Selective removal of the non-herbicidal (S)-enantiomer of dichlorprop from agricultural soil by an in-situ enriched consortium

Abstract

Rac-dichlorprop [(R,S)-2-(2,4-dichlorophenoxy)propanoic acid], a commonly used chiral phenoxyalkanoic acid herbicide, is frequently detected in various environments, posing threats to human health and environmental safety. The (S)-enantiomer of dichlorprop shows a lower herbicidal activity but a higher toxicity as compared to the (R)-enantiomer of dichlorprop. It is of great importance to enantioselectively remove the non-herbicidal (S)-dichlorprop from the rac-dichlorprop in the application sites. In this study, the dissipation of (R)- and (S)-dichlorprop in an agricultural soil was investigated. We found that the dissipation rate of (S)-dichlorprop was higher than that of (R)-dichlorprop in an agricultural soil. Although the influences of different enantiomers of dichlorprop on soil bacterial community were not different, Sphingobium was significantly enriched in the (S)-dichlorprop-treated soil as compared to (R)-dichlorprop, indicating that Sphingobium species played important roles in the dissipation of (S)-dichlorprop. Furthermore, a bacterial consortium containing Sphingobium sp. strain SP-2 (enantioselectively transforming (S)-dichlorprop to 2,4-dichlorophenol) and Sphingopyxis sp. strain DP-21 (mineralizing 2,4-dichlorophenol), which synergistically mineralized the (S)-enantiomer of dichlorprop, was isolated from the agricultural soil. Bioaugmentation with the in-situ isolated consortium (strains SP-2 and DP-21) resulted in the enhanced removal of the non-herbicidal (S)-dichlorprop from the soil and in the adaptation of the inoculated degrading strains. This study offers new insights into the enhanced bioremediation of the non-herbicidal (S)-dichlorprop contaminated soils while simultaneously ensuring environmental safety and crop yield.