Caiyan Feng

Zoyne Pedrero
email: zoyne.pedrerozayas@univ-pau.fr

Lázaro Lima

Susana Olivares

Daniel De

La Rosa

Sylvain Bérail

Emmanuel Tessier

Florence Pannier

David Amouroux

Daniel De La Rosa

Sylvain Berail

Enmanuel Tessier

Assessment of Hg contamination by a Chlor-Alkali Plant in riverine and coastal sites combining Hg speciation and isotopic signature (Sagua la Grande River, Cuba)

Keywords:

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Chlor-alkali plants (CAP) which use mercury (Hg) in electrolytic cell manufacture has been identified as one of the major sources of Hg pollution. Although alternative methods were established to replace the Hg-cell process [START_REF]Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport[END_REF], many older plants are still in operation in some undeveloped areas [START_REF] Yera | Thermal Treatment for Decontamination of Mercury Containing Wastes From Chlor-Alkali Industry[END_REF]. Due to the large amounts, Hg contamination caused by released legacy Hg is still an environmental threat in nowadays and future even when Hg-cell technology is eliminated from CAP [START_REF]Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport[END_REF][START_REF] Unep | Global Mercury Assessment[END_REF][START_REF]UNEP, Global Estimate of Global Mercury Cell Chlorine Capacity, World Chlorine Report to UNEP on Chlor-Alkali Partnership Data[END_REF]. High Hg concentrations have been reported in sediments and some carnivorous fish (reaching values up to 100 μg g -1 and 5000 ng g -1 , respectively) from different reservoirs and rivers affected by CAP [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Bravo | Mercury human exposure through fish consumption in a reservoir contaminated by a chlor-alkali plant: Babeni reservoir (Romania)[END_REF][START_REF] De La Rosa | Assessment of total mercury levels in Clarias gariepinus from the Sagua la Grande River, Cuba[END_REF][START_REF] Bravo | Extremely elevated methyl mercury levels in water, sediment and organisms in a Romanian reservoir affected by release of mercury from a chlor-alkali plant[END_REF][START_REF] Olivares-Rieumont | Mercury levels in sediments and mangrove oysters, Crassostrea rizophorae, from the north coast of Villa clara, Cuba, Bull[END_REF][START_REF] Diaz-Asencio | One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from 210Pb and 137Cs chronology[END_REF][START_REF] Wiederhold | Mercury isotope signatures in contaminated sediments as a tracer for local industrial pollution sources[END_REF][START_REF] Bonsignore | Tracing mercury pathways in Augusta bay (southern Italy) by total concentration and isotope determination[END_REF]. In the aquatic ecosystems, Hg mainly exists as inorganic Hg (iHg) in sediments and water. However, a small fraction of iHg can be transformed into methylmercury (MeHg), a neurotoxin for human and wildlife health, mainly through biotic or microbial processes [START_REF] Gilmour | Sulfate stimulation of mercury methylation in freshwater sediments[END_REF][START_REF] Monperrus | Mercury methylation, demethylation and reduction rates in coastal and marine surface waters of the Mediterranean Sea[END_REF] and minorly through abiotic processes [START_REF] Ullrich | Mercury in the aquatic environment: a review of factors affecting methylation[END_REF]. MeHg gains great concerns not only due to its toxicity but also considering its efficient bioaccumulation and biomagnification through the food web in comparison to iHg [START_REF] Ullrich | Mercury in the aquatic environment: a review of factors affecting methylation[END_REF][START_REF] Watras | Bioaccumulation of mercury in pelagic freshwater food webs[END_REF].

The quantification of Hg and its species have been effectively used to evaluate regional environmental pollution [START_REF] Bravo | Mercury human exposure through fish consumption in a reservoir contaminated by a chlor-alkali plant: Babeni reservoir (Romania)[END_REF][START_REF] Bravo | Extremely elevated methyl mercury levels in water, sediment and organisms in a Romanian reservoir affected by release of mercury from a chlor-alkali plant[END_REF][START_REF] Feng | Human exposure to methylmercury through rice intake in Mercury Mining Areas, Guizhou Province, China[END_REF]. More recently Hg isotopic composition has been widely applied in the identification, discrimination and quantification of Hg anthropogenic sources and biogeochemical processes before its introduction into the food web [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Gehrke | Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes[END_REF][START_REF] Yin | Identifying the sources and processes of mercury in subtropical estuarine and ocean sediments using Hg isotopic composition[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. Hg isotopic signature has also been used to study the Hg isotopic fractionation during Hg trophic transfer [START_REF] Kwon | Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity[END_REF][START_REF] Kwon | Application of mercury isotopes for tracing trophic transfer and internal distribution of mercury in marine fish feeding experiments[END_REF][START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF] and metabolic processes in vivo from aquatic organisms to humans [START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF][START_REF] Laffont | Anomalous mercury isotopic compositions of fish and human hair in the Bolivian Amazon[END_REF][START_REF] Laffont | Hg speciation and stable isotope signatures in human hair as a tracer for dietary and occupational exposure to mercury[END_REF][START_REF] Sherman | New insight into biomarkers of human mercury exposure using naturally occurring mercury stable isotopes[END_REF][START_REF] Li | Assessing sources of human methylmercury exposure using stable mercury isotopes[END_REF]. Hg fractionates as mass dependent fractionation (MDF) and mass independent fractionation (MIF). MDF can be induced during multiple biogeochemical processes such as methylation [START_REF] Rodŕiguez-Gonźalez | Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic bacteria (Desulfobulbus propionicus) under dark conditions[END_REF][START_REF] Perrot | Identical Hg isotope mass dependent fractionation signature during methylation by sulfate-reducing Bacteria in sulfate and sulfate-free environment[END_REF], demethylation [START_REF] Kritee | Mass dependent stable isotope fractionation of mercury during mer mediated microbial degradation of monomethylmercury[END_REF][START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF] and reduction [START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF][START_REF] Kritee | Mercury stable isotope fractionation during reduction of Hg(II) to Hg(0) by mercury resistant microorganisms[END_REF]. MIF in aquatic ecosystems is mainly recognized to occur during photo-reaction (photo-reduction/demethylation), which has been successfully exploited for tracking Hg sources [START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF]. In addition, one study has suggested that MIF effect may occur during photochemical oxidation of Hg in the upper atmosphere [START_REF] Chen | Unusual fractionation of both odd and even mercury isotopes in precipitation from Peterborough, ON, Canada, Geochimi[END_REF].

