Cellular toxicity and apoptosis-related responses to individual and combined exposure to microplastics and perfluorooctane sulfonic acid (PFOS) in Hediste diversicolor coelomocytes.

Microplastics (MPs) are emerging contaminants of increasing concern in marine ecosystems due to their widespread occurrence and ability to adsorb and transport hazardous chemicals such as perfluorooctane sulfonic acid (PFOS). PFOS is a persistent per- and polyfluoroalkyl substance (PFAS) with high environmental stability, bioaccumulative potential, and well-documented toxicity to aquatic organisms. However, the combined effects of MPs and PFOS on marine invertebrates remain poorly understood. This study evaluated the individual and combined effects of environmentally relevant concentrations of MPs (50 mg kg-1 sediment) and PFOS (0.1, 0.5, and 1 μg kg-1 sediment) on the coelomic fluid of the benthic polychaete Hediste diversicolor after 7 days of sediment exposure. The MPs consisted of particles <30 μm composed of PVC, PET, PS, HDPE, LDPE, and PE with heterogeneous morphologies. PFOS accumulated in the coelomic fluid in a dose-dependent manner, with higher concentrations observed under co-exposure, suggesting that the presence of MPs may influence PFOS bioavailability and uptake. This increased accumulation was accompanied by pronounced cytotoxic and genotoxic effects, including lysosomal membrane destabilization, increased micronucleus frequency, and DNA fragmentation. Co-exposure also upregulated the pro-apoptotic genes p53, Bax, and Casp-3, while downregulating the anti-apoptotic gene Bcl-2, indicating activation of apoptotic pathways. Overall, the effects of combined exposure varied according to the endpoint and PFOS concentration, with co-exposure producing greater responses for some endpoints but not consistently across all treatments. These findings highlight the increased hazard posed by the co-occurrence of MPs and PFOS and emphasize the need to consider contaminant mixtures in marine environmental risk assessment.