Degradation and leaching of bentazone, terbuthylazine and S-metolachlor and some of their metabolites: A long-term lysimeter experiment

The degradation and leaching of bentazone, terbuthylazine and S-metolachlor and their metabolites N-methyl-bentazone, desethyl-terbuthylazine, 2-hydroxy-terbuthylazine, metolachlor ethane sulfonic acid (ESA) and metolachlor oxanilic acid (OA) were investigated using the plant protection products Artett (bentazone/terbuthylazine), Gardo Gold (S-metolachlor/terbuthylazine) and Dual Gold (S-metolachlor) applied to a weighable, monolithic, high precision lysimeter with a loamy, sandy soil. Artett and Gardo Gold were applied at higher doses than recommended according to good agricultural practice. In leachate, S-metolachlor was detected at concentrations of up to 0.15 µg/L, whereas metolachlor-ESA and metolachlor-OA were present at higher concentrations of up to 37 µg/L and 8.4 µg/L, respectively. In a second terbuthylazine application, concentrations of desethyl-terbuthylazine of up to 0.1 µg/L were detected. In soil, bentazone degraded faster than terbuthylazine and S-metolachlor, whereas the metabolization of terbuthylazine after the second application resulted in an enhanced formation of desethyl-terbuthylazine and a highly increased hydroxylation of terbuthylazine. The importance of analysing both parent compounds and metabolites on a long-term scale was demonstrated to better understand the environmental fate and transport.