Effects of microplastics and mercury on manila clam Ruditapes philippinarum: Feeding rate, immunomodulation, histopathology and oxidative stress

Genotoxic Properties of Polystyrene (PS) Microspheres in the Filter-Feeder Mollusk Mytilus trossulus (Gould, 1850)

Microplastic pollution of the aquatic environment is one of the most serious environmental problems today. The potential environmental risks of such particles have become growing concerns in recent years, as direct or indirect exposure to these particles leads to adverse effects on marine organisms. In this study, we investigated the potential risk of polystyrene (PS) microspheres on the genome integrity of cells of different tissues (gills and digestive gland) of the filter-feeder mollusk Mytilus trossulus, using a comet assay. With the help of the comet assay, we estimated the level of genome destruction in the cells of two different mussel tissues after short-term exposure to polystyrene. It was discovered that, despite their chemical inertness, PS microspheres that are 0.9 µm in diameter, at a concentration of 106 particles/L, exhibit genotoxic properties, which are expressed as a two-fold increase in the level of cell DNA damage of the mussel’s digestive gland. It is noted that, after exposure to PS, about half of the mussel’s digestive gland cells experienced damage in 25–35% of their DNA. In addition, the proportion of cells with significant DNA damage (50%) was about 5%. Given the unique role of the genome, DNA damage in these cells may be the earliest stage in the development of biochemical events that lead to toxic effects. These findings provide a basis for studying specific biomarkers of microplastic contamination.

Microplastics: A tissue-specific threat to microbial community and biomarkers of discus fish (Symphysodon aequifasciatus)

As detriments in aquatic environments, microplastics (MPs) have been commonly studied on organisms, but tissue-scale effects of MPs were poorly understood. Discus fish (Symphysodon aequifasciatus), herewith, were exposed to polystyrene MPs (0/20/200 μg/L) for 28 d. We found that MPs significantly inhibited growth performance. MPs were observed in skin, gill and intestine after 14/28-d exposure. MPs bioaccumulation was independent of exposure time, but increased with MPs concentrations. Microbial community diversity of fish gill, but not skin and intestine, in MPs treatments was significantly increased. Bacterial community of MP-treated skin and gill were obviously separated from control. Skin dominant phyla changed from Actinobacteriota to Proteobacteria and Firmicutes. Proteobacteria gradually occupied dominance in gill after exposure. Furthermore, MPs-induced skin oxidative stress was demonstrated by the activation of superoxide dismutase and catalase. Skin malondialdehyde also increased and showed significant correlations with four bacterial phyla, e.g., Proteobacteria. Gill Na⁺/K⁺-ATPase activity decreased, strongly correlating to microbial community changes caused by MPs. Intestinal digestive enzymes activity (pepsin, lipase and α-amylase) reduced, revealing correlation with bacterial community especially Fibrobacterota. These results suggest a tissue-specific effect of MPs to microbial community and biomarkers in aquatic organism.

Microplastics aggravate the bioaccumulation and toxicity of coexisting contaminants in aquatic organisms: A synergistic health hazard

There are ongoing controversies regarding the effects of microplastics (MPs) on the bioaccumulation and toxicity of coexisting contaminants in aquatic organisms. This study aims to quantitatively evaluate this issue based on 870 endpoints from 40 publications. It was shown that the presence of MPs significantly increased the bioaccumulation of co-contaminants by 31%, with high statistical power and without obvious publication bias. The aggravated bioaccumulation was also revealed by the strongly positive correlation between bioconcentration factors in the presence and the absence of MPs. Furthermore, the subgroup/regression analyses indicated that the vector effect of MPs on other chemicals was affected by multiple factors and their interactions, such as particle size and exposure time. In addition, a relatively comprehensive biomarker profile was recompiled from included studies to assess the changes in toxicity caused by combined exposure. Results confirmed that the presence of MPs obviously exacerbated the toxicity of co-contaminants by 18%, manifested by the potentiated cytotoxicity, endocrine disruption, immunotoxicity and oxidative stress, implying a synergistic health hazard. Ultimately, the mismatches between laboratory and field conditions were discussed, and the recommendations for future research were offered.

Microplastics influence physiological processes, growth and reproduction in the Manila clam, Ruditapes philippinarum

Microplastics (<5 mm) are widely distributed in marine environments and pose a serious threat to bivalves. Here, the ingestion and accumulation of polystyrene microplastics (PS microplastics, diameters 5 and 10 μm) by the Manila clam, Ruditapes philippinarum, and their impacts on physiological processes, growth and reproduction were studied. The results showed that both PS microplastics were ingested by the Manila clam and accumulated in their gills, hepatopancreases and intestines. Furthermore, the accumulation of 5 and 10 μm PS microplastics significantly increased the rates of respiration and excretion while significantly decreasing feeding and absorption efficiency (AE), leading to a dramatically reduced amount of energy available for growth (SfG) and ultimately led to slower growth. The dynamic energy budget (DEB) model predicts that PS microplastic exposure for 200 days would cause lower shell/flesh growth rates and reproductive potentiality. Transcriptomic profiles support these results, as carbon and protein metabolism and oxytocin and insulin-related signaling pathways were significantly altered in clams in response to PS microplastics. This study provides evidence that microplastics strongly affect the physiological activities, energy allocation, growth and reproduction of filter-feeding bivalves.

