Non-target effects of three formulated pesticides on microbially-mediated processes in a clay-loam soil

An experiment was performed to study non-target effects of difenoconazole (fungicide), deltamethrin (insecticide) and ethofumesate (herbicide) on microbial parameters in a clay-loam soil. Pesticides were applied as commercial formulations to soil samples at different concentrations (5, 50 and 500mgkg−1 DW soil) and then incubated under laboratory conditions for 3months. Throughout the incubation period, microbial parameters were determined at days 7, 30, 60 and 90. At 5mgkg−1 DW soil, none of the three pesticides caused significant changes in soil microbial parameters. In contrast, at 500mgkg−1 DW soil, pesticide application decreased overall soil microbial activity, negatively affecting the activity of soil enzymes. Similarly, at 500mgkg−1 DW soil, difenoconazole and ethofumesate, but not deltamethrin, caused a pesticide-induced stress on soil microbial communities, as reflected by the respiratory quotient. Besides, deltamethrin and ethofumesate at 50 and 500mgkg−1 DW soil resulted in lower values of denitrification potential. It was concluded that, although pesticide concentration had a somewhat inconsistent and erratic effect on soil microbial parameters, pesticide application at 500mgkg−1 DW soil did have an impact on many of the microbial parameters studied here. ► Degradation rate decreased with increasing pesticide concentration. ► The lowest dose of pesticides did not cause changes in soil microbial communities. ► Higher pesticide concentration did not consistently increase impact on microorganisms. ► Pesticides increased soil NO3−, suggesting beneficial effect on the bacteria involved.