Spermatozoa: A relevant biological target for genotoxicity assessment of contaminants in the estuarine bivalve Scrobicularia plana

Designing and applying a methodology to assess sperm cell viability and DNA damage in a model amphipod

Sperm quality is defined as the sperm cell ability to successfully fertilize eggs and allow normal embryo development⁠. Few studies explore sperm quality using aquatic invertebrates. Parhyale hawaiensis is a marine amphipod with a circumtropical distribution and considered a model for evolution, development, and ecotoxicological studies. We aimed to develop a methodology to collect sperm cells of P. hawaiensis and evaluate their viability and DNA damage (comet assay). We directly exposed the sperm cells to different mutagenic agents to optimize/develop the protocols. Then, as a proof of concept, we exposed the males to mutagenic compounds (EMS, benzo[a]pyrene (BaP), azo and anthraquinone dyes) at non-lethal concentrations verified by the proposed viability test and analyzed their sperm cells for DNA damage (comet assay). Organisms exposed to EMS presented a clear concentration response in the DNA damage response. We also showed that BaP was able to induce a statistically significant increase in DNA damage of the sperm cells. For the two dyes, although DNA damage increased, statistically differences were not observed. We believe we successfully developed a test to detect genotoxicity of chemicals in sperm cells using an invertebrate model. The protocol for sperm cell viability needs to be further explored with different chemicals to verify its utility as a toxicity endpoint. The developed genotoxicity test has the advantages to employ organisms that are easily cultivated in reduced space, use simple laboratory resources and reduced amount of material and reagents. Positive responses with this model could be used to disclose new germ cell mutagen candidates which could be further confirmed in vertebrates' systems.

Effect of aging on the toxicity of polyethylene microplastics on the estuarine bivalve Scrobicularia plana

Microplastics (MP) are now present in all ecosystems and undergo weathering processes, including physical or chemical degradation. Although most studies have been carried out on MP toxicity in the marine ecosystem, interest is growing for the terrestrial and entire aquatic compartments. However, the interface between both environments, also known as the soil/water continuum, is given little consideration in MP toxicity studies. Only a few studies considered the toxicity of artificially aged or soil field-collected MP on species living at this interface. The present study evaluates the impact of artificial and field aging polyethylene (PE) MP on the bivalve Scrobicularia plana, a key organism of the estuarine compartment, living at the soil/water interface. Clams were exposed for 21 days to environmental concentrations (0.008, 10 and 100 μg L-1) of unaged as well as artificially and field aged PE MP. Toxicity was assessed from individual to molecular levels including condition index, clearance rate, burrowing behavior, energy reserves, enzyme activities and DNA damage. Results showed differential effects at all biological levels depending on the type and the concentration of the MP tested. Indeed, a decrease in burrowing behavior was observed in S. plana exposed to aged and field PE at low concentration (0.008 μg L-1). In the gills of clams, exposures to aged PE (0.008 and 100 μg L-1), virgin PE (10 μg L-1) and field PE (all tested concentrations) decreased CAT activity while DNA damage increased after exposure to virgin PE (0.008 μg L-1 and 10 μg L-1) and field PE (0.008 μg L-1). Our findings suggest that aging modifies the toxicity profile of PE polymer on S. plana and considering plastic from field at environmental concentrations is important when performing ecotoxicological studies.

Study on epigenotoxicity, sex hormone synthesis, and DNA damage of benzo[a]pyrene in the testis of male Ruditapes philippinarum

Research on the mechanisms of reproductive toxicity caused by persistent organic pollutants (POPs) in marine animals has received significant attention. One group of typical POPs, called polycyclic aromatic hydrocarbons (PAHs), has been found to cause various reproductive toxicities in aquatic organisms, including epigenotoxicity, reproductive endocrine disruption, DNA damage effects and other reproductive toxicity, thereby affecting gonadal development. Interestingly, male aquatic animals are more susceptible to the disturbance and toxicity of environmental pollutants. However, current studies primarily focus on vertebrates, leaving a large gap in our understanding of the reproductive toxicity and mechanisms of PAHs interference in marine invertebrates. In this study, male Ruditapes philippinarum was used as an experimental subject to investigate reproduction-related indexes in clams under the stress of benzo[a]pyrene (B[a]P) at different concentrations (0, 0.8, 4 and 20 μg/L) during the proliferative, growth, maturity, and spawning period. We analyzed the molecular mechanisms of reproductive toxicity caused by PAHs in marine bivalves, specifically epigenotoxicity, reproductive endocrine disruption, and gonadal damage-apoptotic effect. The results suggest that DNA methylation plays a crucial role in mediating B[a]P-induced reproductive toxicity in male R. philippinarum. B[a]P may affect sex hormone levels, impede spermatogenesis and testis development in clams, by inhibiting the steroid hormone synthesis pathway and downregulating genes critical for cell proliferation, testis development, and spermatid expulsion. Moreover, the spermatids of male R. philippinarum were severely impaired under the B[a]P stress, leading to reduced reproductive performance in the clams. These findings contribute to a better understanding of the reproductive toxicity response of male marine invertebrates to POPs stress.

