Multifaceted toxicity of dimethoate in the Pacific oyster (Magallana gigas): Biochemical, molecular, and physiological responses.

Understanding more about the risks posed by hazardous pesticides is essential, particularly for ecologically and economically important species such as the Pacific oyster (Magallana gigas). Although dimethoate toxicity has been widely studied and has led to regulatory measures in certain regions, it is still used in others, such as Tunisia. Investigations on sensitive species in such contexts can provide valuable insights for better assessing and managing potential environmental risks. This study offers a novel evaluation of the toxic effects of experimental concentrations of dimethoate after a 72-h exposure period on the redox state, cholinergic system, and fatty acid composition in the gills of M. gigas oysters, as well as in terms of DNA damage on their hemocytes. Throughout the exposure period, we observed an increase in lipid and protein oxidation, along with changes in the activities of the antioxidant enzymes catalase, superoxide dismutase, and glutathione peroxidase, as well as an inhibition of the acetylcholinesterase activity in the tested oysters. Changes in fatty acid composition were detected, characterized by a decrease in saturated fatty acids and an increase in unsaturated fatty acids, particularly docosahexaenoic acid and arachidonic acid. After exposure to higher concentrations of dimethoate, genotoxic effects were observed, as evidenced by increased DNA damage in the oysters' hemolymph. Together, these biochemical and molecular alterations indicate that dimethoate exposure triggers complex physiological and behavioral adjustments in oysters when subjected to more severe stressors. These findings underscore potential threats to oyster quality and consumer safety under continued use of unregulated toxic pesticides.