Chronic nephrotoxicity and Nrf2-mediated oxidative stress response in zebrafish (Danio rerio) kidneys following environmentally relevant co-exposure to lead and chromium.

Lead (Pb) and chromium (Cr) co-occur in contaminated waters, yet their combined toxicity remains inadequately explored. This study assessed the nephrotoxic effects of chronic Pb and Cr exposure, alone and in combination, in zebrafish over 15, 30, and 60 days using environmentally relevant concentrations. Exposure to Pb induced moderate oxidative stress and renal alterations, whereas Cr exposure caused greater antioxidant imbalance. Combined treatment induced the strongest responses, including elevated reactive oxygen species, lipid peroxidation, and catalase activity, alongside depletion of reduced glutathione. Histological studies exhibited renal damage, including vacuolization, tubular necrosis, and glomerular degeneration, most evident at 30 days. Molecular analyses associated these alterations to activation of the Nrf2-Keap1-ARE pathway, with upregulation of antioxidant and detoxification genes and downregulation of keap1. Enhanced nuclear localization of Nrf2 was confirmed by immunofluorescence. Our findings demonstrated that Pb-Cr mixtures exerted enhanced nephrotoxic effects, emphasizing the necessity for mixture-based risk assessment in aquatic ecosystems.