Mathieu Leroy

Emmanuel Flahaut
email: emmanuel.flahaut@univ-tlse3.fr

Camille Larue
email: camille.larue@ensat.fr

Carbon based nanomaterial interactions

Keywords: adsorption, carbon nanotube, cocktail effect, organism, metal(loid), toxicity, soil Highlights 0, Pb: 34.0 Cd: 0.21, Cu: 0.97, Pb: 0.97 5

come

Introduction

Scientific and industrial interest in carbon-based nanomaterials (CNMs) continues to grow because of their remarkable properties and the applications they make possible 1 . A CNM is a nanomaterial essentially composed of carbon with any external dimension in the nanoscale or having internal structure or surface structure in the nanoscale (i.e. nanometric scale particles aggregated together) 1 . Among CNMs, most have a structure based on graphene, a sheet of carbon atoms joined together in a hexagonal lattice, one atom thick, sp 2 bonded [START_REF] Singh | Graphene Based Materials: Past, Present and Future[END_REF][START_REF] Bianco | All in the Graphene Family -A Recommended Nomenclature for Two-Dimensional Carbon Materials[END_REF][START_REF] Wick | Classification Framework for Graphene-Based Materials[END_REF] . Over the years, the number of derived materials using graphene as a precursor grew up [START_REF] Huang | Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications[END_REF] . Examples include multilayer graphene, functionalized graphene materials such as graphene oxide (GO), carbon nanotubes (CNTs), fullerene, and many metal-CNT composite

The potential applications of CNMs are such that models already predict the evolution of their concentrations in natural ecosystems after release at the end of life of commercial goods in which they are included, or expected during their life cycle. For example, Sun al. [START_REF] Gottschalk | Environmental Concentrations of Engineered Nanomaterials: Review of Modeling and Analytical Studies[END_REF] predicted that agricultural soils treated with sewage sludge are the main sink for CNTs with an annual increase of 74 ng.kg -16 . Furthermore, the use of CNMs as nanofertilizers 7 , nanopesticides [START_REF] Paramo | Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends[END_REF] and as decontamination agents [START_REF] Perreault | Environmental Applications of Graphene-Based Nanomaterials[END_REF] is also increasingly being considered. Indeed, CNMs are capable of adsorbing different compounds on their surface. Among these many compounds are metal(loid)s, which are elements present in natural conditions in biotope at concentrations below 100 mg.kg -1 including copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), molybdenum (Mo), boron (B), cobalt (Co), nickel (Ni), lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and selenium (Se) [START_REF] Ramade | Dictionnaire Encyclopédique Des Sciences De La Nature Et De La Biodiversité[END_REF] . Cu, Zn, Fe, Mn, Mo, and B are essential for plant growth, and Cu, Zn, Fe, Mn, Mo, Co and Se are essential to the growth and health of animals including human beings [START_REF] Marschner | s Mineral Nutrition of Higher Plants[END_REF] while others are toxic (Ni, Pb, Cd, As). For example, it has been largely reported that CNTs can adsorbed metal(loid)s in aqueous solution [START_REF] Addo Ntim | Adsorption of Arsenic on Multiwall Carbon Nanotube-Zirconia Nanohybrid for Potential Drinking Water Purification[END_REF][START_REF] Tofighy | Adsorption of Divalent Heavy Metal Ions from Water Using Carbon Nanotube Sheets[END_REF][START_REF] Moradi | The Removal of Ions by Functionalized Carbon Nanotube: Equilibrium, Isotherms and Thermodynamic Studies[END_REF][START_REF] Moradi | Adsorption of Pb(II), Cd(II) and Cu(II) Ions in Aqueous Solution on SWCNTs and SWCNT -COOH Surfaces: Kinetics Studies[END_REF][START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF][START_REF] Gao | Behaviors and Influencing Factors of the Heavy Metals Adsorption onto Microplastics: A Review[END_REF] and this ability raises questions about its influence on heavy metal transfer and subsequent impacts along food webs.

Agrosystems seems to be particularly suitable for the coexistence of both CNMs and metal(loid)s (among others) due to cultural practices. Indeed, the continuous spreading of organic and inorganic fertilizers and the application of sludge from wastewater treatment plants have progressively led to the accumulation of both CNMs and metal(loid)s in agrosystems [START_REF] Nicholson | An Inventory of Heavy Metals Inputs to Agricultural Soils in England and Wales[END_REF][START_REF] Nagajyoti | Occurrence and Toxicity for Plants: A Review[END_REF][START_REF]Toxic Metals in Soil-Plant Systems[END_REF] .

Toxicological risk assessment of contaminants is usually carried out using additive models that do not take into account the interactions between contaminants and their underlying toxicological effects. For several years, metal(loid)s are submitted to a close monitoring in sludge and food to ensure safety for populations, but the emerging contaminants such as CNMs are not yet regulated. Studies report that interactions (both synergy and/or antagonism) between contaminants can modify their transfer and toxicity to different organisms [START_REF] Zhao | Carboxylated Graphene Oxide-Chitosan Spheres Immobilize Cu2+ in Soil and Reduce Its Bioaccumulation in Wheat Plants[END_REF][START_REF] He | Graphene Oxide Promoted Cadmium Uptake by Rice in Soil[END_REF][START_REF] Li | The Mutual Effects of Graphene Oxide Nanosheets and Cadmium on the Growth, Cadmium Uptake and Accumulation in Rice[END_REF][START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF][START_REF] Gao | Effects of Foliar Application of Graphene Oxide on Cadmium Uptake by Lettuce[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Lian | Do Polystyrene Nanoplastics Affect the Toxicity of Cadmium to Wheat (Triticum Aestivum L.)?[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF][START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF] (Figure 1). Tools have been developed to reveal possible interactions between stressors such as mixture of substances [START_REF] Vijver | Response Predictions for Organisms Water-Exposed to Metal Mixtures: A Meta-Analysis[END_REF][START_REF] Yang | Evaluation of the Combined Toxicity of Multi-Walled Carbon Nanotubes and Cadmium on Earthworms in Soil Using Multi-Level Biomarkers[END_REF][START_REF] Rodea-Palomares | Additivity and Interactions in Ecotoxicity of Pollutant Mixtures: Some Patterns, Conclusions, and Open Questions[END_REF] . A meta-analysis by Vijver et al. aimed at predicting the response of organisms exposed to mixtures of metals (Cd, Cu and Zn) and showed that the frequency of occurrence of antagonism was 51%, and a synergistic response was detected in 28% of cases [START_REF] Vijver | Response Predictions for Organisms Water-Exposed to Metal Mixtures: A Meta-Analysis[END_REF] . Thus, in nearly 80% of the cases, interactive and non-additive patterns were demonstrated. This finding may lead to a profound questioning of the current risk assessment performed by the authorities.

The main goal of this work was to extensively review articles related to 1) CNM-metal(loid) interactions in aqueous medium to better understand implied mechanisms and the influencing parameters and 2) ecotoxicological studies related to simultaneous CNM-metal(loid) contamination and their consequences on the transfer and impacts on agrosystem organisms to reveal the extent of the interactive phenomenon.

Interaction CNMs -metal(loid)s

Mechanisms of interactions between CNMs and metal(loid)s

Several interaction mechanisms have been described between CNMs and metal(loid)s and their predominance depends on the material considered. Interactions can be related to physical adsorption, chemical interaction, electrostatic attraction and sorption-precipitation [START_REF] Ren | Carbon Nanotubes as Adsorbents in Environmental Pollution Management: A Review[END_REF][START_REF] Gupta | Study on the Removal of Heavy Metal Ions from Industry Waste by Carbon Nanotubes: Effect of the Surface Modification: A Review[END_REF][START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] .

For CNMs with surface functional groups, the chemical interactions between CNMs and metal cations is the most observed mechanism [START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF] . Metal cations are adsorbed onto the surface of CNMs via oxygenated functional groups (e.g., -COOH, -OH, or C=O) and then release a H + ion from the surface of the CNMs (Figure 2, example for GO and CNT). The release of H + causes a decrease in the pH of the medium. The adsorption mechanism of divalent metal ions on CNMs is illustrated according to the following equations (where CNM stands for carbonbased nanomaterials, and M for metal(loid)): Metal ion adsorption can also result from the combined effects of electrostatic attraction and sorption-precipitation processes [START_REF] Li | Competitive Adsorption of Pb2+, Cu2+ and Cd2+ Ions from Aqueous Solutions by Multiwalled Carbon Nanotubes[END_REF][START_REF] Liang | Facile Synthesis of Alumina-Decorated Multi-Walled Carbon Nanotubes for Simultaneous Adsorption of Cadmium Ion and Trichloroethylene[END_REF] . Liang et al. [START_REF] Liang | Facile Synthesis of Alumina-Decorated Multi-Walled Carbon Nanotubes for Simultaneous Adsorption of Cadmium Ion and Trichloroethylene[END_REF] observed that Cd 2+ ions were adsorbed on the surface of modified Al 2 O 3 -CNTs via physical interactions as electrostatic interactions and van der Waals interactions occurred between Cd 2+ ions and carbon atoms in the CNTs [START_REF] Liang | Facile Synthesis of Alumina-Decorated Multi-Walled Carbon Nanotubes for Simultaneous Adsorption of Cadmium Ion and Trichloroethylene[END_REF] . On another study, following an increase in the pH value of the medium, Zn 2+ ions were adsorbed more on the surface of the CNTs due to the prevalence of carboxylate functions on their surface. The authors attributed this observation to the electrostatic interactions between the surface and divalent Zn 2+ ions [START_REF] Lu | Adsorption of Zinc(II) from Water with Purified Carbon Nanotubes[END_REF] .

