Freshwater snails avoid perfluorooctanesulfonic acid (PFOS) but only at concentrations well above U. S. Environmental Protection Agency safe water standards

Per- and polyfluoroalkyl substances (PFAS) are environmentally persistent synthetic chemicals with known toxicological effects, including endocrine and developmental disruption. Perfluorooctanesulfonic acid (PFOS), one of the most prevalent PFAS, can enter freshwater ecosystems via runoff and effluents, potentially transferring through food webs to humans. Freshwater pulmonate snails (family: Lymnaeidae) occupy a basal trophic position and may act as PFOS bioindicators and contaminant vectors. We tested whether Stagnicola elodes snails could detect and behaviorally avoid PFOS at environmentally relevant concentrations using a Y-tube choice assay. Snails were given a choice between control water and PFOS solutions ranging from 4 to 2,500 ng/L. Behavioral outcomes were classified as movement toward PFOS, toward control water, or no decision. Avoidance behavior was significant at 300 ng/L when excluding nondecision snails and at 100, 300, and 400 ng/L when including them. These results suggest that S. elodes can detect PFOS within a narrow concentration range, but behavioral responses are modest and at levels above safe drinking water standards (∼4 ng/L), minimizing their potential as a strong bioindicator species for PFOS contamination and their ability to limit trophic transport.