Comparing toxicity and biodegradation of racemic glufosinate and L-glufosinate in green algae Scenedesmus obliquus

Abstract

Glufosinate-ammonium, a widely used chiral herbicide, has become the focus of attention because of its toxicity toward non-target organisms and its degradation behavior in the environment. With the introduction of L-glufosinate-ammonium products, the toxicity and environmental behavior of rac-glufosinate-ammonium and L-glufosinate-ammonium have become the subject of increasing interest. The overall goal of this study was to investigate the differences in toxicity and biodegradation of rac-glufosinate-ammonium and L-glufosinate-ammonium in an aquatic organism, Scenedesmus obliquus. The toxicity of rac-glufosinate-ammonium and L-glufosinate-ammonium to S. obliquus was compared by measuring EC₅₀, malondialdehyde (MDA) content, protein content and antioxidant enzyme activity. The 96-h EC₅₀ values of rac-glufosinate-ammonium and L-glufosinate-ammonium were 57.22 μg/mL and 25.55 μg/mL, respectively, which indicated that L-glufosinate-ammonium was more toxic to S. obliquus than rac-glufosinate-ammonium. Based on the MDA content, protein content, and antioxidant enzyme (SOD and CAT) activity, we found that L-glufosinate-ammonium could cause more serious oxidative damage than rac-glufosinate-ammonium. The residual amount of glufosinate-ammonium and its metabolites in the culture medium and S. obliquus were determined by HPLC-HRMS. Comparison of glufosinate-ammonium concentrations in algae-free and algae-containing media, showed that glufosinate-ammonium degradation in the S. obliquus system was significantly increased, and the degradation rate of L-glufosinate-ammonium was faster than that of D-glufosinate-ammonium. No enantiomerization was observed for pure L-glufosinate-ammonium treatment. N-acetyl-glufosinate was identified as the main metabolite of glufosinate-ammonium.

Keywords: Algae; Degradation; Glufosinate-ammonium; Metabolites; Oxidative damage.