Accumulation, Depuration, and Biological Effects of Polystyrene Microplastic Spheres and Adsorbed Cadmium and Benzo(a)pyrene on the Mussel Mytilus galloprovincialis

Filter feeders are target species for microplastic (MP) pollution, as particles can accumulate in the digestive system, disturbing feeding processes and becoming internalized in tissues. MPs may also carry pathogens or pollutants present in the environment. This work assessed the influence of polystyrene (PS) MP size and concentration on accumulation and depuration time and the role of MPs as vectors for metallic (Cd) and organic (benzo(a)pyrene, BaP) pollutants. One-day exposure to pristine MPs induced a concentration-dependent accumulation in the digestive gland (in the stomach and duct lumen), and after 3-day depuration, 45 µm MPs appeared between gill filaments, while 4.5 µm MPs also occurred within gill filaments. After 3-day exposure to contaminated 4.5 µm MPs, mussels showed increased BaP levels whilst Cd accumulation did not occur. Here, PS showed higher affinity to BaP than to Cd. Three-day exposure to pristine or contaminated MPs did not provoke significant alterations in antioxidant and peroxisomal enzyme activities in the gills and digestive gland nor in lysosomal membrane stability. Exposure to dissolved contaminants and to MP-BaP caused histological alterations in the digestive gland. In conclusion, these short-term studies suggest that MPs are ingested and internalized in a size-dependent manner and act as carriers of the persistent organic pollutant BaP.

Combined polystyrene microplastics and chlorpyrifos decrease levels of nutritional parameters in muscle of rainbow trout (Oncorhynchus mykiss)

Microplastic (MP) is a major contaminant in the aquatic environment. In addition to the physical threats posed by microplastic ingestion, their potential as a vector for the transport of hydrophobic pollutants is required to be adequately addressed. This study examined the effects of polystyrene microplastics individually or combined with chlorpyrifos insecticide on nutritional parameters in muscle of rainbow trout (Onchorhynchus mykiss). Fish were exposed to individual polystyrene microplastic concentrations (30 or 300 μg/L), or individual chlorpyrifos concentrations (2 or 6 μg/L), and their combination at similar concentrations of chlorpyrifos and microplastics. Results showed individual polystyrene microplastics had minimal effects on amino acid and fatty acid composition and no effect on protein contents of fish muscle. However, significant alterations in amino acid and fatty acid composition, and protein contents, were observed in combined polystyrene microplastics and chlorpyrifos groups. These findings suggested that polystyrene microplastics cause toxicity and increase the adverse effects of chlorpyrifos on the muscle of fish. This investigation provided evidence toward low nutritional value of farmed or wild fish muscle that grows in areas with high concentrations of microplastics and pesticides.

Microplastic inventory in sediment profile: A case study of Golden Horn Estuary, Sea of Marmara

Assessment of microplastics (MPs) in sediment cores is necessary to unveil global plastic pollution since most of the plastic litter might have been stored in sediment columns. In the current study, MPs inventory was determined in a 105 cm sediment core, collected in the Golden Horn Estuary, Sea of Marmara. Radiodating of sediment profile by using naturally occurring ²¹⁰Pb and fission product ¹³⁷Cs allowed us to couple the retrospective of global MP production to sediment MPs inventory. More than 90% of total MPs inventory was found in the deep layer of the sediment column (below 15 cm). Small MPs (20-200 μm) were more abundant than large ones (200-4000 μm). Elevated concentrations of MPs were attributed to industrial and municipal effluent of Istanbul metropolitan. On a local scale, this study suggests that the Golden Horn Estuary was polluted with MPs before the 1950s, and the abundance of MPs reached a maximum in the 1980s. We also propose on a global scale that "the missing" plastics might have been buried in deep sediment and radiodating of sediment is useful to reveal their historical input records.

