Reproductive toxicity induced by a repeated 28-day oral exposure to a commercial mixture of the herbicides S-metolachlor and flumioxazin in male rats

Male reproductive health has become a growing concern, with evidence indicating a global decline in sperm quality. Among the contributing factors, pesticide exposure stands out. Flumioxazin and S-metolachlor are herbicides widely used in agriculture, and isolated studies report adverse effects on the reproductive physiology of rodents. Toxicological information on their combined exposure remains limited, even though these compounds are frequently applied together in agricultural settings. The objective of this study was to investigate the reproductive toxicity of a commercial formulation containing S-metolachlor and flumioxazin in adult male Wistar rats. The animals received the herbicide by gavage for 28 consecutive days at doses of 250, 500, or 1000 mg/kg/day, while the control group received only the vehicle (corn oil). Daily sperm production and the number of mature spermatids declined in the 500 and 1000 mg/kg groups. Epididymal transit time was prolonged at the highest dose, associated with reduced sperm viability and a rise in morphological sperm head anomalies. Motility was unchanged, but DNA integrity was compromised at the upper doses. Acrosome analysis revealed fewer intact structures and a greater proportion of acrosome-reacted spermatozoa. Marked imbalances in oxidative stress parameters were observed, with elevated malondialdehyde and protein carbonyl levels and decreased activities of superoxide dismutase, catalase, and glutathione peroxidase in the testes and sperm. No changes were detected in the absolute and relative masses of the reproductive organs, serum hormone levels, or the frequency of seminiferous epithelial stages. The present findings indicated that exposure to the herbicides flumioxazin and S-metolachlor induced sperm damage mediated by oxidative stress, suggesting an impact on reproductive function even when histological and hormonal parameters appear preserved.