Maternal transfer of trace elements to shark eggs and their dietary assimilation efficiencies.

Dogfish (Scyliorhinus canicula) transferred trace elements (110Ag, 109Cd, 54Mn and 75Se) from their diet to eggs, and their components (yolk and embryo, case and jelly) at greatly varying rates. Trace element levels in eggs showed positive linear relationships (p < 0.001; r2-0.83-0.91) with their cumulative rates of maternal ingestion over 61 days (maternal-to-egg transfer rates: mTFs). These mTFs varied by 2-3 orders of magnitude, with 54Mn > 110Ag > 75Se > 109Cd, and their range encompassed those previously measured for 60Co, 65Zn, 241Am and 134Cs. For six of the eight trace elements, their mTFs were significantly influenced (p < 0.05; r2 = 0.72) by both their dietary assimilation efficiency and their location within the egg (case). In contrast, both 110Ag and 54Mn greatly exceeded the mTFs predicted by this multiple regression model by one and 2-3 orders of magnitude, respectively, and were predominantly transferred to the egg case. Among elements, contrasting rates of transfer and percentage distributions in egg components imply differing ecotoxicological and radiological detriments to the developing embryo.

Cadmium-109 Internal Kinetics in Diamond Sturgeon Acipenser gueldenstaedtii are Strongly Influenced by Salinity, Exposure Pathway and History.

Cadmium-109 whole-body and internal biokinetics were experimentally investigated in critically endangered diamond sturgeon Acipenser gueldenstaedtii after uptake from water or food, in fresh (FW) and brackish (BW; 9‰) salinities typical of the Caspian Sea. Whole-body rates of uptake of 109Cd from water and subsequent depuration were quantified over 14 and 28 days, respectively. Uptake was greater in FW than BW by a factor of 2.4, but depuration rates were similar in both salinities. In contrast, for the dietary (chironomid) exposure pathway 109Cd assimilation efficiencies (AEs) were higher in BW (13%) compared to FW (9.5%). Head (including gills) or digestive tract were major repositories of 109Cd following aqueous and dietary exposures, respectively, including both uptake and depuration phases. The point-of-entry of 109Cd into the body was also a major and persistent determiner of its subsequent internal distribution. For aqueous exposures, the internal distributions of 109Cd changed appreciably during depuration with increased activity concentrations in some body components, which again varied with salinity. Increased salinity appreciably enhanced the percentage distributions and activity concentrations of 109Cd in the liver, kidney and digestive tract, which are typically most pathologically altered by elevated Cd exposure. For dietary exposure, increased salinity also enhanced 109Cd activity concentrations in most body components. The results repeatedly indicate the important role of salinity in the whole-body and internal biokinetics of 109Cd in A. gueldenstaedtii, a representative of both a phylogenetically distinct and most endangered family of fishes.

Microplastic-sorbed persistent organic pollutants in coastal Mediterranean Sea areas of Tunisia.

Microplastics (MPs) are emerging pollutants of global concern due to their pervasiveness, high sorption ability for persistent organic pollutants (POPs) and direct and indirect toxicity to marine organisms, ecosystems, as well as humans. As one of the major coastal interfaces, beaches are considered among the most affected ecosystems by MPs pollution. The morphological characteristics of MPs (pellets and fragments) collected from four beaches along the Tunisian coast and sorbed POPs, including polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), were investigated in this study. The results showed that the MPs varied greatly in color, polymer composition and degradation degree. The color varied from colored to transparent and the most prevalent polymer identified using Raman spectroscopy was polyethylene. Scanning electron microscope (SEM) images exhibited various surface degradation features including cavities, cracks, attached diatom remains, etc. The concentrations of Σ12PCBs over all beaches ranged from 14 to 632 ng g-1 and 26 to 112 ng g-1 in the pellets and fragments, respectively, with a notable presence and dominance of highly-chlorinated PCBs such as CB-153 and -138. Among the OCPs, γ-HCH is the only compound detected with concentrations ranging from 0.4 to 9.7 ng g-1 and 0.7 to 4.2 ng g-1 in the pellets and fragments, respectively. Our findings indicate that MPs found on the Tunisian coast may pose a chemical risk to marine organisms as the concentrations of PCBs and γ-HCH in most of the analysed samples exceeded the sediment-quality guidelines (SQG), especially the effects range medium (ERM) and the probable effects level (PEL). As the first report of its kind, the information gathered in this study can serve as the baseline and starting point for future monitoring work for Tunisia and neighbouring countries, as well as for stakeholders and coastal managers in decision-making processes.

