Evidence of microplastic-mediated transfer of PCB-153 to sea urchin tissues using radiotracers.

The present study reports the first experimental microplastic-mediated transfer of a key PCB congener into adult specimens of the sea urchin Paracentrotus lividus. Three experiments were conducted to assess whether 14C-PCB-153 adsorbed onto negatively buoyant microplastics (MPs) (500-600 µm) is bioavailable to the sea urchin: (1) exposure to a low concentration of 14C-PCB-153 sorbed onto a high number of virgin MPs ("lowPCB highMP" experiment), (2) exposure to a high concentration of 14C-PCB-153 sorbed onto a relatively low number of virgin MPs ("highPCB lowMP" experiment), and (3) exposure to a low concentration of 14C-PCB-153 sorbed onto a relatively low number of aged MP ("lowPCB lowMP" experiment). Results showed that the transfer of 14C-PCB-153 from MPs to sea urchin tissues occurred in each of the three 15-day experiments, suggesting that MPs located on the seafloor may act as vectors of PCB-153 to sea urchins even during short-term exposure events.

Bioaccumulation of inorganic and organic mercury in the cuttlefish Sepia officinalis: Influence of ocean acidification and food type.

The bioaccumulation of mercury (Hg) in marine organisms through various pathways has not yet been fully explored, particularly in cephalopods. This study utilises radiotracer techniques using the isotope 203Hg to investigate the toxicokinetics and the organotropism of waterborne inorganic Hg (iHg) and dietary inorganic and organic Hg (methylHg, MeHg) in juvenile common cuttlefish Sepia officinalis. The effect of two contrasting CO2 partial pressures in seawater (400 and 1600 µatm, equivalent to pH 8.08 and 7.54, respectively) and two types of prey (fish and shrimp) were tested as potential driving factors of Hg bioaccumulation. After 14 days of waterborne exposure, juvenile cuttlefish showed a stable concentration factor of 709 ± 54 and 893 ± 117 at pH 8.08 and 7.54, respectively. The accumulated dissolved i203Hg was depurated relatively rapidly with a radiotracer biological half-life (Tb1/2) of 44 ± 12 and 55 ± 16 days at pH 8.08 and 7.54, respectively. During the whole exposure period, approximately half of the i203Hg was found in the gills, but i203Hg also increased in the digestive gland. When fed with 203Hg-radiolabelled prey, cuttlefish assimilated almost all the Hg provided (>95%) independently of the prey type. Nevertheless, the prey type played a major role on the depuration kinetics with Hg Tb1/2 approaching infinity in fish fed cuttlefish vs. 25 days in shrimp fed cuttlefish. Such a difference is explained by the different proportion of Hg species in the prey, with fish prey containing more than 80% of MeHg vs. only 30% in shrimp. Four days after ingestion of radiolabelled food, iHg was primarily found in the digestive organs while MeHg was transferred towards the muscular tissues. No significant effect of pH/pCO2 variation was observed during both the waterborne and dietary exposures on the bioaccumulation kinetics and tissue distribution of i203Hg and Me203Hg. Dietary exposure is the predominant pathway of Hg bioaccumulation in juvenile cuttlefish.

Size-dependent transfer of microplastics across the intestinal wall of the echinoid Paracentrotus lividus.

The fate and toxicity of ingested marine microplastics (MPs) have been of major concern in aquatic ecotoxicology for the last decade. Although their ingestion by a wide range of marine organisms has been proven, the uptake of MPs within organs is not yet fully understood and relies on the ability of ingested microplastics to transfer from the gut to tissues beyond the digestive wall (i.e., translocation). The present study investigates the in vitro transfer of fluorescent high-density polyethylene particles of different sizes classes (1-5 µm; 10-29 µm; 38-45 µm) across the intestinal wall of the sea urchin Paracentrotus lividus using Ussing chambers. Small microplastics (1-5 µm) were proven to be able to cross the intestinal wall of P. lividus and reach the coelomic fluid, while larger microplastics (≥ 10 µm) were not observed to cross the intestinal wall. Results demonstrate a size-dependent passage of polyethylene microparticles across the intestinal walls of P. lividus for the first time, highlighting the suitability of Ussing chamber systems to study the transfer of MPs across the intestinal wall of animals.

