Richard H. Coupe Paul D. Capel Richard M. Webb Claire E. Rose 2017 <p><strong>Background</strong>: Metolachlor [(RS)-2-Chloro-<i>N</i>-(2-ethyl-6-methyl-phenyl)-<i>N</i>-(1-methoxypropan-2-yl)acetamide] and two degradates (metolachlor ethane-sulfonic acid and metolachlor oxanilic acid) are commonly observed in surface and groundwater. The behavior and fate of these compounds were examined over a 12-year period in seven agricultural watersheds in the United States. They were quantified in air, rain, streams, overland flow, groundwater, soil water, subsurface drain water, and water at the stream/groundwater interface. The compounds were frequently detected in surface and groundwater associated with agricultural areas. A mass budget approach, based on all available data from the study and literature, was used to determine a percentage-wise generalized distribution and fate of applied parent metolachlor in typical agricultural environments.<br></p><p><strong>Results</strong>: In these watersheds, about 90% of applied metolachlor was taken up by plants or degraded, 10% volatilized, and 0.3% returned as rainfall. One percent was transported to surface water, while an equal amount infiltrated into the unsaturated zone soil water. &lt; 0.02% reached the groundwater. Subsurface flow paths resulted in greater degradation of metolachlor because degradation reactions had more time to proceed.<br></p><p><strong>Conclusions</strong>: An understanding of the residence times of water in the different environmental compartments, and the important processes affecting metolachlor as it is transported along flowpaths among the environmental compartments allows for a degree of predictability of metolachlor's fate. Degradates with long half-lives can be used (in a limited capacity) as tracers of metolachlor, because of their persistence and widespread occurrence in the environment.</p> application/pdf 10.1016/j.scitotenv.2017.08.154 en Elsevier Holistic assessment of occurrence and fate of metolachlor within environmental compartments of agricultural watersheds article