Extruded polystyrene microplastics as a source of brominated flame retardant additives in the marine environment: long-term field and laboratory experiments.

Microplastics (MPs) in the environment have become a global concern, not only for the physical effects of the plastic particles themselves but also for being vectors of chemical additives. In this context, little is known about the ability of MPs, particularly extruded polystyrene microplastics (XPS-MPs), to release organic chemical additives in the marine environment. In this study, a series of field and laboratory experiments were carried out to determine the leaching behaviour of organic additives including brominated flame retardants from XPS-MPs into seawater. The conducted experiments confirmed a rapid release of bisphenol A (BPA), 2,4,6-tribromophenol (TBP), tetrabromobisphenol A (TBBPA) and hexabromocyclododecane diastereoisomers (α-, ß-, and γ-HBCDD) from the studied MPs followed by a slower rate of release over time. The effects of environmental factors on the leaching rates of these additives were also examined. Increasing Dissolved Organic Matter (DOM) concentrations and the temperature of the seawater enhanced the release of additives by increasing their solubility and polymer flexibility. In contrast, pH tested at 7, 7.5 and 8 was found to have a minor effect on additives leaching; and salinity negatively affected the leaching rate likely due to their reduced solubility and reduced diffusion from the MPs. The present study provides empirical evidence of the behaviour of XPS-MPs as a source of organic additives in the marine environment that merit further investigation.

A multifaceted assessment of the effects of polyethylene microplastics on juvenile gilthead seabreams (Sparus aurata).

Plastic pollution has become a major environmental and societal concern in the last decade. From larger debris to microplastics (MP), this pollution is ubiquitous and particularly affects aquatic ecosystems. MP can be directly or inadvertently ingested by organisms, transferred along the trophic chain, and sometimes translocated into tissues. However, the impacts of such MP exposure on organisms' biological functions are yet to be fully understood. Here, we used a multi-diagnostic approach at multiple levels of biological organization (from atoms to organisms) to determine how MP affect the biology of a marine fish, the gilthead seabream, Sparus aurata. We exposed juvenile seabreams for 35 days to spherical 10-20 µm polyethylene primary MP through food (Artemia salina pre-exposed to MP) at a concentration of 5 ± 1 µg of MP per gram of fish per day. MP-exposed fish experienced higher mortality, increased abundance of several brain and liver primary metabolites, hepatic and intestinal histological defects, higher assimilation of an essential element (Zn), and lower assimilation of a non-essential element (Ag). In contrast, growth and muscle C/N isotopic profiles were similar between control and MP-exposed fish, while variable patterns were observed for the intestinal microbiome. This comprehensive analysis of biological responses to MP exposure reveals how MP ingestion can cause negligible to profound effects in a fish species and contributes towards a better understanding of the causal mechanisms of its toxicity.

An experimental approach to assess the post-depositional mobility of 134Cs.

The partitioning coefficient, Kd, which is defined by the reversible sorption processes between a solid and an aqueous phase at equilibrium, is one of the most important parameters to assess environmental transport and risk. In this study, a series of simple laboratory experiments were conducted to investigate sorption properties of 134Cs on a model sediment under two treatments (shaken vs non-shaken) and with three (small: <75 µm, large: > 75 µm and bulk i.e., composite) particle size fractions. Vertical transport of 134Cs across the water-sediment interface and into sediment was also evaluated. As expected, grain size had the strongest influence on 134Cs Kd values, with the small particle size fraction yielding significantly higher Kd values than the large and bulk fractions. The mean Kd values obtained from the various experiments ranged from 89 ± 13-130 ± 5 L kg-1 (small), 44 ± 10-91 ± 13 L kg-1 (large), 73 ± 3-112 ± 11 L kg-1 (bulk, shaken) and 73 ± 5-110 ± 4 L kg-1 (bulk, non-shaken). Most of the 134Cs partitioning processes occurred rapidly (<2 h) into the experiment. Physical mixing (shaken) did not appear to significantly affect the 134Cs Kd values. In complement, a separate experiment on the vertical penetration of 134Cs into a bulk sediment column showed that 134Cs was able to penetrate up to 5 cm into the sediment column after 88 days (∼0.6 mm d-1) and this flux rate is comparable to natural settings. Adsorption and contact time were found to be key for the 134Cs penetration process. Results from these experiments add to the literature on post-event radionuclide transport studies in marine settings and provide an experimental perspective that can be built upon to complement field observations.

