Metal and metalloid bioaccumulation in the Pacific blue shrimp Litopenaeus stylirostris (Stimpson) from New Caledonia: laboratory and field studies

Assessing Metal Toxicity on Crustaceans in Aquatic Ecosystems: A Comprehensive Review

Residual concentrations of some trace elements and lightweight metals, including cadmium, copper, lead, mercury, silver, zinc, nickel, chromium, arsenic, gallium, indium, gold, cobalt, polonium, and thallium, are widely detected in aquatic ecosystems globally. Although their origin may be natural, human activities significantly elevate their environmental concentrations. Metals, renowned pollutants, threaten various organisms, particularly crustaceans. Due to their feeding habits and habitat, crustaceans are highly exposed to contaminants and are considered a crucial link in xenobiotic transfer through the food chain. Moreover, crustaceans absorb metals via their gills, crucial pathways for metal uptake in water. This review summarises the adverse effects of well-studied metals (Cd, Cu, Pb, Hg, Zn, Ni, Cr, As, Co) and synthesizes knowledge on the toxicity of less-studied metals (Ag, Ga, In, Au, Pl, Tl), their presence in waters, and impact on crustaceans. Bibliometric analysis underscores the significance of this topic. In general, the toxic effects of the examined metals can decrease survival rates by inducing oxidative stress, disrupting biochemical balance, causing histological damage, interfering with endocrine gland function, and inducing cytotoxicity. Metal exposure can also result in genotoxicity, reduced reproduction, and mortality. Despite current toxicity knowledge, there remains a research gap in this field, particularly concerning the toxicity of rare earth metals, presenting a potential future challenge.

The use of copper as plant protection product contributes to environmental contamination and resulting impacts on terrestrial and aquatic biodiversity and ecosystem functions

Copper-based plant protection products (PPPs) are widely used in both conventional and organic farming, and to a lesser extent for non-agricultural maintenance of gardens, greenspaces, and infrastructures. The use of copper PPPs adds to environmental contamination by this trace element. This paper aims to review the contribution of these PPPs to the contamination of soils and waters by copper in the context of France (which can be extrapolated to most of the European countries), and the resulting impacts on terrestrial and aquatic biodiversity, as well as on ecosystem functions. It was produced in the framework of a collective scientific assessment on the impacts of PPPs on biodiversity and ecosystem services in France. Current science shows that copper, which persists in soils, can partially transfer to adjacent aquatic environments (surface water and sediment) and ultimately to the marine environment. This widespread contamination impacts biodiversity and ecosystem functions, chiefly through its effects on phototrophic and heterotrophic microbial communities, and terrestrial and aquatic invertebrates. Its effects on other biological groups and biotic interactions remain relatively under-documented.

Trace element accumulation in the muscles of reef fish collected from southern new Caledonian lagoon: Risk assessment for consumers and grouper Plectropomus leopardus as a possible bioindicator of mining contamination

Flesh of 141 fish specimens collected along the southern coast of New Caledonia, close to the mining industry Prony Resources New Caledonia, were analyzed for 10 elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni and Zn). The leopard coral grouper Plectopomus leopardus revealed significant spatial variations for Cr, Fe, Mn and Zn and size-dependent accumulation of Hg. Sanitary risk assessment suggests that Hg and Me-Hg could potentially be a concern for heavy fish consumers. A previous study in New Caledonia had demonstrated the capacity of P. leopardus to differentially accumulate Ag, Cd, Cu, Hg and Zn and as such its potential as bioindicator specie to monitor contamination status in urban areas (Metian et al., 2013). Our results demonstrate that this specie can also to be used as a bioindicator to monitor the contamination status of Cr, Fe and Mn in New Caledonian lagoon in relation to mining activities.

Wild shrimp have an order of magnitude higher arsenic concentrations than farmed shrimp from Brazil illustrating the need for a regulation based on inorganic arsenic

BACKGROUND

Shrimp is a worldwide food commodity, it is a source of several nutrients and vitamins; however, this food is one of the major sources of arsenic for humans. Legislation around the world set limits for the concentration of this element in crustaceans but is mainly concerned with total analysis. Although, arsenic species have different toxicities and total analysis could be ineffective for making decisions about food security.

METHODS

Samples of wild (Farfantepenaeus brasiliensis) and farmed shrimps (Litopenaeus vannamei) from NE Brazil were fractionated in subsamples of carapace, muscle tissue and viscera. The whole shrimp as well as the animal tissue fractions were decomposed using microwave digestion and total arsenic was analyzed by mass spectrometry inductively coupled plasm (ICP-MS). The water-soluble arsenic species were extracted, and the extract was carried for speciation analysis using HPLC-ICP-MS with an anionic and cationic column.