Shipping can be achieved but cargo arrives with damage - titanium dioxide nanoparticles affect the DNA of Pacific oyster sperm

Titanium dioxide nanoparticles (TiO₂ NP) were reported to be reprotoxic in humans and fish. However, the effects of these NP on the reproduction of marine bivalves, namely oysters, remain unknown. Thus, a short-term (1 h) direct exposure of sperm of the Pacific oyster (Crassostrea gigas) to two TiO₂ NP concentrations (1 and 10 mg.L-1) was performed, and sperm motility, antioxidant responses, and DNA integrity were evaluated. Although no changes occurred in sperm motility and the activities of the antioxidants, the genetic damage indicator increased at both concentrations, demonstrating that TiO₂ NP affects the DNA integrity of oyster sperm. Although DNA transfer can happen, it does not fulfill its biological mission since the transferred DNA is not intact and may compromise the reproduction and recruitment of the oysters. This vulnerability of C. gigas sperm towards TiO₂ NP highlights the importance of studying the effects of NPs exposure to broadcast spawners.

Continuum from microplastics to nanoplastics: effects of size and source on the estuarine bivalve Scrobicularia plana

Plastic has been largely detected in estuarine environments and represents major concern towards aquatic living organisms. The present study evaluates the impact of microplastics (MPs) and nanoplastics (NPs) under realistic exposure conditions. Scrobicularia plana individuals were exposed to low concentrations (0.008, 10, and 100 µg L^-1) of environmental MPs and NPs as well as to standard PS NPs, as a comparison condition. The aim of this study was to understand the ecotoxicological effects of environmental plastic particles on S. plana gills and digestive glands but also to compare the effects of plastic polymers size in order to highlight if the size could induce different toxicity profiles within this model organism, at different levels of biological organization. Results showed a differential induction of detoxification enzymes (CAT, GST), immunity (AcP), DNA damage processes as well as a differential effect on behavior and condition index of animals depending upon the type of plastic, the size, the concentration tested, and the type of organ. This study underlines the necessity of testing (i) plastics collected from the environment as compared to standard ones and (ii) the effect of size using plastics coming from the same batch of macrosized plastics. This study concludes on the future need directions that plastic-based studies must take in order to be able to generate a large quantity of relevant data that could be used for future regulatory needs on the use of plastic.

Genotoxic Effects of Exposure to Water-Soluble Fraction of Diesel Fuel in Sand Dollar Scaphechinus mirabilis Gametes

Pollution of marine areas with oil and oil products is steadily growing. As part of this connection, the study of the impact of petroleum hydrocarbons on marine hydrobionts is an urgent issue of modern ecotoxicology. In our study, the genotoxic effect of the water-soluble fraction of diesel fuel at different concentrations on the gametes of the sand dollar Scaphechinus mirabilis was evaluated. It was shown that during the incubation of sperm and eggs of a sand dollar in WAF with an oil hydrocarbon content of 1.32; 2.64; 5.37; 7.92 mg/L caused the destruction of the DNA molecule to varying degrees in both types of gametes. In addition, it has been shown that with an increase in the concentration of petroleum hydrocarbons in WAF, a large number of cells with a high level of DNA damage appear. The success of fertilization after exposure of gametes to a water-soluble extract of petroleum hydrocarbons was also evaluated. The relationship between an increase in the concentration of hydrocarbons in the tested solutions and a decrease in the level of fertilization is shown.

