ENANTIOSELECTIVITY IN CHRONIC TOXICOLOGY AND ACCUMULATION OF THE SYNTHETIC PYRETHROID INSECTICIDE BIFENTHRIN IN DAPHNIA MAGNA

Introduced in the early 1980s, synthetic pyrethroids (SPs) are widely used in controlling a multitude of agricultural and domestic insect species, but they are highly toxic to fish and aquatic invertebrates. To date, however, studies have not adequately associated enantioselectivity in biological behavior with toxicity, especially regarding uptake and chronic toxicity. This study aimed to elucidate the relationship between chronic enantioselective toxicity and enantioselective accumulation of cis-bifenthrin (cis-BF) in Daphnia magna by C-14-labeled assay. The results demonstrated a clear enantioselectivity in chronic toxicity, for which 1R-cis-BF was evidently more toxic to D. magna than 1S-cis-BF. The lowest-observed-effective concentration in terms of survival and fecundity for 1R-cis-BF were almost 40- and 80-fold higher than that of 1S-cis-BF on day 7 and day 14, respectively. Further studies indicated that the accumulation of 1R-cis-BF was approximately 14- to 40-fold more than that of 1S-cis-BF in D. magna. This enantioselective accumulation also was consistent with the enantioselectivity in chronic toxicity of cis-BF. Thus, our results support the notion that enantioselectivity in chronic toxicity may be caused primarily by an enantiomer-specific biological process, such as uptake in aquatic organisms. This suggests that to properly assess the risk associated with use of SPs, the potential for enantioselectivity in their biotransformation and toxicity should be evaluated concurrently.