5(CO3)2(OH)6) the β-factor is lower relative to hemimorphite due to the fact that Zn is found in both tetrahedral and octahedral sites. Smithsonite where Zn is octahedrally coordinated have the lowest β-factor. With β-factor close to smithsonite and Zn tetrahedrally coordinated, sphalerite is out of this general trend because Zn-S bond properties differ from Zn-O bonds (Fig. S1).

For sphalerite and other sulfur-containing minerals like galena (PbS) and chalcopyrite (CuFeS2) sampled worldwide, the Zn isotope variations (δ 66/64 Zn) are relatively low with an interquartile range (IQR) of between +0.05 and +0.26‰ and a mean and median of +0.16‰

(n = 294) [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Chapman | Chemical separation and isotopic variations of Cu and Zn from five geological reference materials[END_REF][START_REF] Deng | Insights into ore genesis of the Jinding Zn-Pb deposit, Yunnan Province, China: Evidence from Zn and in-situ S isotopes[END_REF][START_REF] Duan | Zinc and lead isotope signatures of the Zhaxikang Pb-Zn deposit, South Tibet: Implications for the source of the ore-forming metals[END_REF][START_REF] Gagnevin | Zn, Fe and S isotope fractionation in a large hydrothermal system[END_REF][START_REF] John | Zinc stable isotopes in seafloor hydrothermal vent fluids and chimneys[END_REF][START_REF] Kelley | Zinc isotopes in sphalerite from base metal deposits in the Red Dog District, Northern Alaska[END_REF][START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF]Mason et al., 2005;[START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF][START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF][START_REF] Novak | Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime[END_REF][START_REF] Pašava | Zinc and sulfur isotope variation in sphalerite from carbonate-hosted zinc deposits, Cantabria, Spain[END_REF][START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF][START_REF] Sonke | Historical variations in the isotopic composition of atmospheric zinc deposition from a zinc smelter[END_REF][START_REF] Voldrichova | Zinc isotope systematics in snow and ice accretions in Central European mountains[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF][START_REF] Weiss | Atmospheric deposition and isotope biogeochemistry of zinc in ombrotrophic peat[END_REF][START_REF] Wilkinson | Zinc isotope variation in hydrothermal systems: Preliminary evidence from the Irish Midlands ore field[END_REF][START_REF] Zhou | Zinc, sulfur and lead isotopic variations in carbonate-hosted Pb-Zn sulfide deposits, southwest China[END_REF] (Fig. 2; supplementary Fig. S2). The variability of δ 66/64 Zn signatures for sphalerite within a deposit is likely due to a kinetic fractionation and Rayleigh distillation during progressive sphalerite precipitation from hydrothermal fluids [START_REF] Wilkinson | Zinc isotope variation in hydrothermal systems: Preliminary evidence from the Irish Midlands ore field[END_REF]. Theory predicts that kinetically controlled reactions favor the incorporation of isotopically light zinc in mineral precipitates relative to the bulk ore-forming fluid [START_REF] Wilkinson | Zinc isotope variation in hydrothermal systems: Preliminary evidence from the Irish Midlands ore field[END_REF], which likely explains the mean and median value for δ 66/64 Zn values in sulfide ore deposits, depleted in heavy isotopes compared to the BSE value (+0.28 ± 0.05‰, 2σ).

Secondary minerals, such as willemite, smithsonite, hydrozincite, and hemimorphite, formed through low-temperature hydrothermal and/or supergene oxidation of primary sulfide deposits, have more variable Zn isotope compositions than primary sulfide ores with δ 66/64 Zn values generally between +0.05 and +0.48‰ and a median value of +0.28‰ (n = 23, IQR) (Araújo et al., 2017a;[START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF][START_REF] Pašava | Zinc and sulfur isotope variation in sphalerite from carbonate-hosted zinc deposits, Cantabria, Spain[END_REF][START_REF] Voldrichova | Zinc isotope systematics in snow and ice accretions in Central European mountains[END_REF] (Fig. 2; Fig. S2). These minerals form through the total or partial release of zinc by dissolution from a precursor phase (primary sphalerite or an earlier secondary phase). The complete breakdown of primary sulfides/minerals and quantitative reprecipitation of zinc leads to low fractionation, whereas partial dissolution and incorporation causes high fractionation between phases. [START_REF] Pašava | Zinc and sulfur isotope variation in sphalerite from carbonate-hosted zinc deposits, Cantabria, Spain[END_REF] studied Zn isotope composition in minerals at La Florida mine (Spain), where an intense supergene alteration of sphalerite leads to the formation of secondary minerals like hydrozincite that are significantly enriched in heavy isotopes relative to sphalerite (∆ 66/64 Zn = +0.60‰). For ores coming from the Czech Republic, [START_REF] Voldrichova | Zinc isotope systematics in snow and ice accretions in Central European mountains[END_REF] showed a strong enrichment in heavy isotopes for hemimorphite relative to sphalerite (∆ 66/64 Zn = +0.80‰). These fractionations are consistent with β-factors calculated between hydrozincite, hemimorphite and aqueous Zn by [START_REF] Ducher | Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations[END_REF] (∆ 66/64 Zn=+0.30‰ and ∆ 66/64 Zn=+0.90‰ respectively). [START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF] studied Zn isotope compositions in secondary zinc minerals collected from Zn deposits in Ireland, Belgium, Poland, Namibia, and Zambia, formed during low-temperature hydrothermal and/or supergene oxidation of primary sulfide deposits. Most of the data observed on minerals can be explained as described above by an isotopic fractionation model in which the partial dissolution of primary sphalerite is followed by the precipitation of an initial secondary phase that preferentially incorporates light Zn isotopes (smithsonite) or heavy Zn isotopes (hemimorphite, willemite, hydrozincite) (Fig. S1). However, [START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF] observed also strong negative isotopic shifts for late crystallizing phases (∆ 66/64 Zn = -0.50‰ for Willemite and ∆ 66/64 Zn=-0.66‰ for hemimorphite relative to a precursor phase).

Authors explained these low Zn isotope signatures for late crystallizing phases relative to the precursor mineral by the progressive precipitations from fluids that form phases enriched in heavy Zn isotopes leading to a gradual decrease in the δ 66/64 Zn values of such phases, and the fluids involved, in time and space. In conclusion, the variability of δ 66/64 Zn values in secondary ores (between +0.05 and +0.48‰, n = 23, IQR), higher than for primary sulfides (between +0.05 and +0.26‰, n = 294, IQR), can be explained by a combination of equilibrium isotope fractionation and open system Rayleigh distillation during incomplete dissolution-reprecipitation reactions.

Coal

In coal, the Zn content can reach several hundreds of mg/kg [START_REF] Novak | Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime[END_REF]. Zn isotope compositions in coal vary very widely with δ 66/64 Zn values generally between -0.10 and +1.35‰ (n = 14, IRQ) for samples taken in Spain, the Czech Republic, Germany and the USA [START_REF] Borrok | Zinc isotopic composition of particulate matter generated during the combustion of coal and coal + tire-derived fuels[END_REF][START_REF] Novak | Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime[END_REF][START_REF] Ochoa Gonzalez | Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion[END_REF][START_REF] Voldrichova | Zinc isotope systematics in snow and ice accretions in Central European mountains[END_REF] (Fig. S2). The wide variability of coal isotope compositions is related to diagenetic processes (uptake by plants, exchange with pore waters) that occur in peat, a coal precursor (Ochoa Gonzalez and Weiss, 2015).