Sediments act as an important sink for anthropogenic Hg pollution (e.g. industry, mining, urban discharges, atmospheric deposition, etc). In sediments, total Hg isotopic composition has been reported as the sum of both anthropogenic and background contributions, whose isotopic composition can be differentiated [START_REF] Yin | Identifying the sources and processes of mercury in subtropical estuarine and ocean sediments using Hg isotopic composition[END_REF][START_REF] Blum | Mercury isotopes in earth and environmental sciences[END_REF]. However, in highly contaminated sediment, the Hg isotopic compositions are dominated by the contamination source as a result of pool size effect [START_REF] Balogh | Tracking the fate of mercury in the fish and bottom sediments of Minamata Bay, Japan, using stable mercury isotopes[END_REF][START_REF] Wiederhold | Metal stable isotope signatures as tracers in environmental geochemistry[END_REF]. Despite that sediments represent the main Hg source to the surrounding food web, biota may display a different Hg isotopic signature according to the trophic position as shown in previous studies [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. Higher MDF values are observed in biota compared to their nearby sediments in most of the investigated Hg contaminated lakes, coastal oceans or reservoirs ecosystem [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Bonsignore | Tracing mercury pathways in Augusta bay (southern Italy) by total concentration and isotope determination[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF], which were in contrast to one recent study in a stream contaminated by historical gold mining [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. The mentioned MDF variations are probably related to biogeochemical processes such as methylation/demethylation, but also to environmental aspects (turbidity, water flow rate, etc) in each specific system [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. MIF extent in contaminated sediment is generally close to zero [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Wiederhold | Mercury isotope signatures in contaminated sediments as a tracer for local industrial pollution sources[END_REF][START_REF] Bonsignore | Tracing mercury pathways in Augusta bay (southern Italy) by total concentration and isotope determination[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. However, a wide range of positive MIF values is observed in biota, which is attributed to the MIF signature of MeHg inherited from photo-degradation [START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF]. Though rarely exception has been observed in which slightly negative MIF of MeHg have been found in aquatic biota, suggesting nearly absence of photo-degradation in certain habitats [START_REF] Tsui | Understanding sources of methylmercury in songbirds with stable mercury isotopes: challenges and future directions[END_REF]. To date, a better comprehension of the biogeochemical fate of Hg species can be established in contaminated sites by combining MDF and MIF signatures, while several hypotheses still need to be validated among different impacted ecosystems.

Sagua la Grande River (SG River), Cuba, hosted a CAP with Hg-cell technology since early 1980s [START_REF] Diaz-Asencio | One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from 210Pb and 137Cs chronology[END_REF] and still working [START_REF] Yera | Thermal Treatment for Decontamination of Mercury Containing Wastes From Chlor-Alkali Industry[END_REF]. Despite a wastewater treatment system that installed to trap Hg in 1990 [START_REF] De La Rosa | Assessment of total mercury levels in Clarias gariepinus from the Sagua la Grande River, Cuba[END_REF][START_REF] Olivares-Rieumont | Mercury levels in sediments and mangrove oysters, Crassostrea rizophorae, from the north coast of Villa clara, Cuba, Bull[END_REF][START_REF] Diaz-Asencio | One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from 210Pb and 137Cs chronology[END_REF] and Hg-immobilized sludge is disposed in concrete niches [START_REF] Yera | Thermal Treatment for Decontamination of Mercury Containing Wastes From Chlor-Alkali Industry[END_REF], due to its low efficiency, Hg contaminations in the sediments remain in the river and even extend to the coastal zone [START_REF] Olivares-Rieumont | Mercury levels in sediments and mangrove oysters, Crassostrea rizophorae, from the north coast of Villa clara, Cuba, Bull[END_REF][START_REF] Diaz-Asencio | One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from 210Pb and 137Cs chronology[END_REF]. Hg levels in omnivorous fish from the mentioned ecosystem reach values up to 700 ng g -1 (d w). In this work, Hg concentration, speciation and isotopic composition were determined in selected surface sediments and biota samples which are frequently consumed by local populations, including catfish (Claria gariepinus) from the riverine section and oysters (Crassostrea rizophorae) from the coastal zone. The same fish species from Mampostón Dam (M Dam, fish farming away from SG River, Cuba), was used as a control. The main objective of this work is to estimate the Hg contamination extent and its fate from the CAP (SG River) by combining its speciation and isotopic composition in both sediments and biota. The obtained data is also compared to other Hg contaminated aquatic ecosystems investigated by using a similar approach.

Materials and methods

Study area and sampling details

Monitoring was performed from 2008 to 2010. Sediments from six sampling sites along SG River (Fig. 1, Table S1, Table S2) were collected: Ss(0), located at 2.54 km upper from the confluence of the old CAP waste discharge stream within SG River, was considered a river background ("SG River background"). Three sampling sites were selected as "SG River Upper": Ss(1) is in the vicinity of the old CAP discharge to evaluate the influence of historical pollution and Ss(2) ˜Ss(3) are close to the CAP's new discharge point as indicators of CAP activi ties nowadays. Ss(4) ˜Ss [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF] sites are considered as "SG River Lower". In the coastal zone (Fig. 1, Table S2), located at around 12 km from the SG River, including river estuary and some small keys near the coast, three sediments samples Sc(1) ˜Ss(3) were collected.

