LAUSR

The ubiquity of microplastics in aquatic ecosystems has raised concerns over their interaction with biota. However, microplastics research on freshwater species, especially molluscs, is still scarce. We, therefore, investigated the factors affecting microplastics ingestion in the freshwater mussel Dreissena polymorpha. Using polystyrene spheres (5, 10, 45, 90 µm), we determined the body burden of microplastics in the mussels in relation to (1) exposure and depuration time, (2) body size, (3) food abundance and (4) MP concentrations. D. polymorpha rapidly ingested microplastics and excreted most particles within 12 h. Few microplastics were retained for up to one week. Smaller individuals had a higher relative body burden of microplastics than larger individuals. The uptake of microplastics was concentration-dependent, while an additional food supply (algae) reduced it. We also compared the ingestion of microplastics by D. polymorpha with two other freshwater species (Anodonta anatina, Sinanodonta woodiana) highlighting that absolute and relative uptake depends on the species and the size of the mussels. In addition, we determined toxicity of polystyrene fragments (≤ 63 µm, 6.4-100,000 p mL-1 ) and diatomite (natural particle, 100,000 p mL-1 ) in D. polymorpha after 1, 3, 7 and 42 days of exposure investigating the clearance rate, energy reserves and oxidative stress. Despite ingesting large quantities, exposure to polystyrene fragments only affected the clearance rate of D. polymorpha. Further, results of the microplastic and diatomite exposure did not differ significantly. D. polymorpha, therefore, is unaffected by or can compensate for polystyrene fragment toxicity even at concentrations beyond current environmental levels. This article is protected by copyright. All rights reserved.