Natural water

In rivers that are largely unaffected by human activity, Zn concentrations in solution (dissolved load) are generally between 1 and 2 µg/L [START_REF] Gaillardet | Trace elements in river waters[END_REF]. For rivers with little human impact, the Zn concentrations in solution are substantially lower than the European (7.8 µg/L) and US (66.6 µg/L) EQS values. The particulate phase (sediment & SPM) in rivers generally contains higher quantities of zinc, at around 200 mg/kg for rivers with little human impact [START_REF] Martin | Elemental mass-balance of material carried by major world rivers[END_REF][START_REF] Viers | Chemical composition of suspended sediments in World Rivers: New insights from a new database[END_REF]. In waters with little human impact ([Zn]dissolved ≤ 2 µg/L), the isotope compositions of Zn in solution are generally between δ 66/64 Zn = +0.29 and +0.57‰ (n=63, IQR) [START_REF] Chen | Zn isotope compositions of the thermal spring waters of La Soufrière volcano, Guadeloupe island[END_REF][START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Little | The oceanic mass balance of copper and zinc isotopes, investigated by analysis of their inputs, and outputs to ferromanganese oxide sediments[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF] this study) (Fig. S2). However, we note great variability in δ 66/64 Zn values in estuaries. A study on the Garonne estuary (France) showed that in the turbidity zone the dissolved δ 66/64 Zn values varied from +0.19 to +0.90‰ from upstream to downstream unlike δ 66/64 Zn in SPM, which remained constant (+0.37 ± 0.05‰, 2σ, n=10) [START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF] (Fig. 3). Although not consistent with fractionation experiments at isotopic equilibrium (Fig. 1), the authors explained this enrichment by kinetically driven adsorption due to strongly increasing sorption sites in the turbidity zone [START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF]. The δ 66/64 Zn values for zinc in solution in the estuary of the river Kalix (Sweden) and the Amazon estuary (Brazil), between +0.36 and +0.80‰ (n = 7, [START_REF] Little | The oceanic mass balance of copper and zinc isotopes, investigated by analysis of their inputs, and outputs to ferromanganese oxide sediments[END_REF], are also high compared to the BSE level (+0.28 ± 0.05‰, 2σ) (Fig. 3). As shown previously (see section 3) the part of "dissolved" Zn complexed to organic ligands relative to free and inorganically complexed Zn increases widely in estuaries compared to upstream. The organic complexed Zn enriched in 66 Zn compared to the free Zn 2+ (Fig. 1), could participate in the enrichment in heavy isotopes of dissolved Zn in the estuary zone compared to upstream. At the river-sea interface, in addition to physical and chemical processes, mixing between fresh water and seawater (δ 66/64 Zn ~ +0.50‰; [START_REF] Boyle | GEOTRACES IC1 (BATS) contamination-prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration[END_REF][START_REF] Zhao | Biogeochemical cycling of zinc and its isotopes in the Southern Ocean[END_REF] may also explain part of the variability observed. If we do not consider estuaries, the variation in δ 66/64 Zn in solution in rivers with little human impact ([Zn]dissolved ≤ 2 µg/L) is quite small, with values between +0.28 and +0.43‰ (n=46, IQR) and a median value of +0.33‰ close to the BSE value (+0.28 ± 0.05‰, 2σ) (Fig. 3). Most of the sediments and SPM taken from lakes and rivers with little human impact ([Zn]particulate ≤ 200 mg/kg) have Zn isotope compositions varying from δ 66/64 Zn=+0.14 to +0.32‰ (n= 129, IQR, Araújo et al., 2017aAraújo et al., , 2017b[START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF][START_REF] Araújo | Zinc isotopes as tracers of anthropogenic sources and biogeochemical processes in contaminated mangroves[END_REF]Chen et al., 2009b;[START_REF] Guinoiseau | Fate of particulate copper and zinc isotopes at the Solimões-Negro river confluence, Amazon Basin, Brazil[END_REF][START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF][START_REF] Thapalia | Zinc isotopic signatures in eight lake sediment cores from across the United States[END_REF] this study) (Fig. S2). SPM generally has isotope compositions similar to or slightly lower than the associated dissolved phase (Chen et al., 2009b[START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF]. This result suggests that adsorption processes are not the dominant process by which Zn enrichment in SPM occurs (Chen et al., 2009b), and that the organic matter in both the sediment and aqueous phase likely plays a crucial role in the distribution of Zn isotopes between these phases. In Fig. 3 where δ 66/64 Zn values are shown for sediments and SPM of lakes and rivers with little human impact ([Zn]particulate ≤ 200 mg/kg) we see that the Amazon and its tributaries, including the Rio Negro, have a considerably lower isotope signature (+0.07 ± 0.30‰, 2σ, n = 48) compared to the BSE value (+0.28 ± 0.05‰, 2σ). This specific isotope composition is related to the presence in Rio Negro SPM of kaolinite in which zinc is structurally incorporated [START_REF] Guinoiseau | Fate of particulate copper and zinc isotopes at the Solimões-Negro river confluence, Amazon Basin, Brazil[END_REF]. If we do not consider this watershed, Zn isotope compositions in SPM and sediments for lakes and rivers with little human impact ([Zn]particulate ≤ 200 mg/kg) have quite a narrow variation with values between +0.23 and +0.40‰ (n=81, IQR) and a median value of +0.30‰, similar to the BSE value (+0.28 ± 0.05‰, 2σ) (Fig. 3). These data on δ 66/64 Zn values in the dissolved phase (between +0.28 and +0.43‰, n=46, IQR) and the particulate phase (between +0.23 and +0.40‰, n=81, IQR) for lakes and rivers let us define a composition for the geological background for surface water (GBSW) with values between +0.24 and +0.41‰ (n=127, IQR) and a median value +0.30‰, similar to the BSE value (+0.28 ± 0.05‰, 2σ) (Fig. S2).

Isotope composition of anthropogenic zinc sources

Considerable quantities of zinc are emitted into the environment by industry, urbanization and agriculture. A summary of major anthropogenic zinc flows emitted into the environment in France is presented in supplementary Table S4. Industries and urban WWTP discharge effluents rich in zinc directly into river. Large quantities of zinc-rich solid waste are also emitted into soils and the atmosphere by industry, urbanization and agriculture. The runoff and erosion from industrial, urban, and agricultural soils and atmospheric deposits releases large quantities of zinc into surface freshwater. As well as natural physical and chemical processes (see section 3), the processes used by humans to concentrate, extract or treat the zinc contained in natural materials will impact their δ 66/64 Zn value. In particular, hightemperature industrial processes, involving evaporation and condensation reactions with kinetic isotope effects, can induce significant isotopic fractionation between industrial and natural samples.

Mining and industrial activities

Zinc is widely dispersed in soils and the atmosphere because of past and current mining and industrial activity (supplementary Fig. S3). For example, according to IREP (Registre Français des Emissions Polluantes), 502 metric tons of zinc are emitted by industrial activity into soils and the atmosphere each year in France (2010-2017 average; http://www.irep.ecologie.gouv.fr/IREP/index.php). The main emitting activities are the production and smelting of metal, but also power plants [START_REF] Gouzy | Données technico-économiques sur les substances chimiques en France : Zinc et principaux composés[END_REF].

Industries also discharge metal-rich effluents directly into surface water. In France according to the IREP, 94 metric tons of zinc are emitted directly into surface water each year (2010-2017 average; http://www.irep.ecologie.gouv.fr/IREP/index.php). These come mainly from the metallurgy, surface treatment (e.g. electroplating, chemical deposit), and chemical industries.

Mining activities

Mining operations, in particular related to the extraction of sulfide minerals, cause enormous stocks of waste rock piles that contain notable residual Zn quantities. Samples collected in waste rock piles at sulfide mineral mines in the USA (Fe-Zn-Cu mine) and Peru (Cu-Zn-Mo mine) contained large quantities of zinc (up to 0.4% by mass) [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF]. The water percolating through these waste rock piles (i.e. effluent) can be also rich in zinc. [START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF] showed that experimental waste-rock weathering can produce effluents with high Zn content (up to 16 mg/L). The δ 66/64 Zn values for these samples are shown in Fig. S4. The Zn isotope compositions of various samples (solid waste and effluent) generally had values between +0.18 and +0.28‰ (n = 34, IQR, Fig. S3), which are consistent with those of sulfide mineralizations (+0.05 and +0.26‰, n = 294, IQR). This similarity in δ 66/64 Zn values between mining residue and ores is because these residues have an isotope signature similar to the mineralizations that they accompany and the zinc in solution in effluents results from the dissolution of zinc-rich minerals, so this process only causes low enrichment of the isotope composition of the solution relative to the solid (Fig. 1).

Industrial activities

Metallurgical processes. The extraction of non-ferrous metals produces enormous quantities of waste called tailings. This solid waste can contain several % by mass of zinc [START_REF] Bigalke | Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil[END_REF][START_REF] Juillot | Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF]. The particles emitted by smelter chimneys contain several hundreds of mg/kg of zinc [START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF]. In general, for high-temperature zinc pyrometallurgy processes in smelters, the zinc recovery yield is close to 100%, so the isotope fractionation between the ore and the resulting metal is low [START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF][START_REF] Sonke | Historical variations in the isotopic composition of atmospheric zinc deposition from a zinc smelter[END_REF]. John et al. (2007b) showed that the zinc in diverse metal parts (money, raw metals, etc.) has a range of isotope variations (between +0.09 and +0.31‰, n = 14) similar to that of ores (between +0.05 and +0.26‰, n = 294, IQR). [START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF] also showed by analyzing refined zinc alloy produced in Zn-Pb refining that the fractionation between the ore used (+0.17 ± 0.06‰) and the alloy produced (+0.22 ± 0.06‰) is low. Using these data for zinc metal, a signature for "common zinc" is defined between +0.15 and +0.22‰, and a median value of +0.19‰ (n = 15, IQR) (Fig. S3 and Fig. S4). Because of evaporation and condensation reactions that occur during the extraction process, waste from the operations (slags) have a considerably higher isotope signature (up to +1.5‰) [START_REF] Bigalke | Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil[END_REF][START_REF] Couder | Zinc isotopes in polluted substrates The influence of phase separation on the flow patterns of mid-ocean ridge hydrothermal systems[END_REF][START_REF] Juillot | Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF], and particles emitted have a very low signature (up to -0.7‰) [START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF] compared to ores (between +0.05 and +0.26‰, n = 294, IQR) (Fig. S4). From analyzing various waste and products in metallurgic sites in France, a kinetic fractionation factor has been calculated for Rayleigh evaporation of zinc during refining (αsolid-vapor) that is generally between 1.0001 and 1.0004 [START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF]. By following a Rayleigh model [START_REF] Wiederhold | Metal stable isotope signatures as tracers in environmental geochemistry[END_REF], simulating the δ 66/64 Zn variations in separated and accumulated vapor and solid residue, it is possible to estimate the Zn isotope composition in waste produced during the smelting operations:

(1)

Where εvapor-solid is the isotope enrichment factor (‰) with εvapor-solid≈ -1000 ln αsolid-vapor and f the fraction remaining.