Experimental Evidence of Ciguatoxin Accumulation and Depuration in Carnivorous Lionfish.

Ciguatera poisoning is a food intoxication associated with the consumption of fish or shellfish contaminated, through trophic transfer, with ciguatoxins (CTXs). In this study, we developed an experimental model to assess the trophic transfer of CTXs from herbivorous parrotfish, Chlorurus microrhinos, to carnivorous lionfish, Pterois volitans. During a 6-week period, juvenile lionfish were fed naturally contaminated parrotfish fillets at a daily dose of 0.11 or 0.035 ng CTX3C equiv. g-1, as measured by the radioligand-receptor binding assay (r-RBA) or neuroblastoma cell-based assay (CBA-N2a), respectively. During an additional 6-week depuration period, the remaining fish were fed a CTX-free diet. Using r-RBA, no CTXs were detectable in muscular tissues, whereas CTXs were measured in the livers of two out of nine fish sampled during exposure, and in four out of eight fish sampled during depuration. Timepoint pooled liver samples, as analyzed by CBA-N2a, confirmed the accumulation of CTXs in liver tissues, reaching 0.89 ng CTX3C equiv. g-1 after 41 days of exposure, followed by slow toxin elimination, with 0.37 ng CTX3C equiv. g-1 measured after the 6-week depuration. These preliminary results, which need to be pursued in adult lionfish, strengthen our knowledge on CTX transfer and kinetics along the food web.

Internal distributions of a radio-element array in cartilaginous and bony marine fishes: Different and heterogeneous.

This experimental study determined internal distributions of an array of radio-elements (54Mn, 60Co, 65Zn, 134Cs, 241Am, 109Cd, 110mAg, 75Se and 51Cr) accumulated from seawater by three chondrichthyan fish species (Scyliorhinus canicula (dogfish), Raja undulata (undulate ray) and Torpedo marmorata (spotted torpedo)) and three teleost species (Scophthalmus maximus (turbot), Sparus aurata (seabream) and Dicentrarchus labrax (seabass)). The study tested the hypothesis that the chondrichthyan (cartilaginous) fish taxon and teleost (bony) fish taxon have different patterns of bioaccumulation of these radio-elements in six body components (head, digestive tract, liver, kidneys, skin and muscle), consistent with their long period of evolutionary divergence. Comparisons of body component CFs between the two taxa for each radio-element and the full array of radio-elements showed highly significant differences (p ≤ 0.001) between cartilaginous and bony fishes in each body component, confirming the existence of a strong and pervasive phylogenetic signal; however, the subset of radio-elements most determinant of these differences were unique for each body component. Partitioning between the three individual bony species and the three individual cartilaginous species also occurred repeatedly among their body components, particularly for bony fishes. Distributions of these radio-elements among body components were typically highly heterogeneous for both fish taxa.

An effective method to assess the sorption dynamics of PCB radiotracers onto plastic and sediment microparticles.

One important aspect of marine plastic pollution is that small particles are ubiquitously present in seawater and can transport a large variety of co-contaminants. The sorption-desorption kinetics of these co-contaminants sorbed to microplastics (MPs) are not fully understood, partially due to the lack of any standardised procedures between studies. The present work aims at describing a new and efficient method to investigate the sorption of co-contaminants onto different types of particles using proven radiotracer techniques. This work provides recommendations as well as a thorough description of the materials, conditions and procedures required to optimise the adsorption of polychlorinated biphenyl (PCB) onto particles. Details of the controlled experimental conditions, such as the volume of the container, the concentration of particles, and specifics of the radiotracer are provided. In addition, a thorough description of the novel filtration methodology specific to these radiotracer techniques is presented, for the first time in the literature. To validate the efficiency of the method, we examined the partition coefficients (Kd) of ¹4C-PCB#153 onto virgin MP (10-29 µm polyethylene beads) and onto natural sediment particles that are similarly sized (1-17.8 µm) in seawater. After 40 h, plastic particles adsorbed 25.7% of ¹4C-PCB#153 while sediment particles adsorbed 89.3% of the same compound. Results suggest that in this scenario, polyethylene MP particles may be less effective transport vectors of ¹4C-PCB#153 than natural sediment particles.•Details of experimental conditions, such as the volume of the container, and the concentration of particles and of radiotracer, were defined•A thorough description of the filtration methodology specific to radiotracer techniques is presented•Results highlight that virgin polyethylene MPs may be less effective transport vectors of ¹4C-PCB#153 than natural sediment particles.

