Abstract
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.
Highlights
Among the multitude of factors which have been implicated as contributing to global amphibian species decline, agricultural practices and agrochemicals have gained much scientific attention (Beebee and Griffiths 2005; Mann et al 2009; Bruhl et al 2011; Wagner et al 2013; Lanctot et al 2014)
The control D. melanostictus tadpoles and the tadpoles exposed to the pesticide at 0.3 mg/L carbosulfan displayed active swimming patterns in the water column whereas the tadpoles exposed to ≥ 0.6 mg/L carbosulfan displayed uncontrolled rapid movements initially and later loss of coordination in swimming, rotating swiftly in a spiral orbit and erratic swimming patterns
Carbosulfan is a procarbamate pesticide and its toxicity is mediated by the inhibition of the enzyme acetylcholinesterase, the key enzyme in cholinergic transmission in the nervous system (Fukota 1990)
Summary
Among the multitude of factors which have been implicated as contributing to global amphibian species decline, agricultural practices and agrochemicals have gained much scientific attention (Beebee and Griffiths 2005; Mann et al 2009; Bruhl et al 2011; Wagner et al 2013; Lanctot et al 2014). Even though limited toxicological data relevant to carbosulfan are available for several fish species (Yi et al 2006; Chandrasekera and Pathiratne 2007; Capkin et al 2010; Nwani et al 2010; Altinok et al 2012), to our knowledge, no scientific studies were found in the global literature on toxicity of carbosulfan or a carbosulfan-based pesticide to amphibians. Duttaphrynus melanostictus is a widely distributed and abundant bufonid in tropical Asia. It is found in disturbed lowland habitats especially in human dominated agricultural and urban areas (IUCN 2004). The present study evaluated potential short term toxicity of a widely used carbosulfan-based pesticide
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