Temporal evolution of atrazine and metolachlor concentrations exported in runoff and subsurface water with vegetated filter strips

Metolachlor and atrazine are herbicides used in corn agriculture and detected in surface- and groundwater. Vegetated filters reduce masses of herbicides in runoff, but less attention has been given to their impact on degradation products and subsurface infiltrated water. The objective was to study the temporal evolution of dissolved metolachlor, atrazine and deethylatrazine concentrations in runoff and subsurface infiltrated water with two types of vegetated filters over 2 years for the first three rains following herbicide application. Runoff and subsurface infiltrated at 90-cm water samples from 12 plots of 30 × 5 m in a completely randomized block design of four replicates of three treatments-control without filter, 5-m-long grass filter, 5-m-long grass and tree filter were analysed using gas chromatography/mass spectrometry. Controls in runoff generally had the highest average atrazine, as high as 739 μg L−1, and metolachlor average concentrations, as high as 1,725 μg L−1. The first rain after application was mainly responsible for atrazine and metolachlor exports. Vegetated filters reduced concentrations of atrazine and metolachlor in runoff below their respective Canadian criterion of 1.8 μg L−1 for atrazine and 7.8 μg L−1 for metolachlor (provisory) (CCME 2002) for the protection of aquatic life when rain did not occur shortly after application. With the need to increase food production and agricultural yields to sustain the increasing world population came the need to develop efficient mitigation tools such as vegetated filter strips to reduce the ecotoxicologial impacts of pesticides. The present study is among the few that examined herbicide degradation products and subsurface infiltrated water under filter strips in order to provide new knowledge on the relationship between herbicide loss pathways and the environmental benefits of these strips. Such knowledge will provide much needed information to modellers, decision makers, ecotoxicologists and agronomists involved in the regulation, design and implementation of vegetated filter strips for the protection of water quality.