A Holistic Assessment of the Occurrence of Metolachlor and 2 of its Degradates Across Various Environmental Compartments in 7 Environmental Settings

Author(s): Rose, C.; Welch, H.; Coupe, R.; Capel, P.

The widely used herbicide, metolachlor, is one of the most frequently detected pesticides in surface water and groundwater throughout the United States in both agricultural and urban settings. Metolachlor has also been detected in rain and in the unsaturated zone. The U.S. Geological Survey conducted a study to assess the controlling factors in the transport and fate of metolachlor and its degradates across seven watersheds in California, Indiana, Iowa, Maryland, Mississippi, Nebraska, and Washington during 1997-2007. The occurrence of metolachlor and two degradates (metolachlor ethane-sulfonic acid and metolachlor oxanilic acid) was examined in several environmental compartments within these environmental settings; groundwater, surface water, overland flow, subsurface drains, the unsaturated zone, and the atmosphere. Within these environmental compartments, the occurrence of metolachlor and its degradates primarily is affected by a number of factors including use, management, environmental setting, and physical and chemical properties of metolachlor and its degradates. The fate of metolachlor can be generalized by the environmental compartments. The majority (90%) of metolachlor is taken up by plants, degraded in the soil, or is trapped in/adsorbed to soil. About 10% of the applied metolachlor is volatilized into the atmosphere, and about 0.3% returns by rainfall. Some (0.4%) metolachlor is transported to surface water, while an equal amount (0.4%) is infiltrated into the unsaturated zone and may move downward into groundwater. Generally, groundwater stores less than 0.02% and does not serve as a metolachlor source to receiving surface waters.
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1 Best Management Practices #1
2 Delta Water Assessment
3 Flood Assessment & Mgmt.
4 Wetlands
5 Watershed Mgmt. #1
6 Non-Point Source Assessment
7 Modeling
8 Water Quality
9 Best Mgt. Practices #2
10 Delta Water Conservation
11 Sedimentation
12 Storm Water
13 Watershed Mgt. #2
14 Public Water Systems
15 Surface Water Assessment & Evaluation

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