Trophic transfer of trace elements in a euryhaline fish, the turbot Scophthalmus maximus: Contrasting effects of salinity on two essential elements.

Trace elements can be accumulated from coastal environment by aquatic organisms from their food and be transferred throughout the food webs. Studying the effects of salinity on the trophic transfer of trace elements in a euryhaline fish, able to deal with large variations in salinity, is therefore key to understand their dynamics in aquatic environments. In this context, we investigated the potential influence of salinity on the trophic transfer of two essential elements (Mn and Zn) in the euryhaline fish, the turbot Scophthalmus maximus using radiotracer techniques. After acclimation to three salinities (10, 25 and 38), turbots were fed with radiolabelled pellets (54Mn and 65Zn). Kinetic parameters of depuration were determined after a 21-d period and trophic transfer factors were calculated. Trophic transfer of Mn at the highest salinity was significantly lower than for the other conditions whereas salinity did not significantly influenced Zn trophic transfer. Differences in the processes involved in the regulation (homeostasis) of the two tested trace elements may explain the contrasting influence of seawater salinity for Mn and Zn.

Effects of variable deoxygenation on trace element bioaccumulation and resulting metabolome profiles in the blue mussel (Mytilus edulis).

The dissolved oxygen concentration of the world's oceans has systematically declined by 2% over the past 50 years, and there has been a notable commensurate expansion of the global oxygen minimum zones (OMZs). Such wide-scale ocean deoxygenation affects the distribution of biological communities, impacts the physiology of organisms that may affect their capacity to absorb and process contaminants. Therefore, the bioaccumulation efficiencies of three contrasting radionuclides, 110mAg, 134Cs and 65Zn were investigated using controlled aquaria in the blue mussel Mytilus edulis under three contrasting dissolved oxygen regimes: normoxic; 7.14 mg L-1, reduced oxygen; 3.57 mg L-1 and hypoxic 1.78 mg L-1 conditions. Results indicated that hypoxic conditions diminished 110mAg uptake in the mussel, whereas depuration rates were not affected. Similarly, hypoxia appeared to cause a decrease in the 65Zn bioaccumulation rate, as evidenced by both weakened uptake and rapid elimination rates. Effects of hypoxia on the metabolome of mussels were also explored by untargeted Nuclear Magnetic Resonance (NMR) spectroscopic methods. The metabolic response was characterised by significantly greater abundance of several amino acids, amino sulfonic acids, dicarboxylic acids, carbohydrates and other metabolites in the lowest oxygen treatment, as compared to the higher oxygen treatments. Clearance rates significantly dropped in hypoxic conditions compared to normoxia. Results suggest that hypoxic conditions, and even partly moderate hypoxia, alter ventilation, an-aerobic, oxidative and osmoregulation metabolism of this mussel, which may further influence the trace element bioaccumulation capacity.

Biokinetics of the anionic surfactant linear alkylbenzene sulfonate (LAS) in the marine fish Sparus aurata: Investigation via seawater and food exposure pathways.

Uptake and depuration kinetics of [14C]C12-6-linear alkylbenzene sulfonate (LAS) in the fish Sparus aurata were determined during experimental exposure via seawater or food separately under laboratory conditions. The fish concentrated LAS from seawater (using realistic contaminant concentrations) with a mean BCF value of 20 ±â€¯2 L kg-1 reached within 3 days and following a one-compartment exponential model. High differences in BCF were noted among organs, with values ranking in the order gall bladder (1400 ±â€¯600 L kg-1) >>  digestive tract (52 ±â€¯9 L kg-1) > liver (38 ±â€¯4 L kg-1) > gills (16 ±â€¯3 L kg-1) > skin (13 ±â€¯2 L kg-1) > head (9 ±â€¯1 L kg-1) > muscles (4 ±â€¯1 L kg-1). After three days of exposure, 14C activity decreased in gall bladder while it remained constant in other organs. Biotransformation and elimination processes could explain this phenomenon observed in gall bladder. LAS depuration was rapid in all organs (with up to 90% elimination within 2 days) and depuration kinetics was best fitted by a two-compartment exponential-model. When fish were fed with radiolabeled food, ingested LAS was transferred to organs within the first hours following the feeding. Model best describing depuration kinetics of LAS in the whole fish indicated that the contaminant can be considered as not assimilated.