In addition, CNMs have also been explored for the removal of anionic pollutants, such as phosphates (PO 4 3-), perchlorates (ClO 4 -) and fluorides (F -), from aqueous solutions [START_REF] Vasudevan | The Adsorption of Phosphate by Graphene from Aqueous Solution[END_REF][START_REF] Zhang | Graphene-Polypyrrole Nanocomposite as a Highly Efficient and Low Cost Electrically Switched Ion Exchanger for Removing ClO4-from Wastewater[END_REF][START_REF] Shi | Unexpectedly Strong Anion-π Interactions on the Graphene Flakes[END_REF] . In contrast to the immobilization of cationic metal species, the mechanism of anion adsorption was previously attributed to electronic interactions with π electrons of the carbon sp² network [START_REF] Shi | Unexpectedly Strong Anion-π Interactions on the Graphene Flakes[END_REF] . This anion -π association is based on the interaction between the negatively charged anion with an electron-deficient aromatic ring on a graphene layer [START_REF] Shi | Unexpectedly Strong Anion-π Interactions on the Graphene Flakes[END_REF] .

Finally, new adsorbents have also been prepared by modifying CNMs with organic molecules that have a natural ability to complex metal ions. For instance, intrinsic functional groups on GO present a large variety and thus the specificity of interaction with given species of interest may be limited. To counteract this, the number of adsorption sites may be increased by grafting compounds such as ethylenediaminetetraacetic acid (EDTA) [START_REF] Madadrang | Adsorption Behavior of EDTA-Graphene Oxide for Pb (II) Removal[END_REF] and chitosan [START_REF] Liu | Preparation and Characterization of Chitosan/Graphene Oxide Composites for the Adsorption of Au(III) and Pd(II)[END_REF] .

Factors influencing the CNM -metal(loid) interactions in simplified media

CNM intrinsic properties

Due to the predominance of the adsorption mechanism by chemical interaction, it is obvious that the oxidation state of CNMs influences the sorption of metal(loid)s on their surface. The greater the oxidation of the CNMs, the more it provides oxygenated functional groups capable of interacting with the surrounding metal ions, regardless of CNM shape and size 9,46,47 . Similarly, following the same idea, the degree of reduction of the CNMs acts on their adsorption capacity. The maximum adsorption capacity of rGO (12.6% of O) was much lower than that of GO (51.6% of O) due to the decrease in available oxygenated functional groups [START_REF] Li | Uranium(VI) Adsorption on Graphene Oxide Nanosheets from Aqueous Solutions[END_REF] .

If the oxidation state can be tuned upon synthesis, it is very unlikely that it evolves in the natural environment (with the exception of fullerenes). Their reduction may however be easier to occur in environmental conditions. There are many examples of partial reduction of GO by natural molecules extracted from plant leaves [START_REF] Khan | Reduction Efficiencies of Natural Substances for Reduced Graphene Oxide Synthesis[END_REF] . However, enzymatic transformations of CNMs are unfortunately often investigated using only pure enzymes and under laboratory conditions and they are consequently not very representative of enzymatic transformations in the natural environment [START_REF] Sigmund | Environmental Transformation of Natural and Engineered Carbon Nanoparticles and Implications for the Fate of Organic Contaminants[END_REF] The specific surface area (SSA, m².g -1 ) strongly influences the adsorption of metals. In the case of graphene, most interaction sites with pollutants are present at the top and bottom faces [START_REF] Sitko | Graphene as a New Sorbent in Analytical Chemistry[END_REF][START_REF] Zhao | Graphene in the Aquatic Environment: Adsorption, Dispersion, Toxicity and Transformation[END_REF] , even if sites located at the edge may also play some role. While all the surface of monolayer graphene is available for the adsorption, multilayer graphene and CNTs have internal layers respectively little or not accessible by adsorbates [START_REF] Sitko | Graphene as a New Sorbent in Analytical Chemistry[END_REF] . Similarly, it has been observed that single walled CNTs are good adsorbents, which can be attributed to their high SSA. Practically, the measured SSA of graphene-based CNMs is generally very disappointing (often below a few tens of m².g -1 ) when compared to the expected theoretical values (> 2600 m².g -1 for graphene) [START_REF] Peigney | Specific Surface Area of Carbon Nanotubes and Bundles of Carbon Nanotubes[END_REF] due to their significant agglomeration.

Environmental parameters

The relative concentrations of CNMs and metal ions in the medium is an important parameter controlling adsorption phenomenon. To better understand these interactions, some theoretical model isotherms were developed, the most common being the Langmuir and the Freundlich models [START_REF] Xu | A Review of Functionalized Carbon Nanotubes and Graphene for Heavy Metal Adsorption from Water: Preparation, Application, and Mechanism[END_REF] according to the following equations:

where q e and q m (mg.g -1 ) represent equilibrium and maximum adsorption capacities, respectively; C e (mg.L -1 ) is the equilibrium aqueous concentration; k L (L.mg -1 ) the equilibrium constant and k F and n the Freundlich constant.

These two models differ in particular by the fact that Langmuir model is considering the adsorption of a monolayer of atoms on a homogeneous surface and is empirical while Freundlich considers the adsorption of a multilayer of atoms on a heterogeneous surface and is a theoretical model. Adsorption kinetics are generally described by diffusion models such as the pseudo-first-order and pseudo-second-order following the equations [START_REF] Xu | A Review of Functionalized Carbon Nanotubes and Graphene for Heavy Metal Adsorption from Water: Preparation, Application, and Mechanism[END_REF] : where q t and q e are the adsorption capacities (mg.g -1 ) at time t and equilibrium, k 1 (min -1 ) and k 2 (min -1 ) are the rate constants of the pseudo-first-order, pseudo-second-order, respectively.

Results extracted from these models show that the main environmental factors affecting the adsorption of metal ions on the surface of CNMs include the initial metal(loid) ion and CNM concentrations, pH, contact time, temperature, ionic strength and competition with other molecules. Table S1 summarizes the data found in the literature regarding CNM interactions with different metal(loid)s.

Regarding the intrinsic properties of the CNMs and the properties of the experimental medium, which both influence the adsorption of metal(loid)s, a criticism can be raised related to the lack of reported experimental details in the literature. Indeed, out of the 102 CNMs tested, the SSA was reported for only 48 of them. Furthermore, as the Freundlich and Langmuir models are thermodynamic processes, it is unfortunate that the study temperature was provided only in 56 cases out of 102. This lack of reporting makes the intercomparability of the studies impossible and thus weakens the conclusions and slows down the scientific progress, especially for the safer-by-design and nanoecotoxicity fields.

The average adsorption values from the Langmuir model for CNTs, oxidized CNTs and graphene oxide have been extracted from related articles for different metal(loid)s (Cd, Cr, Cu, Hg, Ni, Pb and Zn; Table 1). ) of metal(loid)s (Cd, Cr, Cu, Hg, Ni, Pb and Zn) on the surface of carbon nanotubes (CNT), oxidized carbon nanotubes (CNT-oxidized) and graphene oxide (GO) in monoelemental conditions extracted from the reported studies in Table S1 described with Langmuir model. Data were selected on restricted pH range (4 < pH < 8) The adsorption of each metal(loid) appears to be always higher for GO than for CNTs and oxidized CNTs. Similarly, the oxidation of CNTs promotes the adsorption of metal(loid)s since the average adsorption of metal(loid)s on the surface of oxidized CNTs is higher for each metal (except Zn, probably related to the high variability for Zn adsorption onto oxidized CNTs) than on the surface of raw CNTs. On the basis of the data in Table 1, the sequence of adsorption affinities in mono-elemental conditions can be drawn up:

-for CNTs: Zn≥Pb>Hg≥Cu>Cd≥Ni>Cr -for CNTs oxidized: Pb>Ni>Cu≥Cd>Hg≥Cr≥Zn.

