Enantioselective Behavior of the Fungicide Tebuconazole in Soil

Enantioselectivity (defined as the enantiomer fraction, EF) in sorption, dissipation and bioaccumulation was assessed for the model compound tebuconazole. Tebuconazole sorption in soils was affected by organic carbon (OC) and clay contents and cation exchange capacity, and appeared to be non-enantioselective for both tested soils, soil components and soil amendments. The bioaccumulation test consisted of two phases: the uptake phase and the elimination phase including the assessment of enantiospecific uptake and elimination rates. Unlike dissipation in soils, bioaccumulation of tebuconazole from these soils was enantioselective for both tested earthworm species (Eisenia andrei and Lumbricus terrestris). Peak-shaped bioaccumulation profiles were observed for all tested earthworm–soil variants with the maximum tissue concentrations reached within 7–10 days of exposure. Bioaccumulation factors ranged from 0.03 to 0.87. EF values of earthworm extracts varied from 0.28 to 0.52 with EF values <0.50 dominating. Enantioselectivity in bioaccumulation resulted from different excretion rates of the enantiomers. The interspecies similarity suggests that enantioselectivity in accumulation is a common phenomenon, and therefore, the risk assessment of tebuconazole should preferentially be evaluated at the enantiomer level. If this is not the case, a chiral correction factor of 2 (based on the enantiomer-specific BAF that differed by up to a factor of 2) may be recommended to account for enantioselectivity in tebuconazole bioaccumulation.