Stereoselective metabolism and toxicity of the herbicide fluroxypyr methylheptyl ester in rat hepatocytes.

We investigated the stereoselective degradation kinetics and toxicity of fluroxypyr methylheptyl ester (FPMH) in rat hepatocytes using a chiral high-performance liquid chromatographic method. The T1/2 of (−)-FPMH was about two times longer than that of (+)-FPMH after the rat hepatocytes were incubated with 10, 20, and 50 μM of rac-FPMH. There was no chiral conversion or transformation during their incubation with the hepatocytes. Toxicity differences were observed among the two enantiomers of FPMH and fluroxypyr (FP) in their EC50 values in rat hepatocytes. Of all the tested compounds, FP was most toxic to the rat hepatocytes. The (−)-FPMH enantiomer showed higher toxicity than the (+)-FPMH, whereas the racemic mixture displayed intermediate toxicity. The data presented here are important for a more thorough understanding of this pesticide and should be useful for its full environmental assessment.