It is also important to note that these adsorption experiments were carried out in monoelemental conditions (one adsorbent + one ionic species) thus not considering potential ionic repulsions possibly induced if several ionic species would be present in the solution.

pH

The pH is a parameter that greatly influences the interactions between CNMs and metal cations because it determines not only metal speciation but also surface charge of CNMs and complexation behavior of functional groups [START_REF] Suzuki | Physical and Chemical Properties of Carbon Nanotubes[END_REF][START_REF] Zhu | Graphene and Graphene Oxide: Synthesis, Properties, and Applications[END_REF] . Most of the studies in Table S1 evidenced that the adsorption capacity of CNMs was affected by variations in the pH of the solution [START_REF] Ren | Carbon Nanotubes as Adsorbents in Environmental Pollution Management: A Review[END_REF][START_REF] Rao | Sorption of Divalent Metal Ions from Aqueous Solution by Carbon Nanotubes: A Review[END_REF][START_REF] Marques | PH Effects on the Removal of Cu2+, Cd2+ and Pb2+ from Aqueous Solution by Waste Brewery Biomass[END_REF][START_REF] Fu | Removal of Heavy Metal Ions from Wastewaters: A Review[END_REF] . Adsorption of the metal(loid) is partly related to the point of zero charge (pH PZC ) of a given CNM; when pH > pH PZC , cation adsorption is higher due to the electrostatic interactions between the cations and the negative surface charge of CNM. On the other hand, the adsorption of cations is lower when pH  pH PZC due to the neutralization of the surface charge of CNM, or even the presence of repulsive positive charges. A change in pH also affects competing complexing reactions and metal ion species [START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] . Generally, the state of the divalent metal ions in solution depends on the pH. The most common species would be present in the form of M 2+ , M(OH , M(OH) 2 et M(OH depending on the pH of the medium due to hydrolysis [START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF][START_REF] Ren | Carbon Nanotubes as Adsorbents in Environmental Pollution Management: A Review[END_REF][START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] . It is important to note that precipitation of metal cations may occur when the pH increases, which also affects the removal of metal ions [START_REF] Yu | Recovery and Enrichment of Metals from Aqueous Solutions Using Carbon Nanotubes[END_REF] .

CNM concentration

Increasing the concentration of CNM up to a certain point, increases the overall surface available for reactions and thus increases the sorption of metal(loid)s. For instance, adsorption of Ni 2+ , Cd 2+ , Cu 2+ and Pb 2+ increased with increasing CNT concentration in different experiments [START_REF] Gupta | Study on the Removal of Heavy Metal Ions from Industry Waste by Carbon Nanotubes: Effect of the Surface Modification: A Review[END_REF][START_REF] Rao | Sorption of Divalent Metal Ions from Aqueous Solution by Carbon Nanotubes: A Review[END_REF][START_REF] Li | Competitive Adsorption of Pb2+, Cu2+ and Cd2+ Ions from Aqueous Solutions by Multiwalled Carbon Nanotubes[END_REF][START_REF] Ihsanullah | Adsorptive Removal of Cadmium(II) Ions from Liquid Phase Using Acid Modified Carbon-Based Adsorbents[END_REF] . Similar results were also observed for GO [START_REF] Cui | EDTA Functionalized Magnetic Graphene Oxide for Removal of Pb(II), Hg(II) and Cu(II) in Water Treatment: Adsorption Mechanism and Separation Property[END_REF] . However, beyond a threshold mass (specific to the CNM studied), the adsorption capacity reaches saturation and then decreases [START_REF] Moradi | Adsorption of Pb(II), Cd(II) and Cu(II) Ions in Aqueous Solution on SWCNTs and SWCNT -COOH Surfaces: Kinetics Studies[END_REF][START_REF] Cui | EDTA Functionalized Magnetic Graphene Oxide for Removal of Pb(II), Hg(II) and Cu(II) in Water Treatment: Adsorption Mechanism and Separation Property[END_REF][START_REF] Wang | Adsorption Characteristics and Behaviors of Graphene Oxide for Zn(II) Removal from Aqueous Solution[END_REF] . For a exposition of 50 mg.L -1 of oxidized SWCNT, Moradi et al. [START_REF] Moradi | Adsorption of Pb(II), Cd(II) and Cu(II) Ions in Aqueous Solution on SWCNTs and SWCNT -COOH Surfaces: Kinetics Studies[END_REF] observed a maximum adsorption capacity up to 55, 68 and 90 mg.g -1 for Cd, Cu and Pb respectively, while this adsorption decreased at 45, 58 and 82 mg.g -1 with a exposition to 100 mg.L -1 . Indeed, beyond the threshold, an increase in the concentration of adsorbent could reduce the available sites because the effective surface area is likely to decrease due to homoagglomeration, entanglement and/or folding of the CNMs (depending on its morphology) [START_REF] Moradi | Adsorption of Pb(II), Cd(II) and Cu(II) Ions in Aqueous Solution on SWCNTs and SWCNT -COOH Surfaces: Kinetics Studies[END_REF][START_REF] Sen | Removal of Cadmium Metal Ion (Cd2+) from Its Aqueous Solution by Aluminium Oxide (Al2O3): A Kinetic and Equilibrium Study[END_REF] .

In addition, metal ions can induce CNM agglomeration due to their interactions with carboxylic groups [START_REF] Yang | Folding/Aggregation of Graphene Oxide and Its Application in Cu2+ Removal[END_REF] .

Ionic strength

Increasing the ionic strength of the solution can be achieved by increasing the concentration of an ion or in multi-elemental conditions by having several types of metal ions in the medium. However, this last experimental set-up even though more relevant in environmental context has been much less studied. The adsorption capacities of ions by CNMs decreased with increasing ionic strength for two reasons : (i) the formation of double-layer electrical complexes between cations and CNMs and (ii) the influence of the ionic strength on the activity coefficients of ions, which limit their transfer to the CNM surfaces [START_REF] Li | Competitive Adsorption of Pb2+, Cu2+ and Cd2+ Ions from Aqueous Solutions by Multiwalled Carbon Nanotubes[END_REF] . In multielemental conditions, the increase in number of ions present in the media decreases the part of metal ions adsorbed onto CNMs. Affinity sequences of metal ions for adsorption sites could be deduced from these multi-elemental adsorption experiments (Table 2). For instance, Salam et al. [START_REF] Salam | Simultaneous Removal of Copper(II), Lead(II), Zinc(II) and Cadmium(II) from Aqueous Solutions by Multi-Walled Carbon Nanotubes[END_REF] showed that ion binding affinity followed the order of Cu(II) > Zn(II) > Pb(II) > Cd(II) for MWCNTs (initial metal concentrations = 1 mg.L -1 , pH = 7, contact time = 2h). For GO, Sitko et al. [START_REF] Sitko | Adsorption of Divalent Metal Ions from Aqueous Solutions Using Graphene Oxide[END_REF] observed another ranking of affinity: Pb(II)> Cu(II) > Cd(II) > Zn(II) (initial concentration = 1 mg.L -1 , GO = 0.1 g.L -1 , pH = 5, contact time = 2h). Metal precipitation related to the pH of the solution could explain differences observed on affinity sequences [START_REF] Lewis | Precipitation of Heavy Metals[END_REF] .

Furthermore, the addition of metals in the medium could increase the co-precipitation [START_REF] Patnaik | s Analytical Chemistry Handbook[END_REF] and could modified the fitting of experimental adsorption measured with Langmuir and/or Freundlich modelling. To date, very little studies dealing with competitive adsorptions are available and more work needs to be carried out to understand the underlying mechanisms responsible for the establishment of these adsorption affinity sequences.

Table 2: Maximum adsorption capacity of different CNMs established by adsorption models for various metal(loid)s in multi-elemental conditions extracted from the cited articles (SSA = specific area (m 2 .g -1 ), qm = maximum modelled adsorption (mg.g -1 ), R 2 = correlation coefficient, C = metal concentration range (mg.L -1 ), A = Adsorbent dosage (mg.L -1 ), T = temperature (°C), Ct = Contact time (hours), RPM = agitation (Rotation Per Minutes))

M n+

Adsorbent SSA

Contact time

As the contact time increases, the percentage of metal removal increases until an equilibrium is established [START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF][START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] . The equilibrium depends on all the experimental parameters of the medium, including the initial concentration of metal ions. However, the two most important parameters on the adsorption kinetics of metals is the number of adsorption sites available for a given metal concentration and contact time [START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF][START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] .

Temperature

The most common observation is that sorption capacity increases with rising temperature [START_REF] Peng | A Review on Heavy Metal Ions Adsorption from Water by Graphene Oxide and Its Composites[END_REF][START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF] .

For example, the sorption of Pb 2+ , Cu 2+ and Zn 2+ on CNTs is an endothermic process and increases with increasing temperature [START_REF] Moradi | The Removal of Ions by Functionalized Carbon Nanotube: Equilibrium, Isotherms and Thermodynamic Studies[END_REF][START_REF] Lu | Removal of Zinc(II) from Aqueous Solution by Purified Carbon Nanotubes: Kinetics and Equilibrium Studies[END_REF] . Similar results were observed for the same metals for GO [START_REF] Sitko | Adsorption of Divalent Metal Ions from Aqueous Solutions Using Graphene Oxide[END_REF] . Authors explained that the increase in temperature could lead to an increase in the rate of diffusion of ions through the outer boundary layer and into the pores of CNMs due to a temperature-induced decrease in the viscosity of the solution [START_REF] Ihsanullah; Abbas | Heavy Metal Removal from Aqueous Solution by Advanced Carbon Nanotubes: Critical Review of Adsorption Applications[END_REF][START_REF] Sitko | Adsorption of Divalent Metal Ions from Aqueous Solutions Using Graphene Oxide[END_REF] .

