Toxicological effects of acute and subacute perfluorooctane sulfonic acid exposure on the bivalve Ruditapes decussatus.

Perfluorooctane sulfonic acid (PFOS), a persistent and bioaccumulative per-and polyfluoroalkyl substance (PFAS), is widely distributed in aquatic environments and is known for its toxic effects. This study investigated the toxicological mechanisms of PFOS in the bivalve Ruditapes decussatus under acute and subacute exposure scenarios, with particular emphasis on concentration-dependent and organ-specific responses in gills and digestive glands (DGs). Clams were exposed to nominal PFOS concentrations under acute conditions (1-100 µg/ml for 5 days) and subacute conditions (1, 10, and 20 µg/ml for 15 days). Histological analyses revealed marked tissue-specific alterations, with gills exhibiting early structural damage and inflammatory responses, whereas the DGs showed signs of contaminant accumulation and adaptive pathological changes. Biochemical analyses demonstrated significant oxidative stress at 20 µg/ml, evidenced by increased activities of catalase, superoxide dismutase, and glutathione S-transferase omega, together with elevated malondialdehyde and nitrite levels. Immunohistochemical analyses confirmed the activation of inflammatory and nitrosative pathways, with stronger responses in gill tissues. Overall, PFOS induced concentration-dependent and tissue-specific toxic effects, highlighting the gills as the primary target organ. These findings support the use of R. decussatus as a bioindicator species for assessing PFAS toxicity in marine environments.