Acute Toxicity and LC₅₀ Values of Chlorpyrifos on Eudrilus eugeniae

Present study evaluates acute toxic effects of chlorpyrifos on earthworm ( Eudrilus eugeniae ) under laboratory conditions. Acute toxicity bioassays was performed following OECD ( 1984) guideline 207 using artificial soil. The LC₅₀ values were determined after 7 and 14 days of exposure. For this purpose the earthworms were exposed to graded concentrations of chlorpyrifos ranging from 0.01 to 1000 ppm. Mortality of earthworms exhibited dose- and time-dependent response, with increasing lethality, observed at higher concentrations and prolonged exposure. The LC₅₀ values were calculated as 117.32 ppm for 7 days and 114.20 ppm for 14 days. In addition to the mortality, behavioural abnormalities such as sluggish movement, coiling, excessive mucus secretion, and surface avoidance were also observed, particularly at higher concentrations. The results indicated that chlorpyrifos exerts moderate acute toxicity to E. eugeniae, highlighting ecological risks to soil fauna associated with indiscriminate use of pesticide.