Behavior of two pesticides in a soil subjected to severe drought. Effects on soil biology

Abstract

The behavior of oxyfluorfen herbicide and chlorpyrifos insecticide applied at different concentrations in a soil submitted to a severe and continued 120-day drought and their influence on soil enzymatic activities (dehydrogenase, urease, β-glucosidase and phosphatase activities) and soil biodiversity (analyzed by phospholipid fatty acids) were studied under controlled laboratory conditions. Two levels of irrigation were employed: (1) watered soils, where the soils were maintained at 60% of their water holding capacity, and (2) non-watered soils, without irrigation. In watered soils, the oxyfluorfen herbicide and the chlorpyrifos insecticide both caused a toxic effect on both soil enzymatic activity and soil diversity. This decrease was greatest when the highest dose of herbicide was applied to the soil. The application of pesticides to the non-watered soil caused a greater inhibition of soil enzymatic activities and microbial population possibly due to the combined effect of both pesticide toxicity and soil drought conditions. For this reason, the degradation of pesticides in non-watered soil was lower than in the case of watered soils, which probably made the persistence in soil of both pesticides longer. This suggests that, in drought conditions, soil pollution by these pesticides increases over time.