Regarding biota, fish samples were collected close to the sediments' stations. Three wild catfish individuals (Fs(1)˜Fs( 3)) (Table S3) were caught randomly in SG River between sites S S (3) and Ss [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF]. Considering that catfish is not a sedentary species [START_REF] Lucas | Migration of Freshwater Fishes[END_REF], Hg concentration in such animals should not be consider as a specific indicator of Hg in the precise sampling site. Oysters samples (Oc(1)˜Oc(3)) represent a pool of several individuals which were corresponding to each coastal sediment sampling sites (Fig. 1, Table S3) from the mangrove roots or local oysters' farms. The soft tissues of oyster are selected for analysis. In M Dam, an artificial lake, five catfish individuals (Fm(1)˜Fm( 5)) were collected directly from farms. Animals from this location are fed with bycatch product prepared for fish farming [START_REF] Iglesias | Evaluación de los desechos frescos de pescado y ensilados como única fuente de proteína animal en la alimentación de híbrido de Clarias (Clarias gariepinus x C. macrocephalus[END_REF][START_REF] Llanes Iglesias | Efecto de diferentes niveles de alimentación para Clarias gariepinus en preceba[END_REF], and therefore, considered as an unpolluted biota control (Table S3).

Hg speciation analysis

Sample digestion was carried out with TMAH (tetramethylammonium hydroxide) and HNO 3 for biota and sediments, respectively, in an analytical microwave and analyzed by GC-ICP-MS as detailed elsewhere [START_REF] Monperrus | Evaluating the potential and limitations of double-spiking species-specific isotope dilution analysis for the accurate quantification of mercury species in different environmental matrices[END_REF][START_REF] Clemens | Mercury speciation analysis in seafood by species-specific isotope dilution: method validation and occurrence data[END_REF][START_REF] Rodríguez Martin-Doimeadios | Using speciated isotope dilution with GC-inductively coupled plasma MS to determine and unravel the artificial formation of monomethylmercury in certified reference sediments[END_REF]. Quantification of Hg species was carried out using species specific isotope dilution by adding the adequate amount of isotopically enriched Hg standards ( 199 iHg and 201 MeHg) and by applying isotope pattern deconvolution for data treatment [START_REF] Monperrus | Evaluating the potential and limitations of double-spiking species-specific isotope dilution analysis for the accurate quantification of mercury species in different environmental matrices[END_REF][START_REF] Clemens | Mercury speciation analysis in seafood by species-specific isotope dilution: method validation and occurrence data[END_REF]. Reference materials were analyzed following the same strategy, for method validation (Table S4).

Hg isotopes analysis

Sediments samples (0.2-0.5 g) were digested at 95 °C for 3 h in a Hot Block, (Environmental Express), using 5 mL fresh mixture of HCl and HNO 3 (3:1, v:v). Biological samples, fish and oysters (0.2-0.5 g), were digested with 5 mL HNO 3 in HPA (High Pressure Asher, Anton-Paar), followed by the addition of 1.5 mL H 2 O 2 adding to the obtained extract [START_REF] Estrade | Measuring hg isotopes in bio-geo-environmental reference materials[END_REF]. The yield of THg extracted ranged between 80%-120% (Table S9). Hg isotopic composition was determined by cold-vapor MC-ICP-MS as detailed elsewhere [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF].

MDF is reported as δ 202 Hg in permil (‰) related to NIST SRM 3133 and calculated as: [START_REF] Blum | Reporting of variations in the natural isotopic composition of mercury[END_REF] (1)

MIF represents the difference between the measured δ

xxx Hg value and the value predicted in theoretical based on MDF law [START_REF] Blum | Reporting of variations in the natural isotopic composition of mercury[END_REF]. MIF is thus reported as capital delta notation as suggested elsewhere [START_REF] Blum | Reporting of variations in the natural isotopic composition of mercury[END_REF], according to the following equations:

(2)

We use Δ 201 Hg as the default value to report MIF in this study. The analytical uncertainty is assumed as 2 times the standard deviation (2SD) from replicate analysis of the UM-Almadén secondary standard during each analytical session. Sediments (IAEA 405) and fish muscle (BCR 464) reference materials were used for data validation (Table S5).

Results and discussions

Hg speciation and distribution in sediments and biota

Sediments

Total Hg (THg) concentrations in sediments exhibit a wide variability along the SG River (Fig. 2a, Table S6), decreasing from the CAP discharge point to the coastal zone. Meanwhile SG River background site (Ss(0)) exhibits the lowest THg concentration (149 ± 6 ng g -1

). Higher THg concentrations are observed in the SG River "upper zone", close to the new (Ss(2)) and the old (Ss(1)) CAP discharge points (5072 ± 34 ng g -1 and 1788 ± 36 ng g -1

, respectively). THg concentrations in the sediments from SG River "lower zone" are relatively lower, ranging from 196 to 764 ng g -1 , which are within the same range as in sediments from the coastal zone (from 165 to 301 ng g -1 ). In the coastal area, the estuarine site Sc(1) displays higher THg concentration at the river mouth compare to farther coastal sites. This clearly indicates the strong contribution of the SG River on Hg distribution along the coastal zone.

As presented in Table 1, highest Hg levels in sediments from SG River are comparable to the other contaminated sites such as Bratsk Water Reservoir (Russia), in the vicinity of a CAP [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF]. Relatively lower THg concentrations in sediments from SG River lower portion and the coastal zone nearby are similar to those found in estuaries sediments from Northeastern Coast of U.S.A. impacted by local wastewater and industrial discharges [START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF]. THg content and distribution pattern from SG River to the coastal zone is similar to the one recently reported at Yuba River [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF].