Insights into the Biosynthesis of Cyclic Guanidine Alkaloids from Crambeidae Marine Sponges.

Among the outstanding chemical diversity found in marine sponges, cyclic guanidine alkaloids, present in species of the family Crambeidae, are particularly attractive, not only because of their unique chemical features, but also due to a broad range of biological activities. Despite a growing interest in these natural products as therapeutic agents, their metabolic pathway has not been experimentally investigated. Ex situ feeding experiments using radiolabeled precursors performed on the Mediterranean sponge Crambe crambe suggest arginine and fatty acids as precursors in the metabolic pathway of crambescins. A subsequent bio-inspired approach supported the change of paradigm in the metabolic pathway of cyclic guanidine alkaloids. A large part of the chemical diversity of this family would therefore originate from a tethered Biginelli-like reaction between C-2/C-3 activated fatty acids and a central guanidinylated pyrrolinium.

Allometric relationship in the bioaccumulation of radionuclides (134Cs &241Am) and delineation of contamination pathways (food and seawater) in bloody cockle Anadara senilis using radiotracer techniques.

The uptake and depuration kinetics of 134Cs and 241Am were investigated in the bloody cockle Anadara senilis exposed via seawater and food in controlled conditions, using animals of different weight groups in order to assess how their bioaccumulation is affected by allometry and, hence, the individual's age. This study is one of the few experiments investigating bioaccumulation capacities of radionuclides in a West-African bivalve. Results showed that allometric relationships were mainly dependent on the exposure pathway considered. Significant relationships with body weight of bloody cockles were found during the uptake from dissolved phase for both radionuclides; they followed inverse power functions: smaller cockles concentrated both radionuclides more than larger ones. In contrast, radionuclide absorption and assimilation efficiencies from water and food, respectively, did not show any significant relationship with weight: only slight variation was observed between small and large organisms for the retention of 241Am accumulated from food. A bioaccumulation model was used to assess the contribution of each pathway of exposure (food vs. water) in organisms grouped in small and large individuals. We found that, regardless of the size, 134Cs was mainly bioaccumulated through the dietary pathway. In the case of 241Am, the relative contribution of each pathway is weight-dependent: major contribution of dissolved pathway in smaller organisms and the major dietary contribution in larger organisms.

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.

Application of nuclear techniques to environmental plastics research.

Plastic pollution is ubiquitous in aquatic environments and its potential impacts to wildlife and humans present a growing global concern. Despite recent efforts in understanding environmental impacts associated with plastic pollution, considerable uncertainties still exist regarding the true risks of nano- and micro-sized plastics (<5 mm). The challenges faced in this field largely relate to the methodological and analytical limitations associated with studying plastic debris at low (environmentally relevant) concentrations. The present paper highlights how radiotracing techniques that are commonly applied to trace the fate and behaviour of chemicals and particles in various systems, can contribute towards addressing several important and outstanding questions in environmental plastic pollution research. Specifically, we discuss the use of radiolabeled microplastics and/or chemicals for 1) determining sorption/desorption kinetics of a range of contaminants to different types of plastics under varying conditions, 2) understanding the influence of microplastics on contaminant and nutrient bioaccumulation in aquatic organisms, and 3) assessing biokinetics, biodistribution, trophic transfer and potential biological impacts of microplastic at realistic concentrations. Radiotracer techniques are uniquely suited for this research because of their sensitivity, accuracy and capacity to measure relevant parameters over time. Obtaining precise and timely information on the fate of plastic particles and co-contaminants in wildlife has widespread applications towards effective monitoring programmes and environmental management strategies.

The absence of the pCO2 effect on dissolved 134Cs uptake in select marine organisms.

