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

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 LC 50 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.

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

“…Tail bending due to the curvature in the spinal cord (scoliosis) especially could affect swimming patterns in the tadpoles (Alvarez et al 1995). Similar malformations have been reported earlier in D. melanostiscus tadpoles after exposure to some organophosphate insecticides and herbicides (Jayawardena et al 2011;Wijesinghe et al 2011). These deformed and abnormally behaved tadpoles could be highly vulnerable in the wild to increased predation due to reduced ability to evade predators (Relyea 2005;Yadav et al 2013).…”

“…It is likely that pesticide exposed tadpoles are at a disadvantage under natural conditions and may face threats and indirect mortality as a consequence of delayed development. Delayed development and metamorphosis due to exposure to other pesticides have also been reported earlier for D. melanostiscus (Jayawardena et al 2011;Wijesinghe et al 2011) and other amphibian species (Svartz et al 2012;Saka et al 2013). Among other factors, increased energetic costs involved in abnormal behaviour could have led to prolong developmental period of these tadpoles.…”

“…Sri Lanka is considered as a global amphibian hotspot; 103 species of anurans and caecilians have been described so far in Sri Lanka, which accounts for 2% of the world's known anuran species (Pethiyagoda and ManamendaArachchi 1998). Although no data are yet available on population trends of Sri Lankan amphibians, concerns have been raised that amphibian larval stages are particularly at a risk and may be vulnerable to adverse effects of the agricultural pesticides and may undergo range reductions or population declines in the future (Jayawardena et al 2011). Asian common toad, Duttaphrynus melanostictus is a widely distributed and abundant bufonid in tropical Asia.…”

Acute Toxicity of an Organophosphate Insecticide Chlorpyrifos to an Anuran, Rana cyanophlyctis

“…About 96 h LC 50 for chlorpyrifos ranged from 1µg/L for B. americanus to 3 mg/L for R. pipiens [28]. Totally, 48 h LC 50 value were studied for chlorpyrifos in five d posthatch tadpoles of B. melanostictus and reported it as 1.47 ppm [29]. "Chlorpyrifos caused significantly high and dose-dependant mortality and the weekly LC 50 (7 d-21 d) values ranged from 3003 µg/L to 462 µg/L" [30].…”

Ecotoxicidade comparativa dos herbicidas da cana-de-acúcar para larvas de anfíbios

“…Para tal, A maioria dos trabalhos publicados sobre os efeitos letais do glifosato em exposição prolongada, manipulou formulações comerciais, sem analisar separadamente os efeitos do ingrediente ativo dos efeitos do surfactante POEA (JAYAWARDENA et al, 2010;JAYAWARDENA et al, 2011;) presentes nas formulações, que é por si só sabidamente mais tóxico (PERKINS et al, 2000;RELYEA, 2012 et al, 2012). Em outro estudo com embriões de Cyprinus carpio expostos por 30 dias, observou-se mortalidade de apenas 4% e 8,7% nas concentrações de 0,9 mg/L e 4 mg/L, respectivamente, sendo que o efeito letal significativo só foi observado na maior concentração (32mg/L) (STEPANOVÁ et al, 2012).…”