Toxicity of environmental and polystyrene plastic particles on the bivalve Corbicula fluminea: focus on the molecular responses.

Among aquatic organisms, filter feeders are particularly exposed to the ingestion of microplastics (MPs) and nanoplastics (NPs). The present study investigates the effect of environmental microplastics (ENV MPs) and nanoplastics (ENV NPs) generated from macro-sized plastic debris collected in the Garonne River (France), and polystyrene NPs (PS NPs) on the freshwater bivalve Corbicula fluminea. Organisms were exposed to plastic particles at three concentrations: 0.008, 10, and 100 µg L-1 for 21 days. Gene expression measurements were conducted in gills and visceral mass at 7 and 21 days to assess the effects of plastic particles on different functions. Our results revealed: (i) an up-regulation of genes, mainly involved in endocytosis, oxidative stress, immunity, apoptosis, and neurotoxicity, at 7 days of exposure for almost all environmental plastic particles and at 21 days of exposure for PS NPs in the gills, (ii) PS NPs at the three concentrations tested and ENV MPs at 0.008 µg L-1 induced strong down-regulation of genes involved in detoxication, oxidative stress, immunity, apoptosis, and neurotoxicity at 7 days of exposure in the visceral mass whereas ENV MPs at 10 and 100 µg L-1 and all ENV NPs induced less pronounced effects, (iii) overall, PS NPs and ENV MPs 0.008 µg L-1 did not trigger the same effects as ENV MPs 10 and 100 µg L-1 and all ENV NPs, either in the gills or the visceral mass at 7 and 21 days of exposure. This study highlighted the need to use MPs and NPs sampled in the environment for future studies as their properties induce different effects at the molecular level to living organisms.

Effect of an environmental microplastic mixture from the Seine River and one of the main associated plasticizers, dibutylphthalate, on the sentinel species Hediste diversicolor.

The aim of this study was to explore the adverse effects of a microplastic (MP) mixture obtained from litter accumulated in the Seine River (France) compared to those of their major co-plasticizer, dibutylphthalate (DBP), on the sentinel species Hediste diversicolor. A suite of biomarkers has been investigated to study the impacts of MPs (100 mg kg-1 sediment), DBP (38 µg kg-1 sediment) on worms compared to non-exposed individuals after 4 and 21 days. The antioxidant response, immunity, neurotoxicity and energy and respiratory metabolism were investigated using biomarkers. After 21 days, worms exposed to MPs showed an increasing aerobic metabolism, an enhancement of both antioxidant and neuroimmune responses. Energy-related biomarkers demonstrated that the energy reallocated to the defence system may come from proteins. A similar impact was depicted after DBP exposure, except for neurotoxicity. Our results provide a better understanding of the ecotoxicological effects of environmental MPs and their associated-contaminants on H. diversicolor.

Toxicity assessment of environmental MPs and NPs and polystyrene NPs on the bivalve Corbicula fluminea using a multi-marker approach.

Small plastic particles, microplastics (MPs) and nanoplastics (NPs) represent a major threat in aquatic environments. Freshwater organisms are exposed to MPs and NPs, particularly in industrial and urban areas. The present study aimed to compare the toxicity between polystyrene NPs (PS NPs) and environmental microplastics (ENV MPs) and nanoplastics (ENV NPs) generated from macro-sized debris collected in the Garonne River on the freshwater bivalve C. fluminea. The organisms were exposed to the different plastic particles at three environmentally relevant concentrations: 0.008, 10, and 100 µg L-1 for 21 days. The biological responses of organisms were assessed using a multi-biomarker approach from the sub-individual to the individual level. The results demonstrated that: i) ENV NPs triggered more effects on detoxification processes and immune response, confirming that using manufactured NPs for laboratory exposure can lead to misleading conclusions on the risks posed by plastic particles; ii) effects of ENV MPs were less marked than ENV NPs, emphasizing the importance of testing a size continuum of plastic particles from NPs to MPs; iii) some effects were only observed for the low and/or intermediate concentrations tested, underlining the importance of using environmentally relevant concentrations. In light of these results, laboratory studies should be continued by exposing aquatic species to environmental MPs and NPs. The properties of these particles have to be characterized for a better risk assessment of environmental plastic particles.

Aquatic worms: relevant model organisms to investigate pollution of microplastics throughout the freshwater-marine continuum.