Physiological role of CYP17A1-like in cadmium detoxification and its transcriptional regulation in the Pacific oyster, Crassostrea gigas

Cadmium (Cd) is one of the most harmful heavy metals due to its persistence and bioaccumulation through the food chains, posing health risks to human. Oysters can bioaccumulate and tolerate high concentrations of Cd, providing a great model for studying molecular mechanism of Cd detoxification. In a previous study, we identified two CYP genes, CYP17A1-like and CYP2C50, that were potentially involved in Cd detoxification in the Pacific oyster, Crassostrea gigas. In this work, we performed further investigations on their physiological roles in Cd detoxification through RNA interference (RNAi). After injection of double-stranded RNA (dsRNA) into the adductor muscle of oysters followed by Cd exposure for 7 days, we observed that the expressions of CYP17A1-like and CYP2C50 in interference group were significantly suppressed on day 3 compared with control group injected with PBS. Moreover, the mortality rate and Cd content in the CYP17A1-like dsRNA interference group (dsCYP17A1-like) was significantly higher than those of the control on day 3. Furthermore, the activities of antioxidant enzymes, including SOD, CAT, GST, were significantly increased in dsCYP17A1-like group, while were not changed in dsCYP2C50 group. More significant tissue damage was observed in gill and digestive gland of oysters in RNAi group than control group, demonstrating the critical role of CYP17A1-like in Cd detoxification. Dual luciferase reporter assay revealed three core regulatory elements of MTF-1 within promoter region of CYP17A1-like, suggesting the potential transcriptional regulation of CYP17A1-like by MTF-1 in oysters. This work demonstrated a critical role of CYP17A1-like in Cd detoxification in C. gigas and provided a new perspective toward unravelling detoxification mechanisms of bivalves under heavy metal stress.

Micro/nanoplastics effects on organisms: A review focusing on 'dose'

Microplastics have become predominant contaminants, attracting much political and scientific attention. Despite the massively-increasing research on microplastics effects on organisms, the debate of whether environmental concentrations pose hazard and risk continues. This study critically reviews published literatures of microplastics effects on organisms within the context of "dose". It provides substantial evidence of the common occurrence of threshold and hormesis dose responses of numerous aquatic and terrestrial organisms to microplastics. This finding along with accumulated evidence indicating the capacity of organisms for recovery suggests that the linear-no-threshold model is biologically irrelevant and should not serve as a default model for assessing the microplastics risks. The published literature does not provide sufficient evidence supporting the general conclusion that environmental doses of microplastics cause adverse effects on individual organisms. Instead, doses that are smaller than the dose of toxicological threshold and more likely to occur in the environment may even induce positive effects, although the ecological implications of these responses remain unknown. This study also shows that low doses of microplastics can reduce whereas high doses can increase the negative effects of other pollutants. The mechanisms explaining these findings are discussed, providing a novel perspective for evaluating the risks of microplastics in the environment.

Bioaccumulation and ecotoxicological responses of clams exposed to terbium and carbon nanotubes: Comparison between native (Ruditapes decussatus) and invasive (Ruditapes philippinarum) species

In the last decades the use of rare earth elements (REEs) increased exponentially, including Terbium (Tb) which has been widely used in newly developed electronic devices. Also, the production and application of nanoparticles has been growing, being Carbon Nanotubes (CNTs) among the most commonly used. Accompanying such development patterns, emissions towards the aquatic environments are highly probable, with scarce information regarding the potential toxicity of these pollutants to inhabiting species, especially considering their mixture. In the present study the effects of Tb and CNTs exposure (acting alone or as a mixture) on native and invasive clams' species (Ruditapes decussatus and Ruditapes philippinarum, respectively) were evaluated, assessing clams' accumulation and metabolic capacities, oxidative status as well neurotoxic impacts. Results obtained after a 28-days exposure period showed that the accumulation of Tb in both species was not affected by the presence of the CNTs and similar Tb concentrations were found in both species. The effects caused by Tb and CNTs, acting alone or as a mixture induced greater alterations in R. philippinarum antioxidant capacity in comparison to native R. decussatus, but no cellular damages were observed in both species. Nevertheless, although metabolic impairment was only observed in clams exposed to Tb, loss of redox balance and neurotoxicity were evidenced by both species regardless the exposure treatment. These findings highlight the potential impacts caused by CNTs and Tb, which may affect clams' normal physiological functioning, impairing their reproduction and growth capacities. The obtained results point out the need for further investigation considering the mixture of pollutants.

Environmentally relevant concentrations of microplastics influence the locomotor activity of aquatic biota

The occurrence of microplastics (MPs) in various marine and freshwater matrices has attracted great attention. However, the effect of MPs in natural environment on the locomotor performance of aquatic biota is still controversial. Therefore, this meta-analysis was conducted, involving 116 effect sizes from 2347 samples, to quantitatively evaluate the alteration in locomotor behavior of aquatic organisms induced by MPs at environmentally relevant concentrations (≤ 1 mg/L, median = 0.125 mg/L). It was shown that MP exposure significantly inhibited the average speed and moved distance of aquatic organisms by 5% and 8% (p < 0.05), respectively, compared with the control, resulting in an obvious reduction of locomotor ability by 6% (p < 0.05). Egger's test indicated that the results were stable without publication bias (p > 0.05). The complex influence of MPs on the locomotor ability were characterized through random-effects meta-regression analyses, presenting size-, time-, concentration-dependent manners and multi-factors interactions. In addition, several physiological changes, including energy reserve reduction, metabolism disorder, gut microbiota dysbiosis, inflammation response, neurotoxic response, and oxidative stress, of aquatic organisms triggered by MP exposure at environmentally relevant concentrations were also provided, which might account for the MPs-induced locomotor activity decline.

