Polyethylene microplastics as a vector of tributyltin in Mytilus galloprovincialis and their consequences

Microplastic pollution is an increasing environmental issue in the marine environment due to its ubiquitous presence and its role as a vector for organic pollutants such as tributyltin (TBT). Adsorption of TBT onto microplastics (MP) can increase its availability to filter-feeding organisms by prolonging its retention time in the water column. We investigated whether polyethylene (PE) MP spheres (10-63 μm) could act as vectors for TBT transfer in the mussel Mytilus galloprovincialis by exposing it to PE MP (50 mg L^-1) and TBT (0.001 mg L^-1) separately and in co-exposure for 21 days. Efficient adsorption on PE MP was confirmed, and higher concentration of TBT was observed in the PE MP + TBT group compared to TBT only exposed group, indicating a vector effect. This led to higher toxicity in mussels, as the combined stress conditions in the PE MP + TBT group resulted in a significant decrease in the catalase activity after 14 days of the exposure. Higher ETS activity was observed in both exposed groups after seven days of exposure, followed by lower ETS activity at 14 and 21 days, indicating depletion of energy reserves. Pronounced responses in catalase and electron transport system (ETS) activity were observed in the hepatopancreas compared to the gill tissue. DNA damage was present in all exposed groups and increased over time.