Impact of Cypermethrin and Chlorpyrifos on Microbial Activity and Biomass in a Nigerian Soil
O.O. Adebisi, D.O. Adetitun, and A.B. Olayemi (pp. 97-111)
Abstract
The impacts of a synthetic pyrethroid—cypermethrin—and organophosphate insecticide—chlorpyrifos—on soil bacterial, fungal, and pseudomonad populations; basal and substrateinduced respiratory activities; and biomass-C in paddy rice and uncultivated soils were evaluated over a 30-day exposure period. The pesticides were applied at two rates: normal field concentration (NFC) and five times field concentration (X5FC). The growth on and mineralization of different concentrations of the pesticides by three Pseudomonas species were also assessed for 14 days. The effect on paddy rice root and shoot growth was evaluated. Results indicated that the dynamics of temporal changes in soil microbial populations were dependent on pesticide concentration and type. The suppressive effect on bacterial population lasted 14 days and over 30 days for fungal population in the X5FC pesticide-contaminated paddy rice soils. The suppressive effect was less than 7 days for both bacterial and fungal populations in the uncultivated soils contaminated at X5FC, though pseudomonad population was promoted almost immediately in the same soils. The mean shoot/root ratio of rice seedlings in the control soil (2.38 ± 0.16) was higher but not significantly different from those in the X5FC cypermethrin-treated (2.13 ± 0.10) and chlorpyrifostreated soils (1.92 ± 0.15). Pesticide concentration aside from affecting microbial numbers in soil can also contribute to water pollution as a nonpoint source pollutant.