MeHg concentrations in the sediments display a similar pattern to THg along SG River and the coastal zone (Fig. 2a, Table S6). The maximum value (16 ± 4 ng g -1

) is observed at the CAP wastewater discharge point (Ss(2)) and relatively high values (˜6 ng g -1

) are observed in the old discharge point (Ss(1)) and lower site (Ss( 5)). All the other sites, including the river background Ss(0) and the coastal zone, exhibit similar MeHg concentration around 2 ng g -1

. The fraction of THg present as MeHg (referred as % MeHg hereafter) is approximately 0.33% in sediments along SG River (Ss(1) to Ss(4) sites). It is found within the range (<0.5% MeHg) of estuarine and marine sediments reported by Ullrich et al [START_REF] Ullrich | Mercury in the aquatic environment: a review of factors affecting methylation[END_REF]. Higher %MeHg is observed in coastal zone sediments (Sc(1) to Sc(3)), where it can reach up to 1%. Prominent %MeHg results are observed in the SG River background site (Ss(0)) and lower site (Ss( 5)) exhibiting 1.7% and 3.1%, respectively. Organic matter (OM) plays an important role on Hg methylation [START_REF] Ullrich | Mercury in the aquatic environment: a review of factors affecting methylation[END_REF]. High OM levels are associated to a decrease of sediments oxygenation, which enhances Hg methylation by anaerobic bacteria, and consequently MeHg accu mulation in biota [START_REF] Ullrich | Mercury in the aquatic environment: a review of factors affecting methylation[END_REF]. In this study, OM (12 ± 2%) (Table S7), is quite homogenous among the sediments and insignificantly correlated with %MeHg (r = 0.563, p = 0.114, n = 9) (Table S8). Therefore, the high %MeHg in the mentioned sites should not be attributed to OM, but related to other environmental parameters (temperature, pH, redox potential).

Biota

THg average concentration in catfish muscle from SG River is 1093 ± 319 ng g -1 (Fig. 2b, Table S6), which is approximately 10 times higher than in fish from the control site (M Dam: 107 ± 36 ng g -1

), though fish size and weight are similar in the two sampling sites. Regarding Hg levels in oysters from the coastal site, it varies between 491 and 732 ng g -1

. Hg content in biota samples of the current study exhibits similar or even higher values than in other polluted areas (Table 1). As expected, %MeHg varies according to both, the organism trophic level and its habitat. For catfish, %MeHg in SG River (72 ± 19%) is not significantly different from M Dam control site (80 ± 12%) (p = 0.456). In contrast, due to their lower trophic position, %MeHg in oyster tissues is less than 50%. The difference of %MeHg in biota reflects both, the different extents of bioaccumulation between iHg and MeHg through the food web and the significant intake of iHg due to its higher exposure level in contaminated sites [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF]. ,4). It should be noticed that the lowest Δ 201 Hg value (-0.18 ± 0.08‰) corresponds to the sampling site (Ss( 2)) which has a slight offset (-0.14‰) from the other sites (-0.04 ± 0.04‰). Considering the proximity of the mentioned sampling point to the CAP and that it exhibits the highest Hg concentration, Hg levels reported in soils close to the CAP are relatively low (in the range of 1-170 ng/g with average value of 34 ± 47 ng/g) [START_REF] Quero-Jiménez | Determinación de la contaminación por metales pesados en suelos aledaños a la empresa electroquímica de Sagua[END_REF], it seems that this negative MIF correspond to the Hg CAP discharge. Element liquid Hg is used in CAP electrolysis process. Hg could be discharged into environment through wastewater, solid waste (sludge), and the atmosphere in the form of Na-Hg amalgam, Hg(II) (HgCl 2 , HgSO 4 and HgO etc), and Hg (0) during the CAP production process [START_REF] Yera | Thermal Treatment for Decontamination of Mercury Containing Wastes From Chlor-Alkali Industry[END_REF][START_REF] Biester | Binding and mobility of mercury in soils contaminated by emissions from chlor-alkali plants[END_REF][START_REF] Hissler | Chlor-alkali industrial contamination and riverine transport of mercury: distribution and partitioning of mercury between water, suspended matter, and bottom sediment of the Thur River, France[END_REF]. The processes, including evaporation of elemental Hg, Na-Hg amalgam formation and decomposition, the oxidative transformation from Hg(0) to Hg(II), Hg binding to organic matter and sulfide phases in the contaminated sediments, will cause Hg undergo MDF and MIF and record Hg isotopic signature in sediments [START_REF] Wiederhold | Mercury isotope signatures in contaminated sediments as a tracer for local industrial pollution sources[END_REF]. The slight negative MIF value observed in sediments may be related to the element Hg evaporation process, which is accompanied by MIF caused by nuclear volume fractionation [START_REF] Ghosh | Estimation of nuclear volume dependent fractionation of mercury isotopes in equilibrium liquid-vapor evaporation experiments[END_REF]. The variation of Δ 201 Hg values among the adjacent sampling sites remains insignificant (<0.1‰) compared to the analytical uncertainty. However, a decreasing trend of Δ 201 Hg values from background riverine and coastal sites to most polluted sites is still observed, indicating the pollution from CAP to the pristine site (Fig. 3a). It should be mentioned that the MIF signature in sediments in the vicinity of SG CAP (Δ 201 Hg: -0.05 ± 0.13‰) matches the ones found in the area of the CAP at Bratsk Water Reservoir (Δ 201 Hg: -0.02 ± 0.09‰) [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF], Brackish Water at Skutskär and Köpmanholmen sites in Sweeden (Δ 201 Hg: -0.02 ± 0.02‰) [START_REF] Wiederhold | Mercury isotope signatures in contaminated sediments as a tracer for local industrial pollution sources[END_REF] and Augusta Bay in Italy (Δ 201 Hg: -0.02 ± 0.03‰) [START_REF] Bonsignore | Tracing mercury pathways in Augusta bay (southern Italy) by total concentration and isotope determination[END_REF].