Metal(loid) adsorption by CNMs in complex media

Due to the increasing use of CNMs, their potential in the agricultural and environmental fields and their interactions with metal(loid)s in simplified environments (aqueous solution), it is important to investigate how interactions investigated in simplified medium can be transposed in more complex environments. Various studies have thus recently been carried out (i) to characterize interactions of CNMs with compounds that are widely found in ecosystems, such as organic matter (OM) and sedimentary matrices and (ii) to investigate the role of some key parameters.

Organic Matter

Humic substances generally represent a predominant part of the natural OM distributed in soils, sediments and water [START_REF] Morales | Degradation of Carbofuran and Carbofuran-Derivatives in Presence of Humic Substances under Basic Conditions[END_REF] . It has been reported that 3 to 28% of the OM dissolved in wastewater treatment plant effluents are humic substances [START_REF] Imai | Characterization of Dissolved Organic Matter in Effluents from Wastewater Treatment Plants[END_REF] . They are hydrophobic organic acids mainly derived from soil humus and plants. These humic substances are often encountered in agrosystems especially due to the use of wastewater treatment plant effluents for fertilizing agricultural soils. Humic acid (HA) and fulvic acid (FA) are the two most important components of humic substances. It is expected that HA/FA will have a significant influence on the sorption of metal ions by CNMs because the hydrophobic parts as well as the aromatic monomers of HA/FA have a strong affinity for CNMs via hydrophobic and ππ interactions. At the same time, the hydrophilic fractions of HA/FA contain various functional groups (carboxyl, phenol, hydroxyl, amine and quinine) which can bind to metal(loid)s [START_REF] Lin | Surface-Bound Humic Acid Increased Pb2+ Sorption on Carbon Nanotubes[END_REF] . For instance, Lin et al. [START_REF] Lin | Surface-Bound Humic Acid Increased Pb2+ Sorption on Carbon Nanotubes[END_REF] observed that HA bound to the surface of MWCNTs significantly favoured Pb(II) sorption (pH = 5.0 ) (Figure 3A). Similar results were also observed for the sorption of Cd(II) (pH = 6.0) on HA-coated MWCNTs [START_REF] Tian | Effect of Humic Acids on Physicochemical Property and Cd(II) Sorption of Multiwalled Carbon Nanotubes[END_REF] . Additionally, OM can also increase the stability of CNMs in suspension as the OM polymeric chains adsorbed to their surface tend to avoid each other in solution so as not to constrain the conformational space available to each of them inducing repulsive forces and thus decreasing the chances of homoagglomeration [START_REF] Bandyopadhyaya | Stabilization of Individual Carbon Nanotubes in Aqueous Solutions[END_REF][START_REF] Hyung | Natural Organic Matter Stabilizes Carbon Nanotubes in the Aqueous Phase[END_REF] (and in turn increasing the potential available sites for metal(loid) adsorption) (Figure 3B and 3C). These interactions also depend on both pH and OM composition. Indeed, Sheng et al. reported an increase in the adsorption of Cu(II) on MWCNTs due to dissolved HA/FA at pH < 7.5 (up to 90%), while a decrease was found at pH > 7.5 (to 80%) [START_REF] Sheng | Adsorption of Copper(II) on Multiwalled Carbon Nanotubes in the Absence and Presence of Humic or Fulvic Acids[END_REF] . In parallel, Sun et al. [START_REF] Sun | Effect of Natural Organic Matter (NOM) on Cu(II) Adsorption by Multi-Walled Carbon Nanotubes: Relationship with NOM Properties[END_REF] found that there was a higher binding affinity between Cu(II) and FA compared to HA, due to more oxygenated functional groups present in FA that could also complex with Cu(II) (pH = 6). Thus, it seems that there are different OM-metal(loid)-CNM interaction processes.

Soil

First of all, it should be reminded that due to the complexity of both soil and sediment, very few studies have been conducted to understand (i) what are the properties of these matrices that influence the mobility and/or agglomeration of CNMs and (ii) the related mechanisms.

However, as in simplified conditions, CNMs influence the fate of metal(loid)s in soil. For instance, a study revealed that Pb and Cu immobilization in soil increased with increasing MWCNT concentration correlated with the increased adsorption sites on the surface of CNTs available for Pb and Cu ion adsorption [START_REF] Rizwan | Immobilization of Pb and Cu in Polluted Soil by Superphosphate, Multi-Walled Carbon Nanotube, Rice Straw and Its Derived Biochar[END_REF] .

These interactions between CNMs and metal(loid)s in soil vary according to CNM intrinsic properties such as their morphology (diameter, length) and their surface chemistry (surface charge and functionalization) [START_REF] Jaisi | Single-Walled Carbon Nanotubes Exhibit Limited Transport in Soil Columns[END_REF][START_REF] Kasel | Limited Transport of Functionalized Multi-Walled Carbon Nanotubes in Two Natural Soils[END_REF][START_REF] Lu | Transport of Surfactant-Facilitated Multiwalled Carbon Nanotube Suspensions in Columns Packed with Sized Soil Particles[END_REF] . While it can be expected that the smaller the CNM, the higher their mobility in soils, it remains difficult to support this assumption from available data in the literature.

In addition, properties such as soil texture, structure, porosity, permeability, or type of clay contribute to the actual flow of CNMs through the soil [START_REF] Jaisi | Single-Walled Carbon Nanotubes Exhibit Limited Transport in Soil Columns[END_REF] . It appears that MWCNTs [START_REF] Zhang | Effect of Clay Minerals on Transport of Surfactants Dispersed Multi-walled Carbon Nanotubes in Porous Media[END_REF][START_REF] Han | Transport of Multi-Walled Carbon Nanotubes Stabilized by Carboxymethyl Cellulose and Starch in Saturated Porous Media: Influences of Electrolyte, Clay and Humic Acid[END_REF] and GO [START_REF] Lu | Effects of Clay Minerals on Transport of Graphene Oxide in Saturated Porous Media[END_REF] generally tend to have higher retention (low transport) in clay than in sandy soils. For example, the retention profile indicated that retention was higher in soil with smaller size sand particles (240 μm) than soil with higher size sand particles (607 μm) [START_REF] Kasel | Transport and Retention of Multi-Walled Carbon Nanotubes in Saturated Porous Media: Effects of Input Concentration and Grain Size[END_REF] . Lu et al. showed that the type of clay influenced CNM transport because the addition of 5% of kaolinite inhibited more graphene transport in soil column than montmorillonite and illite which presented the same particle size (Kaolinite: 28.0 µm, montmorillonite: 20.0 µm and illite: 23.9 µm) due to greater amounts of positively charged edge sites. Furthermore, the ionic strength of the soil solution is also a key parameter to consider. Indeed, Qi et al. demonstrated that the addition of 0.5 mM of Ca 2+ significantly inhibited GO transport in clay soil in contrast to sandy soil by complexing with the surface oxygen of GO and soil components leading to enhance GO agglomeration and link GO with soil grains [START_REF] Qi | Transport of Graphene Oxide Nanoparticles in Saturated Sandy Soil[END_REF] .

Several studies using Toxicity Characteristic Leaching Procedures (TCLP) determined the leachability of metal(loid)s in CNT-amended soils. For instance, Yang et al. [START_REF] Vithanage | Effects of Carbon Nanotube and Biochar on Bioavailability of Pb, Cu and Sb in Multi-Metal Contaminated Soil[END_REF] observed that the bioaccessible Sb content in a loamy soil was significantly reduced (20.7%) with the addition of 0.9 wt.% MWCNTs compared to control (without CNT addition). In sandy soil, Vithanage et al. [START_REF] Yang | Effect of Multi-Walled Carbon Nanotubes on Extractability of Sb and Cd in Contaminated Soil[END_REF] did not observe any significant difference in extractable Sb at the tested MWCNT concentrations (0.5, 1 and 2.5 wt.%). The immobilisation and, consequently, the bioavailability of Sb differed between the two studies, which could be related to different texture and other related parameters (cation exchange capacity, structure, water holding capacity).

As in simplified medium, the interaction of CNMs and metal(loid)s is metal dependent.