RESULTS

Total As in wild shrimp samples exceeded Brazilian and USA food legislation by one order of magnitude, with concentrations of 11.5 ± 0.5 mg kg-1, while farmed shrimp had significantly lower total arsenic levels (0.53 ± 0.09 mg kg-1). More than 60% of the As was in the edible fraction in the wild shrimp, while in farmed shrimp this was less than 50%. The speciation analysis showed that arsenobetaine (AsB) was the predominant As form and iAs was below the Chinese legislation levels (iAs <0.50 mg kg-1) for shrimp in both species.

CONCLUSION

The arsenic uptake in wild and farmed shrimp was discussed and some differences were found related to feed and salinity. About legislation, it has been concluded that most food legislations that consider only tAs are not appropriate to assess the toxicity of As in seafood. It is necessary to update the legislation of food control agencies to insert As speciation analysis in their protocols.

Effect of short-term dietary exposure on metal assimilation and metallothionein induction in the estuarine fish Pseudogobius sp

Metals introduced into the urban aquatic environment through anthropogenic activities have the potential to accumulate in organisms via multiple uptake routes. Understanding the impact different routes have on metal accumulation is important for the continued management of these ecosystems, where current water quality guidelines (WQGs) tend to be derived from aqueous metal exposure tests. In this study, the estuarine fish Pseudogobius sp. was exposed to a mixture of cadmium (Cd) and zinc (Zn) radiotracers dissolved in water or present in experimental food. Metal-spiked food was presented to fish as a single 'pulse-chase' feed or as three consecutive feeds, where the cumulative metal dose provided by both treatments was equal. Fish did not accumulate either metal from water, even after the length of exposure was increased from 12 h to 36 h. Fish did accumulate metals from diet and the assimilation efficiency (AE) was low following a single feed (12% for both Cd and Zn). Following multiple feeds fish displayed a significantly higher AE for zinc only, suggesting that fish are susceptible to retention of dietary Zn over an extended time period albeit at lower daily loadings. The final body burden and efflux rate did not differ between feeding regimes. Tissue accumulation of Cd and Zn indicated metal specific distribution. The gastro-intestinal (GI) tract contained >90% of total Cd body burden, whilst the carcass accounted for the majority (70-88%) of Zn body burden. There was significant induction of the biomarker metallothionein (MT) in the GI tract. These results demonstrate the differences in Cd and Zn metal uptake characteristics in this estuarine fish species, and how feeding frequency and metal loading of food may influence assimilation. This study highlights the importance of considering the inclusion of dietary exposures in WQG frameworks.

Cadmium Accumulation and Kinetics in Solea senegalensis Tissues under Dietary and Water Exposure and the Link to Human Health

Bioaccumulation of cadmium was assessed in different tissues of the benthic fish Solea senegalensis. Juvenile Senegalese soles were simultaneously exposed to cadmium-contaminated diet (Hediste diversicolor) and water during 14 days and allowed to depurate for another 14 days. Cadmium content was measured in muscle, gills, liver and intestine, with recorded values increasing in these tissues in this same order. Muscle showed a considerably lower cadmium accumulation after 14 days of uptake. Cadmium kinetics in juvenile Senegalese soles revealed that the highest uptake flux of this metal occurred in the intestine. Cadmium depuration from the liver was not detected, which suggests the existence of a storage compartment for this metal in Solea senegalensis during uptake and depuration. Comparisons between maximum acceptable values for cadmium in the muscle, the Target Hazard Quotient and the Estimated Weekly Intake, indicated that acceptable limits were not exceeded, and the muscle of juvenile Senegalese soles could be considered safe for human consumption.

Bioaccumulation kinetics of cadmium and zinc in the freshwater decapod crustacean Paratya australiensis following multiple pulse exposures

Stormwater runoff has been identified as a major source of metal contaminants in urban waterways, where during storm events organisms tend to be exposed to short-term pulses, rather than a constant exposure of contaminants. Current water quality guidelines (WQGs) are generally derived using data from continuous exposure toxicity tests, where there is an assumption that chronic exposures provide a meaningful way of assessing the impacts and effects in organisms as a result of these pulsed storm events. In this current study the radioisotopes ¹⁰⁹Cd and ⁶⁵Zn were used to explore uptake, depuration and organ distribution in the decapod crustacean Paratya australiensis, over three short-term (<10 h) exposures. Exposures to radiolabelled cadmium only, zinc only or a mixture of cadmium and zinc were followed by depuration in metal- and isotope-free water for 7 days. Whole-body metal concentrations were determined by live-animal gamma-spectrometry and an anatomical distribution of the radioisotopes was visualised using autoradiography post-mortem. Both metals were significantly accumulated over the pulsed exposure period. In both treatments cadmium and zinc body burden increased at the same rate over the three pulses. Final metal body burden did not markedly differ when shrimp were exposed to metals individually compared to a binary mixture. Over the course of the depuration period, cadmium efflux was minimal, whereas zinc efflux was significant. Autoradiography indicated the presence of both metals in the gills and hepatopancreas throughout the depuration period. These results demonstrate how short-term repeated exposures result in the accumulation of contaminants by shrimp. This study highlights the importance of considering the inclusion of pulsed toxicity tests in frameworks when deriving WQGs.

