Leaching of S-metolachlor, terbuthylazine, desethyl-terbuthylazine, mesotrione, flufenacet, isoxaflutole, and diketonitrile in field lysimeters as affected by the time elapsed between spraying and first leaching event

Abstract

The effect of elapsed time between spraying and first leaching event on the leaching behavior of five herbicides (terbuthylazine, S-metolachlor, mesotrione, flufenacet, and isoxaflutole) and two metabolites (desethyl-terbuthylazine and diketonitrile) was evaluated in a 2011–2012 study in northwest Italy. A battery of 12 lysimeters (8.4 m² long with a depth of 1.8 m) were used in the study, each filled with silty-loam soil and treated during pre-emergence with the selected herbicides by applying a mixture of commercial products Lumax (4 L ha⁻¹) and Merlin Gold (1 L ha⁻¹). During treatment periods, no gravity water was present in lysimeters. Irrigation events capable of producing leaching (40 mm) were conducted on independent groups of three lysimeters on 1 day after treatment (1 DAT), 7 DAT, 14 DAT, and 28 DAT. The series was then repeated 14 days later. Leachate samples were collected a few days after irrigation; compounds were extracted by solid phase extraction and analyzed by high-performance liquid chromatography and gas chromatography–mass spectrometry. Under study conditions, terbuthylazine and S-metolachlor showed the highest leaching potentials. Specifically, S-metolachlor concentrations were always found above 0.25 µg L⁻¹. Desethyl-terbuthylazine was often detected in leached waters, in most cases at concentrations above 0.1 µg L⁻¹. Flufenacet leached only when irrigation occurred close to the time of herbicide spraying. Isoxaflutole and mesotrione were not measured (<0.1 µg L⁻¹), while diketonitrile was detected in concentrations above 0.1 µg L⁻¹ on 1 DAT in 2011 only.

Keywords:

• Herbicides
• metabolite
• lysimeters
• leaching
• water
• contamination
• time

Acknowledgments

The authors thank the experimental station and lab technicians who made valuable contributions to field operations. Appreciation is further extended to group members of Sustainable Weed Management of the Department of Agriculture, Forest and Food Science of the University of Torino, who helped during the study. The paper is equally attributed to all the authors.