Indeed, a study using 0.2, 1 and 5 wt.% GO in a historically polluted soil showed that the availability of Pb and Cu followed a dose-dependent relationship so that at the highest concentration of GO, their availabilities relative to the controls were found to be reduced by 2.5% and 5.6% respectively. This decrease was much smaller for Zn and Cd (ca. 1%) and As availability was increased by 191% [START_REF] Baragaño | Nanoremediation of As and Metals Polluted Soils by Means of Graphene Oxide Nanoparticles[END_REF] . Regarding the kinetics, it seems that reaching the equilibrium takes much longer in more complex environments than in simplified medium. For example, Song et al. [START_REF] Song | Effect of Multi-Walled Carbon Nanotubes on Phytotoxicity of Sediments Contaminated by Phenanthrene and Cadmium[END_REF] observed that in soil solution the adsorption of Cd 2+ on MWCNTs reached 65% after 7 days and up to 87% and 88% after 30 and 60 days, respectively. To compare with aqueous media, the time to reach equilibrium does not exceed 12 hours (Table S1).

Overall, more studies involving solid matrices under environmentally relevant conditions need to be carried out as the risk of CNM release into the environment is increasing. It is important to understand all the physico-chemical characteristics of soils affecting the interactions among contaminants in order to better predict their transfer and toxicity in the environment and along trophic chains.

3. Metal(loid)s, CNM and CNM-metal(loid) complex uptake and impacts on agrosystem organisms

Uptake and impacts of metal(loid)s and CNMs as single contaminant

The toxicological impacts of metal(loid)s and CNMs and their potential consequences on agrosystems have been widely studied. Thus, the scientific corpus available is abundant and compiled in several scientific articles for microorganisms [START_REF] Liné | Carbon Nanotubes: Impacts and Behaviour in the Terrestrial Ecosystem -A Review[END_REF][START_REF] Baath | Effects of Heavy Metals in Soil on Microbial Processes and Populations (a Review)[END_REF][START_REF] Giller | Toxicity of Heavy Metals to Microorganisms and Microbial Processes in Agricultural Soils: A Review[END_REF][START_REF] Giller | Heavy Metals and Soil Microbes[END_REF][100][101] , invertebrates [START_REF] Liné | Carbon Nanotubes: Impacts and Behaviour in the Terrestrial Ecosystem -A Review[END_REF][102][103][104][105][106] and crop plants [START_REF] Nagajyoti | Occurrence and Toxicity for Plants: A Review[END_REF][START_REF] Liné | Carbon Nanotubes: Impacts and Behaviour in the Terrestrial Ecosystem -A Review[END_REF]101,102,[107][108][109][110] which are the major organisms of agrosystems due to their functions and interactions. This corpus is regularly updated according to the technical advances, offering a step further on the scientific knowledge in these fields of research especially for metal(loid)s due to older knowledge.

Microorganisms are essential for many agrosystem services like mineralization, C, N and P biogeochemical cycles and because of their interactions with plants like mycorrhizal association 111 . Microorganisms are capable of accumulating metal(loid)s, this accumulation is generally governed by the sorptivity of the cell envelope and the ability to absorb metal(loid)s into the cytosol 112 . The metal membrane transporters are not highly selective and thus metal(loid)s can be taken up through this pathway 112,113 leading to alterations in the microorganisms at different scales. Metal(loid) toxicity could occur through displacement of essential metals from their original binding sites or through ligand interactions and conformational structure alterations with oxidative phosphorylation and osmotic balance 114 .

Damage to the DNA structure, the cell membrane and the activity of some enzymes was also reported [START_REF] Baath | Effects of Heavy Metals in Soil on Microbial Processes and Populations (a Review)[END_REF][START_REF] Giller | Toxicity of Heavy Metals to Microorganisms and Microbial Processes in Agricultural Soils: A Review[END_REF][115][116][117] . Thus, metal(loid)s can affect the microbial population by decreasing their growth/proliferation, and altering their morphology and biochemical activities 100,118 . Due to these alterations, the functions performed by microorganisms such as the decomposition of organic matter [START_REF] Baath | Effects of Heavy Metals in Soil on Microbial Processes and Populations (a Review)[END_REF][START_REF] Giller | Toxicity of Heavy Metals to Microorganisms and Microbial Processes in Agricultural Soils: A Review[END_REF] , C sequestration or N fixation could be negatively impacted [START_REF] Giller | Toxicity of Heavy Metals to Microorganisms and Microbial Processes in Agricultural Soils: A Review[END_REF][START_REF] Giller | Heavy Metals and Soil Microbes[END_REF]119 .

According to a study that compiled the lowest metal(loid) amount added that resulted in a decrease in the rate of basal respiration (LOAED), the mean LOAED for Hg, C, Cu, Pb, Ni, Cd, Zn was 257, 411, 500, 506, 576, 594 and 697 mg.kg -1 , respectively (Table S2) [START_REF] Giller | Toxicity of Heavy Metals to Microorganisms and Microbial Processes in Agricultural Soils: A Review[END_REF] .

In parallel, for CNMs, transmission electron microscopy observations have evidenced that they may interact strongly with bacterial cell membranes. These interactions may disrupt the integrity of the membrane structure by oxidative stress and/or physical damage, allowing

CNMs to be internalized in bacteria [120][121][122] . In addition, a majority of studies has observed a decrease in soil microbial activity following exposure to CNMs [122][123][124][125][126][127] . CNMs would present an antimicrobial potential since a whole set of studies reported a loss of viability following exposure 123,124,[128][129][130] . Changes in microbial community structure have also been reported 123,126,131,132 . Finally, microbial functions such as mineralization, N and CO 2 fixation could be decreased 133 . The effect of CNMs on microbial activity 122 and biomass appeared at 85 mg.L -1 and 1-5 mg.g -1 , respectively 124,126,127 .

Oligochaetes are considered as soil engineers because of their involvement in physical and chemical processes such as litter mixing, soil porosity, active soil water transport, OM mineralization and nutrient mobilization and cycles [134][135][136] . These organisms present two pathways of contamination: the oral pathway by ingestion of soil and the tegumentary pathway by contact with soil. After absorption, metal(loid)s can accumulate in the posterior alimentary canal 137 . Metal(loid)s may decrease the growth of earthworms through delayed biomass gain [138][139][140][141] and act on energy reserves by decreasing the production of lipid reserves 142,143 and modifying the gut microbiota 144 . In addition, morphological and behavioural changes have been demonstrated following exposure to metal(loid)s 145 . It was observed that metal(loid)s can interfere with earthworm reproduction by reducing the number of juveniles produced 138,139,146 induced by a reduction of number of sperm produced 147 , the production of cocoons 138,141,146,[148][149][150] and the success of cocoon hatching 139,151,152 For CNM exposure, it has been demonstrated that earthworms are able to eliminate orally ingested CNMs by depuration thus limiting the toxicity of these contaminants [153][154][155] . As a result, many studies have not observed any apparent effects on earthworms following CNM exposure 154,156,157 . However, few works reported DNA damages 158,159 and a decreased cocoon production 160 (up to -60% and -78% at 495 and 1000 mg DWCNT.kg -1 food). According to Scott-Fordsmand et al. 160 and Hu et al. 158 , the median effective concentration (EC 50 ) for earthworms exposed to DWCNT and MWCNT would be >500 and 1480.3 mg.kg -1 for growth and mortality, respectively.

Plants can take up metal(loid)s from the soil through their roots, transport them through the xylem and accumulate them in the different tissues of all organs (roots, stem, leaves, grains and fruits) by symplastic and apoplastic pathways 161 . Generally, the roots tend to accumulate metal(loid)s such as Al, Cd, Cr, Cu, Hg, Ni, P and Zn, vegetative parts have a lower accumulation level and the reproductive parts tend to exclude them 162,161 . During their transport in the plant, metal(loid)s are largely bound to the cell walls, which explains why most of the metal(loid)s are bound in the roots (about 75-90%) and a smaller fraction in the shoots 161 . However, some particularities exist and accumulation is a function of the stage of development of the plant and the metal(loid) considered 161 . The stress imposed by meta(loid)l accumulation can induce reactive oxygen species (ROS), promote DNA damage, impair functional membrane integrity, nutrient homeostasis and disrupt protein and enzyme function and activity [163][164][165] . These toxic effects lead to a slowing down of cellular parameters, i.e. a reduction of photosynthetic activity, lipid production 107,166 , plant growth parameters, and consequently of the yield 107,[166][167][168][169][170][171][172] . The phytotoxicity of the metal(loid)s under their ionic form follows the trend (from most to least toxic): Pb≈Hg > Cu > Cd≈As > Co≈Ni > Zn > Mn, with median toxic concentrations of : 0.06, 0.09, 0.13, 0.56, 0.67, 1.00, 1.12, 1.63 and 2.53 mg.L -1 (hydroponic exposure) 173 .

