Effects of Engineered Nanoparticles on the Enantioselective Transformation of Metalaxyl Agent and Commercial Metalaxyl in Agricultural Soils

The adsorption coefficient of racemic metalaxyl onto an agriculture soil was small and nonenantioselective. Biotransformation was the predominant pathway for the elimination of R-metalaxyl, while abiotic and biotransformation made a comparable contribution to the degradation of S-metalaxyl. Metalaxyl acid was the main transformation intermediate. The enantiomer fraction of metalaxyl decreased with an increase in its initial spike concentration or the presence of the co-constituents in metalaxyl commercial products. Under simulated solar irradiation, the presence of TiO2 promoted the overall transformation kinetics through enhanced biotransformation and extra photoinduced chemical reactions. The promotion was enantioselective and thereafter changed the enantiomer fraction. The results obtained in this study showed that some achiral parameters, although they have no direct impact on enantioselective reactions with enantiomers, can significantly affect the enantioselective transformation of racemic metalaxyl. Thus, our results indicate that the contribution of chemical interactions on the enantioselective transformation of chiral pesticides may be underestimated.