A One Health perspective of the impacts of microplastics on animal, human and environmental health

Microplastics contamination is widespread in the environment leading to the exposure of both humans and other biota. While most studies overemphasize direct toxicity of microplastics, particle concentrations, characteristics and exposure conditions being used in these assays needs to be taken into consideration. For instance, toxicity assays that use concentrations over 100,000 times higher than those expected in the environment have limited practical relevance. Thus, adverse effects on animal and human health of current environmental concentrations are identified as a knowledge gap. Conversely, this does not suggest the lack of any significant effects of microplastics on a global scale. The One Health approach provides a novel perspective focused on the intersection of different areas, namely animal, human, and environmental health. This review provides a One Health transdisciplinary approach to microplastics, addressing indirect effects beyond simple toxicological effects. Microplastics can, theoretically, change the abiotic properties of matrices (e.g., soil permeability) and interfere with essential ecosystem functions affecting ecosystem services (e.g., biogeochemical processes) that can in turn impact human health. The gathered information suggests that more research is needed to clarify direct and indirect effects of microplastics on One Health under environmentally relevant conditions, presenting detailed knowledge gaps.

Photolytic degradation elevated the toxicity of polylactic acid microplastics to developing zebrafish by triggering mitochondrial dysfunction and apoptosis

Biodegradable plastics (BPs), as alternatives to conventional plastics, are increasingly consumed, but pose potential threats to aquatic ecosystems. In addition, the impact of natural aging on the toxicity of BPs is poorly understood. In this study, the photodegradation of polylactic acid (PLA, a typical BP) microplastics (MPs) under ultraviolet irradiation in water for 90 days was investigated, and the toxicities of virgin and degraded PLA to infantile zebrafish were compared. The results revealed that the size of MPs was reduced from ~25.56 to ~11.22 µm after degradation and nanoparticles were generated with a maximum yield of 7.13%. The formation of abundant oxygen-containing groups (i.e. C˭O and C-O-C) improved the hydrophilia and stability of MPs. Compared with pristine PLA, the efflux and detoxification of degraded PLA mediated by ABC transporters and P450 enzymes were slower, leading to higher bioaccumulation and skeletal development inhibition of zebrafish. Further, oxidative stress-triggered mitochondrial structural damage, depolarization, fission inhibition, and apoptosis were identified as crucial mechanisms underlying the elevated toxicity of PLA after degradation. These findings highlight the importance and necessity of considering natural degradation of BPs and related toxicity, which poses great implications for risk assessment and management of BPs.

Do Polystyrene Beads Contribute to Accumulation of Methylmercury in Oysters?

To clarify whether microplastics contribute to elevated bioaccumulation of methylmercury (MeHg) in aquatic organisms, we studied the sorption pattern of MeHg on polystyrene beads (PBs) and evaluated MeHg accumulation, via uptake of MeHg-adsorbed PB, in the oyster Crassostrea gigas. MeHg-cysteine conjugates were added to seawater at 10, 100, and 1000 µg/L as Hg. Polystyrene beads (φ = 0.02, 0.2, and 2 µm) were immersed in the seawater for 24 h. The concentrations of total mercury (T-Hg) adsorbed onto the PBs were then measured using the reduction vaporization method. T-Hg concentrations for the PBs with diameters of 0.02, 0.2, and 2 µm were 10.6 ± 0.4, 1.8 ± 0.1, and 1.3 ± 0.1 ng/mg-PBs, respectively, when immersed in 2 mL of MeHg-added seawater (100 µg/L as Hg). Thus, the adsorption efficiency of MeHg onto PBs was higher in the presence of smaller diameter PBs. Next, 1 mg of PBs immersed in 2 mL of seawater containing 100 µg/L of MeHg for 24 h was added to an oyster tank containing 1 L of seawater. The T-Hg concentration of the oysters was measured after 6 h of exposure. No significant difference was found in the T-Hg concentration of oysters in the presence of PBs (0.30 ± 0.01 to 0.37 ± 0.05 ng/mg as dry weight) with MeHg and in the absence of PBs (0.36 ± 0.03 ng/mg as dry weight). Our results suggest that the presence of PBs in seawater has little effect on MeHg uptake by oysters.

