Low-dose cadmium affects the enantioselective bioaccumulation and dissipation of chiral penflufen in zebrafish (Danio rerio)

Pesticides are currently extensively used in agriculture, forestry, animal husbandry, and environmental hygiene, and their residues have become a global environmental problem, which can easily form combined pollution with heavy metals. The present study examined the effects of chronic (28 days) aqueous exposure of chiral penflufen (rac-penflufen, R-(-)-penflufen and S-(+)-penflufen), a widely used fungicide, with/without cadmium (Cd), a highly toxic heavy metal in zebrafish (Danio rerio). After rac-penflufen individual or combined exposure with Cd, the bioaccumulation and residual levels of S-(+)-penflufen were significantly higher than R-(-)-penflufen, and the effects of Cd were insignificantly. But for penflufen enantiomer, the effects of Cd were more serious for R-(-)-penflufen, which could increase the bioaccumulation (up to1.73 times), inhibit the dissipation (up to 32.3%) and enhance the residue (up to 5.35 times) of R-(-)-penflufen in zebrafish, decreasing the enantioselectivity. However, significant increase of S-(+)-penflufen concentrations was only found in viscera under co-exposure of Cd. The tissue distribution of penflufen enantiomers were not affected by the presence of Cd, and no interconversion of the two enantiomers occurred regardless of the presence of Cd. These findings indicated that co-contamination with Cd could increase the persistence of R-(-)-penflufen in zebrafish, thus increasing the environmental risks. The significant differences of Cd effects on chiral pesticide enantiomer and racemate indicated that the combined pollution of heavy metal and chiral pesticide might have enantiomer-specific, which should raise concern, and the enantioselective mechanism deserve further study.