Plastic pollution has become a global and emergency concern. Degradation processes of plastic macrowaste, either at the millimetre- and micrometre-size scales (microplastics, MP) or a nanometre one (nanoplastic, NP), is now well documented in all environmental compartments. It is hence necessary to study the environmental dynamic of MNP (micro(nano)plastic) on aquatic macrofauna considering their dispersion in different compartments. In this context, worms, having a large habitat in natural environments (soil, sediment, water) represent a relevant model organism for MNP investigations. In aquatic systems, worms could be used to compare MNP contamination between freshwater and seawater. The aim of this review was to discuss the relevance of using worms as model species for investigating MNP pollution in freshwater, estuarine, and marine systems. In this context, studies conducted in the field and in laboratory, using diverse classes of aquatic worms (polychaete and clitellate, i.e. oligochaete and hirudinea) to assess plastic contamination, were analysed. In addition, the reliability between laboratory exposure conditions and the investigation in the field was discussed. Finally, in a context of plastic use regulation, based on the literature, some recommendations about model species, environmental relevance, and experimental needs related to MNP are given for future studies.

Effect of aging of microplastics on gene expression levels of the marine mussel Mytilus edulis: Comparison in vitro/in vivo exposures.

In the present study, effects of aging MPs of polyethylene (PE) were investigated in the marine mussel Mytilus edulis, commonly used as bioindicator of aquatic ecosystem, using both in vitro and in vivo exposures, using concentrations found in marine waters (0.008, 10 and 100 µg.L-1). Changes in gene expression levels implicated in detoxification, immune system, cytoskeletton and cell cycle control were evaluated by quantitative RT-qPCR. Results demonstrated differential expression levels depending upon the state of plastic degradation (aged vs non-aged) and way of exposure (vitro vs vivo). This study highlighted the interest of using molecular biomarkers based on analysis of gene expression pattern in an ecotoxicological context that gives indication of relative slight changes between tested conditions as compared to other biochemical approaches (e.g. enzymatic activities). In addition, in vitro analysis could be used to generate large amount of data as regards to the toxicological effects of MPs.

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.

Effect of size continuum from nanoplastics to microplastics on marine mussel Mytilus edulis: Comparison in vitro/in vivo exposure scenarios.

For several decades, plastic has been a global threat in terms of pollution. Plastic polymers, when introduce in the aquatic environment, are exposed to fragmentation processes into microplastics (MPs) and nanoplastics (NPs) which could potentially interact with living organisms. The objective of this work was to study the effects of plastic particles representative of those found in the environment, on the marine mussels Mytilus edulis, under two exposure scenarios: in vivo and in vitro. Whole mussels or cultured hemocytes were exposed for 24 h to NPs and MPs generated from macro-sized plastics collected in the field, but also to reference NPs, at concentrations found in the environment: 0.08, 10 µg and 100 µg·L-1. Results showed that immune response was only activated when mussels were exposed in vivo. However, cytotoxicity (hemocyte mortality) and genotoxicity (DNA damage) parameters were induced after both types of exposure, but in a dose-dependent manner after in vitro hemocyte exposure to all tested plastic conditions. These results indicate that in vitro approaches could be considered as potential predictors of in vivo exposures.

Is cell culture a suitable tool for the evaluation of micro- and nanoplastics ecotoxicity?

Plastic particles have been described in aquatic ecosystems worldwide. An increasing number of studies have tried to evaluate the toxic impacts of microplastics (1-5000 µm) but also nanoplastics (<1 µm) in marine and freshwater organisms. However, the wide variety of plastic particles characteristics such as various sizes, shapes, functionalization or types of polymer, makes it difficult to evaluate their impact with regular ecotoxicity testing. In this context, cell culture, mainly used in human toxicology, could be a promising tool to evaluate micro- and nanoplastics toxicity with a wide diversity of conditions allowing to generate a large set of data. This review presents the current research on micro and nanoplastics using cell culture of marine and freshwater organisms, describes the limitations of cell culture tool and defines whether this tool can be considered as a relevant alternative strategy for ecotoxic evaluation of micro and nanoplastics especially for future regulatory needs. Articles using specifically cell culture tool from aquatic organisms such as fish or bivalves were identified. The majority evaluated the toxicity of polystyrene nanobeads on immune parameters, oxidative stress or DNA damage in fish cells. Although most of the papers characterized nanoplastic particles into the cell culture media, the relevance of testing conditions is not always clear. The development of cell culture can offer many opportunities for the evaluation of plastic particles' cellular impacts, but more research is needed to develop relevant culture models, on various aquatic organisms, and with consideration of abiotic parameters especially composition of cell culture media for nanoplastic evaluation.