How do humans recognize and face challenges of microplastic pollution in marine environments? A bibliometric analysis

Microplastics (MPs) are abundant in marine environments, drawing global attention from scientists and rendering it significant to review the research progress and predict future trends of this field. To achieve that, we collected 1898 publications on marine MPs from Web of Science and performed a bibliometric analysis by CiteSpace and VOSviewer. Additionally, we utilized an unrestricted retrieval of literature from ScienceDirect to supplement our major findings. Trends in publication numbers show the growth in study from the initial stage ( 2012 and before), when microplastic (MP) occurrence, abundance, and distribution were primarily investigated. Throughout the ascent stage (between 2013-2016), when diverse sampling and analytical methods were applied to capture and identify MPs from the ocean, baseline data have been gleaned on physiochemical properties of MPs. The research focus then shifted to the bioaccumulation and ecotoxicological effects of MPs on marine biota, further highlighting their potential deleterious impacts on human health via dietary exposure, and this period was defined as the exploration stage (2017 and onwards). Nevertheless, key challenges including the lack of standard procedures for MP sampling, technical limitations in MP detecting and identification, and controversy about the underlying effects on the marine ecosystems and humans have also been arisen in the last decade. The present study elucidates how we gradually recognize MP pollution in marine environments and what challenges we face, suggesting future avenues for MP research.

Genotoxic and cytotoxic effects of polyethylene microplastics on human peripheral blood lymphocytes

Currently, we need emerging initial data regarding how plastic exposures affect cellular and molecular components and how such interactions will be crucial for human health. We aimed to determine the genotoxic and cytotoxic effects of microplastic (MPs,10-45 μm, polyethylene) on human peripheral lymphocytes by using the cytokinesis-block micronucleus cytome (CBMN) assay, which is a comprehensive method to reveal a range of mechanisms, not only diseases but also response to environmental exposures. We measured micronucleation (MN), nucleoplasmic bridge formation (NPB), and nuclear bud formation (NBUD) in human peripheral blood lymphocytes. We also measured the cytokinesis-block proliferation index (CBPI) to calculate cytostasis, which indicates cytotoxicity in lymphocytes treated with five different MPs concentrations for 48 h. Even lower concentrations of MPs increased the level of genomic instability. We found that the in vitro MP exposure significantly increased MN, NPB, and NBUD frequencies. Since we investigated the effect of larger particles relative to the lymphocytes, mechanic interaction of MPs with cells, the release of monomer and additives from MPs could be suggested as possible mechanisms accounting for increasing genomic instabilities. We did not observe a decrease in the cell proliferation index, indicating a lack of MPs' cytotoxic potential. To the best of our knowledge, our study is the first to identify MPs' genotoxic potential in human peripheral blood lymphocytes. We suggested further studies to investigate the genotoxic and cytotoxic potential of smaller plastics and the chronic effect of MP on the human population.

Effects of environmentally relevant levels of polyethylene microplastic on Mytilus galloprovincialis (Mollusca: Bivalvia): filtration rate and oxidative stress

The objective of the present study was to evaluate the potential toxic effects of polyethylene microplastics (PE-MPs) (40-48 μm) on the Mediterranean mussel Mytilus galloprovincialis in controlled laboratory conditions. The exposure was carried out for 14 days with three environmentally relevant PE-MPs concentrations of 1, 10, and 100 and a high concentration of 1000 μg/L. Effects of PE-MPs were assessed by evaluating the filtration rate (FR) after 7 and 14 days of exposure and by analyzing biochemical biomarkers of oxidative stress (catalase - CAT, glutathione S-transferase - GST, and the levels of lipid peroxidation - LPO) in the M. galloprovincialis digestive gland after 14 days of exposure. Results showed that M. galloprovincialis does not accumulate PE-MPs of 40-48 μm size in its whole tissues. The filtration rate was significantly reduced with the increase of PE-MPs concentrations. The biochemical biomarkers indicated that PE-MPs induced oxidative damage (LPO) at low concentrations (1 and 10 μg/L) with a significant reduction in females of 1000 μg/L treated group and inactivate antioxidative system (CAT and GST) in the digestive gland of both sexes at high concentrations (100 and 1000 μg/L). This study demonstrates that PE-MPs have biological effects on M. galloprovincialis at environmentally relevant concentrations thus brings new insights on the potential impacts of PE-MPs in marine bivalves.

Microplastics and associated contaminants in the aquatic environment: A review on their ecotoxicological effects, trophic transfer, and potential impacts to human health

The microplastic pollution and related ecological impacts in the aquatic environment have attracted global attention over the past decade. Microplastics can be ingested by aquatic organisms from different trophic levels either directly or indirectly, and transferred along aquatic food chains, causing different impacts on life activities of aquatic organisms. In addition, microplastics can adsorb various environmental chemical contaminants and release toxic plastic additives, thereby serving as a sink and source of these associated chemical contaminants and potentially changing their toxicity, bioavailability, and fate. However, knowledge regarding the potential risks of microplastics and associated chemical contaminants (e.g., hydrophobic organic contaminants, heavy metals, plastic additives) on diverse organisms, especially top predators, remains to be explored. Herein, this review describes the effects of microplastics on typical aquatic organisms from different trophic levels, and systematically summarizes the combined effects of microplastics and associated contaminants on aquatic biota. Furthermore, we highlight the research progress on trophic transfer of microplastics and associated contaminants along aquatic food chain. Finally, potential human health concerns about microplastics via the food chain and dietary exposure are discussed. This work is expected to provide a meaningful perspective for better understanding the potential impacts of microplastics and associated contaminants on aquatic ecology and human health.

