Acute and chronic toxicity of four commonly used agricultural pesticides on the Asian common toad, Bufo melanostictus Schneider uri icon

abstract

  • Laboratory and field studies provide evidence that pesticides may play a role in population declines, range reductions and species extinctions of amphibians. The present study examined the acute and chronic toxicity of four commonly used agricultural pesticides, chlorpyrifos, dimethoate, glyphosate and propanil on the survival, growth and development of malformations in the Asian common toad, Bufo melanostictus, under laboratory conditions. The 48 hour LC50 values of the chemicals were within the Pesticide Area Network (PAN) specified limits, except for propanil, which was less than the PAN specified value. Acute exposure to high concentrations of propanil may have a high direct toxic effect on the Asian common toad. The survival of the tadpoles with chronic exposure to ecologically relevant doses of the four pesticides was significantly reduced (survival in chlorpyrifos 39%, dimethoate 41%, glyphosate 36% and propanil 40% in the highest concentration) than in the control group (93%). Exposed tadpoles took more time to metamorphose but were larger in size than the control tadpoles. They also developed malformations at high frequencies (chlorpyrifos 30%, dimethoate 25%, glyphosate 35% and propanil 15% in the highest concentration). Malformations were mainly axial, including kyphosis (hunched back) and scoliosis (curvature) while skin ulcers and oedemas were also observed. Severe limb malformations such as extra or missing limbs as reported for other species of amphibians exposed to pesticides were not observed in the Asian common toad. None of the tadpoles in the control group had any malformations. Glyphosate exposed metamorphs recorded the highest mortality and malformations at high concentrations (1.0 ppm). However, a profound toxic effect was observed in chlorpyrifos exposed group even at low concentrations (0.1 ppm). The study shows that exposure to commonly used agrochemicals poses serious risk to amphibians in Sri Lanka and highlights the importance of investigating the level of agricultural pesticides in freshwater ecosystems and their effect on non-target organisms.

publication date

  • 2011
  • 2011