Genotoxicity of Polystyrene (PS) Microspheres in Short-Term Exposure to Gametes of the Sand Dollar Scaphechinus mirabilis (Agassiz, 1864) (Echinodermata, Echinoidea)

Microplastic pollution appears to be one of the major environmental problems in the world today, and researchers have been paying special attention to the study of the impact of microplastics on biota. In this article, we studied the short-term effects of polystyrene micro-spheres on genome integrity using the gametes of the Scaphechinus mirabilis sand dollar with the comet assay method. This highly sensitive method allowed us to identify the level of genome damage in both gametes before and after short-term exposure to PS microparticles. It was shown that primary polystyrene microspheres at concentrations of 104, 105, and 106 particles/L had a genotoxic effect during short-term exposure to the sperm of the sand dollar S. mirabilis, which was expressed as a significant increase in sperm DNA damage. The highest percentage of DNA damage (more than 20%) was detected in spermatozoa exposed for 1 h in water containing 105 microspheres of plastic per 1 L. Additionally, at all concentrations of microplastic studied in the experiment, the genetic damage index (GDI) values in spermatozoa exceeded the control level. However, regardless of the level of DNA damage, spermatozoa retained the ability to fertilise eggs with up to 97% efficiency. We must acknowledge that the genotoxic property of microplastic against sperm to some extent predicts the development of long-term adverse effects of environmental significance.

Damages to biological macromolecules in gonadal subcellular fractions of scallop Chlamys farreri following benzo[a]pyrene exposure: Contribution to inhibiting gonadal development and reducing fertility

Benzo[a]pyrene (B[a]P), a representative polycyclic aromatic hydrocarbon (PAH) compound in marine ecosystem, has great potential for chronic toxicity to marine animals. It is becoming increasingly apparent that reproductive system is the major target of B[a]P, but the adverse effects of B[a]P on subcellular fractions in bivalve gonads have not been elucidated. Scallops Chlamys farreri are used as the experimental species since they are sensitive to environmental pollutants. This study was conducted to investigate how B[a]P affected the gonadal subcellular fractions, including plasma membrane, nucleus, mitochondria and microsome in scallops, and whether subcellular damages were related to reproductive toxicity. The results showed that mature gametes' counts were significantly decreased in B[a]P-treated scallops. Three biological macromolecules (viz., DNA, lipids and proteins) in gonadal subcellular fractions obtained by differential centrifugation suffered damages, including DNA damage, lipid peroxidation and protein carbonylation in B[a]P treatment groups. Interestingly, mitochondria and microsome were more vulnerable to lipid peroxidation and protein carbonylation than plasma membrane and nucleus, meanwhile males were more susceptible to DNA damage than females under B[a]P exposure. In addition, histological analysis showed that B[a]P delayed gonadal development in C. farreri. To summarize, our results indicated that B[a]P caused damages to biological macromolecules in gonadal subcellular fractions and then induced damages to gonadal tissues of C. farreri, which further inhibited gonadal development and ultimately leaded to reduction in fertility. This study firstly reports the impacts of PAHs on subcellular fractions in bivalves and their relationship with reproductive toxicity. Moreover, exposure of reproductive scallops to B[a]P leads to defects in reproduction, raising concerns on the possible long-term consequences of PAHs for natural populations of bivalves.

Application of the comet assay for the evaluation of DNA damage in mature sperm

DNA integrity is considered an important parameter of semen quality and is of significant value as a predictor of male fertility. Currently, there are several methods that can assess sperm DNA integrity. One such assay is the comet assay, or single-cell gel electrophoresis, which is a simple, sensitive, reliable, quick and low-cost technique that is used for measuring DNA strand breaks and repair at the level of individual cells. Although the comet assay is usually performed with somatic cells from different organs, the assay has the ability to detect genotoxicity in germ cells at different stages of spermatogenesis. Since the ability of sperm to remove DNA damage differs between the stages, interpretation of the results is dependent on the cells used. In this paper we give an overview on the use and applications of the comet assay on mature sperm and its ability to detect sperm DNA damage in both animals and humans. Overall, it can be concluded that the presence in sperm of significantly damaged DNA, assessed by the comet assay, is related to male infertility and seems to reduce live births. Although there is some evidence that sperm DNA damage also has a long-term impact on offspring's health, this aspect of DNA damage in sperm is understudied and deserves further attention. In summary, the comet assay can be applied as a useful tool to study effects of genotoxic exposures on sperm DNA integrity in animals and humans.

