Leaching of different maize herbicides as affected by the time elapsed from spraying and first leaching event

The study was conducted in 2011 in North-West of Italy, on a battery of 12 lisymeters (8.4m2 large with a depth of 2m) filled with silty-loam soil. The aim of the study was to evaluate the leaching behavior of five herbicides (terbuthylazine, S-metolachlor, mesotrione, flufenacet, and isoxaflutole) and two metabolites (desethyl-terbuthylazine and diketonitrile) as affected by time elapsed from spraying and first leaching event. All lisymeters were treated in pre-emergence with the selected herbicides applying a mixture of the commercial products Lumax (2.5 L/ha) and Merlin Gold (1 L/ha). An irrigation able to produce leaching (40mm) was carried out on independent groups of three lysimeters at 1 days after treatment (1DAT), 7 DAT, 14 DAT and 28 DAT and then repeated fourteen days later. At the time of the treatment soil of the lysimeters was at the field capacity. Samples of leachate were collected within few days after the irrigation. The compounds were extracted by SPE, and analyzed by HPLC and GC-MS. For all compounds, the highest concentrations were detected at 1DAT and fourteen days later (1+14 DAT). At these time the concentrations detected were respectively: 2.88 µg/L and 0.95 µg/L (S-metolachlor), and 0.96 µg/L and 0.52 µg/L(terbuthylazine). Flufenacet leached only in case of irrigation interventions close to herbicide spraying, isoxaflutole and mesotrione have never been found (<0.1 µg/L), while diketonitrile has been detected in concentrations above 0.1 µg/L at 1DAT only. Desethyl-terbuthylazine has frequently been found, but at concentrations never above 0.3 µg/L.