The combined effects of polyethylene microplastics and benzoanthracene on Manila clam Ruditapes philippinarum

Genes of filter-feeding species as a potential toolkit for monitoring microplastic impacts

Microplastics (MPs) are ubiquitous in the marine environment and impact organisms at multiple levels. Understanding their actual effects on wild populations is urgently needed. This study develops a toolkit to monitor changes in gene expression induced by MPs in natural environments, focusing on filter-feeding and bioindicator species from diverse ecological and taxonomic groups. Six candidate genes -Caspase, HSP70, HSP90, PK, SOD, and VTG- and nine filter-feeding species -two branchiopods, one copepod, five bivalves and one fish- were selected based on differential expression in response to MPs exposure (mainly the widely used polystyrene and polyethylene polymers) reported in over 30 publications. Some genes are particularly determinant, such as HSP70 and HSP90 (key to managing a wide range of stressors) and SOD (critical for addressing oxidative stress), as they are more directly related to stress. PK is related to carbohydrate metabolism (alterations in energy metabolism); VTG is associated with reproductive problems; Caspase mediates in apoptosis. Each gene in the toolkit plays a role depending on the type of stress assessed, and their combination provides a comprehensive understanding of the impacts of MPs. Differences in gene expressions between species and the exposure thresholds were found. These genes were examined in various scenarios with different types, concentrations, and sizes of MPs, alone or with other stressors. The toolkit offers significant advantages, allowing a comprehensive study of the impact of MPs and focusing on filtering bioindicator species, thus enabling pollution assessment and long-term monitoring. It will outperform traditional methods like tissue counts of MPs where only physical damage is visible, providing a deeper understanding. To our knowledge, this is the first toolkit of its kind.

Metabolic profiles and protein expression responses of Pacific oyster (Crassostrea gigas) to polystyrene microplastic stress

The underlying toxicity mechanisms of microplastics on oysters have rarely been explored. To fill this gap, the present study investigated the metabolic profile and protein expression responses of oysters to microplastic stress through metabolomics and biochemical analyses. Oysters were exposed to microplastics for 21 days, and the results indicated that the microplastics induced oxidative stress, with a significant decrease in SOD activity in the 0.1 mg/L exposure group. Metabolomics revealed that exposure to microplastics disturbed many metabolic pathways, such as amino acid metabolism, lipid metabolism, biosynthesis of amino acids, aminoacyl-tRNA biosynthesis, and that different concentrations of microplastics induced diverse metabolomic profiles in oysters. Overall, the current study provides new reference data and insights for assessing food safety and consumer health risks caused by microplastic contamination.

Microplastics in commercial marine bivalves: Abundance, characterization and main effects of single and combined exposure

Microplastics (MPs) are persistent and ubiquitous pollutants in marine ecosystems, and they can be ingested and accumulated by marine organisms with economic value to humans, such as marine bivalves, which may pose a threat to the marine food chains and to human health. In this literature review, we summarized the recent findings on the abundance and main characteristics (shape, size, color, polymer) of MPs detected in valuable marine bivalve species. Furthermore, we surveyed the major impacts triggered by MP exposure, alone or in combination with other pollutants, in these organisms. Additionally, we discussed the methodologies, techniques and equipment commonly used by researchers for the determination of the abundance, characterization and effects of the MP particles in these organisms. We verified that MPs have been widely detected in multiple species of commercial marine bivalves, with a great variety of shapes, sizes, colors and polymer types. In general, the methodologies used by researchers to determine the MP abundance in marine bivalves need to be harmonized to facilitate the comparability between studies. So far, previous research showed that the main effects of MPs, either alone or combined with other pollutants, on commercial marine bivalves include the induction of immunological, physiological and behavioral responses, reproductive modifications, genotoxicity and neurotoxicity, which were surveyed by using a wide variety of techniques and analytical equipment. In the future, researchers should focus on less studied bivalve species and should use the most precise and innovative methodologies to assess the effects of MPs and other pollutants on marine bivalves.

Polycyclic aromatic hydrocarbons in commercial marine bivalves: Abundance, main impacts of single and combined exposure and potential impacts for human health

Polycyclic aromatic hydrocarbons (PAHs) are emerging pollutants with a broad distribution in marine environments. They can interact with other pollutants and be bioaccumulated by marine bivalves, which can be consumed by humans. This is the first review that focuses on the presence and effects of PAHs, single or combined with other pollutants, in commercial marine bivalves. Around the world, researchers have detected several PAHs in valuable marine bivalves and reported immunological, genotoxic, neurotoxic, physiological, reproductive, and biochemical effects in these species caused by exposure to PAHs, alone or combined with other pollutants, using efficient and accurate methods. Commercial marine bivalves contaminated with PAHs may pose a risk to marine food chains and environments and to human health. We recommend further research on the abundance and neurotoxic, physiological, reproductive and biochemical effects of PAHs, alone and with other pollutants, in commercial marine bivalves and more human health risk assessments.