Although the entry mechanisms of CNMs are not well known, it is established that they can interact with plants at the root system level. Once absorbed, they can share the vascular system with water and nutrients and can be transported by transpiration in the upper part of the plants [START_REF] Liné | Carbon Nanotubes: Impacts and Behaviour in the Terrestrial Ecosystem -A Review[END_REF] . Several studies have observed CNM accumulations in all parts of the plant 110,174,175 . CNMs can act on plants starting from the seed germination process with a trend to activate and increase the seed germination rate [176][177][178][179] . The scientific corpus of research on the effects of CNMs reports contrasting effects on plant growth and physiological status. It reports an increase, a decrease or even a neutral effect on growth parameters (root system, biomass production, flowers and fruits) 110,174 . In case of toxicity, it was associated with generation of ROS, antioxidant activity, necrotic lesions of cells and leaf tissues as well as root and leaf morphological changes, decreased chlorophyll, and programmed cell death 180- 183 . The inherent properties of CNMs (functionalization, length, diameter) and experimental designs (exposure medium, duration, plant species) could be a reason for the observed variability in CNM toxicity. The mean "lowest observed effect level" (LOEC) for plants exposed to CNTs was 389 mg.L -1 according to Jackson et al. 120 .

Regardless to LOAED, NOEC, LOEC and EC 50 , it seems that metal(loid) concentrations needed to induce toxicity were much lower than those required for CNMs. Decrease in Cd concentration: at 2 mg.L -1 of Cd -24%, -18%, and -12% with addition of 10, 50 and 100 mg.kg -1 of MWCNT. Decrease more pronounced at 10 mg.L -1 of Cd (-42%, -34%, -26%

of Cd with addition of 10, 50 and 100 mg.kg -1 of MWCNT).

There appear to be an interaction: decreased percentage of inhibition of worm growth, detoxifying enzymes, and metabolites for the lowest the MWCNT concentration. Increase in Cd concentration: in leaves by +15%, +12% and +9% at 100, 500 and 1000 mg.kg -1 , in stems by +33% and +28% at 100 and 500 mg.kg -1 . Decreased Cd transfer: in stems by -10% at 5000 mg.kg -1 , in roots by -22%, -21%, -29% and -30% at 100, 500, 1000, 5000 mg.kg -1

Interactive effects: increase in leaf dry mass with the addition of 1000 mg.kg -1 of MWCNT, stem dry mass at 500 mg.kg -1 of MWCNT and root dry mass at 500 and 1000 mg.kg -1 of MWCNT, increase in H 2 O 2 , MDA concentration and SOD activity from the addition of 100 mg. kg -1 of MWCNT and decrease of POD activity from 100 mg.kg -1 of MWCNT In lower contaminated soil: no effects on metals transfer for earthworms. Increase in Cd (+37%) and Zn (+21%) transfer with 10 mg.kg -1 of MWCNT for lettuces. In higher contaminated soil: increase in Pb (+34%) and Zn (+25%) transfer with 10 mg.kg -1 of MWCNT for earthworms. Decrease in Cd (-29%) and Zn (-30%) transfer with 0.1 mg.kg -1 of MWCNT for lettuces.

Interactive effects on higher contaminated soil: biomass reduction for lettuces exposed to 0.1 mg.kg -1 of MWCNT. Increase in flavonoid concentration with 10 mg.kg -1 of MWCNT.

Leroy et al. 30

Impacts of the interaction between metal(loid)s and CNMs

After an extensive literature survey on the topic, only articles focusing on CNTs, graphene and GO together with a proper statistical analysis were kept for this review. Considering studies evaluating both the transfer and the toxicity of metal(loid)s and CNMs (Table 3) ( 11studies), 18% focused on bacteria, 18% on earthworms and 82% on plants. Among these studies, about 64% reported interactive toxicological effects due to the simultaneous presence of CNMs and metal(loid)s. Within these interactive effects, when all control conditions were set-up (without metal(loid) and without CNM contamination, metal(loid) alone, CNM alone), we could distinguish antagonist (18%) and synergic (18%) effects (Figure 1).

Bacteria

For bacteria, very few studies have been conducted. Furthermore, in the available articles the experimental design did not permit to highlight the existence of interactive effects since the impact of CNM alone or metal(loid)s alone were not tested (not the purpose of the study).

However, a study using soil contaminated with Cd (0.1 mg.kg -1 ) and GO (1000 and 2000 mg.kg -1 ) evidenced a decrease in soil microbial diversity after addition of GO, indicating that the microbial communities in the Cd-contaminated group without GO were more diverse than those in the treated groups (Cd x GO) 188 . In addition, authors observed some changes in bacterial communities after addition of GO with an increase in several bacterial abundances (Acidobacteria and Actinobacteria) compared to single Cd contamination and a decrease in phyla such as WD272 and TM6 revealing phylum-specific sensitivities 188 . Interestingly, the abundance of Rhodospirillales and Nitrospirae which are symbiotic N 2 -fixing bacteria was reduced at 3 days and then restored at 15 and 60 days evoking some resilience in the ecosystem.

These few studies alone do not allow generalization to be made and highlight the need to initiate more studies on microorganisms with simultaneous CNM and metal(loid) exposure.

Indeed, due to adsorption of metal(loid)s on CNM and to CNM strong interactions with bacterial cell membranes, CNMs could be a vector to increase metal(loid) transfer to microorganisms and associated toxicity or depending on their interactions with soil particle they could also mitigate the metal(loid) toxicity (i.e. the complex CNM-metal(loid) could adsorb to soil particles making metal less bioavailable to bacteria cells and thus less toxic).

Earthworms

Studies focused on earthworms report contrasting results of the addition of CNMs on metal(loid) transfer and toxicity. Yang et al. observed a decrease of Cd transfer (antagonist effect) ranging from -43% to -31% with the addition of 10 mg.kg -1 and 100 mg.kg -1 of MWCNTs, respectively after 14 days of exposure in the model Eisenia fetida (Cd: 10mg.kg - 1 ) [START_REF] Yang | Evaluation of the Combined Toxicity of Multi-Walled Carbon Nanotubes and Cadmium on Earthworms in Soil Using Multi-Level Biomarkers[END_REF] . The decrease in Cd transfer was thus inversely proportional to the dose of MWCNTs.

Additionally, the change in transfer was also metal dose-dependent: at 10 mg.kg -1 MWCNTs, a -43% decrease was noticed at 10 mg.kg -1 of Cd but decreased to -28% at 2 mg.kg -1 of Cd. In agreement with transfer results, the addition of MWCNTs decreased earthworm growth inhibition caused by Cd, detoxifying enzymes and metabolites [START_REF] Yang | Evaluation of the Combined Toxicity of Multi-Walled Carbon Nanotubes and Cadmium on Earthworms in Soil Using Multi-Level Biomarkers[END_REF] . At the highest Cd concentration (10 mg.kg -1 ), a growth inhibition rate of 27% was registered in comparison with earthworms exposed to control conditions (no Cd, no MWCNTs), this rate was decreased to 8% and 22% at 10 and 100 mg.kg -1 of MWCNTs, respectively.

In contrast, Leroy et al. rather observed synergic effects of metals and CNTs when earthworms were exposed to two contaminated soils (Zn, Pb and Cd) and demonstrated either no impact of the addition of MWCNTs on metal uptake in one soil or an increase up to +34% and +25% of Pb and Zn in the second soil (with no impact on Cd transfer) after 6 weeks [START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF] .

Furthermore, when an increased uptake was detected it was CNT dose dependent. Even though earthworms are able to eliminate orally ingested CNMs by depuration, it appears that CNM ingestion could lead to metal release in earthworm tissues, maybe due to changing physico-chemical conditions in the gut (especially pH) leading to desorption. Despite transfer increase, no toxicological effects were found.

The difference between these articles could partly be explained by different soil texture.

Indeed, the first one which induced Pb and Zn transfer increase upon CNT addition had a lower OM content than the other soil. Authors reminded that a low OM is less favorable for earthworm feeding an burrowing activities 189 and thus metal transfer [START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF]190 .

Plants

Among studies on the transfer and toxicological impacts of simultaneous contamination with CNMs and metal(loid)s on plants (9 studies reviewed), 89% present results on the transfer of metal(loid)s from the exposure medium to the plants and 100% on toxicity. In the transfer studies, 91% of the studies showed CNM -metal(loid) interactions with either an increase [START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Li | The Mutual Effects of Graphene Oxide Nanosheets and Cadmium on the Growth, Cadmium Uptake and Accumulation in Rice[END_REF][START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF][START_REF] Zhao | Carboxylated Graphene Oxide-Chitosan Spheres Immobilize Cu2+ in Soil and Reduce Its Bioaccumulation in Wheat Plants[END_REF][START_REF] He | Graphene Oxide Promoted Cadmium Uptake by Rice in Soil[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF]191,192 and/or a decrease [START_REF] Zhao | Carboxylated Graphene Oxide-Chitosan Spheres Immobilize Cu2+ in Soil and Reduce Its Bioaccumulation in Wheat Plants[END_REF][START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Gao | Effects of Foliar Application of Graphene Oxide on Cadmium Uptake by Lettuce[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF][START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF] of metal(loid) transfer differing from the additive risk model.

