Genotoxic effects of two industrial effluents and ethyl methane sulfonate in Clarias lazera

The genotoxic effects of industrial effluents from a brewery and a textile mill and of ethyl methane sulfonate (EMS) were investigated by the micronucleus test in Clarias lazera, a tropical freshwater fish. Fish obtained from a local market were kept in laboratory aquaria for 3 wk and then exposed to different concentrations (0.5 to 8 mg/litre) of EMS or brewery or textile-mill effluent (10–60%, v/v) for 14 days. The frequency of micronucleated erythrocytes was determined from blood smears and the results were analysed by linear regression and variance analysis. Exposure to EMS or effluent resulted in statistically significant increases in micronucleus frequency and there was a positive dose-response effect over the entire dose range. The textile-mill effluent dose-response curve was significantly higher than that of the brewery effluent. The suitability of the micronucleus test in fish for the screening of aquatic genotoxicants is highlighted and the importance of intensified monitoring of the aquatic environment is emphasized.