Sperm quality assessment in Ficopomatus enigmaticus (Fauvel, 1923): Effects of selected organic and inorganic chemicals across salinity levels

Contamination by organic and inorganic compounds remains one of the most complex problems in both brackish and marine environments, causing potential implications for the reproductive success and survival of several broadcast spawners. Ficopomatus enigmaticus is a tubeworm polychaete that has previously been used as a model organism for ecotoxicological analysis, due to its sensitivity and ecological relevance. In the present study, the effects of five trace elements (zinc, copper, cadmium, arsenic and lead), one surfactant (sodium dodecyl sulfate, SDS) and one polycyclic aromatic hydrocarbon (benzo(a)pyrene, B(a)P) on the sperm quality of F. enigmaticus were investigated. Sperm suspensions were exposed in vitro to different concentrations of each selected contaminant under four salinity conditions (10, 20, 30, 35). Possible adverse effects on sperm function were assessed by measuring oxidative stress, membrane integrity, viability and DNA damage. Sperm quality impairments induced by organic contaminants were more evident than those induced by inorganic compounds. SDS exerted the largest effect on sperm. In addition, F. enigmaticus sperm showed high tolerance to salinity variation, supporting the wide use of this species as a promising model organism for ecotoxicological assays. Easy and rapid methods on polychaete spermatozoids were shown to be effective as integrated sperm quality parameters or as an alternative analysis for early assessment of marine and brackish water pollution.

Benzo[a]pyrene exposure disrupts steroidogenesis and impairs spermatogenesis in diverse reproductive stages of male scallop (Chlamys farreri)

Benzo[a]pyrene (BaP), a model compound of polycyclic aromatic hydrocarbon known to impair reproductive functions of vertebrates, while the data is scarce in marine invertebrates. To investigate the toxic effects of BaP on invertebrates reproduction, we exposed male scallop (Chlamys farreri) to BaP (0, 0.38 and 3.8 μg/L) throughout three stages of reproductive cycle (early gametogenesis stage, late gametogenesis stage and ripe stage). The results demonstrated that BaP decreased the gonadosomatic index and mature sperms counts in a dose-dependent manner. Significant changes in sex hormones contents and increased 17β-estradiol/testosterone ratio suggested that BaP produced the estrogenic endocrine effects in male scallops. In support of this view, we confirmed that BaP significantly altered transcripts of genes along the upstream PKA and PKC mediated signaling pathway like fshr, lhcgr, adcy, PKA, PKC, PLC and NR5A2. Subsequently, the expressions of genes encoding downstream steroidogenic enzymes (e.g., 3β-HSD, CYP17 and 17β-HSD) were impacted, which corresponded well with hormonal alterations. In addition, BaP suppressed transcriptions of spermatogenesis-related genes, including ccnd2, SCP3, NRF1 and AQP9. Due to different functional demands, these transcript profiles involved in spermatogenesis exhibited a stage-specific expression pattern. Furthermore, histopathological analysis determined that BaP significantly inhibited testicular development and maturation in male scallops. Overall, the present findings indicated that, playing as an estrogenic-like chemical, BaP could disrupt the steroidogenesis pathway, impair spermatogenesis and caused histological damages, thereby inducing reproductive toxicities with dose- and stage-specific effects in male scallops. And the adverse outcomes might threaten the stability of bivalve populations and destroy the function of marine ecosystems in the long term.

Effects of the UV filter, oxybenzone, adsorbed to microplastics in the clam Scrobicularia plana