Hg isotopic composition in

MDF isotopic signature in sediments MDF values (δ 202

Hg) in sediments (Fig. 3) vary significantly, exhibiting a shift of approximately 1‰ (from -0.51‰ to 0.42‰) between the coastal zone and SG River upper portion. This variation is slightly larger than the one observed at Yuba River sediments, where δ 202 Hg decrease from -0.18‰ to -0.95‰ along the river [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. The significant decrease trend of MDF values from SG River upper portion to the coastal zone is in good agreement with THg distribution (Fig. 3b). The highest positive δ 202 Hg value corresponds to the CAP closest site (Ss(2)), which also exhibits the highest Hg concentration. Lower MDF isotopic signatures are observed in both SG River background end-member (upstream to the CAP) and the coastal zone, exhibiting negative δ 202 Hg values down to -0.48 and -0.51‰, respectively. The δ 202 Hg variations in sediments are attributed to the Hg transport and consequently to the distance from the CAP discharge point (Fig. 3a). In order to confirm the main influence of the CAP inputs, δ 202 Hg values were plotted against 1/THg concentrations [START_REF] Wiederhold | Metal stable isotope signatures as tracers in environmental geochemistry[END_REF] in sediments (Fig. 3b). The resulting graphic exhibits a linear negative correlation (r= -0.675, p < 0.05) which demonstrates a binary mixing relationships between a background end-member (both SG river background and coastal end-members) and the main Hg anthropogenic source (Fig. 3b). Taking these results, by using a simple binary mixing model [START_REF] Wiederhold | Metal stable isotope signatures as tracers in environmental geochemistry[END_REF], CAP contribution to the THg content in sediments along the river to coastal transect is estimated as 60-65%, 1-28%, and 2-38% in SG River upper portion, lower portion and coastal sediments.

An abnormal MDF signature is observed in the site Ss(5), being higher than in the nearby upper site Ss(4). In order to discriminate different Hg sources, elements compositional characteristic of the sediments was compared (see details in Supplementary Information). The distribution of conservative lithogenic tracers (e.g. Ti) usually reflects mineralogical origins and grain size distribution of the sediments. The δ 202 Hg relative to Hg content normalized by Ti, clearly reveals a difference between Ss(5) site and the other sites (Fig. S2). Therefore such anomaly in the isotopic composition (0.26‰) may result from the contribution of other Hg sources. Considering that Cu, Pb and Zn concen For the Florida Lake, data were selected from three lakes (Lake Rousseau, Little Lake Henderson, Lake Davis), where sediments and fish were both collected, all of these lakes are <50 m to the Coal-Fired Utility. For the Northeastern Coast in U.S.A, the estuaries were selected only the contaminated estuaries: the most polluted estuary (Mill Creek, New Jersey (MILL)), less contaminated estuaries (Bold Point, Rhode Island (BOLD) and Barn Island, Connecticut (BARN) ) for comparison. For the Yuba River upstream, one sediment sample is treated as an outlier and excluded. trations (Table S7) reached their highest values at Ss(5), the contribution of an additional pollution source should be considered, although no other direct evidence can be established with this single sample. Hg) of 0.13 ± 0.03‰ and 1.09 ± 0.11‰, respectively. MIF signature in oysters from the coastal zone (Δ 201 Hg 0.16 ± 0.08‰) matches the pattern exhibited by fish from SG River (Fig. 4, Table 1), probably as a result of the CAP impact. These Δ 201 Hg values in catfish and oysters are in the same range of that reported in the biota contaminated by other anthropogenic Hg sources (0.1‰˜1‰) (Table 1). Positive MIF signature in biota from aquatic ecosystems has been associated to the incorporation of MeHg resulting from photo-chemical processes [START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF]. The relatively larger MIF values of catfish from M Dam could be partially a consequence of their diet (marine bycatch products [START_REF] Iglesias | Evaluación de los desechos frescos de pescado y ensilados como única fuente de proteína animal en la alimentación de híbrido de Clarias (Clarias gariepinus x C. macrocephalus[END_REF][START_REF] Llanes Iglesias | Efecto de diferentes niveles de alimentación para Clarias gariepinus en preceba[END_REF] Hg has been used to distinguish between photochemical degradation and reduction of MeHg versus iHg in natural aquatic ecosystems, with values of 1.34 ± 0.04 and 1.00 ± 0.01, respectively [START_REF] Bergquist | Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems[END_REF]). However, it should be considered that this catfish species is usually fed by a wide variety of prey like insects, plankton, rotting flesh, plants, invertebrates and small fish [START_REF] De La Rosa | Assessment of total mercury levels in Clarias gariepinus from the Sagua la Grande River, Cuba[END_REF]. The difference of Hg MIF in fish between the two sites cannot be exclusively related to their diet, significantly lower Hg residence time and water clarity that influence light exposure [START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF] in rivers compared to lakes could also play a key role on the MIF divergences observed, as influenced by photo-chemical processes.

U N C O R R E C T E D P R O O F

Biota isotopic composition to trace

Sediments show lighter Hg MIF values relative to biota (Fig. 4), as reported in other Hg affected ecosystems (Table 1). The MIF offset values vary in a large range in the mentioned studies (Table 1), from approximately 0.1‰ to 1.5‰. These variations can be attributed to biota habitats, fed habits and the contribution of major anthropogenic sources. In general, MIF increases along the food web as a consequence of the Hg species (MeHg and iHg) accumulation and their species specific isotopic composition [START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF].