Deoxygenation reduces growth rates and increases assimilation of essential trace metals in gilthead seabream (Sparus aurata).

The widespread decline in oceanic dissolved oxygen (DO), known as deoxygenation, is a threat to many marine ecosystems, and fish are considered one of the more vulnerable marine organisms. While food intake and growth rates in some fish can be reduced under hypoxic conditions (DO ~ 60 µmol kg-1), the dietary transfer of essential metals remains unclear. In this context, we investigated the influence of DO on the dietary acquisition of two essential metals (Zn and Mn) in the commercially important gilthead seabream (Sparus aurata) using radiotracer techniques. Fish were exposed to variable DO conditions (normoxia 100% DO, mild-hypoxia 60% DO, and hypoxia 30% DO), and fed a single radiolabeled food ration containing known activities of 54Mn and 65Zn. Depuration and assimilation mechanisms under these conditions were followed for 19 d. Based on whole body activity after the radio-feeding, food consumption tended to decrease with decreasing oxygen, which likely caused the significantly reduced growth (- 25%) observed at 30% DO after 19 d. While there was an apparent reduction in food consumption with decreasing DO, there was also significantly higher essential metal assimilation with hypoxic conditions. The proportion of 65Zn remaining was significantly higher (~60%) at both low DO levels after 24 h and 19 d while 54Mn was only significantly higher (27%) at the lowest DO after 19 d, revealing element specific effects. These results suggest that under hypoxic conditions, stressed teleost fish may allocate energy away from growth and towards other strategic processes that involve assimilation of essential metals.

Influence of pH on Pb accumulation in the blue mussel, Mytilus edulis.

Changes in seawater pH can alter the chemical speciation of waterborne chemical elements, affecting their bioavailability and, consequently, their bioaccumulation in marine organisms. Here, controlled environmental conditions and a 210Pb radiotracer were used to assess the effect of five distinct pH conditions (pHT ranging from 7.16 to 7.94) on the short-term (9 days) accumulation of Pb in the blue mussel, Mytilus edulis. After 9 days of exposure, higher levels of Pb were observed in the soft tissues of mussels maintained in the lower pH conditions, while Pb levels accumulated by mussel shells showed no difference across pH conditions. These results suggest that pH decreases such as those predicted by ocean acidification scenarios could enhance Pb contamination in marine organisms, with potential subsequent contamination and effect risks for human consumers.

Preferential adsorption of Cd, Cs and Zn onto virgin polyethylene microplastic versus sediment particles.

Plastic pollution has become a major environmental concern worldwide, and marine ecosystems have become polluted with ubiquitous microplastic particles (MP). MP can contain chemical additives and can also scavenge pollutants from the surrounding environment, and these co-contaminants may threaten the marine biota when MP become inadvertently ingested and transferred up the food chain. However, our understanding of the sorption-desorption kinetics of chemical compounds bound to MP remains limited. Moreover, whether MP are better transport vectors of co-contaminants than other natural particles (e.g. sediment) has not received much attention. Here, we used radiotracers to examine the partition coefficients (Kd) of three trace metals (109Cd, 134Cs, and 65Zn) to virgin MP (32-75 µm polyethylene beads) and to natural sediment particles of a similar size (35-91 µm) in seawater. After 72 h, sediment particles adsorbed 2.5% of 109Cd, 68.0% of 134Cs, and 71.0% of 65Zn, while MP adsorbed <0.8% of these three elements. Results highlight that under these experimental conditions, virgin polyethylene MP may not be effective transport vectors for these trace metals. Important variations in Kd were observed between elements, inciting for further studies to decipher how chemical characteristics, MP composition, and associated-biofilms, all interact in these biokinetic processes. These results demonstrate how radiotracers can allow us to address important knowledge gaps and broaden our understanding regarding the interactions between waterborne contaminants, naturally occurring particles and marine wildlife.

