From biocide to biohazard: influence of methylchloroisothiazolinone on physiological integrity of Mytilus galloprovincialis

Methylchloroisothiazolinone (CMIT), an isothiazolinone-based compound, is extensively used in several commercial products as a biocide and has recently been identified as an emerging contaminant in aquatic environments. This study investigates the impact of this substance on key cellular, physiological, and biochemical endpoints in the Mediterranean mussel ( Mytilus galloprovincialis ). Mussels were exposed for 14 days to two sublethal CMIT concentrations (0.01 and 0.1 mg/L), and responses were assessed in haemocytes (H) and digestive gland (DG). Cytotoxic effects were determined in H and DG through cell viability assays. Phagocytic activity was quantified in H. The osmoregulatory performance of DG isolated cells was evaluated using the Regulatory Volume Decrease (RVD) assay. Furthermore, oxidative stress biomarkers catalase and glutathione (GHS/GSSG), cytochrome P450-related activity (EROD) and neurotoxicity were measured in DG. Results revealed significant impairments in physiological functionality and osmoregulatory capacity, accompanied by high susceptibility of biochemical responses. In the DG, a clear association was observed between EROD activation and oxidative stress manifestations indicating the toxicity of CMIT derivatives. Overall, these findings confirm CMIT’s toxic potential toward vital physiological and biochemical processes in M. galloprovincialis and provide a basis for further research aimed at demonstrating the ecological consequences of isothiazolinone contamination, with potential implications for both marine ecosystem health and human well-being.