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Effect of Potassium Dihydrogen Phosphate and Bovine Manure Compost on the Degradation of Chlorothalonil in Soil

The effects of potassium dihydrogen phosphate (KH2PO4) and bovine manure compost (BMC) on the degradation and metabolism of chlorothalonil were examined in a sandy loam soil under laboratory conditions. In non-sterilized, non-amended soil, chlorothalonil degradation half-life was 8.8 days. However, it was up to 19.0 days in sterilized non-amended soil, suggesting that the degradation rate was about 2-fold slower than that in non-sterilized non-amended soil. Biological mechanisms accounted for 54.7% of chlorothalonil degradation in non-sterilized soil, indicating that the indigenous microorganisms in soil play an important role in the degradation process. In non-sterilized soil, the more acutely toxic metabolite, 4-OH-chlorothalonil (HTI), of chlorothalonil started forming after the second day of incubation. The concentration of HTI reached its maximum level (2.9 μ g g− 1) at 10 days after treatment, and no further degradation of HTI was observed in the following span of 20 days (10–30 days of incubation). However, the degradation rate of chlorothalonil was decreased substantially by the addition of KH2PO4 with a half-life of 17.5 days. No formation of HTI was observed before 10 days of incubation and no significant difference of the metabolite concentration at the end of experiment was observed between KH2PO4-amended and non-amended treatments, which denoted that the addition of KH2PO4 did not reduce the formation of HTI in the longer incubation course. In BMC-amended soil, the degradation rate was about 1.8 times faster than in non-amended soil. At 30 days of incubation, both chlorothalonil and HTI were degraded to a lower level in BMC-amended soil than in non-amended soil. The application of farm litter is a common fertilizing practice in vegetable fields in China, and thus this practice could not only improve soil fertility but also promote the removal of chlorothalonil and its metabolite HTI to further increase safety in crop rotations.