Effects of Acute Ammonia Stress on Antioxidant Responses, Histopathology and Ammonia Detoxification Metabolism in Triangle Sail Mussels (Hyriopsis cumingii)

Ammonia is one of the major pollutants in the aquatic ecosystem. Hyriopsis cumingii has great potential for the restoration of eutrophic water. However, there is no study investigating the effect of ammonia exposure in H. cumingii. The median lethal concentration (96 h LC50) of unionized ammonium was 12.86 mg/L in H. cumingii. In the study, H. cumingii were exposed to 6.43 mg L−1 unionized ammonium (1/2 96 h LC50) for 0, 6, 12, 24, 48, 72, and 96 h. High environment ammonia induced antioxidant response to protect the body from oxidative damage. After exposure to ammonia, there was a same trend of induction followed by inhibition of the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferases (GST) in the hepatopancreas and gills of H. cumingii. However, the antioxidant response could not completely counteract the oxidation effect during the exposure period, resulting in lipid peroxidation (LPO) and tissue injury in the hepatopancreas and gills of H. cumingii eventually. Moreover, this study indicated that glutamine synthetase (GS), glutamate dehydrogenase (GDH), alanine aminotransaminase (ALT), and aspartate aminotransaminase (AST) in the hepatopancreas and gills may play an important role in ammonia detoxification of H. cumingii. Our results will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in shellfish.

Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos‎

Microplastic (MP) sorption and transfer of chemical contaminants has been widely reported, yet few studies have investigated combined effects of contaminant-loaded MPs on organisms. This study examined effects of pristine or chlorpyrifos (CPF)-loaded polystyrene (PS)‎ fragments on histopathological and histomorphometrical biomarkers in rainbow trout (Onchorhynchus mykiss)‎. In laboratory, O. mykiss were exposed for 96 h to pristine PS-MPs concentrations (30 or 300 µg/L), concentrations of CPF ‎alone (2 or ‎‎6 µg/L), and the same concentrations of CPF in the presence of PS-MPs in aquaria‎. Results showed the highest histopathological alterations in both CPF concentrations and when combined with PS-MPs in fish gills. Alternatively, high histopathological lesions including massive necrosis, infiltration of inflammatory cells, and shed of villi tips were observed in fish gut in high CPF concentrations combined with high PS-MP concentrations of ‎(6 μg/L CPF+300 μg/L PS-‎MPs). Individual CPF and PS-MP concentrations or combined together showed significant changes in histomorphometrical biomarkers in fish gills, gut and skin. Findings highlight that pristine PS-MPs cause toxicity and increase adverse effects of CPF in O. mykiss, especially in gill tissue. We present evidence that pristine short-term exposure to even low concentrations of PS-MPs has a significant impact on biomarker responses in O. mykiss.

Linking effects of microplastics to ecological impacts in marine environments

Recently, efforts to determine the ecological impacts of microplastic pollutants have increased because of plastic's accelerated contamination of the environment. The tiny size, variable surface topography, thermal properties, bioavailability and biological toxicity of microplastics all offer opportunities for these pollutants to negatively impact the environment. Additionally, various inorganic and organic chemicals sorbed on these particles may pose a greater threat to organisms than the microplastics themselves. However, there is still a big knowledge gap in the assessment of various toxicological effects of microplastics in the environment. Ecological risk assessment of microplastics has become more challenging with the current data gaps. Thus, a current literature review and identification of the areas where research on ecology of microplastics can be extended is necessary. We have provided an overview of various aspects of microplastics by which they interact negatively or positively with marine organisms. We hypothesize that biogeochemical interactions are critical to fully understand the ecological impacts, movement, and fate of microplastics in oceans. As microplastics are now ubiquitous in marine environments and impossible to remove, we recommend that it's not too late to converge research on plastic alternatives. In addition, strict actions should be taken promptly to prevent plastics from entering the environment.

Microplastic accumulation via trophic transfer: Can a predatory crab counter the adverse effects of microplastics by body defence?

