High microplastic exposure affects survival and health of Dreissena spp. mussels: implications for freshwater pollution monitoring

The occurrence and concentrations of microplastics in freshwater environments are far less studied than in marine ecosystems, despite rivers being the receptacle of plastic pollution from terrestrial activities. Since microplastics impact aquatic organisms at multiple levels, the development of reliable and efficient methods for their quantification is crucial to improve ecological risk assessment and support regulatory efforts. In this study, we investigated the potential of Dreissena spp. mussels as bioindicators for microplastic pollution by exposing them to fluorescent polyethylene microbeads (10-20 μm) for 2 months at two environmental concentrations (200 and 2000 MP L). Both microplastic uptake and health indicators (survival rates, condition index, and energy reserves) were assessed. Our results confirmed microplastic uptake by dreissenids under both exposure concentrations. Exposure to 2000 MP L led to a decrease in condition index and energy reserves within 15 days, resulting in increased mortality, whereas exposure to 200 MP L had no significant effect. These findings support the use of Dreissena spp. mussels as bioindicators for microplastic pollution in freshwater ecosystems, highlighting the bioaccessibility of MPs to filter-feeders and allowing the assessment of both microplastic accumulation in tissues and associated health effects.