Abstract

The increasing global demand for food, driven by rapid population growth, has intensified the application of pesticides in agriculture. While these agrochemicals enhance crop yield, their pervasive use poses profound ecological risks, particularly to aquatic ecosystems vulnerable to pesticide runoff. Express, a widely used herbicide in Nigeria, contains 1,1′-dimethyl-4,4′-bipyridinium dichloride, an active ingredient with a well-documented global footprint in weed management. This study assessed the acute and sub-lethal genotoxic effects of Express on juvenile Clarias gariepinus, focusing on the liver, gonads, and gills, using the Comet assay as a biomarker of DNA damage. Acute toxicity tests revealed a concentration-dependent increase in mortality, with Probit analysis estimating a 96-hour LC₅₀ of 0.095 mL/L, underscoring the compound’s high lethality. Sub-lethal exposures (0.03, 0.07, 0.10, and 0.13 mL/L) elicited marked behavioural and physiological disruptions, including hyperactivity, immobility, and skin depigmentation, with severity escalating at higher concentrations. Comet assay results demonstrated significant (p < 0.01) DNA strand breaks in all examined tissues, with damage patterns indicating organ-specific susceptibility. The pronounced genotoxic potential of Express raises critical concerns for aquatic biodiversity, trophic stability, and food security, as well as potential implications for human health via the aquatic food chain. These findings underscore the urgent need for stringent environmental regulations, robust ecotoxicological monitoring, and the promotion of sustainable weed management strategies to protect aquatic life and maintain ecosystem integrity.

Keywords:1,1′-Dimethyl-4,4′-Bipyridinium Dichloride (Express), Comet assay, DNA damage, Pesticides, Agrochemicals, Genotoxicity