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 to PE MP with adsorbed TBT (50 mg L⁻¹; 0.02 mg TBT g⁻¹ PE MP) for 21 days. Efficient adsorption on PE MP was confirmed by quantification of TBT-Cl on MP, and tissue content analysis after exposure showed higher TBT concentrations in mussels from the PE MP + TBT group than in those exposed to aqueous TBT only. More pronounced responses in catalase and electron transport system (ETS) activity were observed in the hepatopancreas than in the gill tissue, with the PE MP + TBT treatment showing catalase depletion or disruption of the antioxidant defence system under combined stress conditions in the hepatopancreas. 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. DNA damage was present in all exposed groups and increased over time.