Discovering the effects of octylisothiazolinone: analysis of physiological changes in the Mediterranean mussel (Mytilus galloprovincialis).

Isothiazolinones represent a class of biocidal agents employed in industrial and medical formulations. Among this class, the 2-n-octyl-4-isothiazolin-3-one (OIT) is increasingly recognized as an emerging contaminant in aquatic systems. This study investigated cellular and physiological impact of OIT on Mytilus galloprovincialis. Specimens were exposed for 14 days to two sublethal concentrations of OIT (0.01 and 0.1 mg L⁻¹), and cellular and tissue-level responses were assessed in haemolymph and digestive gland (DG). Cytotoxic effects in haemocytes and digestive gland (DG) cells were assessed through cell viability assays. Also, phagocytic activity of haemocytes was measured and the osmoregulatory capacity of DG isolated cells was investigated via Regulation Volume Decrease (RVD) assay. Gene expression was measured by quantitative real-time PCR (qRT-PCR), using genes involved in oxidative stress (MnSOD, Cu/ZnSOD), xenobiotic metabolism (CYP4Y1), and inflammatory signaling (TNF-α, IL-17-2). This study highlights the toxicity of OIT on M. galloprovincialis, which activates complex physiological responses to xenobiotic stress. These results lay a basis for future studies aimed at an in-depth understanding of the effects of isothiazolinones on model organisms, on the health of the entire ecosystem and, indirectly, on human health in order to be able to implement mitigation strategies and proper management of these contaminants.