Furthermore in the studies evidencing a synergic effect with an increased uptake of metal(loid)s, some authors demonstrated a dose dependent effect of the addition of CNMs on the transfer of metal(loid)s both in hydroponics and in soil [START_REF] Zhao | Carboxylated Graphene Oxide-Chitosan Spheres Immobilize Cu2+ in Soil and Reduce Its Bioaccumulation in Wheat Plants[END_REF][START_REF] He | Graphene Oxide Promoted Cadmium Uptake by Rice in Soil[END_REF][START_REF] Li | The Mutual Effects of Graphene Oxide Nanosheets and Cadmium on the Growth, Cadmium Uptake and Accumulation in Rice[END_REF][START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF][START_REF] Gao | Effects of Foliar Application of Graphene Oxide on Cadmium Uptake by Lettuce[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Lian | Do Polystyrene Nanoplastics Affect the Toxicity of Cadmium to Wheat (Triticum Aestivum L.)?[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF] . For example, Gao et al. found that the addition of GO to a Cd contaminated medium (1 mg.L -1 Cd) led to a dose-dependent increase in Cd concentration in both roots and leaves: the addition of 5 mg.L -1 of GO increased by 12% the Cd concentration in leaves while an addition of 40 mg.L -1 led to a 50% increase [START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF] . Hypotheses such as facilitating metal entry into root cells due to interactions between CNMs and root cells and/or uptake of CNMs with surface adsorbed metals may explain the increased transfer observed in these examples. Additionally, it seems that at high concentrations, CNMs may have a different impact than at lower concentrations in the medium [START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF] . Indeed, wheat plants exposed to As(III) took up 20% of this As while the uptake rate of As increased to 25% and 32% in presence of GO concentrations of 0.1 and 1 mg.L -1 , then decreased to 16% at 10 mg.L -1 24 . Likewise, Leroy et al. also observed contrasted results

depending on CNM concentrations and explained these results by CNM dispersion in the medium (soil): at low concentrations (0.1 mg.kg -1 ), CNTs may be better dispersed in the soil than at higher concentration (10 mg.kg -1 ) 193,194 offering thus, a higher exchange surface and higher adsorption. This hypothesis is supported also by the study of Zhang et al. in which the authors observed that the agglomeration of CNTs decreased the adsorption of some organic compounds 193 . Several hypotheses can be suggested for this increased uptake: CNMs with adsorbed metal(loid)s can act as vectors by damaging root cell walls and facilitate metal(loid)s entry in crops tissues or this complex might accumulate in the rhizosphere and lead to an enhanced metal release with the pH modification at the vicinity of the root surface.

When an increased transfer of metals due to the presence of CNMs in the medium was detected, it was mostly accompanied by an increased toxicity. Indeed, among the studies that investigated the toxicological impacts of simultaneous contamination, 75% of them found interactive effects highlighting an increase in oxidative stress [START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Lian | Do Polystyrene Nanoplastics Affect the Toxicity of Cadmium to Wheat (Triticum Aestivum L.)?[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF]184 , decrease in different plant components 24-26,29,184,195 (chlorophyll, protein, sugar) and in plant biomass [START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF][START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF][START_REF] Gao | Effects of Foliar Application of Graphene Oxide on Cadmium Uptake by Lettuce[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Lian | Do Polystyrene Nanoplastics Affect the Toxicity of Cadmium to Wheat (Triticum Aestivum L.)?[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF]184,195,196 (Table 3). For instance, synergistic effects were evidenced on rubisco concentration : indeed a decrease by 53% was detected in the presence of both Cd (5 mg.L -1 ) and GO (40 mg.L -1 )

while Cd alone reduced it by 14.5% and GO alone by 18.5%; additive model would have suggested a decrease by 33% ((-14.5%) + (-18.5%)) = -33%) much lower than the 53% observed here [START_REF] Gao | Effects of Graphene Oxide on Cadmium Uptake and Photosynthesis Performance in Wheat Seedlings[END_REF] . This observation was similar for other parameters (root and shoot biomass, As solution (10 mg.L -1 ) [START_REF] Hu | Graphene Oxide Amplifies the Phytotoxicity of Arsenic in Wheat[END_REF] ; for instance after exposure to the co-contamination SOD increased by 426%, while it increased by 56% after exposure to As alone and decreased by 4% after exposure to GO alone (additive model would suggest a 52% increase).

However, some studies also highlighted antagonist interactions between metal(loid)s and CNMs with a decrease in the transfer of metal(loid)s from soil to plants and finally lower or no toxicity symptoms [START_REF] Gao | Effects of Foliar Application of Graphene Oxide on Cadmium Uptake by Lettuce[END_REF][START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF][START_REF] Lian | Do Polystyrene Nanoplastics Affect the Toxicity of Cadmium to Wheat (Triticum Aestivum L.)?[END_REF][START_REF] Dong | Microplastic Particles Increase Arsenic Toxicity to Rice Seedlings[END_REF]184 . These effects can also be organ dependent. Indeed, Zhao et al.

showed that GO-chitosan spheres significantly decreased Cu bioaccumulation in roots (-60%) and stems (-67%) of wheat compare to single metal contamination, but not in leaves (almost similar with an increase of Cu bioaccumulation around +2%) [START_REF] Zhao | Carboxylated Graphene Oxide-Chitosan Spheres Immobilize Cu2+ in Soil and Reduce Its Bioaccumulation in Wheat Plants[END_REF] . Despite changes in Cu transfer with the addition of GO, the co-exposure did not impact growth parameters studied (root, stem and leaf length) but decreased the photosynthetic rate and stomatal conductance up to -58% and -34%, respectively. Likewise, Gong et al. found similar pattern with a decrease in Cd bioaccumulation in roots up to -22% upon MWCNT addition (100 mg.kg -1 ) and an increase in Cd accumulation in stem and leaves up to +15% and +33%, respectively [START_REF] Gong | Roles of Multiwall Carbon Nanotubes in Phytoremediation: Cadmium Uptake and Oxidative Burst in Boehmeria Nivea (L.) Gaudich[END_REF] . These differences on metal bioaccumulation according to plant organ could reflect a plant defence strategy. It is known that plants have defence mechanisms against metal(loid) exposure like accumulating metal(loid)s in specific compartments of the plant such as cell walls and leaves to reduce their toxicity 197 .

There are some disparities on transfer and toxicity of CNM-metal(loid) simultaneous exposure. The adsorption mechanism alone does not seem to explain such disparities and the concentration in CNMs, which directly affects their dispersion and aggregation in the medium, could be a possible explanation.

Although the studies carried out in liquid media (water, culture solution, soil solution, etc.) are a first approach privileged at the beginning of new researches on new substances, they do not allow to apprehend the complex relations between solid matrix and contaminants since some studies show their importance to determine the fate of contaminants in organisms [START_REF] Leroy | Interactive Effects of Metals and Carbon Nanotubes in a Microcosm Agrosystem[END_REF] .

Indeed, the type of soil could explain differences observed on interactive effects on transfer and toxicity due to the strong influence of soil physico-chemical parameters (clay, OM, pH etc.). Whatever the types of interactive effects, these largely dominate in the studies compared to additive effects used in risk assessment.

Conclusion -Knowledge gaps and Perspectives

In 2012, the European Commission stated that they are "committed to ensuring that the risks associated with chemical mixtures are properly considered and assessed". In parallel, in 2019, the European Environmental Agency warned again about the "cocktail effect" of chemical pollutants, especially those found in European waters, whose cocktail effects are assumed or proven 198 . However up to date lots of progress remain to be done on that matter.

Indeed, after reviewing extensively the literature, we can conclude that strong interactions exist between CNMs and metal(loid)s which have been demonstrated in simplified medium (solution) and whose impacts are visible in the environment by modifying the behaviour of contaminants in cocktail and their impact on organisms. These interactions include physical adsorption, chemical interaction, electrostatic attraction and sorption-precipitation. In the environment, the vast majority of studies concluded that these interactions modify the fate (uptake and toxicity) of these contaminants in cocktail in comparison with an additive model.

The nature of the impact (synergic or antagonist) is influenced by many parameters : 1) CNM nature which influences metal(loid) adsorption capabilities, 2) CNM concentration which influences their behaviour, in particular their agglomeration, 3) CNM morphology and SSA as well as adsorption abilities and CNM transfer through biological barriers, 4) metal(loid) nature and number of different metallic species because of their specific affinity and potential competition and repulsion for adsorption sites onto CNMs, 5) exposure medium which influences CNM and metal(loid) behaviour, 6) soil characteristics (clay content, OM and pH) which influence metal(loid) adsorption onto CNMs as well as organism behaviour and 7) type of organisms (crops, earthworms or bacteria) and environmental relevance of exposure conditions (exposure pathways, organism lifestyle, organism interactions, …). So, in conclusion, the additive model used so far for risk assessment of chemical substances in mixture is not relevant; instead a multiplicative model which integrates synergy and antagonism would seem more suitable with correction factors for the different influencing parameters highlighted in this review to encompass processes which remain unclear so far and leading to seemingly contradictory results in the literature.

