Comparison of sensitivity to Dichlorvos of Rhacophorus megacephalus tadpole at different developmental stages

Dichlorvos is the most common organophosphate pesticide used in agricultural fields in China. It appears to be a contact and stomach poison in insects caused by interference with cholinesterase, a neurological enzyme which plays an important role in neurotransmission. The contamination of various bodies of water by run-off from fields treated with the chemical could have a negative impact on indigenous aquatic fauna. In this report, the sensitivities of treefrog Rhacophorus megacephalus tadpoles at early, middle and late developmental stages, respectively, to Dichlorvos at various concentrations(2.08 mg/L to 10.40 mg/L) were evaluated using alkaline single-cell gel electrophoresis assay(SCGE). The results showed that 24 h exposure to Dichlorvos induced significant DNA damage in tadpoles at early and middle stages(P0.01) with significant increases(P0.05) in the length-to-width ratios of the DNA patterns even at concentrations as low as 2.08 mg/L. Statistical analysis revealed linear correlations between the mean DNA length-to-width ratios and the doses of Dichlorvos at the first two developmental stages. The correlation coefficient values were 0.950(P0.01) at early and 0.954(P0.01) at middle stages. However, exposure to all treatment levels of Dichlorvos tested did not result in significant increases of DNA damage in tadpoles at late stage studied, suggesting that the sensitivity to Dichlorvos may diminish with the development of tadpoles to the metamorphic stage. These results indicate that the early and middle phases of R.megacephalus tadpoles may serve as a suitable tool for biomonitoring environmental genotoxicity using alkaline SCGE.