Uptake and accumulation of cadmium, manganese and zinc by fisheries species: Trophic differences in sensitivity to environmental metal accumulation

Fishery targeted species living in estuaries face multiple anthropogenic pressures including habitat contamination. However, trace metal concentrations in aquatic organisms can be highly variable, making it difficult to interpret accumulation responses. Understanding sources for metal accumulation in these organisms and their biokinetics is important for management of local fisheries and ensuring safety and quality of consumed seafood, particularly in urbanised areas. In this study, we exposed Australian sand clams, school prawns and sand whiting to a combination of cadmium (Cd), manganese (Mn) and zinc (Zn) radioisotopes 1) dissolved in seawater, 2) adsorbed to suspended sediment particles and 3) in radiolabelled food. Sand clams were sensitive to Cd, Mn and Zn uptake and accumulation from all sources because of their filter feeding physiology. Mean Cd and Zn assimilation efficiencies (AE) were higher in clams fed benthic diatoms (51, 43, 63% for Cd, Mn and Zn, respectively) than clams fed an algal flagellate species (22, 32, 33% for Cd, Mn and Zn, respectively). Metal uptake by prawns from seawater was low, whereas assimilation from diet was high (67, 59, 64% mean AEs from Cd, Mn and Zn, respectively). Sand whiting did not accumulate metals from seawater, even after concentrations were increased. Assimilation from diet (labelled prawns) was also low for sand whiting, particularly for Cd and Zn (11, 26, 14% mean AEs from Cd, Mn and Zn, respectively). These results may help explain the persistence of sand whiting in contaminated estuaries. Suspended sediment exposures showed that prawns and fish are less likely than clams to be negatively affected by disturbance events such as floods, which can bring metals into estuaries. The findings of this study have implications for fisheries management, both for protection and remediation of important habitats, and to ensure safe standards for seafood consumption by humans.

Environmental-friendly Contamination Assessment of Habitats Based on the Trace Element Content of Dragonfly Exuviae

We tested the usefulness of exuviae as an environmentally friendly method for exploring the variability of the trace element contents of protected insect populations without killing specimens. It is a notable characteristic of dragonflies that they are good ecological indicators for both aquatic and terrestrial habitat quality. Thus, we investigated the trace element accumulation in different stages of dragonflies: larva, exuvia, and adult. Using microwave plasma atomic emission spectrometry (MP-AES), we analysed the concentrations of Al, Ba, Cr, Cu, Fe, Mn, Pb, Sr and Zn. We found that the trace element contents of exuviae are a good proxy of the trace element contents of both the larvae and the adults. We conclude that exuvia is useful for assessing the environmental health of aquatic ecosystems. It is an environmentally friendly method and it can be used even in the case of protected dragonfly species.

Delineation of metals and radionuclides bioconcentration in eggs of seabream Sparus aurata and effect of environmental pCO2

Considered as the most vulnerable ontogenic stages to environmental stressors, the early-life stages of fish paid a peculiar attention with respect to their vulnerability to metal and radionuclides contamination. Concomitantly, the increasing anthropogenic CO₂ release in the atmosphere will cause major change of the seawater chemistry that could affect the trace elements and radionuclides bioconcentration efficiencies by marine organisms. The aim of this work was to 1) delineate the uptake behaviours of Ag, Am, Cd, Co and Zn in seabream eggs during 65 h of development and retention by newly hatched and 7 h-old larvae maintained in clean seawater, respectively, and 2) investigate the effects of elevated pCO₂ on the bioconcentration efficiencies of these elements in eggs. Besides differing in terms of maximal concentration factors values, the uptake kinetics showed element-specific patterns with Am being linearly bioconcentrated and Co and Zn showing a saturation state equilibrium. The ^110mAg and ¹⁰⁹Cd uptake kinetics shared a two-phases pattern being best described by a saturation equation during the first 24 h of development, and then an exponential loss of accumulated elements although the radiotracer concentrations in the surrounding water remained constant. At hatching time, the radioactivity of ^110mAg was the highest among radiotracers detected in the larvae. After 7 h in depuration conditions, 60% of this metal was still detected whereas ²⁴¹Am, ⁶⁰Co and ⁶⁵Zn were almost totally lost, suggesting an efficient incorporation of Ag in the embryo during the egg development. Finally, this study brought first qualitative data on the effect of pCO₂/pH on metal bioconcentration in eggs, raising the need to unravel chemical and biological processes to predict a potential shift of the toxicity of environmental contamination of fish early life stages with future ocean change.

