Eco-toxicity of Neonicotinoid: a case study on the impact of imidacloprid using Drawida willsi earthworm as bioindicator

Abstract

Many pesticides are used in the world and in India to boost the crop productivity, among which imidacloprid; a neonicotinoid is widely used now a day due to its low toxicity. These pesticides no doubt have protected the crops from the dangerous pest but in turn are becoming dangerous for soil health. Therefore an experiment was conducted to find out the eco-toxicity of imidacloprid. For this, earthworm (Drawida willsi, Michaelsen) and soil was collected from such agricultural field where there had no record of input of agrochemicals. Different concentrations of imidacloprid were prepared in dilution with acetone and sprayed on the soil surface. Five replicates for each concentration of the pesticides were prepared. Then ten numbers of juvenile, immature and adult earthworms were added separately into all the replicates of different concentrated samples. All the samples were kept in the laboratory under close vigil for 96 hours. Number of earthworm death with respect to doses and replicates were recorded and the 96h LC50 values for juvenile, immature and adult earthworm were calculated by Finney's Probit Method (Finney, 1971). It was found that the 96 h LC50 values with their 95% confidence limit of juvenile, immature and adult earthworm were 4.43, 7.96 and 12.45 mg a.i. imidacloprid/kg dry soil respectively. Although the recommended dose of imidacloprid was lower than the 96 h LC50 values of D. willsi for imidacloprid, but still it could affect the soil biota by altering its vital rates and metabolism due to bioaccumulation of the agrochemicals.