For a starting composition of δ 66/64 Zn in ores between +0.05 and +0.26‰ (n=294, IQR), a αsolid-vapor fractionation factor between 1.0001 and 1.0004 and assuming a recovery of 98% for pure zinc production in smelting processes, the estimated δ 66/64 Zn values are between +0.44 and +1.82‰ for slags and -0.34 and +0.16‰ for particles (Fig. S4). These values are consistent with slags and particles reported in previous studies [START_REF] Bigalke | Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil[END_REF][START_REF] Couder | Zinc isotopes in polluted substrates The influence of phase separation on the flow patterns of mid-ocean ridge hydrothermal systems[END_REF][START_REF] Juillot | Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France[END_REF][START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF].

Water that percolates through slag tailings (between +0.51 and +1.40‰, n=4, Fig. S4) has a similar isotope signature to slags (between +0.50 and +0.78‰, n=12, IQR, Fig. S3) [START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF]. These similar signatures for slag and effluents are related to the fact that dissolution processes only cause low isotope fractionation of dissolved fraction relative to the solid (Fig. 1). However, metallurgical slags are very heterogeneous materials, composed of many mineral phases: mainly glassy phases but also crystalline phases like spinels (franklinite (ZnFe2O4), gahnite (ZnAl2O4)), silicates (willemite (Zn2SiO4)) and zinc metal [START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF]. Theoretical equilibrium isotopic factors show that the dissolution of these phases leads to a wide range of Zn fractionation between aqueous Zn and minerals phases (Fig. S1). Moreover, weathering experiments on slags with different pH, atmospheres and contact times showed that because of the slags' heterogeneity (various amorphous glassy and crystalline phases), and because of multiple low-temperature inorganic chemical reactions (precipitation of secondary phase, coprecipitation, adsorption) that take place while they are altered, the δ 66/64 Zn values between the slags and the leachate may vary considerably from one experiment to another (up to 3‰) [START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF].

Since zinc is a chalcophile element, it is found as an impurity in other sulfide minerals like galena (PbS) and chalcopyrite (CuFeS2). For instance, in the Cubatão industrial region in Brazil, which holds various metallurgical industries, the particles present in the atmosphere have a very low signature (δ 66/64 Zn between -0.59 and -0.06‰, n = 10, Souto-Oliveira et al., 2019, 2018) compared to that of mineralizations (between +0.05 and +0.26‰, n = 294, IQR) and similar to that of particles emitted by zinc smelters (between -0.38 and +0.05‰, n = 17, IQR, Fig. S3). Zinc is also present in slags produced during lead production (up to 9% by mass) [START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF]. In their study of a former lead smelter in the south of France, [START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF] showed that Zn isotope compositions in slags have low values (between -0.04 and +0.18‰, n=8) compared to those of the slags analyzed in previous studies on zinc smelters (between +0.50 and +0.78‰, n=12, IQR) (Fig. S4). The same applies for the slags produced in a lead blast furnace in the north of France, whose Zn isotope composition (+0.13 ± 0.06‰, [START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF] is similar to those in the tailings analyzed by [START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF] This depletion is likely not due to the starting material, i.e. galena that has a mean δ 66/64 Zn value (+0.23 ± 0.12‰, 2σ, n=8) close to that of other sulfide ores (+0.16 ± 0.48‰, 2σ, n=294) (Fig. 2). This is likely related to a different yield for this process, whose aim was not to recover the zinc.

Galvanization. Zinc is also used widely to protect metallic parts from corrosion. Zinc can be deposited on the part by submerging it in a liquid bath of molten zinc ("hot-dip" galvanization) or by electrolytic deposit (electroplating). John et al., (2007b) showed that galvanized objects have an isotope signature (between +0.12 and +0.58‰, n=3) similar to the levels in ores (between +0.05 and +0.26‰, n=294, IQR) and "common zinc" (between +0.15 and +0.22‰, n=15, IQR), whereas the parts with an electrolytic deposit have a strongly depleted signature (up to -0.60‰) (Fig. S4). This result was confirmed by laboratory experiments, which also showed depletion of the metal deposited that leads to enrichment of liquid bath with kinetic fractionation (αsolution-metal) between 1.0010 and 1.0020 [START_REF] Black | Coupled effects of temperature and mass transport on the isotope fractionation of zinc during electroplating[END_REF][START_REF] Kavner | Redox-driven stable isotope fractionation in transition metals: Application to Zn electroplating[END_REF]. This fractionation is likely due to that fact that not all the zinc present in the electrolytic bath is electrodeposited during this process (60% recovery) and that the light isotopes are preferably electrodeposited [START_REF] Black | Coupled effects of temperature and mass transport on the isotope fractionation of zinc during electroplating[END_REF][START_REF] Kavner | Redox-driven stable isotope fractionation in transition metals: Application to Zn electroplating[END_REF]. By following a Rayleigh model (see equation 1), using a starting isotope composition close to that of ores (between +0.05 and + 0.26‰, n = 294, IQR), kinetic fractionation (αsolution-solid) between 1.0010 and 1.0020 and a 60% recovery yield, the estimated values for δ 66/64 Zn in the electrodeposited metal are between -1.17 and -0.35‰, which is similar to the δ 66/64 Zn values obtained for commercial electrodeposited (screw and chain) zinc-coated articles (between -0.34 and -0.20‰, n = 3, John et al., 2007b) (Fig. S4).

Coal and waste combustion in power plants.

The combustion of coal and waste in power plants releases high Zn contents into the atmosphere. Fly ash and flue gases sampled in coal-fired power plants and waste incineration plants contain large proportions of zinc (up to 3% by mass, [START_REF] Cloquet | Isotopic composition of Zn and Pb atmospheric depositions in an urban/periurban area of northeastern France[END_REF][START_REF] Novak | Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime[END_REF]. While smelters operate between 600 °C and 700 °C, in coal-fired power plants, coal is combusted at higher temperatures (from 1200 to 1500 °C). At those temperatures, most of the zinc evaporates and condenses onto the fly ash particles, which are removed in electrostatic precipitators (ESPs) [START_REF] Ochoa Gonzalez | Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion[END_REF]. Although ESPs exhibit good retention for large particles, their efficiency is significantly lower for particles smaller than 0.8 μm remaining in flue gases and about 50% of the starting zinc is emitted through the stack (Ochoa Gonzalez and Weiss, 2015). The signatures in the fly gas are controlled by condensation processes with isotope fractionation kinetic factors (αsolid-vapor) ranging between 1.0003 and 1.0007 [START_REF] Ochoa Gonzalez | Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion[END_REF]. From the analysis of fly ash and bottom ash samples coming from three power plants in Spain, Ochoa Gonzalez and Weiss (2015) predicted that the incineration of coal and pet coke with δ 66/64 Zn between +1.05 and +1.50‰ leads to zinc emission through the plant stack between +0.96 and +1.27‰. By following a Rayleigh model (see equation 1), for a starting composition of δ 66/64 Zn in coal between -0.10 and +1.35‰ (n=14, IQR), an αsolid-vapor factor between 1.0003 and 1.0007 and assuming a loss of 50% of zinc in the flue gas, δ 66/64 Zn values are estimated between -0.31 and +1.26‰ for zinc emission (Fig. S4).

The Zn isotope signatures of flue gases from French urban waste incineration are between +0. 07 and +0.19‰ (n = 3, Cloquet et al., 2006). These values match the estimated Zn isotope compositions for flue gases (between -0.06 and +0.13‰) obtained from incinerating material having an isotope signature similar to that of "common zinc" (between +0.15 and +0.22‰, n = 15, IQR) under the conditions set out previously (αsolid-vapor =1.0003 -1.0007, a loss of 50%) (Fig. S4).

In conclusion, the zinc emitted by coal-fired power plants and waste incineration plants has an isotope signature that is highly dependent on the combustible material. Given that the coal has very variable δ 66/64 Zn values (-0.10 and +1.35‰, n = 14, IQR), Zn isotope compositions emitted when coal is combusted will also be very variable (estimated values between -0.31 and +1.26‰) with values that include the BSE (+0.28 ± 0.05‰, 2σ) and sulfide ore (between +0.05 and + 0.26‰, n=294, IQR) ranges. For waste incineration, if we consider that the starting materials have a signature similar to "common zinc" (between +0.15 and +0.22‰, n = 15, IQR), the variation in Zn isotope compositions in the particles emitted will be narrower (value estimated between -0.06 and +0.13‰) with lower values than ores (between +0.05 and +0.26‰, n = 294, IQR).

Other industries.

As zinc metal is widespread in hardware, chemical components and organic materials, liquid effluents discharged into surface water by industries that do not work Zn metal as core processes (e.g. the chemical and agro-food industries), also contain high quantities of dissolved zinc (up to 500 µg/L, Table S1). Effluents coming from various industries (hospitals, chemicals, agro-food and surface treatment industries) are presented in supplementary Fig. S4 (this study). Industrial effluents have values for δ 66/64 Zn generally between +0.10 and +0.15‰ (n=7, IQR, Fig. S3), lower than the BSE value (+0.28 ± 0.05‰, 2σ) and close to that of "common zinc" (between +0.15 and +0.22‰, n = 15, IQR).

