Aquatic Ecological Risk Evaluation of Chiral Triazole Fungicide Prothioconazole and Its Metabolite Prothioconazole-Desthio on Lemna minor

The potential risk posed by the chiral triazole fungicide prothioconazole and its metabolite, prothioconazole-desthio to aquatic ecosystems has attracted attention. At present, the aquatic toxicity of prothioconazole is focused on aquatic animals, and the study of aquatic plants is limited. In this work, the acute toxicity of prothioconazole (PTZ) and its metabolite, prothioconazole-desthio (PTD), to the aquatic plant Lemna minor (L. minor) was evaluated at the enantiomer level. The effects of the prothioconazole and its metabolite enantiomer on the physiological and biochemical indices, including growth rate, photosynthetic pigment content, and antioxidant-defense-enzymes activity, of L. minor were measured to evaluate the potential risk. The results showed that prothioconazole and prothioconazole-desthio possessed obvious stereoselective toxicity to Lemna minor with an LC50 (7 days) of 0.76–5.63 mg/L. The toxicity order was S-PTD > Rac-PTD > S-PTZ > R-PTD > Rac-PTZ > R-PTZ. The S-PTZ, which had the highest toxicity, obviously inhibited the biosynthesis of photosynthetic pigments and the activity of antioxidant-defense enzymes (malondialdehyde, catalase and superoxide dismutase), leading to an increase in MDA content and oxidative damage. The results further confirmed that the metabolism of PTZ in aquatic ecosystems increased its exposure risk, providing data support and a theoretical basis for the risk assessment of PTZ.