Ecological safety evaluation of chlorpyrifos on agricultural soil: Effects on soil microbes

The health of farmland soils is directly related to the proper application of pesticides. Chlorpyrifos is a widely used broad-spectrum organophosphorus insecticide, and its ecological security risk to farmland soils requires evaluation. A trial was conducted to study the effects of chlorpyrifos on soil microbes in a wheat–maize rotation field. A 45 % chlorpyrifos emulsion was sprayed at the recommended and dual doses, after which the chlorpyrifos residue, soil microbial content, bacterial community structure, functional microbial abundance, and enzyme activities were measured. The results showed that chlorpyrifos had a half-life of 8.94–9.88 and 2.17–2.18 days in soil for wheat and maize, respectively. Although the final chlorpyrifos residues in the crop grains were lower than the maximum residue limit recommended by the Chinese government, soil fungal abundance was significantly inhibited, and the structure and function of soil bacterial communities were disturbed. Furthermore, the quantities of nitrification-related genera (Acidobacteria GP4 and Acidobacteria GP6) and functional genes (AOB-amoA and AOA-amoA) decreased, whereas those of denitrification-related functional genes (nirS and nirK) and urease activity increased. Gemmatimonas and alkaline phosphatase involved in phosphorus cycling were activated, and the abundance of cbbLR and cbbLG genes involved in carbon fixation decreased. The integrated biomarker response index showed that nirK and β-glucosidase were the most sensitive indicators in wheat and maize stages. The present study provides toxicological data and theoretical guidance for the ecological safety evaluation and rational application of chlorpyrifos in soil.