Microplastics (MPs) lipophilic nature and widespread distribution raises concerns due to their increasing presence in the marine environment and their ability to adsorb organic contaminants, as being potential vehicles for transport and potential source of accumulation of organic contaminants by marine organisms. The organic UV-filter, oxybenzone (BP-3) is a constituent of sunscreens and personal care products, entering the marine environment either by direct contact with swimmers or by wastewater effluents. In this study the ecotoxicological effects of exposure to low-density polyethylene (LDPE) microplastics with and without adsorbed BP-3 were investigated in the peppery furrow shell clam, Scrobicularia plana. LDPE microplastics with a size range of 11-13 μm were previously contaminated with an environmentally relevant concentration of BP-3 (82 ng g^-1). S. plana individuals were exposed to a concentration of 1 mg L^-1 of microplastics with and without BP-3 adsorbed in a water-sediment exposure system for 14 days. Clams were sampled at the beginning of the experiment and after 3, 7, and 14 days of exposure. Multiple biomarkers were analysed to investigate the effect of exposure in different clam tissues, gills, digestive gland, and haemolymph. Antioxidant (superoxide dismutase, catalase, glutathione peroxidase) and biotransformation (glutathione-S-transferases) enzyme activities, oxidative damage (lipid peroxidation), genotoxicity (single and double strand DNA breaks), and neurotoxicity (acetylcholinesterase activity) were assessed along with two biomarker indexes to assess the overall health status. Results indicate that after 7 days of exposure MPs with adsorbed BP-3 induced oxidative stress and damage, when compared to exposure to virgin MPs and control treatments. Neurotoxic effects were also noted in MPs with adsorbed BP-3 after 14 days exposure, while some evidence points to increased genotoxicity with exposure time. Overall results indicate that gills were more affected by exposure to microplastics than digestive gland and that biomarkers alterations are apparently more related to the toxicity of BP-3 adsorbed than virgin MPs alone.

Effects of the UV filter, oxybenzone, adsorbed to microplastics in the clam Scrobicularia plana

Microplastics (MPs) lipophilic nature and widespread distribution raises concerns due to their increasing presence in the marine environment and their ability to adsorb organic contaminants, as being potential vehicles for transport and potential source of accumulation of organic contaminants by marine organisms. The organic UV-filter, oxybenzone (BP-3) is a constituent of sunscreens and personal care products, entering the marine environment either by direct contact with swimmers or by wastewater effluents. In this study the ecotoxicological effects of exposure to low-density polyethylene (LDPE) microplastics with and without adsorbed BP-3 were investigated in the peppery furrow shell clam, Scrobicularia plana. LDPE microplastics with a size range of 11-13 μm were previously contaminated with an environmentally relevant concentration of BP-3 (82 ng g^-1). S. plana individuals were exposed to a concentration of 1 mg L^-1 of microplastics with and without BP-3 adsorbed in a water-sediment exposure system for 14 days. Clams were sampled at the beginning of the experiment and after 3, 7, and 14 days of exposure. Multiple biomarkers were analysed to investigate the effect of exposure in different clam tissues, gills, digestive gland, and haemolymph. Antioxidant (superoxide dismutase, catalase, glutathione peroxidase) and biotransformation (glutathione-S-transferases) enzyme activities, oxidative damage (lipid peroxidation), genotoxicity (single and double strand DNA breaks), and neurotoxicity (acetylcholinesterase activity) were assessed along with two biomarker indexes to assess the overall health status. Results indicate that after 7 days of exposure MPs with adsorbed BP-3 induced oxidative stress and damage, when compared to exposure to virgin MPs and control treatments. Neurotoxic effects were also noted in MPs with adsorbed BP-3 after 14 days exposure, while some evidence points to increased genotoxicity with exposure time. Overall results indicate that gills were more affected by exposure to microplastics than digestive gland and that biomarkers alterations are apparently more related to the toxicity of BP-3 adsorbed than virgin MPs alone.

Realistic environmental exposure to microplastics does not induce biological effects in the Pacific oyster Crassostrea gigas

The aim of the present study was to evaluate the presence and potential toxic effects of plastic fragments (<400 μm) of polyethylene and polypropylene on the Pacific oyster Crassostrea gigas. Oysters were exposed to environmentally relevant concentrations (0, 0.008, 10, 100 μg of particles/L) during 10 days, followed by a depuration period of 10 days in clean seawater. Effects of microplastics were evaluated on the clearance rate of organisms, tissue alteration, antioxidant defense, immune alteration and DNA damage. Detection and quantification of microplastics in oyster's tissues (digestive gland, gills and other tissues) and biodeposits using infrared microscopy were also conducted. Microplastics were detected in oyster's biodeposits following exposure to all tested concentrations: 0.003, 0.006 and 0.05 particles/mg of biodeposits in oysters exposed to 0.008, 10 and 100 μg of particles/L, respectively. No significant modulation of biological markers was measured in organisms exposed to microplastics in environmentally relevant conditions.