Emission from urban activities

Rivers can be strongly impacted by urban pressure (urban WWTP, zinc roofing, road traffic).

Urban WWTP discharge metal-rich effluents directly into surface water. For example, in

Urban wastewater treatment plants (WWTP)

Urban WWTP effluents can contain high quantities of dissolved zinc (up to 200 µg/L, Table S1). The Zn concentrations and δ 66/64 Zn values for raw wastewater and effluents coming from medium WWTP (10,000 to 100,000 Population Equivalent (PE)) and large WWTP (> 100,000 PE) are presented in Fig. S5 (Chen et al., 2008, this study). Treated wastewater coming from various WWTP have values for δ 66/64 Zn generally between +0.06 and +0.08‰ (n=5, IQR, Fig. S3), close to industrial effluents (+0.10 and +0.15‰, n=7, IQR) and lower than the δ 66/64 Zn values for raw wastewater (+0.28 ± 0.02‰, n = 1) and the BSE value (+0.28 ± 0.05‰, 2σ).

Previous study showed that dissolved Zn in WWTP effluent is mainly organically complexed to organic ligands [START_REF] Chaminda | Metal (Zn, Cu, Cd and Ni) Complexation by Dissolved Organic Matter (DOM) in Wastewater Treatment Plant Effluent[END_REF]. However, the δ 66/64 Zn for WWTP effluents depleted in heavy isotopes compared to wastewater is not consistent with a change in speciation, which tends to enrich in heavy isotopes organic complexed Zn compared to free Zn 2+ (see section 3).

In WWTP, wastewaters undergoes various treatment stages (primary settling, secondary activated sludge and tertiary flocculation by FeCl3) to decrease particulate metal concentrations [START_REF] Buzier | Trace metal speciation and fluxes within a major French wastewater treatment plant: Impact of the successive treatments stages[END_REF]. However, several studies have shown that the dissolved metal content increases along with the wastewater treatment steps in WWTP [START_REF] Buzier | Trace metal speciation and fluxes within a major French wastewater treatment plant: Impact of the successive treatments stages[END_REF][START_REF] Gourlay-Francé | Labile, dissolved and particulate PAHs and trace metals in wastewater: Passive sampling, occurrence, partitioning in treatment plants[END_REF]. According to [START_REF] Gourlay-Francé | Labile, dissolved and particulate PAHs and trace metals in wastewater: Passive sampling, occurrence, partitioning in treatment plants[END_REF], various assumptions may explain this increasing dissolved Zn concentration during the wastewater treatment steps: (1) metal desorption from particles and organic matter, (2) dissolution of iron salts added during the dephosphorization treatment, e.g. FeCl3 containing high trace metal concentrations. Previous studies have reported that the heavier isotopes are preferentially adsorbed onto organic matter, clays and oxides (Fig. 1), so zinc desorption from particles and organic matter should enrich the solution in heavy Zn isotopes. Therefore, treated wastewater's depletion in heavy isotopes compared to untreated wastewater cannot be due to a simple desorption process. Zinc-rich chemical components dissolving during wastewater treatment, depleted in heavy isotopes compared to untreated wastewater, may explain this result. For example, the δ 66/64 Zn signature of ferric chloride may be depleted in heavy isotopes due to isotope fractionation during its industrial production process (see section 5.1.2), or to the initial Fe ore used in this process, which may be, like Zn ores, lower (+0.16‰, n = 294) than the BSE value (0.28 ± 0.05‰, 2σ). Determine the δ 66/64 Zn signature of ferric chloride would be necessary to verify that it is the addition of zinc-rich chemical components with low δ 66/64 Zn value, which explains the lower δ 66/64 Zn values for the effluents produced by WWTP (+0.06 and +0.08‰, n=5, IQR) relative to the BSE value (0.28 ± 0.05‰, 2σ).

Zinc roofing

In their study of the Seine watershed, [START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF] analyzed roof runoff samples collected in the Paris conurbation, known for its zinc roofs. They analyzed also leached samples of zinc roof coverings. These samples contain high Zn contents (up to 2 mg/L for roof runoffs and 92 mg/L for leached sample) and their Zn isotope compositions (δ 66/64 Zn) are generally low (between -0.10 and -0.02‰, n = 5, IRQ, Chen et al., 2008, Fig. S3) compared to that of "common zinc" (between +0.15 and +0.22‰, n = 15, IQR).

This difference of δ 66/64 Zn values between "common zinc" and roof runoff samples is not consistent with fractionations due to metallic zinc dissolution, which tends to enrich the dissolved Zn 2+ relative to metal Zn (Fig. S1). These differences can be due to the starting material (electrodeposited zinc?), or to a contribution from particles of industrial origin (see section 5.1.2).

Road traffic

Zinc emitted by road traffic can be due to non-exhaust emissions (Brake pad liners, tires, roadway equipment) and exhaust emissions (gasoline).

Non-exhaust emissions. Brake pad liners contain a large quantity of zinc (up 2% by mass) mainly in the form of metal (brass), but also zinc oxide and sulfide (ZnO, ZnS, etc.) [START_REF] Blau | Compositions , Functions , and Testing of Friction Brake Materials and Their Additives[END_REF][START_REF] Hjortenkrans | Metal emissions from brake linings and tires: Case studies of Stockholm, Sweden 1995/1998 and 2005[END_REF][START_REF] Legret | Evaluation of pollutant loadings in the runoff waters from a major rural highway[END_REF]. Zn isotope compositions for nonexhaust emissions are shown in Fig. S5. The mean δ 66/64 Zn value for brake pads sold in

France and the UK is 0.19 ± 0.08‰ (2σ, n=3, [START_REF] Dong | Isotopic signatures suggest important contributions from recycled gasoline, road dust and non-exhaust traffic sources for copper, zinc and lead in PM10 in London, United Kingdom[END_REF]this study). This value is similar to "common zinc" (between +0.15 and +0.22‰, n=15, IQR), which matches the fact that zinc in the brake pads is mainly present in metal form. During tire production, zinc is added to the rubber in oxide form (ZnO) and also low quantities in the form of organo-zinc compounds to facilitate vulcanization. Tires also generally contain about 1% by mass of zinc [START_REF] Councell | Tire-wear particles as a source of zinc to the environment[END_REF][START_REF] Legret | Evaluation of pollutant loadings in the runoff waters from a major rural highway[END_REF]. Zn isotope compositions in tires from the USA, Brazil and the UK generally vary between +0.08 and +0.21‰ with a median value of 0.13‰ (n = 15, IQR, [START_REF] Dong | Isotopic signatures suggest important contributions from recycled gasoline, road dust and non-exhaust traffic sources for copper, zinc and lead in PM10 in London, United Kingdom[END_REF][START_REF] Souto-Oliveira | Multi-isotopic fingerprints (Pb, Zn, Cu) applied for urban aerosol source apportionment and discrimination[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF], Fig. S3). This slightly lower value than "common zinc" (between +0.15 and +0.22‰, n = 15, IQR) is probably related to fractionation during production of tires or raw materials used during vulcanization. Safety barriers at roadsides are coated with zinc by hot galvanization (standard ISO 1461). No analysis of safety barriers is available in the literature, however since they are hot-galvanized, their Zn isotope compositions ought to be similar to that of "common zinc" (between +0.15 and +0.22‰, n = 15, IQR).

Exhaust emissions.

Compared with non-exhaust emissions, gasolines contain zinc, added as additive, in a lower quantity (up to 150 µg/L of zinc, [START_REF] Barbusse | Les particules de combustion automobile et leurs dispositifs d'élimination[END_REF][START_REF] Nomngongo | Determination of trace Cd, Cu, Fe, Pb and Zn in diesel and gasoline by inductively coupled plasma mass spectrometry after sample clean up with hollow fiber solid phase microextraction system[END_REF]. Zn isotope compositions in gasolines between -0.50 and -0.23‰ (n=2, [START_REF] Gioia | Accurate and precise zinc isotope ratio measurements in urban aerosols[END_REF] are very low compared with values in tires and brakes (Fig. S5). It is important to note that when fuel combusts in evaporation/condensation reactions it will also tend to reduce this heavy isotope signature compared to its initial composition (See section 5.1.2).

Zinc emissions from agricultural activities

Agricultural operations like animal and arable farming concentrate high quantities of metals, particularly of zinc, which accumulate in the soil's surface layer. Sprayed inorganic and organic fertilizers, and crop protection treatments, especially for vines, are particular zinc sources [START_REF] Gouzy | Données technico-économiques sur les substances chimiques en France : Zinc et principaux composés[END_REF]. From a study of contamination sources in agricultural land and how those are used, [START_REF] Belon | Bilan des flux de contaminants entrant sur les sols agricoles de France métropolitaine[END_REF] have estimated that on average 0.514 kg of zinc are applied each year per hectare of Utilized Agricultural Area. For example, in France, 14,906 metric tons of zinc is sprayed each year on 29 million hectares of agricultural land.

The portion of substance emitted on agricultural land that reaches surface water by runoff was estimated between 0.1 and 1% (mean of 0.4%) by [START_REF] Braun | Rhin inventaire 2000 des émissions prioritaires[END_REF]. From this estimate, it is possible to calculate that each year about 60 metric tons of zinc is added to surface water in metropolitan France because of agricultural activity.