Ocean acidification have been shown to not affect the capacity of bivalves to bioaccumulation 134Cs in their tissue; but as this was studied on only one species to date. There is therefore a need to verify if this holds true for other bivalve species or other marine invertebrates. The present short communication confirms that in the scallop Mimachlamys varia and the prawn Penaeus japonicus, two species that supposedly have a record to preferentially concentrates this radionuclide, that bioconcentration of 134Cs was shown not to be influenced by a decreasing pH (and thereby increasing seawater pCO2). Although the dissolved 134Cs was taken up in a similar manner under different pH values (8.1, 7.8, and 7.5) in both species, being described by a saturation state equilibrium model, the species displayed different bioconcentration capacities of 134Cs: CFss in the prawns was approximately 10-fold higher than in scallops. Such results suggest that the Cs bioconcentration capacity are mainly dependent of the taxa and that uptake processes are independent the physiological ones involved in the biological responses of prawns and scallops to ocean acidification.

Ocean acidification modulates the incorporation of radio-labeled heavy metals in the larvae of the Mediterranean sea urchin Paracentrotus lividus.

The marine organisms which inhabit the coastline are exposed to a number of anthropogenic pressures that may interact. For instance, the accumulation of toxic metals present in coastal waters is expected to be modified by ocean acidification through e.g. changes in physiological performance and/or elements availability. Changes in bioaccumulation due to lowering pH are likely to be differently affected depending on the nature (essential vs. non-essential) and speciation of each element. The Mediterranean is of high concern for possible cumulative effects due to strong human influences on the coastline. The aim of this study was to determine the effect of ocean acidification (from pH 8.1 down to -1.0 pH units) on the incorporation kinetics of six trace metals (Mn, Co, Zn, Se, Ag, Cd, Cs) and one radionuclide (241Am) in the larvae of an economically- and ecologically-relevant sea urchin of the Mediterranean coastline: Paracentrotus lividus. The radiolabelled metals and radionuclides added in trace concentrations allowed precise tracing of their incorporation in larvae during the first 74 h of their development. Independently of the expected indirect effect of pH on larval size/developmental rates, Paracentrotus lividus larvae exposed to decreasing pHs incorporated significantly more Mn and Ag and slightly less Cd. The incorporation of Co, Cs and 241Am was unchanged, and Zn and Se exhibited complex incorporation behaviors. Studies such as this are necessary prerequisites to the implementation of metal toxicity mitigation policies for the future ocean. We discuss possible reasons and mechanisms for the specific effect of pH on each metals.

A double-tracer radioisotope approach to assess simultaneous bioaccumulation of caesium in the olive flounder Paralichthys olivaceus.

To better understand bioaccumulation of radiocaesium in the commercially important Japanese flatfish, Paralichthys olivaceus, the uptake and depuration kinetics of caesium via both seawater and food were assessed simultaneously using controlled aquaria. The pre-conditioned fish were exposed to radionuclides via the two different pathways (aqueous versus dietary) concurrently using two isotopes of caesium, 137Cs and 134Cs, respectively. Dissolved caesium uptake was linear and did not reach a steady state over the course of the 8-day exposure period. Consumption of 134Cs-labelled food led to higher bioaccumulation rates of radioactive Cs than via seawater exposure of 137Cs during uptake and following depuration, though the model-derived long-lived biological half-lives of both pathways was approximately 66 d. Further development of this method for assessing multiple radiocaesium bioaccumulation pathways simultaneously could lead to a promising new approach for studying Cs contamination in marine organisms.

The role of salinity in the trophic transfer of 137Cs in euryhaline fish.

In order to better understand the influence of changing salinity conditions on the trophic transfer of 137Cs in marine fish that live in dynamic coastal environments, its depuration kinetics was investigated in controlled aquaria. The juvenile turbot Scophthalmus maximus was acclimated to three distinct salinity conditions (10, 25 and 38) and then single-fed with compounded pellets that were radiolabelled with 137Cs. At the end of a 21-d depuration period, assimilation efficiencies (i.e. AEs = proportion of 137Cs ingested that is actually assimilated by turbots) were determined from observational data acquired over the three weeks. Our results showed that AEs of 137Cs in the turbots acclimated to the highest salinity condition were significantly lower than for the other conditions (p < 0.05). Osmoregulation likely explains the decreasing AE observed at the highest salinity condition. Indeed, observations indicate that fish depurate ingested 137Cs at a higher rate when they increase ion excretion, needed to counterbalance the elevated salinity. Such data confirm that ambient salinity plays an important role in trophic transfer of 137Cs in some fish species. Implications for such findings extend to seafood safety and climate change impact studies, where the salinity of coastal waters may shift in future years in response to changing weather patterns.