Microplastics are considered detrimental to aquatic organisms due to their potential accumulation along food chains. Thus, it is puzzling why some of them appear unaffected by microplastics. Here, we assessed the contribution of water filtration and food consumption to microplastic accumulation in a predatory marine crab (Charybdis japonica) and examined the associated impacts of microplastics (particle size: 5 μm) following ingestion for one week. Results showed that water filtration and food consumption contributed similarly to the accumulation of microplastics, which were distributed among organs in this order: hepatopancreas > guts > gills > muscles. Yet, biomagnification (i.e. accumulation through consumption of microplastic-contaminated mussels) did not occur possibly due to egestion of microplastics. The crabs upregulated detoxification capacity (EROD) and antioxidant defence (GST) in response to the microplastics accumulated in their tissues. However, these defence mechanisms collapsed when the microplastic concentration in hepatopancreas exceeded ~3 mg g^-1, leading to severe hepatic injury (elevated AST and ALT) and impaired neural activity (reduced AChE). Our results suggest that marine organisms have an innate capacity to counter the acute effects of microplastics, but there is a limit beyond which the defence mechanisms fail and hence physiological functions are impaired. As microplastic pollution will deteriorate in the future, the fitness and survival of marine organisms may be undermined by microplastics, affecting the stability and functioning of marine ecosystems.

Perfluorooctane sulfonic acid (PFOS) adsorbed to polyethylene microplastics: Accumulation and ecotoxicological effects in the clam Scrobicularia plana

Microplastics are widespread in the marine environment, whereby the uptake of these tiny particles by organisms, can cause adverse biological responses. Plastic debris also act as a vector of many contaminants, herein depending on type, size, shape and chemical properties, possibly intensifying their effects on marine organisms. This study aimed to assess the accumulation and potential toxicity of different sizes of microplastics with and without adsorbed perfluorooctane sulfonic acid (PFOS) in the clam Scrobicularia plana. Clams were exposed to low-density polyethylene microplastics (1 mg L^-1) of two different sizes (4-6 and 20-25 μm) virgin and contaminated with PFOS (55.7 ± 5.3 and 46.1 ± 2.9 μg g^-1 respectively) over 14 days. Microplastic ingestion, PFOS accumulation and filtration rate were determined along with a multi biomarker approach to assess the biological effects of microplastics ingestion. Biomarkers include oxidative stress (superoxide dismutase, catalase, glutathione peroxidases), biotransformation enzymes (glutathione-S-transferases activity), neurotoxicity (acetylcholinesterase activity), oxidative damage and apoptosis. Microplastics ingestion and PFOS accumulation was microplastic size dependent but not PFOS dependent and filtration rate was reduced at the end of the exposure. Reactive oxygen species in gills and digestive gland were generated as a result of exposure to both types of microplastics, confirming the disturbance of the antioxidant system. Larger virgin microparticles lead to stronger impacts, when compared to smaller ones which was also supported by the Integrated Biomarker Responses index calculated for both tissues. An anti-apoptotic response was detected in digestive glands under exposure to any of the MPs treatments.

Alleviation of tributyltin-induced toxicity by diet and microplastics in the marine rotifer Brachionus koreanus

To determine the effects of tributyltin (TBT) upon multiple exposures of diet and microplastic in rotifer, in vivo life parameters were measured. In 10 μg/L TBT-exposed rotifer, the 1 and 0.5 x diet groups resulted in reproduction reduction. However, 10 x diet treatment showed no significant changes in the total fecundity, despite a decrease in daily reproduction. Besides, differences in the lifespan were observed in response to different diet regimens. TBT and/or MP-exposed parental rotifer (F0) showed a significant delay in the pre-reproductive day under 0.5 x diet regimen. In all dietary regimens, exposure to TBT and MP induced an increase in reactive oxygen species, but antioxidant activities were perturbed. To further verify the carryover effect of TBT toxicity, progeny rotifer (F1) obtained from 24 h TBT and/or MP-exposed F0 was used. Interestingly, the faster hatching rate was observed only in F1 obtained from 1 x diet regimen-exposed F0. However, in the 0.5 x diet, the total fecundity was reduced and the pattern of the daily reproduction was collapsed. Thus, the toxicity of TBT can be alleviated by MP and nutrition status, but TBT-induced toxicity and its carryover effect are inevitable.