Fertilizers

Sewage sludge from water treatment plants used as fertilizers generally contains more than 500 mg/kg of zinc [START_REF] Eriksson | Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops[END_REF][START_REF] Meeddat | Eléments de contexte et réglementation française relatifs à la valorisation des boues issues du traitement des eaux usées[END_REF]. Organic fertilizers also include animal waste from manure and slurry. Effluents from pig farming contain several hundreds of mg/kg of zinc [START_REF] Eriksson | Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops[END_REF][START_REF] Levasseur | Teneur en cuivre et zinc des lisiers et des fumiers de porcs charcutiers après réduction de leur concentration dans les aliments après réduction de leur concentration dans les aliments[END_REF][START_REF] Nicholson | Heavy metal contents of livestock feeds and animal manures in England and Wales[END_REF]. These high contents are due to nutritional supplements with particularly high Zn contents that are given to animals to promote growth, but also supplied from weathering galvanized metal parts present in industrial farming (grating, tubes, etc.) [START_REF] Levasseur | Teneur en cuivre et zinc des lisiers et des fumiers de porcs charcutiers après réduction de leur concentration dans les aliments après réduction de leur concentration dans les aliments[END_REF][START_REF] Levasseur | Teneurs en éléments-trace métalliques des aliments et des lisiers de porcs à l'engrais, de truies et de porcelets[END_REF][START_REF] Smith | Effect of source of protein on zinc requirement of the growing pig[END_REF]. Manure generally has lower metal concentrations than slurries, because it is diluted by hay provided that contains little metals. Bovine feces contains less zinc (around 100 mg/kg) than pig feces, but cattle producing almost 10 times as much excrement as pigs [START_REF] Brassard | Révision de l[END_REF][START_REF] Eriksson | Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops[END_REF][START_REF] Nicholson | Heavy metal contents of livestock feeds and animal manures in England and Wales[END_REF]. With Zn contents of the order of a few tens of mg/kg, inorganic fertilizers have lower Zn concentrations than organic fertilizers and their concentration varies widely, even in products coming from a single manufacturer [START_REF] Eriksson | Concentrations of 61 trace elements in sewage sludge, farmyard manure, mineral fertiliser, precipitation and in oil and crops[END_REF]. The isotope compositions for various fertilizers are shown in supplementary Fig. S5. The range of variation for "common zinc" (between +0.15 and +0.22‰, n = 15, IQR) is also shown because of the many galvanized hardware present in farms. Since we do not have data on nutritional supplements given to pigs, we used the values for δ 66/64 Zn supplements intended for humans. These health products have quite variable Zn isotope compositions with δ 66/64 Zn values between +0.10 and +0.20‰ (n = 5, IQR, John et al., 2007b, Fig. S3). A study conducted by [START_REF] Balter | Bodily variability of zinc natural isotope abundances in sheep[END_REF] on sheep showed that Zn isotope signatures in urine and feces of an animal are similar to that of their food. The only manure analyzed (this study) has an isotope signature (+0.31 ± 0.03‰, n = 1) similar to that of BSE (+0.28 ± 0.05‰, 2σ). It is therefore likely from an animal that was fed with feed having a geogenic signature, without any nutritional supplement, which would have a lighter isotope composition (John et al., 2007b) (Fig. S5). The sewage sludge analyzed by [START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF] also has a Zn isotope signature (+0.31 ± 0.02‰, n = 1) similar to that of BSE (+0.28 ± 0.05‰, 2σ). Pig slurries have δ 66/64 Zn values between +0.07 and +0.24‰ (n = 3) [START_REF] Fekiacova | Tracing contamination sources in soils with Cu and Zn isotopic ratios[END_REF] this study), which likely reflect both the Zn isotope composition of the animal feed with varying supplements with variable δ 66/64 Zn values (between +0.10 and +0.20‰, n = 5, IQR), but also reflect runoff from metal parts on the farm ("common zinc" between +0.15 and +0.22‰, n = 15, IQR).

δ 66/64 Zn values for inorganic fertilizers vary widely (between -0.06 and +0.42‰, n = 4, [START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Szynkiewicz | Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition[END_REF] (Fig. S5).

Crop protection treatments

Vineyards are treated by either copper-based fungicides, such as Bordeaux mixture

Application of zinc isotopes to trace sources and fate of zinc in rivers

Fig. 4 summarizes Zn isotope compositions for various anthropogenic contributions compared to the BSE signature (+0.28 ± 0.05‰, 2σ) and to non-impacted rivers (GBSW, between +0.24 and 0.41‰, n = 127, IQR). In Fig. 4, contributions are represented by a boxplot when they are composed of more than four pieces of data. The distribution of data for the various anthropogenic contributions is in Fig. S3. The capacity of Zn isotopes to track anthropogenic contributions (mines, metallurgy, urbanization, agriculture) in surface water was applied and investigated by various studies described below.

Rivers impacted by mining activity

Rivers and groundwater in mining zones can have very high dissolved Zn concentrations (up to 70 mg/L) and δ 66/64 Zn values generally between +0.01 and +0.29‰ (n = 99, IQR, [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Borrok | Application of iron and zinc isotopes to track the sources and mechanisms of metal loading in a mountain watershed[END_REF][START_REF] Szynkiewicz | Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF] this study) (Fig. 5). This range of δ 66/64 Zn values is very close to that of sulfide mineralizations (between +0.05 and +0.26‰, n = 294, IQR) and solid waste and effluents present in mining areas (between +0.18 and +0.28‰, n=34, IQR). These similar isotope signatures are due to the fact that zinc in solution in rivers and groundwater results from the dissolution of zinc-rich minerals contained in ores and tailings, so this process only slightly enriches the solution (Fig. 1). However, δ 66/64 Zn values have lower heavy isotope levels for samples from Sardinia (-0.10 ± 0.24‰, 2σ, n = 10) compared with other water courses impacted by mining activity (0.16 ± 0.42‰, 2σ, n = 89) (Fig. 5). [START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF] state that these signatures are due to the biologically-mediated production of hydrozincite (Zn5(CO3)2(OH)6), which concentrates heavy isotopes. These results are consistent with laboratory experiments and theoretical data, which showed that hydrozincite precipitation tends to reduce the δ 66/64 Zndissolved value relative to precipitate (see section 3). In conclusion, Zn isotope signatures for rivers impacted by mining activity are close to those of natural water. This precludes the use of Zn isotopes to track mining pollution in rivers. However, Zn isotope compositions are a valuable tool for highlighting secondary processes (dissolution, precipitation, etc.) between particulate and dissolved phases [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF][START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF], which control the attenuation and release of zinc in surface water.

Rivers impacted by industrial activity

In their studies in the Sepetiba Bay (Brazil), [START_REF] Araújo | Zinc isotopes as tracers of anthropogenic sources and biogeochemical processes in contaminated mangroves[END_REF]Araújo et al. ( , 2017aAraújo et al. ( , 2017b) ) used Zn isotope compositions for core samples of stream sediments and SPM to reconstitute a timeline for changes in zinc contamination related to industrial metallurgy. From studying core samples of stream sediment, [START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF] and [START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF] have also shown how zinc ore-smelter activity affects the river Lot's watershed (France). In Fig. 6, the data from these studies are mixtures between a natural GBSW contribution and an anthropogenic contribution seen in the slags that is related to metallurgic activity. To date no dedicated study has been published on how industrial metallurgy activity impacts the Zn isotope signature in solution in surface water. However, a recent laboratory study on lixiviation of slags showed great diversity in Zn isotope signatures in the lixiviates (See section 5.1.2, [START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF]. The use of Zn isotope compositions to trace the impact of metallurgic activity in surface water must therefore be considered with precaution.

The contribution of atmospheric particles from metallurgical industries can be evaluated in urban aerosols because of their very low signature (between -0.38 and +0.05‰, n = 17, IQR) compared to the GBSW (between +0.24 and +0.41‰, n=127, IQR) [START_REF] Dong | Isotopic signatures suggest important contributions from recycled gasoline, road dust and non-exhaust traffic sources for copper, zinc and lead in PM10 in London, United Kingdom[END_REF][START_REF] Souto-Oliveira | Multi-isotope approach of Pb, Cu and Zn in urban aerosols and anthropogenic sources improves tracing of the atmospheric pollutant sources in megacities[END_REF], 2018). However, it is more difficult to establish the contribution of these atmospheric particles in surface water because of the physical and chemical processes (adsorption, precipitation, etc.) that take place in water (see section 3) modifying their Zn isotope signature.

Regarding the effluents discharged by different types of industries, their depleted signatures (between +0.10 and +0.15‰, n=7, IQR) compared to the GBSW (between +0.24 and 0.41‰, n = 127, IQR) ought to allow them to be traced in surface water (see section 5.1.2 concerning industrial effluents).

Rivers impacted by urbanization

Urbanization impacts surface water for several known reasons. One is point-source discharges in the form of effluents from large WWTP; another is release by runoff and/or erosion of zinc contained in emissions related to road traffic and runoff on zinc-coated roofs.

