Enantioselective degradation and chiral stability of malathion in environmental samples

The dissipation behaviors of the two enantiomers of the organophosphorus pesticide malathion (MA) in environment samples were elucidated using a normal-phase high-performance liquid chromatography with a cellulose-tris(3,5-dimethylphenylcarbamate) (CDMPC) chiral column. A validated chiral residue analysis method in soil and water was established; the average recoveries for the two enantiomers were 88-102% in soil and 81-99% in water. Racemic and enantiopure R-(+)- and S-(-)-MA were incubated in five soil and water systems. The results of the degradation of racemate in all of the environment samples showed the inactive S-(-)-enantiomer degraded more rapidly than the active R-(+)-enantiomer, resulting in a relative enrichment of the R-form. Moreover, when the enantiopure S-(-)- and R-(+)-MA were incubated in three well-chosen soil and water samples, respectively, inversion from one enantiomer to another was found, indicating that using the optically pure enantiomer will not help to increase the bioactivity and reduce the environmental pollution.