Physiological stress response of the scleractinian coral Stylophora pistillata exposed to polyethylene microplastics.

We investigated physiological responses including calcification, photosynthesis and alterations to polar metabolites, in the scleractinian coral Stylophora pistillata exposed to different concentrations of polyethylene microplastics. Results showed that at high plastic concentrations (50 particles/mL nominal concentration) the photosynthetic efficiency of photosystem II in the coral symbiont was affected after 4 weeks of exposure. Both moderate and high (5 and 50 particles/mL nominal) concentrations of microplastics caused subtle but significant alterations to metabolite profiles of coral, as determined by Nuclear Magnetic Resonance (NMR) spectroscopy. Specifically, exposed corals were found to have increased levels of phosphorylated sugars and pyrimidine nucleobases that make up nucleotides, scyllo-inositol and a region containing overlapping proline and glutamate signals, compared to control animals. Together with the photo-physiological stress response observed and previously published literature, these findings support the hypothesis that microplastics disrupt host-symbiont signaling and that corals respond to this interference by increasing signaling and chemical support to the symbiotic zooxanthellae algae. These findings are also consistent with increased mucus production in corals exposed to microplastics described in previous studies. Considering the importance of coral reefs to marine ecosystems and their sensitivity to anthropogenic stressors, more research is needed to elucidate coral response mechanisms to microplastics under realistic exposure conditions.

How Do Actinyls Interact with Hyperphosphorylated Yolk Protein Phosvitin?

The development of the nuclear industry has raised multiple questions about its impact on the biotope and humans. Proteins are key biomolecules in cell machinery and essential in deciphering toxicological processes. Phosvitin was chosen as a relevant model for phosphorylated proteins because of its important role as an iron, calcium, and magnesium storage protein in egg yolk. A multitechnique spectroscopic investigation was performed to reveal the coordination geometry of two oxocations of the actinide family (actinyl UVI , NpV ) in speciation with phosvitin. IR spectroscopy revealed phosphoryl groups as the main functional groups interacting with UVI . This was confirmed through laser luminescence spectroscopy (U) and UV/Vis absorption spectroscopy (Np). For UVI , X-ray absorption spectroscopy at the LIII edge revealed a small contribution of bidentate binding present, along with predominantly monodentate binding of phosphoryl groups; for NpV , uniquely bidentate binding was revealed. As a perspective to this work, X-ray absorption spectroscopy speciation of UVI and NpV in the extracted yolk of living eggs of the dogfish Scyliorhinus canicula was determined; this corroborated the binding of phosphorous together with a reduction of the actinyl moiety. Such data are essential to pinpoint the mechanisms of heavy metals (actinyls) accumulation and toxicity in oviparous organisms, and therefore, contribute to a shift from descriptive approaches to predictive toxicology.

Radioecological aftermath: Maternal transfer of anthropogenic radionuclides to shark progeny is sustained and enhanced well beyond maternal exposure.

Cartilaginous dogfish Scyliorhinus canicula continued to transfer four anthropogenic radionuclides (65Zn, 60Co, 134Cs and 241Am) to their eggs for over six months, after two months of continued maternal exposure to radio-labelled food. Unexpectedly, rates of radionuclide transfers to eggs and their yolk & embryo during maternal depuration were equivalent for 60Co and 241Am, or even enhanced for 65Zn and 134Cs by factors of c.200-350%, over two-three months, compared to their maximal transfer rates at the end of the maternal uptake phase. These rates of maternal transfer of radionuclides to yolk & embryo were positively associated with their previously determined efficiencies of assimilation (AE) from ingested radio-labelled food. Thus progeny may be more exposed via maternal transfer to those radionuclides which have greater rates of maternal assimilation from food. As maternal depuration continued beyond 60-80 up to 180-200 days the transfers of all four radionuclides to eggs did diminish but were still substantial at mean values of 18% for 241Am, 17% for 134Cs and 9 and 8% for 60Co and 65Zn, respectively. In the yolk & embryo the mean rates of transfer over this period were further reduced for 241Am (13.5%), 60Co (2.5%) and 65Zn (5.8%), but were still appreciable for 134Cs at 56%. These results for S. canicula have demonstrated a potential enhanced radiological risk of extended duration due to the particular biokinetics of maternal transfer in this species. This study draws further attention to the current paucity of knowledge about the maternal: progeny transfer pathway, particularly in the context of the known heightened radio-sensitivity of early life stages in fish and other vertebrates, compared to later life stages.

Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish.

Ciguatoxins (CTXs) are potent algal toxins that cause widespread ciguatera poisoning and are found ubiquitously in coral reef food webs. Here we developed an environmentally-relevant, experimental model of CTX trophic transfer involving dietary exposure of herbivorous fish to the CTX-producing microalgae Gambierdiscus polynesiensis. Juvenile Naso brevirostris were fed a gel-food embedded with microalgae for 16 weeks (89 cells g-1 fish daily, 0.4 µg CTX3C equiv kg-1 fish). CTXs in muscle tissue were detectable after 2 weeks at levels above the threshold for human intoxication (1.2 ±â€¯0.2 µg CTX3C equiv kg-1). Although tissue CTX concentrations stabilized after 8 weeks (∼3 ±â€¯0.5 µg CTX3C equiv kg-1), muscle toxin burden (total µg CTX in muscle tissue) continued to increase linearly through the end of the experiment (16 weeks). Toxin accumulation was therefore continuous, yet masked by somatic growth dilution. The observed CTX concentrations, accumulation rates, and general absence of behavioural signs of intoxication are consistent with field observations and indicate that this method of dietary exposure may be used to develop predictive models of tissue-specific CTX uptake, metabolism and depuration. Results also imply that slow-growing fish may accumulate higher CTX flesh concentrations than fast-growing fish, which has important implications for global seafood safety.

Radionuclide biokinetics in the Russian sturgeon and phylogenetic consistencies with cartilaginous and bony marine fishes.

The biokinetics of eight radionuclides (241Am, 109Cd, 134Cs, 75Se, 54Mn, 110mAg, 65Zn, 60Co) absorbed from the aquatic medium by juvenile Russian sturgeon (Acipenser gueldenstaedtii) were experimentally determined in fresh (0.42‰) and brackish (9.0‰) waters, of a similar salinity range to the Caspian Sea, and in conjunction with chemical speciation modelling. Uptake and loss rate constants were determined for each radionuclide for a 14 day exposure at each salinity and during 28 days of exposure to radionuclide-free conditions. Whole body (wet): water concentration factors (CF) achieved over 14 days for these eight radionuclides were used in a comparison with the same radionuclide CFs previously determined experimentally for six species of marine teleosts and chondrichthyans, to further test a phylogeny-based model of multi-nuclide bioaccumulation based on marine chordates. Multivariate analyses (multidimensional scaling and hierarchical clustering) identified the relative affinities among these taxa and also those radionuclides which distinguished most between them, in their differing CFs. They consistently showed that sturgeon aggregated as a group, which was also slightly differentiated with salinity. Sturgeon were distinguished from all teleosts and chondrichthyans but were more dissimilar from chondrichthyans than teleosts, in accordance with sturgeon's different periods of divergence from them in evolutionary time. Variable salinity among experiments may also cause changes in radionuclide bioaccumulation due to variations in (i) bioavailability (ii) osmolarity, and (iii) competitive inhibition of a radionuclide's bioaccumulation by its stable analogue or metabolic model. Their potentially confounding effects on these patterns of radionuclide CFs among taxa were critically evaluated for those radionuclides which discriminated most between sturgeon and teleosts or chondrichthyans. Bioavailability, osmolarity and competitive inhibition effects were identified among salinity treatments, however they were not appreciable enough to override the phylogeny-based signal. The results of this study are thus consistent with a phylogeny-based model of radionuclide bioaccumulation by marine chordates being valid for a fish species living in lower salinity regimes.

How Do Radionuclides Accumulate in Marine Organisms? A Case Study of Europium with Aplysina cavernicola.

