Combined toxic effects of nanoplastics and norfloxacin on mussel: Leveraging biochemical parameters and gut microbiota.

Antibiotics and nanoplastics (NPs) are among the two most concerned and studied marine emerging contaminants in recent years. Given the large number of different types of antibiotics and NPs, there is a need to apply efficient tools to evaluate their combined toxic effects. Using the thick-shelled mussel (Mytilus coruscus) as a marine ecotoxicological model, we applied a battery of fast enzymatic activity assays and 16S rRNA sequencing to investigate the biochemical and gut microbial response of mussels exposed to antibiotic norfloxacin (NOR) and NPs (80 nm polystyrene beads) alone and in combination at environmentally relevant concentrations. After 15 days of exposure, NPs alone significantly inhibited superoxide dismutase (SOD) and amylase (AMS) activities, while catalase (CAT) was affected by both NOR and NPs. The changes in lysozyme (LZM) and lipase (LPS) were increased over time during the treatments. Co-exposure to NPs and NOR significantly affected glutathione (GSH) and trypsin (Typ), which might be explained by the increased bioavailable NOR carried by NPs. The richness and diversity of the gut microbiota of mussels were both decreased by exposures to NOR and NPs, and the top functions of gut microbiota that were affected by the exposures were predicted. The data fast generated by enzymatic test and 16S sequencing allowed further variance and correlation analysis to understand the plausible driving factors and toxicity mechanisms. Despite the toxic effects of only one type of antibiotics and NPs being evaluated, the validated assays on mussels are readily applicable to other antibiotics, NPs, and their mixture.

Ingestion of nano/micro plastic particles by the mussel Mytilus coruscus is size dependent.

Plastic particles are thought to accumulate in aquatic organisms and cause potential physiological effects. The uneven sizes of plastic particles may affect the ingestion by marine filter feeding bivalves and may lead to differential further physiological effects. To tackle this scientific question, we investigated the size dependent ingestion and dynamic accumulation of nano/micro plastic particles with different diameters (0.07, 0.5, 5, 10 and 100 µm) in the thick shell mussel Mytilus coruscus. The accumulation of particles in gill, digestive tract and mantle of mussels was measured after 3, 15, 87 h exposure and following 87 h depuration. The results showed that particle ingestion was negatively size dependant and positively related to time in digestive tract. In mantle, particles accumulated over the depuration time with a delay, indicating the translocation of particles. Moreover, our results showed that gill was not a target tissue for steady particle accumulation but the digestive tract was. This study showed size dependent and dynamic ingestion of nano/micro particles in mussels which are one of the main marine organisms for accumulating microplastics.