ECOTOXICOLOGICAL RISK ASSESSMENT OF THREE INSECTICIDES USING AN EPIGEIC EARTHWORM

摘要

Bioassays were made in the laboratory with age synchronized specimens of the epigeic earthworm Eisenia fetida using OECD guidelines to assess ecological implications of application of three insecticides carbaryl, chlorpyrifos and endosulfan in the crop fields. The specimens were exposed to control (T1) and three sub-lethal doses representing 12.5 % (T2), 25 % (T3) and 50 % (T4) of the LC_(50) value of the respective insecticide to E. fetida. Biomass of earthworms increased from the initial value under all treatments of chlorpyrifos and T2 of carbaryl, though significantly lower than the control, but reduced from the initial value under T3 and T4 treatments of carbaryl and all treatments of endosulfan. Cocoon production, hatching success and juvenile production of the earthworms significantly reduced under T2 dose of endosulfan and T2-T4 doses of carbaryl and chlorpyrifos as compared to control. The earthworms failed to produce cocoon even at 0.5 μg.kg~(-1) soil of endosulfan (T3), which was only 2.0 % of the recommended agricultural dose (RAD) of this insecticide. Activitiy of the enzyme alkaline phosphatase was elevated and that of acetylcholinesterase inhibited by the sub-lethal doses of all insecticides, except endosulfan, which produced no effect on acetylcholinesterase activity. It was concluded that application of carbaryl and endosulfan in the agricultural fields at the recommended agricultural dose (RAD) was ecologically dangerous for soil agro-ecosystems and unsafe for soil organisms like earthworms.