The influence of chlorothalonil on the activity of soil microorganisms and enzymes.

As one of the most widely used pesticides in agriculture, chlorothalonil can pose threat to soil ecosystems. Therefore, the impact of this substance on the development of microbiological and biochemical properties of the soil as well as on the growth of spring wheat was evaluated. The study was conducted with two soils (loamy sand with pH 5.6 and sandy loam with pH 7.00), to which fungicide was used in the following doses: 0.00, 0.166 (recommended dose), 1.660, and 16.60 mg kg dry matter of soil (DM of soil). In addition, we determined the effectiveness of fertilizing substances (Lignohumat Super and Bioilsa N 12.5) in the restoration of soil homeostasis and chlorothalonil degradation in the soil. Chlorothalonil caused modifications in the count and biological diversity of soil microorganisms. It stimulated the growth of heterotrophic bacteria and actinobacteria, and inhibited the growth of fungi. This pesticide was a potent inhibitor of dehydrogenase, catalase and acid phosphatase activities. It showed variable effects on urease and alkaline phosphatase. The fungicide also a reduction the yield of dry matter of the aboveground parts of spring wheat. It should, however, be noted that these changes in the soil environment occurred after the introduction of higher doses of chlorothalonil. The fertilizing substances used contributed to enhanced microbial and biochemical activities of soils, while they did not significantly affect plant yields. The Bioilsa N 12.5 preparation was effective in chlorothalonil degradation, while Lignohumat Super reduced the degradation rate of the tested fungicide. Based on the conducted experiment, an ecological risk assessment of chlorothalonil was made by estimating the changes occurring in the soil environment evaluated through the microbiological and biochemical analyses of the soil.