Acute toxic effects of Endosulfan and Diazinon pesticides on adult amphibians (Bufo regularis )

The acute toxicity of Endosulfan (organochlorine) and Diazinon (organophosphate) pesticides to adult amphibians, Bufo regularis was evaluated to determine uptake and effect of environmentally relevant concentrations on survival, morphology and behaviour. Toxicity characterizations were also assessed using standard indices. Toads were exposed for 96 h to varying concentrations of the pesticides; 0.25, 0.50, 0.75 and 1 mg/L. Mean percentage mortality increased significantly (p < 0.05) with concentrations and exposure duration for Endosulfan and Diazinon pesticides and was significantly (p < 0.05) different from the control, indicating that pesticide induced lethality. The results showed that Diazinon (LC50 = 0.44 mg/l) was more toxic than Endosulfan (LC50 = 0.73 mg/l). Derived safe concentrations were 0.07 and 0.04 mg/l for Endosulfan and Diazinon, respectively. Estimated toxicity index values (TIV) and Hazard Quotients (HQ) for all the concentrations were above one (1) indicating potential risk of the pesticides to the toad. Bioconcentration of the pesticides after 96 h increased with increasing concentrations indicating that uptake was concentration dependent. There was a significant positive correlation between tissue concentration and mortality (p < 0.01) for both pesticides. The pesticides also caused dose-dependent deformities and behavioural abnormalities. More pronounced poisoning symptoms were observed in Diazinon and at higher concentrations. Key words: Acute toxicity, Endosulfan, Diazinon, adult amphibian.