In the ocean, complex interactions between natural and anthropogenic radionuclides, seawater, and diverse marine biota provide a unique window through which to examine ecosystem and trophic transfer mechanisms in cases of accidental dissemination. The nature of interaction between radionuclides, the marine environment, and marine species is therefore essential for better understanding transfer mechanisms from the hydrosphere to the biosphere. Although data pertaining to the rate of global transfer are often available, little is known regarding the mechanism of environmental transport and uptake of heavy radionuclides by marine species. Among marine species, sponges are immobile active filter feeders and have been identified as hyperaccumulators of several heavy metals. We have selected the Mediterranean sponge Aplysina cavernicola as a model species for this study. Actinide elements are not the only source of radioactive release in cases of civilian nuclear events; however, their physicochemical transfer mechanisms to marine species remain largely unknown. We have targeted europium(III) as a representative of the trivalent actinides such as americium or curium. To unravel biological uptake mechanisms of europium in A. cavernicola, we have combined radiometric (γ) measurements with spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLIFS, and X-ray absorption near-edge structure, XANES) and imaging (transmission electron microscopy, TEM, and scanning transmission X-ray microscopy, STXM) techniques. We have observed that the colloids of NaEu(CO3)2·nH2O formed in seawater are taken up by A. cavernicola with no evidence that lethal dose has been reached in our working conditions. Spectroscopic results suggest that there is no change of speciation during uptake. Finally, TEM and STXM images recorded at different locations across a sponge cross section, together with differential cell separation, indicate the presence of europium particles (around 200 nm) mainly located in the skeleton and toward the outer surface of the sponge.

Speciation of americium in seawater and accumulation in the marine sponge Aplysina cavernicola.

The fate of radionuclides in the environment is a cause of great concern for modern society, seen especially in 2011 after the Fukushima accident. Among the environmental compartments, seawater covers most of the earth's surface and may be directly or indirectly impacted. The interaction between radionuclides and the marine compartment is therefore essential for better understanding the transfer mechanisms from the hydrosphere to the biosphere. This information allows for the evaluation of the impact on humans via our interaction with the biotope that has been largely undocumented up to now. In this report, we attempt to make a link between the speciation of heavy elements in natural seawater and their uptake by a model marine organism. More specifically, because the interaction of actinides with marine invertebrates has been poorly studied, the accumulation in a representative member of the Mediterranean coralligenous habitat, the sponge Aplysina cavernicola, was investigated and its uptake curve exposed to a radiotracer (241)Am was estimated using a high-purity Ge gamma spectrometer. But in order to go beyond the phenomenological accumulation rate, the speciation of americium(III) in seawater must be assessed. The speciation of (241)Am (and natural europium as its chemically stable surrogate) in seawater was determined using a combination of different techniques: Time-Resolved Laser-Induced Fluorescence (TRLIF), Extended X-ray Absorption Fine Structure (EXAFS) at the LIII edge, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) and the resulting data were compared with the speciation modeling. In seawater, the americium(III) complex (as well as the corresponding europium complex, although with conformational differences) was identified as a ternary sodium biscarbonato complex, whose formula can be tentatively written as NaAm(CO3)2·nH2O. It is therefore this chemical form of americium that is accumulated by the sponge A. cavernicola.

Marine radionuclide transfer factors in chordates and a phylogenetic hypothesis.

Previous radiotracer experiments that compared multi-elemental whole organism: water transfer factors among chondrichthyan and teleost fishes, including an ICRP reference flatfish Psetta maxima, demonstrated distinctive contrasts in their bioaccumulation characteristics, with generally elevated bioaccumulation in chondrichthyans. These results supported a hypothesis that phylogenetic divergence may influence marine radionuclide transfer factors. This notion has been further evaluated in an amphioxus species Branchiostoma lanceolatum, sub-phylum Cephalochordata. This taxon diverged about 800 MYBP from a common ancestor of the teleosts and the chondrichthyans, which in turn diverged from each other around 500 MYBP. Our experimental results indicate that amphioxus is indeed more divergent in its multi-elemental bioaccumulation patterns from teleosts and chondrichthyans than they are from each other, consistent with our hypothesis. The experimental comparisons with the ICRP reference flatfish P. maxima also revealed an unexpectedly enhanced capacity in amphioxus to accumulate all eight tested trace elements from seawater, and for some by more than two orders of magnitude. These results have practical applications for the strategic selection of marine biota for further radioecological investigations to better guarantee the radiological protection of marine biodiversity. Such seemingly anomalous results for understudied biota like amphioxus and chondrichthyans suggest that more effort in marine radioecology be directed to assessing the bioaccumulatory capacities of other phylogenetic groups that have received less attention so far, particularly those that are phylogenetically more remote from commonly investigated taxa and those nominated as ICRP marine reference organisms.