The need to investigate continuums of plastic particle diversity, brackish environments and trophic transfer to assess the risk of micro and nanoplastics on aquatic organisms

Plastic particles are ubiquitous in marine and freshwater environments. While many studies have focused on the toxicity of microplastics (MPs) and nanoplastics (NPs) in aquatic environments there is no clear conclusion on their environmental risk, which can be attributed to a lack of standardization of protocols for in situ sampling, laboratory experiments and analyzes. There are also far more studies concerning marine environments than fresh or brackish waters despite their role in the transfer of plastics from continents to oceansWe systematically reviewed the literature for studies: (1) using plastics representative of those found in the environment in laboratory experiments, (2) on the contamination of plastic particles in the continuum between fresh and marine waters, focusing in particular on estuaries and (3) on the continuum of contamination of plastic particles between species through trophic transfer in aquatic environments. We found that the exposure of aquatic organisms in the laboratory to plastic particles collected in the environment are very scarce. Moreover, plastic exposures of estuarine species in the laboratory are generally carried out for a single salinity and a single temperature that do not reflect the fluctuating environmental conditions of estuaries. Finally, the trophic transfer of plastic particles is mainly studied in the laboratory through simple food chains which are not representative of the complexity of the trophic networks observed in the aquatic environment. We pointed out that future studies in the laboratory should include both MPs and NPs sampled in the environment and focus on the precise characterization of the composition and surface of these plastics as well as on their absorbed pollutants, additives or biofilms. Moreover, investigations must be continued concerning the toxicity of plastic particles in brackish water environments such as estuaries and the trophic transfer of plastic particles in complex food chains.

Comparative acute toxicity of benzophenone derivatives and bisphenol analogues in the Asian clam Corbicula fluminea

Among UV-filters, benzophenones are one of the most abundantly used and detected groups in the environment. Bisphenols are also one of the most widely used chemicals in plastics, but their demonstrated deleterious effects on several organisms and humans have led to the production of alternative analogues. However, few comparative studies on the ecotoxicological effects of these derivatives or analogues have been carried out. The present study aimed to investigate the effects of two benzophenones (BP-3 and BP-4) and two bisphenols (BPA and BPS) in a short-term exposure of the freshwater endobenthic bivalve Corbicula fluminea. Clams were exposed for 96 h to several concentrations of the four pollutants: BP-3 (0.63; 1.25; 2.5; 5 mg l^-1), BP-4 (4.75; 9.5; 19; 38 mg l^-1), BPA (3.75; 7.5; 15; 30 mg l^-1), and BPS (2.5; 5; 10; 20 mg l^-1). The comparative acute toxicity of these pollutants was evaluated by the analysis of the post-exposure filtering capacity of clams, lipid peroxidation (LP) levels and the activity of the antioxidant enzymes catalase (CAT) and glutathione reductase (GR). After the exposure period, except for BP-4, the chemicals tested seemed to be detected by clams and provoked valve closure, decreasing filter-feeding in a concentration-dependent manner. Furthermore, C. fluminea exposed to the highest concentrations of BP-3, BP-4 and BPA showed a significant increase in LP, CAT and GR activities with respect to their controls. BP-3 and BPA were the most toxic compounds showing significant differences in all the parameters analysed at the highest concentrations assayed. However, clams exposed to BPS showed only significant alterations in filtration parameters and in GR activity, in the two highest concentrations tested, indicating that this compound was the least toxic to clams. Obtained results highlight the importance of investigating the effects that emerging pollutants have on aquatic organisms.

Distribution patterns of microplastics in various tissues of the Zhikong scallop (Chlamys farreri) and in the surrounding culture seawater

Microplastics have adverse effects on marine organisms. However, there are limited data on microplastics distribution patterns in various tissues of marine organisms. Microplastics in seawater and nine types of tissues of the Zhikong scallop (Chlamys farreri) from three coastal aquaculture areas were analysed. The results showed that in seawater, microplastics were mainly fibrous. There were no significant differences in microplastics abundance among the three areas. The concentrations of microplastics in the scallop anus, intestinal tract and kidney were substantially higher than those in the other tissues. Microplastics abundance ranged from 8 to 13 particles per scallop. Microplastics colours were mainly black, transparent and blue, and there were no significant tissue distribution patterns. Microplastics size ranged from 5 μm to 1 mm. The microplastics abundance in the haemolymph was significantly correlated with those of the surrounding seawater. Additional study is necessary to determine the toxic effects of microplastics on marine organisms.

Interaction of Environmental Pollutants with Microplastics: A Critical Review of Sorption Factors, Bioaccumulation and Ecotoxicological Effects

Microplastics have become one of the leading environmental threats due to their persistence, ubiquity and intrinsic toxic potential. The potential harm that microplastics impose on ecosystems varies from direct effects (i.e., entanglement and ingestion) to their ability to sorb a diversity of environmental pollutants (e.g., heavy metals, persistent organic compounds or pharmaceuticals). Therefore, the toxicological assessment of the combined effects of microplastics and sorbed pollutants can produce in biota is one of the hottest topics on the environmental toxicology field. This review aims to clarify the main impacts that this interaction could have on ecosystems by (1) highlighting the principal factors that influence the microplastics sorption capacities; (2) discussing the potential scenarios in which microplastics may have an essential role on the bioaccumulation and transfer of chemicals; and (3) reviewing the recently published studies describing toxicological effects caused by the combination of microplastics and their sorbed chemicals. Finally, a discussion regarding the need for a new generation of toxicological studies is presented.