Discovering isothiazolinones: comparison of the effects of octylisothiazolinone and methylisothiazolinone on physiological parameters in a marine model organism

Isothiazolinones, including octylisothiazolinone (OIT) and methylisothiazolinone (MIT), are widely used biocides whose increasing presence in aquatic ecosystems raises ecotoxicological concerns. In the two studies analysed, specimens of Mytilus galloprovincialis were exposed to sub-lethal concentrations of OIT (0.01 and 0.1 mg L-1) and MIT (0.2 and 0.4 mg L-1) for a period of 14 days, with the aim to evaluate the effects on key physiological parameters such as cell viability, phagocytosis along with y-actin expression, and cell volume regulatory capacity. The two compounds under investigation caused a significant decrease in both haemocyte and isolated digestive gland (DG) cell viability, with effects more pronounced at lower concentrations. Phagocytic capacity was significantly impaired in all exposed groups, with reductions of 50-60% compared to controls, a finding also supported by the observed trend in y-actin gene expression. Regulatory volume decrease (RVD) assay indicated impaired DG cell volume recovery in both studies. Indeed, treated cells demonstrated a marked difficulty in returning to their initial volume following hypotonic shock, suggesting damage to the cytoskeleton, membrane, or ion channel activity. Findings demonstrate that both biocides disrupt cellular and immune homeostasis in M. galloprovincialis, with responses exhibiting a tendency to be non-linear dose-dependent.