Toxicokinetics of cadmium in Palaemon varians postlarvae under waterborne and/or dietary exposure

The present study assessed cadmium uptake and depuration rates in the euryhaline estuarine shrimp Palaemon varians under different exposure routes. Postlarval shrimp were exposed for 4 d under different exposure routes: contaminated water, contaminated diet, and a 2-way exposure scenario where both contaminated water and diet were used. After exposure, postlarval shrimp were transferred to a clean medium and fed a noncontaminated diet for 96 h. Bioaccumulation via the different exposure routes was modeled with a standard first-order, one-compartment toxicokinetics model and one with an additional parameter reflecting an inert fraction or storage compartment. The simultaneous 2-way exposure (through water and diet) resulted in accumulation being almost twice as high as the sum of the individual exposure routes, thus indicating that accumulation from multiple routes may be more than additive. Cadmium uptake from water was faster than uptake from food maintained for 48 h at that same cadmium concentration. Shrimp were unable to eliminate cadmium from their body, showing no depuration during 96 h after exposure via different routes, thus suggesting that a longer depuration period is needed. Model comparisons did not provide a significantly better fit when the model included the presence of an inert fraction. The present study highlights the importance of assessing accumulation using multiple exposure routes compared with individual routes because the latter may underestimate bioaccumulation. Environ Toxicol Chem 2018;37:1614-1622. © 2018 SETAC.

A baseline study of the metallothioneins content in digestive gland of the Norway lobster Nephrops norvegicus from Northern Adriatic Sea: Body size, season, gender and metal specific variability

Metallothioneins content was investigated in digestive gland of two wild-caught Norway lobster Nephrops norvegicus populations from the Northern Adriatic Sea, in relation to body size, season and gender. Concomitant accumulation of cadmium, mercury, arsenic, lead, chromium and manganese, reactive oxygen species concentration and energy reserves in digestive gland were also assessed. While differences between genders were not recorded, metallothioneins content seasonal trends were affected by body size. Most of parameters displayed inconsistent trends across sampling sites. Significant correlation between metallothioneins content and cadmium, arsenic and mercury concentrations was recorded only for larger lobsters. A negative correlation of reactive oxygen species concentration and metallothioneins content was observed for small, but not large lobsters. Energy reserves, in particular lipids, could considerably influence biochemical and chemical parameters variations. The present results constitute the essential baseline for future studies aimed at evaluating the N. norvegicus health in relation to metal contamination of coastal sediments.

High contribution of the particulate uptake pathway to metal bioaccumulation in the tropical marine clam Gafrarium pectinatum

The clam Gafrarium pectinatum was investigated to assess its usefulness as a bioindicator species of metal mining contamination in the New Caledonia lagoon. The uptake and depuration kinetics of Ag, Cd, Co, Cr, and Zn were determined following exposures via seawater, sediment, and food using highly sensitive radiotracer techniques (^110mAg, ¹⁰⁹Cd, ⁵¹Cr, ⁵⁷Co, and ⁶⁵Zn). When the clams were exposed to dissolved metals, Co, Zn, and Ag were readily incorporated in their tissues (concentration factors (CF) ranging from 181 to 4982 after 28 days of exposure) and all metals were strongly retained (biological half-lives always >2 months). The estimated transfer factor (TF) in clam tissues after a 35-day sediment exposure was 1 to 4 orders of magnitude lower than the estimated CF, indicating a lower bioavailability of sediment-bound metals than dissolved ones. Once incorporated, metals taken up from sediment and seawater were retained longer than metals ingested with food, indicating that the uptake pathway influences the storage processes of metals in clam tissues. Compilation of our data into a global bioaccumulation model indicated that, except for Ag that essentially originated from food (92%), sediment was the main source of metal bioaccumulation in the clam (more than 80%). These results highlight that bioaccumulation processes strongly depend from one metal to the other. The overall efficient bioaccumulation and retention capacities of the clam G. pectinatum confirm its usefulness as a bioindicator species that can provide time-integrated information about ambient contamination levels in the tropical marine coastal environment.

