Delineating the ecotoxic effects of Chlorpyrifos and Dimethoate on Eisenia fetida

Acute (14 DOE) and chronic toxicity (56 DOE) experiments were conducted to compare the lethal and sub-lethal effects of chlorpyrifos and dimethoate on earthworms ( Eisenia fetida ). Earthworms were cultured in test soil (agricultural soils + cow dung) spiked with various concentrations of these two organophosphorus pesticides of different half-life. The determined effects were avoidance response, biomass change, growth inhibition, mortality, biomass gain per unit feed, cocoon and hatchling production. The resulted order of effects for acute and chronic toxicity exposure periods for E. fetida was dimethoate > chlorpyrifos. The reported median lethal concentration (LC 50 ) in present study was 17.45 and 228.06 mg kg -1 dry test soil for dimethoate and chlorpyrifos, respectively. Growth inhibition was more critically influenced in dimethoate as compare to chlorpyrifos. Rather than lesser growth inhibition in chlorpyrifos, cocoon and hatchling production is influenced greatly at higher concentrations. The cocoon and hatchling production is significantly affected at lower concentrations of dimethoate. All the tested parameters were found to be dose dependent. The present results showed that even a small concentration of dimethoate is potentially dangerous to earthworms than higher concentrations of chlorpyrifos. In comparison the chlorpyrifos was found safer than dimethoate at sub-lethal concentrations for the development and reproduction of E. fetida . Our study provides a clear insight of different antagonistic effects of two organophosphate pesticides with different half-life.