Ecotoxicological studies of pesticide formulations on soil sentinel's microflora (Nitrosomonas and Nitrobacter spp.) and mesofauna (Ephyriodrilus spp.)

The ecotoxicological effect of pesticide formulations at the concentration range of half of the normal field rate (0.5FR), normal field rate (FR), 2FR, 4FR and 8FR respectively on representative microflora and mesofauna soil sentinels was investigated. Inhibition effects over the 1, 2, 3 and 4 hr period of exposure in Winogradsky media were observed for microflora. Avoidance responses were observed for mesofauna in pesticide spiked soils after a 48 hr exposure period. Generally, there was a corresponding decrease in mesofauna population with increase in pesticide concentrations. The LC50 values after 4 hrs of exposure indicated that endosulfan (4.37 ?g/l) and paraquat (10.02 ?g/l) formulations had more toxic effect on Nitrosomonas sp. Cypermethrin and glyphosate showed more toxic effects on Nitrobacter sp. with LC50 values of 10.21 ?g/l and 10.50 ?g/l respectively. Ephyriodrilus spp. were observed to avoid all the pesticide treated soils at different concentrations as compared to pesticide free soils with less than 20 % observed in the soil spiked with 4FR and 8FR for endosulfan and cypermethrin and 8FR for glyphosate and paraquat. Pesticide formulation at the concentration above the recommended rate could adversely affect the soil organisms and affect their important ecological functions.