Tracking trace elements into complex coral reef trophic networks

The integration, accumulation and transfer of trace elements across the main tropic levels of many food webs are poorly documented. This is notably the case for the complex trophic webs of coral reef ecosystems. Our results show that in the south-west lagoon of New Caledonia both abiotic (i.e. sediments) and biotic (i.e. primary producers, consumers and predators) compartments are contaminated by trace elements. However, our analyses revealed different contamination patterns from the sources of organic matter to the predators. The trophic levels involved in the sedimentary benthic food web (S-BFW, based on the sedimentary organic matter) and to a lesser extent in the reef benthic food web (R-BFW, based on algal turf) were mainly contaminated by trace elements that originate from mining activities like Ni and associated trace elements (Co, Cr, Fe, and Mn). Trace elements linked to agro-industrial (As, Hg, and Zn) and urban (Ag, Cd, Cu, Pb, Se, and V) activities were also integrated into the S-BFW, but preferentially into the R-BFW, and to a lesser extent into the detrital benthic food web (D-BFW, supplied by sea-grass plants). Most of the trace elements were biodiminished with increasing trophic levels along food webs. However, a marked biomagnification was observed for Hg, and suspected for Se and Zn. These results provide important baseline information to better interpret trace element contamination in the different organisms and trophic levels in a highly diversified coral reef lagoon.

Comparing single-feeding and multi-feeding approaches for experimentally assessing trophic transfer of metals in fish

Diet is an important pathway for metal uptake in marine organisms, and assimilation efficiency is one of the most relevant parameters to quantify trophic transfer of metals along aquatic food webs. The most commonly used method to estimate this parameter is pulse-chase feeding using radiolabeled food. This approach is, however, based on several assumptions that are not always tested in an experimental context. The present study aimed to validate the approach by assessing single-feeding and multiple-feeding approaches, using a model species (the turbot Scophthalmus maximus). Using the kinetic data obtained from the single-feeding experiment, the reconstruction of a multi-feeding experiment was tested for consistency with data provided by an actual multi-feeding performed under the same experimental conditions. The results validated the single-feeding approach. Environ Toxicol Chem 2017;36:1227-1234. © 2016 SETAC.

Trophic transfer of essential elements in the clownfish Amphiprion ocellaris in the context of ocean acidification

Little information exists on the effects of ocean acidification (OA) on the digestive and post-digestive processes in marine fish. Here, we investigated OA impacts (Δ pH = 0.5) on the trophic transfer of select trace elements in the clownfish Amphiprion ocellaris using radiotracer techniques. Assimilation efficiencies of three essential elements (Co, Mn and Zn) as well as their other short-term and long-term kinetic parameters in juvenile clownfish were not affected by this experimental pH change. In complement, their stomach pH during digestion were not affected by the variation in seawater pH. Such observations suggest that OA impacts do not affect element assimilation in these fish. This apparent pCO₂ tolerance may imply that clownfish have the ability to self-regulate pH shifts in their digestive tract, or that they can metabolically accommodate such shifts. Such results are important to accurately assess future OA impacts on diverse marine biota, as such impacts are highly species specific, complex, and may be modulated by species-specific metabolic processes.

Metal Transfer among Organs Following Short- and Long-Term Exposures Using Autoradiography: Cadmium Bioaccumulation by the Freshwater Prawn Macrobrachium australiense

The uptake, depuration, and organ distribution of the radioisotope ¹⁰⁹Cd were used to explore the internal kinetics of this nonessential metal following accumulation from waterborne cadmium by the freshwater decapod crustacean Macrobrachium australiense. Short- (6 h) and long-term (7 to 14 days) exposures to the radioisotope in solutions of 0.56 μg Cd/L were followed by depuration in metal- and isotope-free water for up to 21 days. The anatomical distribution of the radionuclide was visualized using autoradiography at predefined time points. The gills did not become saturated with cadmium after 14 days of exposure and demonstrated a greater rate of cadmium uptake relative to the hepatopancreas. Cadmium concentrations decreased rapidly during depuration from both gills and hepatopancreas after short exposures but slowly following long-term exposures. This suggests that the duration of cadmium exposure influences the depuration rate for this organism. The study demonstrates the complex behavior of cadmium accumulated by M. australiense and improves our understanding of how exposure duration will influence the internal location and potential toxicity of metals.

Bioaccumulation of (63)Ni in the scleractinian coral Stylophora pistillata and isolated Symbiodinium using radiotracer techniques

Development of nickel mining activities along the New Caledonia coasts threatens the biodiversity of coral reefs. Although the validation of tropical marine organisms as bioindicators of metal mining contamination has received much attention in the literature over the last decade, few studies have examined the potential of corals, the fundamental organisms of coral reefs, to monitor nickel (Ni) contamination in tropical marine ecosystems. In an effort to bridge this gap, the present work investigated the bioaccumulation of (63)Ni in the scleractinian coral Stylophora pistillata and in its isolated zooxanthellae Symbiodinium, using radiotracer techniques. Results highlight the high capacities of coral tissues (zooxanthellae and host tissues) to efficiently bioconcentrate (63)Ni compared to skeleton (Concentration Factors CF at 14 days of exposure are 3 orders of magnitude higher in tissues than in skeleton). When non-contaminated conditions were restored, (63)Ni was more efficiently retained in skeleton than in coral tissues, with biological half-lives (Tb½) of 44.3 and 6.5 days, respectively. In addition, our work showed that Symbiodinium bioconcentrated (63)Ni exponentially, with a vol/vol concentration factor at steady state (VCFSS) reaching 14,056. However, compilation of our results highlighted that despite efficient bioconcentration of (63)Ni in Symbiodinium, their contribution to the whole (63)Ni accumulation in coral nubbins represents less than 7%, suggesting that other biologically controlled processes occur in coral host allowing such efficient bioconcentration in coral tissues.

