Toxicity Effects of Chlorpyrifos on Growth and Survival of Polypedates cruciger (Blyth) in Acute and Chronic Exposures.

Abstract

Endemic amphibian populations are rapidly depleting due to anthropological activities such as deforestation and contamination of habitats with agrochemicals. Polypedates cruciger is an endemic tree frog species and its larval development takes place in stagnant water bodies. Chlorpyrifos, an organophosphate pesticide, is widely used in agriculture. The sensitive'mabitats of P.cruciger may contaminate with Chlorpyrifos resulting in effects at lethal and sub lethal levels. Therefore, the aim of the present study was to find out the potential effects of Chlorpyrifos on the growth and the survival of larval stages of P. cruciger in acute and chronic exposures. Egg masses of P. cruciger were collected from the university premises at Matara, and newly emerged tadpoles were reared in glass tanks. Post-hatched-tadpoles (3 days old) P.cruciger were exposed to different concentrations of Chlorpyrifos (0.5mg/L, 1.0mg/L, 1.5mg/L, 2.0mg/L and 2.5mg/L) and mortality was recorded after 48hrs. Based on the LCso values derived, 0.05mg/L, 0.25mg/L and 0.Smg/L sub lethal concentrations were used as the treatments. Thirty tadpoles were exposed to each concentration ( n=l0, three replicates). The control experiment was carried out using de-chlorinated tap water at the same time (n=lO, three replicates). Snout-vent length (SVL), morphological changes of tadpoles and mortality were recorded on 10, 21, 31, 41, 56 & 61 post-hatched days. The Pro bit analysis and AN OVA test using SPSS were performed to analyse data. 48 hrs LCsovalue for Chlorpyrifos was 0.661 mg/L with 95% confidence intervals of 0.506-0.792 mg/L. Mean SVL values of 10 and 31 days post-hatched tadpoles in 0.5mg/L concentration of Chlorpyrifos were significantly lower (p<0.001) than the control and the other two test concentrations. Though it was not statistically significant, SVL of 61 day old tadpoles in three test concentrations were lower than that of the control. In addition, the survival percentage was also lower in 61-days post-hatched tadpoles in 0.5mg/L solution than in the control (83% in 0.5mg/L and 97% in control). However, any morphological changes of tadpoles were not observed among the control and test solutions. In conclusion, there is a significant toxicity effect of 0.5mg/L Chlopyrifos on growth in 10 and 31 days old tadpoles and the survival of tadpoles of P.cruciger.