Assessing the Efficacy-Risk of the Widely Used Chiral Glufosinate: Switch from the Racemate to the Single Enantiomer?

The chirality of pesticides has emerged as an important issue in pesticide design and applications because enantiomers can differ greatly in their environmental fate and risk. Despite the increasing concern over the unintended effects of inactive or less effective enantiomers, massive amounts of chiral pesticides are applied as racemic mixtures. As a potential substitute for glyphosate, the market of glufosinate is expected to grow rapidly. However, very little information is available on its enantioselective efficacy-risk assessment, especially at the environmentally relevant concentration. The overall aim of this study is to determine if the switch from glufosinate racemic mixture to L-lufosinate was favored regarding environmental health. Thus, we examined (i) the herbicidal activity of Rac- and L-glufosinate to the weed, Echinochloa crus-galli, and (ii) adverse effects on nontarget zebrafish (Danio rerio). Significant higher herbicidal activities were achieved by L-glufosinate at both 1 and 5 mg/L. Embryotoxicity and teratogenicity are significantly different: Rac-glufosinate induced a significantly higher lethality (LC50 = 17.29 mg/L) and malformations. The oxidative stress markers, including superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA), were preferably induced by Rac-glufosinate at mRNA and enzymatic activity levels. In summary, we suggest that L-glufosinate should be applied preferably over Rac-glufosinate.