In their study on the Seine basin, [START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF] showed how urbanization has impacted Zn isotope compositions in the river's dissolved phase (Fig. 7). For zinc in solution present in the Loire, even though the contents are low (+1.3 ± 0.8 µg/L, 2σ, n=10, this study) (Table S2), we see slight decreases in δ 66/64 Zn from upstream to downstream (Fig. 7). The same applies for sediments and SPM taken from urban rivers and lakes [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF]Chen et al., 2009b;[START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF][START_REF] Thapalia | Zinc isotopic signatures in eight lake sediment cores from across the United States[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF]this study), where increased Zn content is accompanied by a lower δ 66/64 Zn value (Fig. 7). Fig. 7 shows that though the contribution of roof runoff may be excluded in these samples, they correspond to mixtures of a natural GBSW contribution and an anthropogenic contribution due to WWTP effluents and/or non-exhaust road traffic emissions.

Rivers impacted by agricultural activity

As previously stated, little data exists on Zn isotope compositions in agricultural contamination sources (fertilizer and crop protection treatment). For French watersheds that mainly hold arable and animal farming land we see that sediments and SPM may contain high Zn contents (up to 417 mg/kg) (Table S3), but their isotope composition is similar (0.27 ± 0.06‰, 2σ, n = 6, this study) to the GBSW (between +0.24 and 0.41‰, n=127, IQR) (Fig. 8). This result matches Zn isotope compositions in organic fertilizers, which show similar δ 66/64 Zn values (between +0.21 and +0.31‰, n = 5, IQR) to GBSW (between +0.24 and +0.41‰, n = 127, IQR) (Fig. S5).

Towards a multi-isotopic approach

Many studies have successful used a multi-isotope approach, i.e. Zn isotopes combined with other metals (Pb, Cu, etc.) to track the origin of pollution in soils and in atmospheric particles (e.g. [START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF][START_REF] Souto-Oliveira | Multi-isotopic fingerprints (Pb, Zn, Cu) applied for urban aerosol source apportionment and discrimination[END_REF]. In rivers and lakes, due to the same chemical separation protocol, analyses of Zn isotopes are associated with Cu isotopes in several studies [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF][START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Guinoiseau | Fate of particulate copper and zinc isotopes at the Solimões-Negro river confluence, Amazon Basin, Brazil[END_REF][START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF][START_REF] Vance | The behaviour of Cu and Zn isotopes during soil development: Controls on the dissolved load of rivers[END_REF]. Combining measurements of stable Cu and Zn isotopes may be helpful for identifying the exchange processes between the particulate and dissolved fractions in river. [START_REF] Aebischer | Disruption of the geochemical metal cycle during mining: Multiple isotope studies of lake sediments from Schefferville, subarctic Québec[END_REF] used a multi-isotopic approach (Zn, Fe, and Pb) in lake sediments impacted by multiple pollution sources (mining, urban, industrial, gasoline). This study highlighted the potential of a multi-isotope approach to identify metal sources and pathways. However, even though it is a powerful tool, especially in soils and atmospheric particles, the multi-isotopic approach should be used with caution in an aquatic environment. The elements used must have a common source and have close chemical properties to be transported in similar ways in aqueous media. Another important factor to consider is post-depositional processes, which can induce substantial isotopic variability according to the element and can hide the initial source signatures.

Summary and future directions

Though zinc is essential for life, in excess it may be toxic to organisms. In addition to natural zinc sources, many human activities mobilize and spread large quantities of zinc in the environment (i.e. industry, agriculture, road traffic and treated domestic effluents).

Discriminating the various natural and anthropogenic zinc sources in the environment, as well as understanding zinc's fate at a catchment scale in both dissolved and solid phases, is a key challenge in order to take the appropriate measures to prevent degradation of the aquatic environment. Isotope approaches, especially for lead, have proven their efficiency in tracing sources in the environment for decades. Compared to these "traditional" isotopes, the worth of tracing with Zn isotopes, more recently developed (2000s), has still to be proven.

This review compiles the major findings of previous studies in order to evaluate the ability of Zn isotope compositions to trace metal sources at a catchment scale.

First of all, we presented the isotope fractionations due to the interactions between minerals or live organisms and aqueous solutions that control how zinc is distributed between the dissolved and particulate phases in surface water and can modify the δ 66/64 Zn initial signatures of anthropogenic zinc sources. Though dissolution processes seem to slightly fractionate Zn isotope signatures (-0.2 -0.0‰), the adsorption of zinc on mineral particulate phases as well as its complexation onto organic compounds decreases δ 66/64 Zn in the remaining solution (~ +0.30‰). Precipitation could increase or decrease δ 66/64 Zn in the remaining solution depending on the nature of the newly formed zinc-bearing minerals.

Uptake by plants and microorganisms generally increases the δ 66/64 Zndissolved when the concentration of free ions in the nutrient solution is high (>~10 µg/L).

Secondly, we summarized available data for the main natural sources of zinc, to define (1) the bulk silicate earth signature (BSE, δ 66/64 Zn = +0.28 ± 0.05‰ (2σ)); (2) the zinc-sulfide ore deposit signature δ 66/64 Zn = +0.05 to +0.26‰, with a mean (or median) value of +0.16‰; (3) coal signatures that are highly variable δ 66/64 Zn = -0.10 to +1.35‰ depending on the diagenetic processes involved. Rivers draining natural environments generally have low dissolved Zn concentrations (<2 µg/L) and about 200 mg/kg in the particulate phases (sediments and SPM). Zn isotope compositions in natural water, SPM and sediments vary slightly and are used to define the "geological background for surface water" (GBSW, δ 66/64 Zn = +0.24 to +0.41‰ with a median value of +0.30‰) that is close to the BSE value.

Thirdly, the main zinc anthropogenic inputs, with their respective Zn isotope signatures as well as the main processes leading to these specific isotope characteristics, can be summarized as follows: (1) Solid wastes and effluents produced during mining activities have Finally, among the environmental studies based on Zn isotopes that track zinc sources in rivers:

(1) Rivers impacted by acid-mine drainage present, in addition to potentially high Zn concentrations, similar δ 66/64 Zn levels to sulfide mineralization because dissolution causes very little fractionation. However, secondary processes (e.g. precipitation and adsorption) can produce Zn isotope shifts.

(2) The impact of the metallurgical industry on river basins has been studied through solid materials (sedimentary cores, stream sediments and SPM) demonstrating that δ 66/64 Zn in these particulate phases results from mixing between the natural background and an anthropogenic end-member represented by slags. These studies showed that Zn isotope composition is a powerful tool for tracking the anthropogenic source of slags in particulate phases of rivers. No studies report data on the dissolved phase in rivers impacted by metallurgical activities; however, since the weathering of slags leads to a wide range of Zn isotope compositions, it seems that tracking their contribution in surface water would be impractical.

(3) The impact of urbanization includes several types of zinc sources (WWTP effluents, roadtraffic emissions, and zinc-covered roof runoff). WWTP effluents and non-exhaust traffic emissions with their close δ 66/64 Zn signatures will be difficult to discriminate. The Zn isotope compositions for dissolved loads, sediments and SPM sampled in urban rivers and lakes are a mix between the natural background and an anthropogenic end-member represented by WWTP effluents, and/or non-exhaust road traffic emissions. Though not allowing a clear distinction between all types of urban zinc sources, δ 66/64 Zn signatures are an efficient tool for tracking a global urban contribution in rivers.

(4) The impact of agriculture is poorly documented to date. Though the scarce data available do not reveal significant isotope shifts compared to the GBSW, this needs to be further investigated as agriculture is a major source of diffuse zinc at a catchment scale.

On this basis, we highlight research needs and propose future work to make Zn isotopes a relevant tracer of zinc and associated trace metals sources and fate at a catchment scale:

(1) As has been done for lead isotopes, the Zn isotope characterization of anthropogenic sources needs to be further investigated. In particular, it will be necessary to increase the number of samples analyzed to create an exhaustive reference database. Zn emissions from agricultural activities, which are a major source of zinc at a catchment scale, have to be widely studied.

(2) Zn isotope fractionations linked to processes (biologically mediated or not) that control the distribution of metals between the dissolved and particulate phases in surface water need to be better understood. A multi-technique approach coupling Zn isotope signatures in natural and experimental samples with theoretical studies using ab initio calculations to predict isotope fractionation and X-ray absorption spectroscopy to establish zinc speciation will be necessary for understanding the dominant processes that play a role in zinc mobility.

(3) Anthropogenic metal releases into the environment often combine zinc with other metals (e.g. Cu in WWTP effluents and Pb in gasoline). In rivers impacted by multiple sources of pollution, it is necessary to combine Zn isotopes with other metal isotopes to clearly evaluate the impact of various anthropogenic contributions. Moreover, coupling zinc and a combination of carefully selected metal isotopes would take us further in understanding the fate of metals in the different compartments of a river basin by constraining various physical and chemical processes governing the metal distributions between particulate and dissolved phases.