A model which combines both speciation and isotopic composition [START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF][START_REF] Laffont | Hg speciation and stable isotope signatures in human hair as a tracer for dietary and occupational exposure to mercury[END_REF] was employed in order to better evaluate the Hg biogeochemical processes from sediments to biota in SG River and coastal zone. Assuming that no MIF occurs during trophic transfer and metabolic processes [START_REF] Kwon | Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity[END_REF][START_REF] Kwon | Application of mercury isotopes for tracing trophic transfer and internal distribution of mercury in marine fish feeding experiments[END_REF][START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF][START_REF] Laffont | Anomalous mercury isotopic compositions of fish and human hair in the Bolivian Amazon[END_REF][START_REF] Laffont | Hg speciation and stable isotope signatures in human hair as a tracer for dietary and occupational exposure to mercury[END_REF][START_REF] Sherman | New insight into biomarkers of human mercury exposure using naturally occurring mercury stable isotopes[END_REF][START_REF] Li | Assessing sources of human methylmercury exposure using stable mercury isotopes[END_REF], sediment Hg is the main Hg source of food web [START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF], MIF signature of iHg is considered similar in sediments (mainly composed of iHg) and biota. Therefore, the MIF signature associated to MeHg in biota can be estimated by the following equations (see details in supporting information): ) from the same location (mainly as iHg) [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF]. This allows us to obtain the following expression: [START_REF] Bravo | Mercury human exposure through fish consumption in a reservoir contaminated by a chlor-alkali plant: Babeni reservoir (Romania)[END_REF] The model provides specific Δ 201 Hg MeHg for catfish and oyster, being 0.21 ± 0.05‰ and 0.37 ± 0.18‰, respectively. These values are clearly higher than their respective iHg MIF (Δ 201 Hg iHg ) signature (catfish: -0.07 ± 0.06‰ and oysters: -0.02 ± 0.04‰) indicating photo-demethylation in this aquatic environment.

(3) (4) (5)
Hg) than catfish. In contrast to fish whose principal Hg source is contaminated sediment [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF], oyster takes up Hg by water active-filter feeding. A recent study [START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF] suggested that MeHg cycling between estuarine sediments and water column via deposition and re-suspension does not affect MeHg isotopic composition. Consequently, MeHg MIF in oysters reveals that MeHg is mainly derived from downstream transport of contaminated sediment that probably undergoes additional photochemical degradation when reaching coastal waters.

3.2.2.2. MDF isotopic signature in biota MDF values in biota (Fig. 4, Table S9) varied from -0.78‰ to +0.68‰ (δ 202 Hg) according to the organism and its sampling sites. Regarding oysters collected in the coastal zone, they exhibit a positive MDF of 0.50 ± 0.14‰ (δ 202 Hg). Catfish from SG River exhibit negative δ 202 Hg value (-0.61 ± 0.15‰), meanwhile it is positive (0.42 ± 0.15‰) in the same fish species from M Dam (Table 1). The different MDF pattern between fish from M. Dam and SG River is due to the divergence on their habitats (and consequently the diet signature), which strongly affect the resulting isotopic signature.

It should be considered that in vivo metabolic processes also contribute to the divergent MDF between sediments and biota [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF][START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. Hg species transformation as well as bioaccumulation, transport and other metabolic processes could induce MDF in vivo [START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF][START_REF] Laffont | Anomalous mercury isotopic compositions of fish and human hair in the Bolivian Amazon[END_REF][START_REF] Laffont | Hg speciation and stable isotope signatures in human hair as a tracer for dietary and occupational exposure to mercury[END_REF][START_REF] Sherman | New insight into biomarkers of human mercury exposure using naturally occurring mercury stable isotopes[END_REF][START_REF] Li | Assessing sources of human methylmercury exposure using stable mercury isotopes[END_REF][START_REF] Masbou | Hg stable isotope time trend in ringed seals registers decreasing sea ice cover in the Alaskan Arctic[END_REF]. Recent studies in model fish evidenced a shift between the MDF signature in the fish organs and their diet [START_REF] Feng | Specific pathways of dietary methylmercury and inorganic mercury determined by mercury speciation and isotopic composition in zebrafish (Danio rerio)[END_REF].

Usually an enrichment of heavier isotopes (MDF) is observed in biota respect to sediments in aquatic ecosystems [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF]. The mentioned pattern is observed in oysters (δ 202 Hg: 0.50‰), where the MDF is higher than in the Coastal Zone sediments (δ 202 Hg: -0.82‰). Interestingly, catfish exhibits lower δ 202 Hg than river sediments. This trend has been recently reported at Yuba river [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF].

Most of the studies performed until the moment corresponds to lakes and marine coastal ecosystems [START_REF] Perrot | Tracing sources and bioaccumulation of mercury in fish of Lake Baikal -Angara River using Hg isotopic composition[END_REF][START_REF] Sherman | Mercury stable isotopes in sediments and largemouth bass from Florida lakes, USA[END_REF][START_REF] Gehrke | Mercury isotopes link mercury in San Francisco Bay forage fish to surface sediments[END_REF][START_REF] Kwon | Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the northeastern USA[END_REF]. In such environments (nonflowing water), the MeHg accumulated in biota is considered as originated by Hg methylation of local sediments. However, as discussed by Donovan et al. [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF] the specific environmental characteristics of flowing water ecosystems (i.e., rivers) could explain the different trend observed in both locations. It is expected that in flowing water systems the MeHg resulting from methylation is continuously removed. Consequently, it decreases the amount of MeHg available for biodegradation leading to lighter MeHg MDF values than for iHg. In contrast, MeHg biodegradation occurs at larger extent in nonflowing water systems, due to its longer residence period, resulting in heavier MeHg MDF. In the current work, catfish exhibit lower δ 202 Hg than river sediments, in good agreement with the pattern reported at Yuba river [START_REF] Donovan | Isotopic composition of inorganic mercury and methylmercury downstream of a historical gold mining region[END_REF]. It suggests a relatively reduced MeHg biodegradation in SG river ecosystem.

