Enantioselective bioaccumulation and metabolism of lactofen in zebrafish Danio rerio and combined effects with its metabolites.

Pesticide residue in agricultural land might led to contamination of fresh waters, creating potential risks to organisms. The environmental behavior of herbicide lactofen may be enantioselective and the metabolites may have high toxic effects in individual or in combination. In this work, the enantioselective bioaccumulation, metabolism and toxic effects of lactofen and three metabolites (desethyl lactofen, acifluorfene, and amino acifluorfene) in zebrafish were investigated. The antioxidase activity (superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase), lipid peroxidation content were measured after exposure, and genetic toxicity was evaluated by a micronucleus test. The integrated biomarker response (IBR) method was used to determine the effects of the lactofen and its metabolites as well as their combinations. The metabolites were found to have higher toxic effects, and enantioselective toxic effects of lactofen and desethyl lactofen were observed, with the S-enantiomer more toxic. Based on IBR values, synergistic effects existed in combination of lactofen and desethyl lactofen, while antagonistic effects of lactofen with acifluorfene or amino acifluorfene were observed. Zebrafish were exposed to 0.5 mg L-1 lactofen and the bioaccumulation were measured during a 15 d period followed by a 7 d elimination. The half-lives of the metabolites varied between 0.66 and 5.21 d, with bioconcentration factors (BCFs) in the range of 39-120. The metabolic pathways of R- and S-lactofen were found to be significantly different. The results supported our hypothesis. Therefore, the assessment of enantiomers and metabolites in individual or in combination should be taken into consideration in evaluating chiral pesticide risks.