The enantioselective environmental fate of mandipropamid in water-sediment microcosms: Distribution, degradation, degradation pathways and toxicity assessment

Mandipropamid (MDP) is a chiral fungicide that has been widely used to control oomycete pathogens. Currently, a comprehensive study of its environmental fate in aquatic ecosystems at the enantiomer level is still lacking. Here, the enantioselective environmental behaviors of MDP in four types of water-sediment microcosms were investigated. The concentrations of MDP enantiomers decreased over time in water due to sedimentation and degradation, while the concentrations in sediment increased to a peak and then slowly decreased because of adsorption and degradation. There were no enantioselective distribution behaviors in all kinds of microcosms. Moreover, R-MDP was preferentially degraded in lake water and Yangtze River water with half-lives of 5.92 d and 25.67 d, respectively. S-MDP was preferentially degraded in Yangtze River sediments, Yellow River sediments, and Yangtze River microcosm system, with half-lives ranging from 36.47 d to 77 d. Five degradation products of MDP in the sediment via hydrolysis and reduction were identified, and potential degradation pathways were proposed. Ecological Structure Activity Relationships (ECOSAR) prediction showed that the acute and chronic toxicities of all the products were higher than those of MDP except CGA 380778, which might pose a potential threat to aquatic ecosystems. This result offers new insights into the fate of chiral MDP in water-sediment ecosystems and will be conducive to the environmental and ecological risk assessment of MDP.