Conclusions

In summary, this work shows that SG River and its adjacent coastal zone are impacted by the CAP Hg release, which is reflected in Hg concentrations, speciation and isotopic composition of sediments and biota. Hg isotopic signature, MDF and MIF, in sediments, allows tracking iHg transport / dispersion and/or dilution in sediments in the impacted area. The combination of speciation and isotopic pattern in biota and sediments displays various Hg biogeochemical processes in the environment before its introduction into the food web. Hg isotopic signature offset between sediments and biota reveals noticeable divergences of Hg biogeochemical processes between river and coastal areas.

Fig. 1 .

 1 Fig. 1. Study area: Sagua la Grande River (SG River) and the adjacent (12 km) coastal zone (Cuba). Sediments sampling sites Ss(0) to Ss(5) are within the SG River, including Ss(1) in the vicinity of old CAP discharge, and Ss(2) and Ss(3) that are close to the new CAP discharge. Sc(1) to Sc(3) are in the coastal zone. Fish samples were collected in SG River, oyster samples were collected in coastal zone.

Fig. 2 .

 2 Fig. 2. Hg distribution and speciation in a) sediments and b) biota along SG River, coastal zone and M Dam.

UFig. 3 .

 3 Fig. 3. a) δ 202 Hg relative to Δ 201 Hg isotopic composition and b) δ 202 Hg isotopic composition versus total Hg concentration in sediments of SG River and coastal zone.

Fig. 4

 4 Fig. 4. δ 202 Hg and Δ 201 Hg isotopic composition in sediments and biota from SG River and coastal zone.

  Hg contamination pathways from contaminated sediments 3.2.2.1. MIF isotopic signature in biota Fish samples from SG River and M Dam exhibited a MIF (Δ 201

U

  N C O R R E C T E D P R O O F C. Feng et al.Journal of Hazardous Materials xxx (2019) xxx-xxxOysters exhibit a slightly higher MIF value for MeHg (˜0.16‰, Δ

U

  N C O R R E C T E D P R O O F

Table 1

 1 Hg concentration, speciation and isotopic composition in different Hg contaminated areas.

	Polluted Source	ID	Samples		THg	%MeHg	δ 202 Hg	Δ 199 Hg	Δ 201 Hg	N	Reference
					ng g -1 ( dw)	%	‰	‰	‰
	Chlor-alkali plants Chlor-alkali plants Multiple source (urban waste, industry, Hg and Au mines) Coal-Fired Utility(<50 km) Multiple Source (landfills, Hg recovery plants, wastewater treatment facilities, industry) Historical Au mining	Bratsk Water Reservoir Augusta Bay San Francisco Bay Florida Lake Northeastern Coast in U.S.A Yuba River (California, U.S.A)	Fish Sediments Fish Sediments Fish Sediments Fish sediments Fish Crab Mussel Sediments Benthic macroinvertebrates	Perch Roach Pelagic Demersal Benthic Mississippi Silverside Topsmelts Largemouth Bass Killifish? Green crab? Blue/ribbed mussel Stonefly Larva Net Spinning Caddisfly Larva Mayfly Larva	5768 ± 5427 (3197˜11676) 1819 ± 2223 (1034˜5209) 2106 ± 1482 (1250˜3200) 540 ± 854 (90˜2270) 441 ± 377 (200˜1420) 1018 ± 481 (600˜1650) 14try align="left">14736 ± 12322 (1780˜55,300) 395 ± 276 (50˜1308) 242 ± 201 (112˜908) 477 ± 357 (161˜1529) 372 ± 227 (44˜672) 187 ± 80 (71˜256) 186 ± 250 (45˜631) 47 ± 30 (26˜68) 139 ± 55 (61˜192) 1075 ± 1464 (42˜2962) 93 ± 14 (67˜122) 106 ± 24 (84˜136) 59 ± 14 (49˜75)	92 ± 4 (82˜94) 94 ± 4 (89˜95) ? ? >90? 94 ± 4 (88˜97) 85 60 ± 4 (56˜64) 0.2 ± 0.1 (0.1˜0.3) 80 ± 9 (69˜100) 66 ± 6 (58˜76) 73 ± 2 (72˜75)	-0.55 ± 0.45 (-0.90˜-0.16) -0.37 ± 0.30 (-0.80˜-0.22) -0.64 ± 0.35 (-0.92˜-0.47) -0.18 ± 0.24 (-0.57˜0.09) -0.50 ± 0.42 (-1.31˜0.18) -0.65 ± 0.39 (-1.18˜-0.18) -0.39 ± 0.21 (-0.91˜-0.11) 0.14 ± 0.25 (-0.25˜0.60) 0.15 ± 0.20 (-0.07˜0.57) -0.60 ± 0.18 (-0.99˜-0.30) -0.35 ± 0.14 (-0.60˜-0.18) -0.88 ± 0.26 (-1.11˜-0.63) 0.02 ± 0.23 (-0.34˜0.23) 0.00 ± 0.07 (-0.05˜-0.05) 0.14 ± 0.44 (-0.31˜0.77) -0.62 ± 0.19 (-0.82˜-0.38) -0.77 ± 0.07 (-0.84-0.61) -0.70 ± 0.09 (-0.83-0.59) -0.62 ± 0.08 (-0.69-0.54)	0.52 ± 0.50 (0.20˜1.04) 1.19 ± 1.00 (0.47˜1.87) -0.04 ± 0.15 (-0.14˜0.06) 1.36 ± 0.30 (0.92˜1.83) 0.30 ± 0.22 (-0.02˜0.56) 0.12 ± 0.12 (-0.04˜0.23) -0.02 ± 0.03 (-0.10˜0.04) 0.80 ± 0.31 (0.46˜1.55) 0.73 ± 0.16 (0.58˜1.08) 0.08 ± 0.03 (0.00˜0.14) 0.69 ± 0.17 (0.52˜0.97) -0.09 ± 0.22 (-0.29˜0.14) 0.56 ± 0.15 (0.37˜0.72) 0.31 ± 0.11 (0.23˜0.39) 0.35 ± 0.11 (0.21˜0.52) 0.00 ± 0.02 (-0.04˜0.02) 1.08 ± 0.10 (0.84˜1.15) 0.94 ± 0.19 (0.64˜1.17) 0.75 ± 0.21 (0.62˜1.00)	0.39 ± 0.41 (0.13˜0.79) 0.90 ± 0.77 (0.30˜1.39) -0.02 ± 0.09 (-0.06˜0.07) 1.21 ± 0.20 (1.06˜1.52) 0.35 ± 0.17 (0.10˜0.63) 0.09 ± 0.08 (-0.04˜0.16) -0.02 ± 0.03 (-0.07˜0.04) 0.64 ± 0.24 (0.38˜1.25) 0.57 ± 0.12 (0.41˜0.82) 0.05 ± 0.03 (-0.01˜0.11) 0.46 ± 0.13 (0.32˜0.69) -0.07 ± 0.22 (-0.26˜0.13) 0.45 ± 0.14 (0.29˜0.54) 0.24 ± 0.30 (0.03˜0.45) 0.12 ± 0.09 (0.06˜0.27) 0.06 ± 0.08 (0.01˜0.18) 0.83 ± 0.06 (0.72˜0.93) 0.68 ± 0.16 (0.47˜0.84) 0.52 ± 0.15 (0.42˜0.69)	12 12 9 6 9 5 28 21 14 20 11 4 5 2 4 6 10 6 3	Perrot et al. (2010) Bonsignore et al. (2015) Gehrke et al. (2011) Sherman et al. (2013) Kwon et al. (2014) Donovan et al. (2016)

