Plant and soil enantioselective biodegradation of racemic phenoxyalkanoic herbicides

The biodegradation of the chiral phenoxyalkanoic herbicides 2-(2,4-dichlorophenoxy)propionic aid (2,4-DP) and 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) was investigated using enantioselective HPLC and chiroptical detection. Racemic mixtures of 2,4-DP and MCPP were applied to three species of turf grass, four species of broadleaf weeds, and soil. Preferential degradation of the S-(-) enantiomer of each herbicide was observed in most species of broadleaf weeds and soil, while the degradation in all species of grass occurred without enantioselectivity. The biodegradation in all systems appeared to follow pseudo first-order kinetics with the fastest degradation occurring in broadleaf weeds, followed by the grasses. The slowest degradation was observed in soil. The results of this work illustrate the need to characterize both enantiomers of chiral agrochemicals in order to have an accurate understanding of their distribution and fate in the environment.