Assessment of Hepatotoxic and Genotoxic Effects of Chromium in Zebrafish ( Danio rerio ) With Emphasis on Recovery Following Exposure Withdrawal

Chromium (Cr), a highly toxic environmental contaminant, is extensively discharged into aquatic ecosystems through industrial activities, posing serious risks to aquatic organisms by triggering oxidative imbalance and genotoxic injury. The present study comprehensively investigated Cr-induced hepatotoxicity and genotoxicity in zebrafish (Danio rerio), with particular emphasis on the extent of recovery following withdrawal of exposure. Adult zebrafish were exposed to environmentally relevant concentrations of Cr (0.5 and 2 ppm) for 30 days, followed by a 30-day postwithdrawal period to evaluate reversibility of toxic effects. Cr exposure elicited pronounced oxidative stress in hepatic tissue, characterized by elevated lipid peroxidation along with significant alterations in reduced glutathione content and catalase activity. Histopathological assessment revealed severe concentration-dependent hepatic injury and disruption of normal hepatic architecture. Genotoxic evaluation demonstrated marked induction of micronuclei and erythrocytic nuclear anomalies, including blebbed, lobed, and notched nuclei, confirming substantial chromosomal and nuclear damage following Cr exposure. Furthermore, immunofluorescence analyses revealed a robust upregulation of Nrf2 expression, indicating the activation of the Nrf2-mediated antioxidant defense pathway in response to Cr-induced oxidative stress. Although withdrawal of Cr exposure attenuated oxidative stress markers, reduced Nrf2 expression, and lower frequencies of nuclear abnormalities, complete restoration was not achieved. Persistent histopathological lesions and residual genotoxic alterations remained evident even after the recovery period, particularly in the higher exposure group. Collectively, these findings demonstrated that Cr induced sustained hepatic and genetic toxicity in zebrafish, highlighting the limited reversibility of Cr-mediated damage and underscoring the long-term ecological implications of Cr contamination in aquatic environments.