The integration of in vivo and in vitro metabolism assays to investigate the stereoselective behaviors of benalaxyl in rainbow trout (Oncorhynchus mykiss).

The bioconcentration and elimination of racemic benalaxyl (BX) in trout liver microsomes and in juvenile rainbow trout (Oncorhynchus mykiss) were investigated to determine whether the fish can bioconcentrate and degrade this fungicide enantioselectively. Both enantiomers of BX were extracted with organic solvents and evaluated using high-performance liquid chromatography. In the microsomes, BX degradation followed first-order kinetics, and the S-(+) enantiomer of BX was eliminated twice as rapidly as the R-(-) enantiomer, resulting in residues enriched for R-(-)-BX. In vivo experiment, chiral analysis showed an obvious selective bioconcentration of BX based on statistically altered enantiomer fractions (EFs) in the fish compared with the values in the water. The R-(-)-BX was initially preferentially bioconcentrated by rainbow trout and then dissipated more slowly than its antipode. The mean half-lives for individual enantiomers were calculated as 31.6 h for R-(-)-BX and 20.3 h for the S-(+)-form. The results of the study showed that the degradation of BX enantiomers was stereoselective in rainbow trout.