Chronic toxicity of cypermethrin, a pyrethroid insecticide to epigeic earthworm Eisenia fetida

Effects of sub-lethal doses of cypermethrin on biomass, reproduction and alkaline phosphatase activity of the epigeic earthworm, Eisenia fetida were investigated in natural grassland soil (pH-6.72±0.02, organic carbon-1.28±0.37) under laboratory conditions. E. fetida exposed to 0.006 to 0.025 mg/kg soil of cypermethrin, corresponding to 12.5 (T2) to 50 % (T4) of LC50 values of cypermethrin did not exhibit any significant reduction in biomass from control. Production of cocoons and juveniles remained significantly unaltered at T2 and T3 doses of the insecticide but was inhibited with exposure to the highest dose (T4) of cypermethrin. Alkaline phosphatase activity was found to remain significantly unaltered at T2 but increased both in T3 and T4 in comparison to control. Thus, though the LC50 value of cypermethrin was much higher than it’s recommended agricultural dose indicating it’s less hazardous nature, it can be concluded from the present study that sub-lethal doses of cypermethrin significantly affected reproduction and alkaline phosphatase activity of the test specimen and their widespread application in agro-ecosystems must be carefully monitored. The present study also indicated the potential use of alkaline phosphatase as a biomarker in assessment of insecticide pollution.