Investigations of temperature and pH variations on metal trophic transfer in turbot (Scophthalmus maximus).

Studying dietary metal transfer kinetics is essential to gain a better understanding in global metal accumulation rates and its impacts in marine fish. While there exists a solid understanding on the influence of various biotic factors on this transfer, metal assimilation in fish might be also affected by abiotic factors, as has been observed in marine invertebrates. The present study therefore aims to understand the potential effects of two climate-related master variables, temperature and pH, on the assimilation efficiency (AE) of essential (Co and Zn) and non-essential (Ag) metals in the turbot Scophthalmus maximus using radiotracer tools. Juvenile turbots were acclimated for 8 weeks at two temperatures (17 and 20 °C) and pH (7.5 and 8.0) regimes, under controlled laboratory conditions, and then fed with radiolabelled shrimp (57Co, 65Zn and 110mAg). Assimilation efficiencies of Co and Ag in juvenile turbot, determined after a 21-day depuration period, were not affected by pre-exposition to the different environmental conditions. In contrast, temperature did significantly influence Zn AE (p < 0.05), while pH variations did not affect the assimilation of any of the metals studied. In fact, temperature is known to affect gut physiology, specifically the membrane properties of anterior intestine cells where Zn is adsorbed and assimilated from the ingested food. These results are relevant to accurately assess the influence of abiotic factors in AEs of metals in fish as they are highly element-dependent and also modulated by metabolic processes.

Dietary Zn and the subsequent organotropism in fish: No influence of food quality, frequency of feeding and environmental conditions (pH and temperature).

Trophic transfer of Zn in fish is affected by the type of food and environmental variables such as temperature. However, there is still a lack of knowledge regarding the effects of such factors on Zn organotropism. For this reason, a series of experimental studies have investigated how the distribution and the concentration of Zn is affected by some environmentally-relevant factors (food quality, food availability, water pH, and temperature) in turbot Scophthalmus maximus using radiotracer techniques. In three different experiments, Zn distribution in seven body compartments of juvenile turbot and the calculation of Zn concentration index (IC) for each compartment were compared. Its distribution as well as its concentration in the body compartments of juvenile turbots were not affected by the experimental conditions tested. This apparent consistency in the Zn organotropism can be explained by the ability of the fish to maintain Zn homeostasis at non-toxic Zn concentrations in their diet. These results are important to better understand the trophic transfer of Zn in fish under realistic environmental conditions.

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.

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.

Bioconcentration of Ag, Cd, Co, Mn and Zn in the Mangrove Oyster (Crassostrea gasar) and Preliminary Human Health Risk Assessment: A Radiotracer Study.

Bioaccumulation kinetics of five dissolved metals were determined in the mangrove oyster Crassostrea gasar, using corresponding radiotracers ((54)Mn, (57)Co, (65)Zn, (109)Cd and (110m)Ag). Additionally, their bioaccessibility to human consumers was estimated. Results indicated that over a 14-day exposure (54)Mn and (57)Co were linearly concentrated in oysters whereas (109)Cd, (65)Zn and (110m)Ag were starting to saturate (steady-state not reached). Whole-body concentration factors at 14 days (CF14d in toto) ranged from 187 ± 65 to 629 ± 179 with the lowest bioconcentration capacity for Co and the highest for Ag. Depuration kinetics were best described by a double-exponential model with associated biological half-lives ranging from 26 days (Ag) to almost 8 months (Zn and Cd). Bioaccessible fraction of the studied elements was estimated using in vitro digestions, which suggested that oysters consumed seasoned with lemon enhanced the accessibility of Cd, Mn and Zn to human consumers, but not Ag and Co.

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.