DNA damages and offspring quality in sea urchin Paracentrotus lividus sperms exposed to ZnO nanoparticles

The recent advances in nanotechnology lead to a potential increase of the release of nanoparticles (NPs) into marine environment through different routes, with possible toxic effects upon the living part of this ecosystem. One of the ways of NPs marine contamination gaining today increasing concern stems from the widespread use cosmetics containing ZnO NPs as UV-filter. Although the possible adverse effects on marine organisms have been already ascertained, the information about the possible genotoxicity of ZnO NPs is still scant. In this work the spermiotoxicity of ZnO particles of different sizes (ZnO Bulk > 200 nm, ZnO NPs 100 nm and ZnO NPs 14 nm) was assessed, using Paracentrotus lividus spermatozoa, by evaluating the DNA damage of the exposed sperm, fertilization capability and DNA damage transmission to progeny. Our results showed that ZnO NPs induced DNA damages in spermatozoa after 30 min of exposure. While the sperm fertilization capability was not affected, morphological alterations (skeletal alterations) in offspring were observed and a positive correlation between sperm DNA damage and offspring quality was reported. This study underlines that a possible spermiotoxic action of ZnO NPs at concentration close to those reported in marine coastal water could occur.

Cytotoxicity and genotoxicity of CuO nanoparticles in sea urchin spermatozoa through oxidative stress

Copper oxide nanoparticles (CuO NPs) are extensively used in various industrial and commercial applications. Despite their wide application may lead to the contamination of marine ecosystem, their potential environmental effects remain to be determined. Toxicity assessment studies have primarily focused on investigating the effects of CuO NPs on fertilization success and embryo development of different sea urchin species while the impact on sperm quality have never been assessed. In this line, this study aims to assess the effects of CuO NPs on the spermatozoa of the sea urchin Paracentrotus lividus. After sperm exposure to CuO NPs, biomarkers of sperm viability, cytotoxicity, oxidative stress, and genotoxicity as well as morphology were evaluated. Results showed that CuO NPs exposure decreased sperm viability, impaired mitochondrial activity and increased the production of reactive oxygen species (ROS) and lipid peroxidation. Furthermore, CuO NPs exposure caused DNA damage and morphological alterations. Together with the antioxidant rescue experiments, these results suggest that oxidative stress is the main driver of CuO NP spermiotoxic effects. The mechanism of toxicity is here proposed: the spontaneous generation of ROS induced by CuO NPs and the disruption of the mitochondrial respiratory chain lead to production of ROS that, in turn, induce lipid peroxidation and DNA damage, and result in defective spermatozoa up to induce sperm cytotoxicity. Investigating the effects of CuO NPs on sea urchin spermatozoa, this study provides valuable insights into the mechanism of reproductive toxicity induced by CuO NPs.

Transcriptomic approach: A promising tool for rapid screening nanomaterial-mediated toxicity in the marine bivalve Mytilus edulis-Application to copper oxide nanoparticles

The extensive development of nanotechnologies will inevitably lead to the release of nanomaterials (NMs) in the environment. As the aquatic environments represent the ultimate sink for various contaminants, it is highly probable that they also constitute a reservoir for NMs and hence aquatic animals represent potential targets. In a regulatory perspective, it is necessary to develop tools to rapidly screen the impact of NMs on model organisms, given that the number of NMs on the market will be increasing. In this context High Throughput Screening approaches represent relevant tools for the investigation of NM-mediated toxicity. The objective of this work was to study the effects of copper oxide nanoparticles (CuONPs) in the marine bivalve Mytilus edulis, using a transcriptomic approach. Mussels were exposed in vivo to CuONPs (10 μg·L^-1CuO NPs) for 24 h and analysis of mRNA expression levels of genes implicated in immune response, antioxidant activities, cell metabolism, cell transport and cytoskeleton was investigated by qPCR on hemocytes and gills. Results showed common effects of CuONPs and its ionic counterpart. However, greater effects of CuONPs on GST, SOD, MT, Actin, ATP synthase gene expressions were observed compared to ionic form indicating that toxicity of CuONPs is not solely due to the release of Cu²⁺. Even though M. edulis genome is not fully characterized, this study provides additional knowledge on the signaling pathways implicated in CuONP-mediated toxicity and demonstrates the reliability of using a qPCR approach to go further in the cellular aspects implicated in response to NPs in marine bivalves.