Seasonal Variation in the Accumulation of Trace Elements and Contaminants in Five Shrimp Species from Iskenderun Bay and Their Consumibility as Human Food

Seasonal accumulation of trace elements and contaminants in the muscle tissue of five shrimp species; Speckled Shrimp, Deepwater Rose Shrimp, Red Shrimp, Grooved Shrimp and Green Tiger Shrimp, from Iskenderun Bay of Eastern Mediterranean Sea were investigated. It was observed the period of year for the accumulation of such elements is important. Results indicate that peaks are generally reached in autumn and in spring. The levels of Zn, Fe, Cu and Ni were the highest in autumn whereas the maximum Sn and Cr concentrations were obtained in spring. The levels of Cu and Zn were found to be within the permissible limits for human consumption. Contaminants were accumulated at the highest levels in autumn. Attention has to be drawn that Cd values were above permissible limits for deepwater pink shrimp caught in autumn and winter, and for green tiger shrimp caught in autumn. Besides, the accumulation of high level of Pb in the tissue of all species except grooved shrimp whose value was low in spring should also be considered as a warning signal.

Gills as a glutathione-dependent metabolic barrier in Pacific oysters Crassostrea gigas: Absorption, metabolism and excretion of a model electrophile

The mercapturic acid pathway (MAP) is a major phase II detoxification route, comprising the conjugation of electrophilic substances to glutathione (GSH) in a reaction catalyzed by glutathione S-transferase (GST) enzymes. In mammals, GSH-conjugates are exported from cells, and the GSH-constituent amino acids (Glu/Gly) are subsequently removed by ectopeptidases. The resulting Cys-conjugates are reabsorbed and, finally, a mercapturic acid is generated through N-acetylation. This pathway, though very well characterized in mammals, is poorly studied in non-mammalian biological models, such as bivalve mollusks, which are key organisms in aquatic ecosystems, aquaculture activities and environmental studies. In the present work, the compound 1-chloro-2,4-dinitrobenzene (CDNB) was used as a model electrophile to study the MAP in Pacific oysters Crassostrea gigas. Animals were exposed to 10μM CDNB and MAP metabolites were followed over 24h in the seawater and in oyster tissues (gills, digestive gland and hemolymph). A rapid decay was detected for CDNB in the seawater (half-life 1.7h), and MAP metabolites peaked in oyster tissues as soon as 15min for the GSH-conjugate, 1h for the Cys-conjugate, and 4h for the final metabolite (mercapturic acid). Biokinetic modeling of the MAP supports the fast CDNB uptake and metabolism, and indicated that while gills are a key organ for absorption, initial biotransformation, and likely metabolite excretion, hemolymph is a possible milieu for metabolite transport along different tissues. CDNB-induced GSH depletion (4h) was followed by increased GST activity (24h) in the gills, but not in the digestive gland. Furthermore, the transcript levels of glutamate-cysteine ligase, coding for the rate limiting enzyme in GSH synthesis, and two phase II biotransformation genes (GSTpi and GSTo), presented a fast (4h) and robust (∼6-70 fold) increase in the gills. Waterborne exposure to electrophilic compounds affected gills, but not digestive gland, while intramuscular exposure was able to modulate biochemical parameters in both tissues. This study is the first evidence of a fully functional and interorgan MAP pathway in bivalves. Hemolymph was shown to be responsible for the metabolic interplay among tissues, and gills, acting as a powerful GSH-dependent metabolic barrier against waterborne electrophilic substances, possibly also participating in metabolite excretion into the sea water. Altogether, experimental and modeled data fully agree with the existence of a classical mechanism for phase II xenobiotic metabolism and excretion in bivalves.

