Thiram-induced oxidative, genotoxic, and biochemical alterations in Pangasius fish: Implications for aquatic toxicology.

The widespread use of thiram in agriculture, veterinary practices, and in pharmaceutical industries as an antifungal agent has raised significant concerns regarding its unexpected ecotoxicological impacts on non-target aquatic organisms. This study assessed the mechanisms of induction of oxidative stress, genotoxicity, biochemical alterations in tissues, and histopathological disorders of thiram in pangasius fish reared in various groups (A-D) and subjected to 5, 10, and 15 µg/L concentrations of thiram for 12 days. Visceral organs, including liver, heart, kidneys, muscles, and brain, were obtained on days 4, 8, and 12th of the experiment for assessment of antioxidant enzymes, oxidative stress biomarkers, DNA damage, and histological changes. Results showed a significant depletion (P≤0.05) in activities/concentrations of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and reduced glutathione (GSH) in all visceral organs (liver, kidneys, heart, muscles, and brain) of fish treated with higher doses of thiram. The results on the activity of acetylcholinesterase (AChE), a biomarker of neurotoxicity, significantly increased in fish exposed to thiram (15 µg/L) when compared to untreated fish. The levels of reactive oxygen species (ROS) and Thiobarbituric acid reactive substances (TBARS) were significantly enhanced in visceral organs in treated fish at higher concentrations (15 µg/L) of thiram. Genotoxicity assessment via the comet assay demonstrated significantly elevated DNA fragmentation in all organs at day 12 of the experiment in fish exposed to thiram (15 µg/L). The histopathological analysis revealed prominent changes in liver (necrosis of hepatocytes, inflammatory exudate, increased sinusoidal space, nuclear atrophy and vacuolation), kidneys (inflammatory infiltration; dilatation of Bowman's space, necrosis of renal tubules, atrophy of glomerulus, necrosis of tubular epithelial cells and melanomacrophage aggregates), heart (myocardial degeneration and edema; disruption of muscles fibers and necrotic myocytes) and brain (degeneration of neuron, eccentric nuclei of neurons, inflammatory reaction and vacuolation). These findings highlight the potential risks of thiram contamination in aquatic ecosystems and emphasize the need for regulatory evaluation and safer pesticide management practices.