Table 1 (

 1 Continued)

	Polluted Source	ID	Samples		THg	%MeHg	δ 202 Hg	Δ 199 Hg	Δ 201 Hg	N	Reference
					ng g -1 ( dw)	%	‰	‰	‰
	Chlor-alkali plants	Sagua la Grande River and coastal zone	Fish Algae Sediments Fish Oyster Sediments	Asian Clam Riffle Sculpin Speckled Dace Filamentous Algae Upper Yuba Fan Lower Yuba Fan Lower Feather River SG River M Dam Coastal Zone SG River Upper SG River Lower Coastal Zone	(323˜405) 302 ± 129 (168˜426) 377 437 140 ± 45 (57˜186) 3039 ± 3156 (237˜6821) 238 ± 57 (170˜309) 321 ± 101 (218˜413) 1093 ± 319 (770˜1407) 107 ± 36 (57˜150) 596 ± 233 (496˜731) 2386 ± 2444 (296˜5072) 480 ± 402 (196˜764) 220 ± 72 (165˜301)	(20˜40) 49 ± 21 (25˜64) 100 93 7 ± 6 (1˜15) 0.6 ± 0.6 (0.1˜1.0) 2.6 1.7 ? 72 ± 19 (50˜83) 80 ± 12 (60˜90) 44 ± 27 (29˜65) 0.3 ± 0.1 (0.3˜0.4) 1.7 ± 2.0 (0.3˜3.1) 0.8 ± 0.3 (0.5˜1.0)	(-0.76-0.61) -0.52 ± 0.14 (-0.68-0.42) -0.43 -0.54 -0.70 ± 0.08 (-0.82-0.61) -0.29 ± 0.18 (-0.50˜0.71) -0.44 ± 0.16 (-0.63-0.25) -0.67 ± 0.26 (-0.95˜-0.39) -0.61 ± 0.15 (-0.78˜-0.49) 0.42 ± 0.15 (0.22˜0.57) 0.50 ± 0.14 (0.30˜0.68) 0.19 ± 0.20 (0.06˜0.42) -0.36 ± 0.18 (-0.49-0.23) -0.32 ± 0.18 (-0.51-0.15)	(0.27˜0.39) 0.44 ± 0.15 (0.30˜0.60) 0.84 0.79 0.11 ± 0.04 (0.06˜0.16) 0.03 ± 0.03 (-0.01˜0.05) 0.05 ± 0.03 (0.02˜0.08) 0.06 ± 0.03 (0.02˜0.07) 0.21 ± 0.05 (0.15˜0.24) 1.39 ± 0.18 (1.13˜1.62) 0.18 ± 0.78 (0.08˜0.34) -0.12 ± 0.04 (-0.16-0.08) -0.12 ± 0.00 (-0.12-0.12) -0.07 ± 0.06 (-0.14-0.03)	(0.19˜0.29) 0.29 ± 0.10 (0.20˜0.40) 0.65 0.61 0.04 ± 0.04 (0.01˜0.10) -0.01 ± 0.03 (-0.05˜-0.02) 0.01 ± 0.03 (-0.02˜0.05) 0.02 ± 0.01 (0.01˜0.04) 0.13 ± 0.03 (0.10˜0.16) 1.09 ± 0.11 (0.94˜1.22) 0.16 ± 0.08 (0.10˜0.25) -0.11 ± 0.07 (-0.18˜-0.06) -0.05 ± 0.04 (-0.08-0.03) -0.02 ± 0.04 (-0.06˜0.01)	3 1 1 7 4 4 4 ? 3 5 3 3 2 3	? This study

Acknowledgements

This work has been supported by the Aquitaine Region, the CNRS and the Agence Nationale de la Recherche (RIMNES Project No ANR 2011 CESA 013 03). Caiyan Feng acknowledges the Chinese Scholarship Council (N. 201204910188) for her PhD grant.

Appendix A. Supplementary data

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.02.092.