(4) Using new sampling techniques should be considered, for example passive DGT samplers (Diffusive gradients in thin films) to determine Zn isotope composition in surface water. DGT can pre-concentrate metals in situ and provide an isotope composition of water integrated over time. Moreover, DGT-measurable metal fractions are also considered as a proxy for the dissolved bioavailable metal fraction, which is a key factor when considering how metals impact the environment. precipitation/dissolution, zinc medium uptake by microorganisms and plants (Archer et al., 2004;[START_REF] Arnold | Iron and zinc isotope fractionation during uptake and translocation in rice (Oryza sativa) grown in oxic and anoxic soils[END_REF]Arnold et al., , 2010b;;[START_REF] Aucour | Dynamics of Zn in an urban wetland soil-plant system: Coupling isotopic and EXAFS approaches[END_REF][START_REF] Aucour | Fractionation of stable zinc isotopes in the zinc hyperaccumulator arabidopsis halleri and nonaccumulator arabidopsis petraea[END_REF][START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Ban | Zinc Isotope Separation by Ligand Exchange Chromatography Using Cation Exchange Resin[END_REF][START_REF] Bryan | Zinc isotope fractionation during adsorption onto Mn oxyhydroxide at low and high ionic strength[END_REF][START_REF] Caldelas | Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc[END_REF][START_REF] Couder | Transpiration flow controls Zn transport in Brassica napus and Lolium multiflorum under toxic levels as evidenced from isotopic fractionation[END_REF][START_REF] Coutaud | Zn isotope fractionation during interaction with phototrophic biofilm[END_REF][START_REF] Dong | Zinc isotope fractionation during adsorption to calcite at high and low ionic strength[END_REF][START_REF] Fernandez | Fractionation of Cu, Fe, and Zn isotopes during the oxidative weathering of sulfide-rich rocks[END_REF][START_REF] Gélabert | Interaction between zinc and freshwater and marine diatom species: Surface complexation and Zn isotope fractionation[END_REF][START_REF] Gou | Zinc Isotope Fractionation during Sorption onto Al Oxides: Atomic Level Understanding from EXAFS[END_REF][START_REF] Guinoiseau | Zn isotope fractionation during sorption onto kaolinite[END_REF][START_REF] Houben | Impact of root-induced mobilization of zinc on stable Zn isotope variation in the soil-plant system[END_REF][START_REF] Jamieson-Hanes | Evaluating zinc isotope fractionation under sulfate reducing conditions using a flow-through cell and in situ XAS analysis[END_REF]John et al., 2007a;[START_REF] John | A role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes[END_REF][START_REF] Jouvin | Stable isotopes of Cu and Zn in higher plants: Evidence for Cu reduction at the root surface and two conceptual models for isotopic fractionation processes[END_REF][START_REF] Jouvin | Zinc Isotopic Fractionation: Why Organic Matters[END_REF][START_REF] Juillot | Zn isotopic fractionation caused by sorption on goethite and 2-Lines ferrihydrite[END_REF][START_REF] Kafantaris | Zinc isotope fractionation during surface adsorption and intracellular incorporation by bacteria[END_REF][START_REF] Nelson | Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces[END_REF][START_REF] Pokrovsky | Zinc stable isotope fractionation during its adsorption on oxides and hydroxides[END_REF][START_REF] Samanta | Zinc isotope fractionation by Emiliania huxleyi cultured across a range of free zinc ion concentrations[END_REF][START_REF] Smolders | Isotopic fractionation of Zn in tomato plants suggests the role of root exudates on Zn uptake[END_REF][START_REF] Tang | Zinc Isotope Fractionation in the Hyperaccumulator Noccaea caerulescens and the Nonaccumulating Plant Thlaspi arvense at Low and High Zn Supply[END_REF][START_REF] Veeramani | Zinc isotope fractionation as an indicator of geochemical attenuation processes[END_REF][START_REF] Viers | Evidence of Zn isotopic fractionation in a soil-plant system of a pristine tropical watershed (Nsimi, Cameroon)[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF][START_REF] Weiss | Isotopic discrimination of zinc in higher plants[END_REF]. and suspended particulate matter (n=96) [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF]Chen et al., 2009b[START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF][START_REF] Thapalia | Zinc isotopic signatures in eight lake sediment cores from across the United States[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF]this study). Error bars represent the 2σ associated with δ 66/64 Zn values. Data are represented with light blue box-plot for "geological background for surface water" (GBSW) (n= 127), pink box-plot for WWTP effluents (n=5), brown box-plot for roof runoff (n=5), and red box-plot for non-exhaust road traffic emissions (n=18). The gray line labeled "BSE" is the mean of bulk silicate earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF]. The dashed lines represent theoretical mixing lines between the range of values for "GBSW contribution" and the "anthropogenic components" due to effluents, roof runoff and road traffic contributions.

FiguresFig. 1 .

 1 Figures

Fig. 7 .

 7 Fig. 7. δ 66/64 Zn value versus zinc content for urbanized rivers and lakes (a) dissolved load (n=46), (b) sediments

  Etudes de la Pollution Atmosphérique) estimates that about 300 metric tons of zinc is emitted into the atmosphere each year in France due to road traffic (Data: https://www.citepa.org/fr/air-etclimat/polluants/metaux-lourds/zinc).

	France, according to the IREP, 69 metric tons of zinc are emitted each year directly into
	surface	water	by	urban	WWTP	(2010-2017 average;
	http://www.irep.ecologie.gouv.fr/IREP/index.php). Galvanized zinc is widely used to cover
	roofs and weathering caused by rainwater carries large quantities of zinc into rivers. Gouzy
	and Brignon (2014) estimated that 6 metric tons of zinc are discharged each year into

surface water in France due to zinc roofing. Road traffic is also a substantial zinc emitter, through engines (gasoline), vehicle wear and tear (brakes, tires) and roadway equipment (safety barriers). As an example, CITEPA (Centre Interprofessionnel Technique d'

  [(CuSO4•5H2O + Ca(OH)2)], or other fungicides containing zinc, such as Mancozeb, a dithiocarbamate (C8H12MnN4S8Zn)[START_REF] Da Rosa Couto | Accumulation of copper and zinc fractions in vineyard soil in the mid-western region of Santa Catarina, Brazil[END_REF]. Until now, no Zn isotope analysis has been carried out on these products. The Bordeaux mixture has been widely used in European vineyards since the end of the 19 th century. Copper sulfate used in preparing the Bordeaux mixture may contain significant amounts of zinc[START_REF] Duplay | Copper, zinc, lead and cadmium bioavailability and retention in vineyard soils (Rouffach, France): The impact of cultural practices[END_REF]. Copper sulfate is produced industrially by treating copper metal with hot concentrated sulfuric acid or its oxides with dilute sulfuric acid. Chalcopyrite has δ 66/64 Zn values generally between -0.09 and +0.19‰ (n=11, IQR, Fig.S2), however given that fractionation can occur during the extraction of copper or the production of copper oxides and sulfates, we cannot use these values as a representative of the Bordeaux mixture.

  Particles released into the atmosphere from combustion in power plants should present wide δ 66/64 Zn variation because of the isotope variability of the burned material. For instance, the δ 66/64 Zn of coal varies between -0.10 and +1.35‰, and covers the range of GBSW values; (6) Treated wastewater effluents have δ 66/64 Zn between +0.06 and +0.08‰, lower than the GBSW values, possibly due to zinc-rich chemicals added during water treatment processes; (7) The δ 66/64 Zn for zinc roof runoff is lower (-0.10 to -0.02‰) compared to GBSW values; (8) Non-exhaust emissions resulting from road traffic have δ 66/64 Zn = +0.11 to +0.21‰, slightly depleted in heavy isotopes compared with GBSW values. Note that non-exhaust emissions and zinc-plated by hot-dip galvanization have close δ 66/64 Zn values because they are both derived from "common Zn".The little data available for gasoline show that δ 66/64 Zn are strongly depleted in heavy isotopes (between -0.50 and -0.23‰) compared to GBSW values; finally; (9) Organic fertilizers have δ 66/64 Zn values = +0.21 to +0.31‰ close to the GBSW values. Mineral fertilizers have wide variations (-0.06 to +0.42‰) that cover the range of GBSW values. Note that no data are available for crop protection treatments, which can have high Zn contents.

	δ 66/64 Zn values between +0.18 and +0.28‰, close to GBSW and zinc sulfide ore values; (2)
	Slags and water leaching the slag tailings have δ 66/64 Zn values between +0.51 and +1.20‰,
	higher than the GBSW values due to condensation and evaporation processes during
	smelting processes. Conversely, particles emitted by smelters into the atmosphere are
	strongly depleted in heavy isotopes, δ 66/64 Zn = -0.38 to +0.05‰ compared to GBSW values;
	(3) Industrial effluents (chemical industry, agro-food industry) have δ 66/64 Zn between +0.10
	and +0.15‰, lower than the GBSW values; (4) Electroplated zinc has an isotope signature of
	δ 66/64 Zn = -0.56 to -0.20‰, depleted in heavy isotopes relative to GBSW values because of
	isotope fractionation during the process, while zinc plated by hot-dip galvanization should
	have δ 66/64 Zn values close to "common zinc" (+0.15 to +0.22‰), slightly depleted in heavy
	isotopes compared to GBSW values; (5)

Acknowledgments

We are grateful to E. Decouchon, C. Innocent, D. Widory, J. Gattacceca and R. Millot for their help during sample collection and to S. Perret and R. Dupuy for sample preparation.

