Effect of fertilization on the degradation and enantioselectivity of fipronil in soil

Background

Fertilizers and pesticides are commonly used simultaneously in agriculture. However, the effects of common fertilizers on the dissipation, enantioselectivity, and metabolites of the chiral insecticide fipronil in soil are yet to be reported.

Result

An enantioselective method for detecting fipronil enantiomers and their metabolites in different soil matrices was developed using ultra‐performance liquid chromatography‐tandem mass spectrometry (UPLC‐MS/MS). The results showed that organic and compound fertilizers significantly decreased the degradation of S‐ and R‐fipronil, whereas phosphatic and microbial fertilizers slightly reduced fipronil dissipation. The half‐life values for S‐ and R‐fipronil were 43.3 and 28.9 d, 99.0 and 63.0 d, 69.3 and 43.3 d, 46.2 and 30.1 d, and 43.3 and 31.5 d, respectively, in the control and the four fertilizer treatments, respectively. The enantioselectivity of fipronil enantiomers occurred and R‐fipronil exhibited preferential degradation with an enantiomeric fraction (EF) of 0.4900‐0.6238 in all treatments; But the four tested fertilizers decreased enantioselectivity with EF values changed from 0.4970‐0.6238 in the control to 0.4900‐0.6171 in fertilizer treatments. Two metabolites, fipronil sulfone and sulfide, were produced, and their amounts increased with culture time in all treatments. Fertilization reduced the content of fipronil sulfide and sulfone but hardly reduced the total amount of fipronil and its metabolites.

Conclusion

Fertilizers affect the environmental behavior of fipronil in the soil. Fertilization alters the soil bacterial community, which may be an important factor. This influence is relatively complicated and should be comprehensively considered in the environmental risk assessment of pesticides.

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