Several studies were conducted on the acute toxicity of agrochemicals. However, very little information is available on the toxic effect of dimethoate which is one of the most popular organophosphorous insecticide widely used in India. Therefore the present experiment was conducted to find out the eco-toxicity of dimethoate on soil health. 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 dimethoate were prepared in dilution with acetone and sprayed on the soil surface. Five replicates for each concentration of the pesticides were prepared and ten numbers of juvenile, immature and adult earthworms were added separately into all the replicates of different concentration of the pesticides. All the samples were kept in the laboratory for 96 hours and number of earthworm death with respect to doses and replicates were recorded. The 96h LC50 values for juvenile, immature and adult earthworm were calculated by the Finney’s Probit Method (Finney, 1971). The juvenile, immature and adult worms did not die in soil containing up to 0.5, 1 and 1 mg/kg of dimethoate respectively. When earthworms were exposed to concentration as high as 13 mg/kg of dimethoate, 100% of juveniles, 94% of immature and 81% of adults died. The 96 h LC50 values with their 95% confidence limits for juvenile, immature and adult worms were 5.5 (4.4-6.6), 6.7 (5.2-8.2) and 9.0 (7.3-10.7) mg/kg respectively. Although the recommended dose of dimethoate (0.4 mg a.i./ kg dry soil) was lower than the 96 h LC50 values of D. willsi, but still due to bioaccumulation, it may hamper the soil biota and also the soil health by triggering the domino effect. - Download as a PDF or view online for free