Differential bioaccumulation of (134)Cs in tropical marine organisms and the relative importance of exposure pathways

Bioaccumulation of (134)Cs was determined in 5 tropical marine species: three bivalves (the oysters Isognomon isognomum and Malleus regula, and the clam Gafrarium pectinatum), one decapod (shrimp Penaeus stylirostris) and one alga (Lobophora variegata). Marine organisms were exposed to the radionuclides via different pathways: seawater (all of them), food (shrimp and bivalves) and sediment (bivalves). Our results indicate that the studied tropical species accumulate Cs similarly than species from temperate regions whereas retention capacities seems to be greater in the tropical species. Bioaccumulation capacities of the two oysters were similar for all the exposure pathways. The alga, and to a lesser extent the shrimp, concentrated dissolved Cs more efficiently than the bivalves (approx. 14 and 7 times higher, respectively). Assimilation efficiencies of Cs in bivalves and shrimp after a single feeding with radiolabelled food were comprised between 7.0 ± 0.4 and 40.7 ± 4.3%, with a variable retention time (half-life -Tb1/2- ranging from 16 ± 3 to 89 ± 55 d). Although the clam lives buried in the sediment, this exposure pathway resulted in low bioaccumulation efficiency for sediment-bound Cs (mean transfer factor: 0.020 ± 0.001) that was lower than the two oyster species, which are not used to live in this media (0.084 ± 0.003 and 0.080 ± 0.005). Nonetheless, Cs accumulated from sediment was similarly absorbed (61.6 ± 9.7 to 79.2 ± 2.3%) and retained (Tb1/2: 37 ± 2 to 58 ± 25 d) for the three bivalves species. Despite the poor transfer efficiency of Cs from food, the use of a global bioaccumulation model indicated that the trophic pathways was the main uptake route of Cs in the bivalves and shrimp. In shelled organisms, shells played a non-negligible role in Cs uptake, and their composition and structure might play a major role in this process. Indeed, most of the Cs taken up from seawater and sediment was principally located on the hard parts of the bivalves and shrimp, with the exception of G. pectinatum, where Cs was mainly distributed in the soft-parts.

Trophic transfer of (110m)Ag in the turbot Scophthalmus maximus through natural prey and compounded feed

Industrial incidents can result in radionuclide release in the environment, among which (110m)Ag. Indeed, under particular circumstances, non-negligible amounts of (110m)Ag have been measured in the marine environment (as observed in Fukushima Dai-ichi incident). This element can therefore be accumulated by aquatic organisms through different pathways including the trophic transfer. The present study aimed at examining the variation of (110m)Ag assimilation efficiency (AE) by turbots, Scophthalmus maximus, when exposed through different feeds. Pulse-chase feeding experiments were carried out in mesocosms, using radiolabelled feeds (natural prey and commercial pellets). Depuration kinetics of (110m)Ag over 21 days were generally fitted by a two-component exponential model; the ingested radioelement was poorly assimilated by turbots regardless of the food item that was used (AE always <3%). Concentration and subcellular distribution of (110m)Ag in prey did not seem to influence its assimilation by turbot. These results suggest that physiological mechanisms could occur in fish that would prevent the transfer of (110m)Ag from gut lumen to internal organs (e.g. (110m)Ag neutralization in the lumen of the stomach, detoxification mechanisms occurring in the gut).

Biokinetics of radiocesium in shrimp (Palaemon adspersus): seawater and food exposures

The bioaccumulation of (134)Cs was studied in the shrimp Palaemon adspersus (Rathke, 1837) using dissolved or food pathways. The uptake and loss kinetics (following seawater and food uptake) were followed for 27 and 38 days, respectively. The steady state concentration factor (CFss) value of (134)Cs in the whole body of the shrimp was found to be 15 ± 0.08. The loss kinetics of radiocesium was described by a two-component exponential model, with a biological half-life of 85.5 days for the whole body. The depuration kinetics of (134)Cs was best fitted to a single-component exponential model for both edible and inedible parts. The depuration kinetics of (134)Cs following exposure via pulse-chase feeding was also described by a two-component exponential model, with a biological half-life of 84.2 days. Assimilation efficiency (AE) was found to be 38.5%. Most of the radioactivity was accumulated in muscular tissues (the edible part) of the shrimp compared to the remaining soft parts. The average of the total body burden of (134)Cs eliminated with molting was %15.3 ± 8.1.

Bioaccumulation and retention kinetics of cadmium in the freshwater decapod Macrobrachium australiense