Microplastics' vector effect on Co-bioaccumulation of it and polychlorinated biphenyls in Crassostrea hongkongensis

Microplastics (MPs) and polychlorinated biphenyls (PCBs) are known with high persistence and toxicity, posing urgent threats to food safety and human health. However, little is known about the synergistic effect of MPs on PCBs bioaccumulation on Crassostrea hongkongensis. In the present study, diverse types of MPs were analyzed on sea water and C. hongkongensis sampled from three distinct estuary sites, and film-shaped MPs were discovered to be preferentially ingested by the oysters. Interestingly, the content of MPs and PCBs showed negative correlation (R2 = 0.452, p< 0.001) in the oysters sampled from site 2. Upon MPs and PCBs co-treatment, the in vivo accumulation of PCBs in C. hongkongensis was inhibited by 25.90 % when compared to the group treated with PCBs solely. PCBs stresses significantly induced the expression of genes of CYP2C31, GST, SOD and HSP70 in C. hongkongensis, while, the elevated state was compromised when co-treated with PCBs. The present research alleviates concerns about the potential effects of MPs on promoting PCBs bioaccumulation and provide a better understanding of the combined impact of MPs and PCBs on C. hongkongensis.

Exploring the co-exposure effects of environmentally relevant microplastics and an estrogenic mixture on the metabolome of the Sydney rock oyster

In aquatic environments the concurrent exposure of molluscs to microplastics (MPs) and estrogens is common, as these pollutants are frequently released by wastewater treatment plants into estuaries. Therefore, this study aimed to evaluate the independent and co-exposure impacts of polyethylene microplastics (PE-MPs) and estrogenic endocrine-disrupting chemicals (EEDCs) at environmentally relevant concentrations on polar metabolites and morphological parameters of the Sydney rock oyster. A seven-day acute exposure revealed no discernible differences in morphology; however, significant variations in polar metabolites were observed across oyster tissues. The altered metabolites were mostly amino acids, carbohydrates and intermediates of the Kreb's cycle. The perturbation of metabolites were tissue and sex-specific. All treatments generally showed an increase of metabolites relative to controls - a possible stimulatory and/or a potential hormetic response. The presence of MPs impeded the exposure of adsorbed and free EEDCs potentially due to the selective feeding behaviour of oysters to microplastics, favouring algae over similar-sized PE-MPs, and the formation of an eco/bio-corona involving faeces, pseudo-faeces, natural organic matter, and algae.

The multistressor effect of pH reduction, microplastic and lanthanum on sea urchin Arbacia lixula

pH reduction (Low pH), microplastic (MP), and lanthanum (La) are substantial stressors due to their increasing trends in marine ecosystems and having adverse effects on marine species. This study investigates the single and combined effects of those stressors (Low pH: 7.45, polyethylene MP: 26 μg L-1, and La: 9 μg L-1) on the physiology and histology of sea urchin Arbacia lixula. Regarding physiological results, while the coelomocytes' quantity was slightly affected by stressors, their viability was significantly affected. The coelomocyte count and viability were suppressed most in Low pH-MP-La treatment. The stressors did not impact the respiration rate. According to the histological examination results, the crypt (villi-like structure) was shorter, and epithelial layers were thinner in single and dual stress treatments like MP, Low pH, Low pH-La, and MP-La. Overall, we suggest that the combination of variable types of those stressors causes negative effects on sea urchin's physiology and histology.

