Stereoselective degradation of fungicide benalaxyl in soils and cucumber plants.

The enantioselective degradation of benalaxyl has been investigated to elucidate its behavior in several agricultural soils and plants (cucumber). Racemic benalaxyl was fortified into five types of agricultural soils and sprayed leaves of cucumber plants, respectively. The degradation kinetics and the enantiomer fraction (EF) were determined by normal-phase high-performance liquid chromatography (HPLC) with diode array detection (DAD) on the chiral column filled cellulose-tri-(3,5-dimethylphenylcarbamate)-based chiral stationary phase (CDMPC-CSP). The process of the degradation of benalaxyl enantiomers followed pseudo-first-order kinetics in cucumber plant. However, the dissipation phases of benalaxyl enantiomers in soils were biphasic ("slow-fast-slow" process). It has been shown that the degradation of benalaxyl was stereoselective. The results indicated that the (+)-S-benalaxyl showed a faster degradation in plants, while the (-)-R-benalaxyl showed a faster degradation in Soils 3, 4, and 5. No stereoselective degradation was observed in other soils.