The potential sources and mechanisms of cadmium bioaccumulation by the native freshwater decapods Macrobrachium species in the waters of the highly turbid Strickland River in Papua New Guinea were examined using (109)Cd-labelled water and food sources and the Australian species Macrobrachium australiense as a surrogate. Synthetic river water was spiked with environmentally relevant concentrations of cadmium and animals were exposed for 7 days with daily renewal of test solutions. Dietary assimilation of cadmium was assessed through pulse-chase experiments where prawns were fed separately (109)Cd-labelled fine sediment, filamentous algae and carrion (represented by cephalothorax tissue of water-exposed prawns). M. australiense readily accumulated cadmium from the dissolved phase and the uptake rate increased linearly with increasing exposure concentration. A cadmium uptake rate constant of 0.10 ± 0.05 L/g/d was determined in synthetic river water. During depuration following exposure to dissolved cadmium, efflux rates were low (0.9 ± 5%/d) and were not dependent on exposure concentration. Assimilation efficiencies of dietary sources were comparable for sediment and algae (48-51%), but lower for carrion (28 ± 5%) and efflux rates were low (0.2-2.6%/d) demonstrating that cadmium was well retained by M. australiense. A biokinetic model of cadmium accumulation by M. australiense predicted that for exposures to environmentally relevant cadmium concentrations in the Strickland River, uptake from ingestion of fine sediment and carrion would be the predominant sources of cadmium to the organism. The model predicted the total dietary route would represent 70-80% of bioaccumulated cadmium.

Spatial variability of metallic and organic contamination of anguilliform fish in New Caledonia

New Caledonia is one of the main hot spots of biodiversity on the planet. Large amounts of contaminants are discharged into the lagoon as a result of increasing anthropogenic activities such as intense mining, urbanization, and industrialization. Concentrations of 14 trace elements and 26 persistent organic pollutants (POPs: PCBs and pesticides) were measured in the muscles of two anguilliform fish species, over a coast to barrier reef gradient in two lagoon areas differently exposed to anthropic disturbances. This study emphasizes the high trace element contamination status of anguilliform fish and also highlights slight but perceptible organic pollution. The contamination extends throughout the lagoon, from coast to barrier reef, even in areas remote from emission points. High levels of trace elements, especially those linked to mining activities (i.e., Co, Cr, Fe, Mn, and Ni), were detected in coastal sites. Furthermore, the large dispersion of most POPs throughout the entire lagoon poses the question of their potential toxicity on marine organisms from numerous habitats. Our results underline the need for long-term monitoring of various contaminants over large spatial and time scales.

Trace element bioaccumulation in reef fish from New Caledonia: influence of trophic groups and risk assessment for consumers

Fourteen trace elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V, and Zn) were analyzed in livers and muscles from 22 fish species from the New Caledonia lagoon, which is subjected to important chemical inputs due to intense land-based mining activities (New Caledonia is the third largest world producer of Ni). The results of this baseline research indicated that livers generally concentrated trace elements to a greater extent than muscles. Nevertheless, the overall trace element concentrations in both tissues were barely above the levels reported in fish and thus contamination at the local scale was poorly discriminated. Although these levels were low, preliminary risk assessment from a global health standpoint suggests that As would be an element potentially leading to exposure of concern for fish consumers. Based on the trace element concentrations in livers and the fish trophic preferences, some trends have been observed among trophic groups: Ag, Cu, Fe, Hg, and Zn concentrations were generally higher in liver of fish with the highest trophic position whereas Cd concentrations were lower in these groups. The use of the leopard coral grouper Plectropomus leopardus as a resident top predator allowed determining the geographical variations in contamination levels with significant differences for six out of the fourteen elements investigated. The sampling sites influenced by anthropogenic inputs were revealed by high Ag, Cd, Cu, Hg, and Pb concentrations. Such geographic differences also applied to Zn but surprisingly not for the typical elements associated with Ni mining, i.e., Co, Cr, Mn and Ni.

Comparative bioaccumulation kinetics of trace elements in Mediterranean marine sponges

While marine organisms such as bivalves, seagrasses and macroalgae are commonly used as biomonitors for the environment pollution assessment, widely distributed sponges received little attention as potential helpful species for monitoring programmes. In this study, the trace element and radionuclide bioaccumulation and retention capacities of some marine sponges were estimated in a species-comparative study using radiotracers technique. Six Mediterranean species were exposed to background dissolved concentrations of (110m)Ag, (241)Am, (109)Cd, (60)Co, (134)Cs, (54)Mn, (75)Se and (65)Zn allowing the assessment of the uptake and depuration kinetics for selected elements. Globally, massive demosponges Agelas oroides, Chondrosia reniformis and Ircinia variabilis displayed higher concentration factor (CF) than the erectile ones (Acanthella acuta, Cymbaxinella damicornis, Cymbaxinella verrucosa) at the end of exposure, suggesting that the morphology is a key factor in the metal bioaccumulation efficiency. Considering this observation, two exceptions were noted: (1) A. acuta reached the highest CF for (110m)Ag and strongly retained the accumulated metal without significant Ag loss when placed in depuration conditions and (2) C. reniformis did not accumulate Se as much as A. oroides and I. variabilis. These results suggest that peculiar metal uptake properties in sponges could be driven by specific metabolites or contrasting biosilification processes between species, respectively. This study demonstrated that sponges could be considered as valuable candidate for biomonitoring metal contamination but also that there is a need to experimentally highlight metal-dependant characteristic among species.