Impact of aged and virgin polyethylene microplastics on multi end-points effects of freshwater fish tissues

The buildup of plastic waste in aquatic environments presents serious threats to the environment, wildlife, and ultimately to humans. Specifically, microplastics (MPs) ingestion by aquatic animals leads to adverse physiological and toxicological effects. In addition, discarded MPs undergo aging and degradation processes which affect their morphological properties and chemical composition, enhancing the absorption of environmental pollutants. Under this prism, the present research was conducted to investigate and compare the impact of 'aged' versus pristine low-density polyethylene microplastics (PE-MPs) on various toxicity endpoints as biochemical and molecular parameters in the muscle tissue and liver of the freshwater fish species Perca fluviatilis. In parallel, the morphological, physicochemical, and structural changes occurred in "aged" PE-MPs, (after being exposed to UV radiation for 120 days) were studied, significantly illustrating signs of oxidation and crack propagation at the surface of the studied MPs. Fish were exposed to artificial diet reached with virgin and "aged" PE-MPs, sized 100-180 μm, at concentrations of 1 mg/g of dry food for a period of 15-days. Thereafter, liver and muscle tissues were analyzed in relation to multi oxidative parameters. Compared to the control group, the observed changes in the examined fish included increased activities of antioxidant enzymes, as superoxide dismutase, catalase and glutathione reductase, enhanced concentrations of malondialdehyde, protein carbonylation, HSP70 levels, elevated MAPK phosphorylation, induction of ubiquitin-proteins, as well as heightened levels of Bax/Bcl-2 proteins, caspases and differentiated levels of LC3 II/I, SQSTM1/p62. From the studied biomarkers, apoptosis, ubiquitin and hsp70 levels, showed a more sensitive response against the ingested MPs, followed by autophagy, p38MAPK levels, antioxidant enzymes, MDA and carbonylation levels. The effect of "aged" PE-MPs was more pronounced compared to that of the virgin ones. When evaluating the response of all oxidative stress biomarkers across the studied tissues, the liver demonstrates the highest response for the majority of the biomarkers against both virgin and "aged" PE-MPs. These findings strongly indicate that "aged" MPs activate the antioxidant defence mechanisms and impact the cellular well-being of the examined fish species.

Surface-Charge-Driven Ferroptosis and Mitochondrial Dysfunction Is Involved in Toxicity Diversity in the Marine Bivalve Exposed to Nanoplastics

Nanoplastics (NPs) pervade daily life, posing serious threats to marine ecosystems. Despite the crucial role that surface charge plays in NP effects, there is a substantial gap in our understanding of how surface charge influences NP toxicity. Herein, by exposing Ruditapes philippinarum (R. philippinarum) to both positively charged NPs (p-NPs) and negatively charged NPs (n-NPs) at environmentally relevant particle number levels for a duration of 35 days, we unequivocally demonstrate that both types of NPs had discernible impacts on the clams depending on their surface charge. Through transcriptomic and proteomic analyses, we unveiled the primary mechanisms behind p-NP toxicity, which stem from induced mitochondrial dysfunction and ferroptosis. In contrast, n-NPs predominantly stimulated innate immune responses, influencing salivary secretion and modulating the complement and coagulation cascades. Furthermore, in vitro tests on clam immune cells confirmed that internalized p-NPs triggered alterations in mitochondrial morphology, a decrease in membrane potential, and the initiation of ferroptosis. Conversely, n-NPs, to a certain extent, moderated the expression of genes related to immune responses, thus mitigating their adverse effects. Taken together, these findings indicate that the differential surface-charge-driven ferroptosis and mitochondrial dysfunction in clams play a critical role in the toxicity profile of NPs, providing an insightful reference for assessing the ecological toxicity associated with NPs.

Hematological Consequences of Polyethylene Microplastics Toxicity in Male Rats: Oxidative stress, Genetic, and Epigenetic links

Microplastics (MPs) pollution is a newly emerging environmental issue. MPs can accumulate within animals and humans, which can pose a serious health threat. Petroleum-based polyethylene (PE) is one of the most popular plastics. Accordingly, its exposure rates have steadily increased over the years. This study aimed to analyze the effects of PE-MPs on the hematological system of albino rats and the epigenetic effect. Five groups of adult male eight-weeks-old rats received either distilled water, corn oil, 3.75mg/kg PE-MPs, 15mg/kg PE-MPs, or 60mg/kg of PE-MPs, daily by oral gavage for 35 days. PE-MPs significantly increased the body weights of the rats and lipid peroxidation, with concomitant reduction of superoxide dismutase activity and depletion of reduced glutathione, thus adversely affecting oxidants/antioxidants balance. Moreover, PE-MPs increased the % of abnormal RBCs, irregular cells, tear drop cells, Schistocyte cells, and folded cells. The genotoxic effects on DNA were evident by increased DNA damage, confirmed by the comet assay, in addition to increased DNA methylation. The effects of PE-MPs have been shown to be dose correlated. In conclusion, this study provides evidence of dose-related PE-MPs-induced hematological, genotoxic, and epigenetic effects in mammals, and thus emphasizes the potentially hazardous health effects of environmental PE-MPs.