Under the shell: Bioaccumulation of pesticides and pharmaceuticals in shells and soft tissues of freshwater gastropods from an urban river

Freshwater ecosystems are increasingly exposed to complex mixtures of pesticides and pharmaceutical compounds, raising concerns about their accumulation in aquatic organisms and implications for biomonitoring. While bioaccumulation has been widely studied in fish and invertebrate soft tissues, the potential role of freshwater gastropod shells as accumulation sites remains largely unexplored. In this study, we explored the occurrence and bioaccumulation of 58 organic pollutants (13 antibiotics, 30 pesticides, and 15 pharmaceuticals) in shells and soft tissues of freshwater gastropods, and correlated these concentrations to contaminant concentrations in one grab water sample and one suspended sediments sample from the Orge River (France). Pollutant concentrations in gastropods were not related to concentrations in water but were significantly correlated with concentrations measured in suspended sediments, highlighting particle-associated exposure as a possible pathway. Overall, soft tissues exhibited higher concentrations and more consistent detection frequencies than shells, except for antibiotics, for which no significant difference was observed. Bioaccumulation factors in soft tissues were generally low, even if high values were observed for diflufenican, tebuconazole, and propranolol. Our results suggest that although gastropod shells can accumulate organic pollutants, soft tissues provide a more reliable and mechanistically interpretable matrix for biomonitoring. Combining biological measurements with suspended sediment analyses appears essential for realistic environmental risk assessment in freshwater systems. These findings should be explored in future studies including broader spatial and temporal replication.