Thanks are also due to N. Baran, M. Barnier and X. Bourrain for helpful discussions. This work was financially supported by BRGM, AQUAREF (BRGM, IFREMER, INERIS, IRSTEA, LNE) and the Agence de l'eau Loire-Bretagne. Karen M. Tkaczyk edited the final English version of the paper. R. Wanty, E. Skierszkan and anonymous reviewers are thanked for their constructive comments and highlights, which greatly helped to improve the manuscript.

Fig. 2. Zinc isotope compositions for sulfide ores (n=294) and non-sulfide ores (n=23) [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF]Araújo et al., 2017a;[START_REF] Chapman | Chemical separation and isotopic variations of Cu and Zn from five geological reference materials[END_REF][START_REF] Deng | Insights into ore genesis of the Jinding Zn-Pb deposit, Yunnan Province, China: Evidence from Zn and in-situ S isotopes[END_REF][START_REF] Duan | Zinc and lead isotope signatures of the Zhaxikang Pb-Zn deposit, South Tibet: Implications for the source of the ore-forming metals[END_REF][START_REF] Gagnevin | Zn, Fe and S isotope fractionation in a large hydrothermal system[END_REF][START_REF] John | Zinc stable isotopes in seafloor hydrothermal vent fluids and chimneys[END_REF][START_REF] Kelley | Zinc isotopes in sphalerite from base metal deposits in the Red Dog District, Northern Alaska[END_REF][START_REF] Maréchal | Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry[END_REF][START_REF] Mason | Zn and Cu isotopic variability in the Alexandrinka volcanic-hosted massive sulphide (VHMS) ore deposit, Urals, Russia[END_REF][START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF][START_REF] Mondillo | A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control[END_REF][START_REF] Novak | Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime[END_REF][START_REF] Pašava | Zinc and sulfur isotope variation in sphalerite from carbonate-hosted zinc deposits, Cantabria, Spain[END_REF][START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF][START_REF] Sonke | Historical variations in the isotopic composition of atmospheric zinc deposition from a zinc smelter[END_REF][START_REF] Voldrichova | Zinc isotope systematics in snow and ice accretions in Central European mountains[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF][START_REF] Weiss | Atmospheric deposition and isotope biogeochemistry of zinc in ombrotrophic peat[END_REF][START_REF] Wilkinson | Zinc isotope variation in hydrothermal systems: Preliminary evidence from the Irish Midlands ore field[END_REF][START_REF] Zhou | Zinc, sulfur and lead isotopic variations in carbonate-hosted Pb-Zn sulfide deposits, southwest China[END_REF]. The mean value for each sample type is represented by a black cross. Box-plots are drawn for sulfide ore data in blue and for non-sulfide ore data in red. The vertical gray line labeled "BSE" is the mean of bulk silicate earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF]. 56 [START_REF] Araújo | Assessment of the metal contamination evolution in the Loire estuary using Cu and Zn stable isotopes and geochemical data in sediments[END_REF][START_REF] Araújo | Zinc isotopes as tracers of anthropogenic sources and biogeochemical processes in contaminated mangroves[END_REF](Araújo et al., , 2017a(Araújo et al., , 2017b;;[START_REF] Chen | Zn isotope compositions of the thermal spring waters of La Soufrière volcano, Guadeloupe island[END_REF]Chen et al., , 2009b[START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Guinoiseau | Fate of particulate copper and zinc isotopes at the Solimões-Negro river confluence, Amazon Basin, Brazil[END_REF][START_REF] Guinoiseau | Zinc and copper behaviour at the soil-river interface: New insights by Zn and Cu isotopes in the organic-rich Rio Negro basin[END_REF][START_REF] Little | The oceanic mass balance of copper and zinc isotopes, investigated by analysis of their inputs, and outputs to ferromanganese oxide sediments[END_REF][START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Petit | Development of Cu and Zn isotope MC-ICP-MS measurements: Application to suspended particulate matter and sediments from the scheldt estuary[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Thapalia | Zinc isotopic signatures in eight lake sediment cores from across the United States[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF]this study). Error bars represent the 2σ associated with δ 66/64 Zn values. Data are also represented with blue box-plots for dissolved zinc in non-impacted rivers without estuary samples (n=46) and solid zinc in non-impacted rivers without Amazon samples (n=81).The horizontal gray line labeled "BSE" is the mean of Bulk Silicate Earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF].

57 and organic fertilizer (n=5) are represented with box-plots [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Bigalke | Stable Cu and Zn isotope ratios as tracers of sources and transport of Cu and Zn in contaminated soil[END_REF][START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Cloquet | Isotopic composition of Zn and Pb atmospheric depositions in an urban/periurban area of northeastern France[END_REF][START_REF] Couder | Zinc isotopes in polluted substrates The influence of phase separation on the flow patterns of mid-ocean ridge hydrothermal systems[END_REF][START_REF] Dong | Isotopic signatures suggest important contributions from recycled gasoline, road dust and non-exhaust traffic sources for copper, zinc and lead in PM10 in London, United Kingdom[END_REF][START_REF] Fekiacova | Tracing contamination sources in soils with Cu and Zn isotopic ratios[END_REF][START_REF] Gelly | Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago[END_REF]John et al., 2007b;[START_REF] Juillot | Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France[END_REF][START_REF] Mattielli | Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb-Zn refinery[END_REF][START_REF] Ochoa Gonzalez | Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion[END_REF][START_REF] Shiel | Evaluation of zinc, cadmium and lead isotope fractionation during smelting and refining[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF][START_REF] Skierszkan | Molybdenum and zinc stable isotope variation in mining waste rock drainage and waste rock at the Antamina mine[END_REF][START_REF] Souto-Oliveira | Multi-isotopic fingerprints (Pb, Zn, Cu) applied for urban aerosol source apportionment and discrimination[END_REF][START_REF] Thapalia | Zn and Cu isotopes as tracers of anthropogenic contamination in a sediment core from an Urban Lake[END_REF][START_REF] Yin | Zn isotopes fractionation during slags' weathering: One source of contamination, multiple isotopic signatures[END_REF]this study).

"Hot dip" galvanized materials (n=3), zinc electroplated hardware (n=3), exhaust road traffic emission (n=2) and mineral fertilizer (n=4) are represented by dot symbols [START_REF] Chen | Zinc isotopes in the Seine River waters, France: A probe of anthropogenic contamination[END_REF][START_REF] Gioia | Accurate and precise zinc isotope ratio measurements in urban aerosols[END_REF][START_REF] Szynkiewicz | Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition[END_REF]. The estimated values for slags and particles coming from zinc smelter, for electrogalvanized hardware and for particles issued from coal combustion and waste incineration are also represented with horizontal lines. Dissolved zinc in non-impacted rivers (n=46), solid zinc in non-impacted rivers (n=81) and "geological background for surface water" (GBSW) (n= 127) are represented by box-plots. The BSE value (+0.28 ± 0.05‰, 2σ) and the non-impacted river domain are represented by vertical lines [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF]. 58 Fig. 5. δ 66/64 Zn value versus zinc content for dissolved zinc in rivers and groundwater in mining area (n=107) [START_REF] Aranda | Zinc isotope investigation of surface and pore waters in a mountain watershed impacted by acid rock drainage[END_REF][START_REF] Balistrieri | Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water[END_REF][START_REF] Borrok | Application of iron and zinc isotopes to track the sources and mechanisms of metal loading in a mountain watershed[END_REF][START_REF] Szynkiewicz | Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition[END_REF][START_REF] Wanty | Zinc isotope and transition-element dynamics accompanying hydrozincite biomineralization in the Rio Naracauli, Sardinia, Italy[END_REF] this study). Error bars represent the 2σ associated with δ 66/64 Zn values. The mean value for each type of samples (USA & France, and Sardinia) is represented by a black cross. Data are represented with light blue box-plot for "geological background for surface water" (GBSW) (n= 127), pink box-plot for rivers and groundwater in mining area (n=107), with green box-plot for mining solid wastes and effluents (n=34) and with blue box-plot for sulfide ores (n=294).The gray line labeled "BSE" is the mean of bulk silicate earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF].

59 Fig. 6. δ 66/64 Zn value versus zinc content for sediments and suspended particulate matter in river and bay impacted by metallurgical industries (n=100) [START_REF] Araújo | Zinc isotopes as tracers of anthropogenic sources and biogeochemical processes in contaminated mangroves[END_REF](Araújo et al., , 2017a(Araújo et al., , 2017b;;[START_REF] Petit | The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France[END_REF][START_REF] Sivry | Zn isotopes as tracers of anthropogenic pollution from Zn-ore smelters The Riou Mort-Lot River system[END_REF]. Error bars represent the 2σ associated with δ 66/64 Zn values. Data are represented with light blue box-plot for "geological background for surface water" (GBSW) (n= 127) and pink box-plot for slag (n=11). The estimated values for slags are also represented with a pink line. The gray line labeled "BSE" is the mean of bulk silicate earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF]. The black dashed lines represent theoretical mixing lines between the range of values for "GBSW contribution" and for the "anthropogenic component" due to metallurgical activities (i.e. slags). box-plot for organic fertilizer (n=5). The gray line labeled "BSE" is the mean of bulk silicate earth: 0.28 ± 0.05‰ (2σ) [START_REF] Chen | Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth[END_REF].