Knowledge gaps

The knowledge gaps we identified through this literature survey are listed below:

(1) More information on CNM characteristics are needed in the articles to further understand contrasted results observed on transfer and toxicity.

(2) The use of element speciation models (such as Minteq or ChemEQL among others) in solution and their comparison with experimental data and their fitting with Langmuir or Freundlich equations would be interesting to identify if these models could give relevant predictions, especially in multi-metallic conditions.

(3) More studies need to be conducted on agrosystem organisms to have more information on the toxicological effects resulting from exposure to a mixture of contaminants. For instance, only 3 metal(loid)s (Cu = 1, As = 1 and Cd = 8, studies and one study with Cd, Pb and Zn simultaneously) were tested in interactions with CNMs, which represents a small proportion of the existing metals.

(4) Another important point is the difficulty to properly analuse the results in many studies due to incomplete experimental designs that do not permit to highlight possible interactions.

On several occasions, the studies did not investigate the effects of CNMs alone or metal(loid)s alone (missing control conditions). Thus, recurrent increases and decreases of the studied biomarkers of toxicity were attributed to the addition of CNMs in the presence of metal(loid)s, but these interpretations are only partial in the absence of tests with single contaminant.

(5) The statistics are sometimes performed only by modality of metal(loid) contamination, not allowing to establish possible interactions between CNMs and metal(loid)s (ANOVA 1-way vs ANOVA 2-ways).

( 6) More studies on ecosystem functions (mineralization and recycling) and biogeochemical cycles (C, N and P) are needed to have a more integrative view of these contaminant impacts on agrosystems. So far, these markers have only been studied after exposure to a single contaminant even though they are very good indicators of an ecosystem health. (7) Studies are also needed to identify a potential bioaccumulation along food webs. Studies in micro-mesocosms with trophic chains seem to be a relevant experimental set-up to answer this question 199 . Due to CNM-metal(loid) interactions, the exposure duration in micromesocosms needs to be adapted to organism cycles, especially to know if CNM-metal(loid) exposure is putting at risk crop productions and human health.

Perspectives

Using combined toxicity interaction indices could be a practice to generalize to gain a deeper understanding of these interactions among contaminants. For example, Yang et al. [START_REF] Yang | Evaluation of the Combined Toxicity of Multi-Walled Carbon Nanotubes and Cadmium on Earthworms in Soil Using Multi-Level Biomarkers[END_REF] demonstrated synergic and antagonist effects using indices such as the Biomarker Response Index (BRI) coupled with the Concentration Addition Index (CAI) and the Effect Addition Index (EAI), which together quantify the joint effects of mixtures for a range of effect levels.

BRI is an index based on the level of alteration of the response of the biomarkers tested in the treatments with contamination(s) compared to the control (without contamination). The level of biomarker impairment is classified into four distinct levels, each corresponding to a score: mild = 4, moderate = 3, major = 2 and severe = 1 200 . The score for each biomarker is multiplied by the corresponding weighting to form an integrated index that is used to assess the overall effect of contaminants in a system submitted to multiple stress 201 . This allows the integration of complex biomarker responses into a single predefined class. It is thus possible to establish a dose-response relationship between contamination levels and biomarker responses 202 . This index has been used in the risk assessment of chemicals under the Water Framework Directive in Wales 200 . The BRI coupled with the CAI and EAI allow to determine respectively additive (=0), synergic (>0) or antagonist (<0) effects 203 . The CAI and EAI are derived from the commonly used concentration addition (CA) and independent action (IA) models that assess the toxicity of substances in non-interactive mixtures.

Another factor which is usually not considered is contamination aging. Indeed, the impact of metal(loid)s is influenced by their origin and aging [204][205][206][207] . The toxicological effects of metal(loid)s spiked in soil in laboratory experiments (in salt form) differ with soils with an aged contamination under the influence of natural processes [204][205][206][207] . For example, oxidation and precipitation of some metal(loid)s can affect their bioavailability and consequently their toxicity 208 . This parameter should be more considered in future experiments.

Although micro and nanoplastics have different properties than CNMs, they are principally made of carbon and also display adsorption capacities leading to similar effects on transfer and toxicity (Table S3). Plastic concentration in agricultural soils could be much higher that the predicted CNM concentrations related to sludge application or mulching practices in particular. Special attention should thus be paid to the potential transfer and toxicological impacts of these micro and nanoplastics in co-exposure situations with other contaminants such as metal(loid)s.

Finally, agrosystems interact closely with other organisms such as insects, small mammals and birds on which they depend for part or all of their life cycles. Considering how these organisms rely on agrosystems, they may be an entry point for the contamination to spread up to other ecosystems.

Figure 1 :

 1 Figure 1 : Schematic differences on additive model compared to synergic and antagonist due to exposure to a cocktail of metal(loid) and CNM substances.

Figure 2 :

 2 Figure 2 : Structure of carbon nanotubes (CNT) and their interactions with metal cations (=M 2+ ) (Figure adapted from Rao et al. (2007)37)

Figure 3 :

 3 Figure 3 : Effects of organic matter (A) bound on CNTs which increase metal(loid) adsorption onto CNTs and (B-C) on the dispersion of CNTs in media (B : without OM, C : with OM)

  chlorophyll, O 2 and H 2 O 2 concentrations) and more pronounced with higher Cd and GO contamination. Similarly, Hu et al. demonstrated that the addition of GO (10 mg.L -1 ) decreased plant development and photosynthetic pigments concentrations together with an increase in antioxidant enzymes activities (SOD and POD) in Triticum aestivum L. exposed to

( 8 )

 8 Technical development is also mandatory as the mechanisms explaining transfer and toxicity results are still not well understood, in particular because data about CNMs actual concentrations in the organisms are rarely available.

Table 1 :

 1 Mean of maximum adsorption (qm = mg.g

	-1

  in which adsorption is favored (n tot =117).

		Cd	Cr	Cu	Hg	Ni	Pb	Zn
		(n=20)	(n=13)	(n=17)	(n=19)	(n=9)	(n=20)	(n=19)
	qm CNT	12.4 (± 9.9)	3.1 (n=1)	22.9 (± 2.6)	24.4 (± 38.9)	11.1 (± 3.8)	30.9 (± 2.6)	35.6 (± 9.4)
	qm CNT-oxidized	35.9 (± 28.2)	21.3 (± 11.7)	37.4 (± 27.3)	27.3 (n = 1)	49.2 (n = 1)	75.7 (± 31.3)	24.4 (± 28.8)
	qm GO	306.9 (± 315.7)	-	183.3 (± 156.6)	-	84.4 (± 19.7)	1280.7 (± 516.5)	345.0 (n=1)

Table 3 :

 3 Effects of simultaneousCNM-metal(loid) exposure on transfer and associated toxicity for three representative agrosystem organisms(bacteria, earthworms and plants). The light blue lines represent studies with hydroponic exposure and the dark blue lines represent studies with soil exposure (SOD = superoxide dismutase, POD = peroxidase, MDA = malondialdehyde, CAT = catalase, GR = glutathione reductase, GP = glutathione peroxidase, Chlo = chlorophyll, n.p = data not provided).

	Type and		Type and
	CNM concentratio	CNM size	metal(loid) concentratio	Organisms	Exposure medium	Exposure duration	Transfer effects	Interactive toxicological effects	References
	n		n
	GO (0, 1 and 10 mg.kg -1 )	n.p	Cd (0 and 1 mg.L -1 )	Plant: Oryza sativa	Culture solution	30 days	Increase of Cd transfer: +15% and +32% of Cd in roots and shoots with addition of 10 mg.L -1 GO compared to control (without GO with Cd)	No interactive effects on germination and dry biomass of roots and shoots	Li et al. 23
	GO (0.1, 1, 10 mg.L -1 )	n.p	As (0 and 10 mg.L -1 )	Plant: Triticum aestivum	Water	n.p	Compared with the 19.9% rate of As uptake recorded without GO exposure, the uptake rate of As increased to 24.6% and 32.1%, then decreased to and 10 mg.L -1 , respectively 16.1% in the presence of GO concentrations of 0.1, 1	Synergic effects in the presence of both contaminants: reduction of root number and pigments (chlo a/b) and POD), decrease of photosynthetic fresh biomass, reduction of root length, increase of antioxidant enzymes activity (SOD	Hu et al. 24
								Synergic effects: decrease in dry mass of roots
	GO (0, 1,							and shoots, decrease in chlorophyll
	2.5, 5, 10, 20, and 40 mg L -1 )	n.p	Cd (0, 1, and 5 mg.L -1 )	Plant: Triticum aestivum	Water	7 days	Increase of Cd transfer in roots and leaves at every GO and Cd concentrations tested.	concentration and rubisco, increase in H 2 O 2 and O 2 concentration in roots and leaves, increase in antioxidant enzymes activity
								(MDA, POD and SOD)

Acknowledgement

The authors would like to acknowledge the Région Occitanie, Toulouse Federal University, and EC2CO program CARBOSTRESS (CNRS-INSU) for their funding support.