Survival and cholinesterase activity of Asian common toad (Duttaphrynus melanostictus) tadpoles following short term exposure to a carbosulfan-based pesticide

Carbosulfan, a carbamate pesticide widely used in agriculture especially in the Asian region has received less attention in ecological impact assessments particularly to non-target amphibians. In this study, short term effects of a carbosulfan-based pesticide (Marshal^®) on survival and cholinesterase (ChE) activity of tadpoles of Duttaphrynus melanostictus, a non-target amphibian in tropical Asia were evaluated. Based on the concentration-toxicity response patterns, estimated median lethal concentration (LC₅₀) and median ChE inhibitory concentration (IC₅₀) for 96 h were 24 and 2.1 mg/L carbosulfan respectively. For the ChE inhibition for 96 h, the lowest observable effect concentration and no observable effect concentrations of carbosulfan were 0.6 and 0.3 mg/L respectively. Upon transfer to pesticide-free water by 14 days, ChE activities of the tadpoles were restored to normal levels. Since the tadpoles exposed to 0.3 mg/L carbosulfan have not exhibited lethality, morphological deformities, abnormal behavior or statistically significant ChE depression, it is unlikely that the carbosulfan-based pesticide could induce neurotoxic effects for D. melanostictus tadpoles at the concentration of ≤ 0.3 mg/L of active ingredient under short term exposure.