Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2001
Publication Date: N/A
Interpretive Summary: The use of herbicides (weed-killers) is an important agricultural management practice to increase crop yields. It is important that these chemicals be properly applied to insure minimal off-site movement that reduces the likelihood of surface water contamination. Development and evaluation of best management practices to reduce the potential contamination of surface water sources require sampling of these sources and measurement of herbicides in the water. Comparison of the amount of herbicides applied in the watershed with the amount of herbicide transported by surface water sources can provide feedback information for the effectiveness of these management practices. We examined a stream system in an agriculturally intensive watershed in the Coastal Plain region for five commonly used herbicides and determined if these herbicides were leaving the watershed. Over a two-year period, we found a few traces of these herbicides in the water system and the amount of these five herbicides exiting the watershed was very small. This indicates that the majority of the herbicides remained at the site of application, and when trace amounts of the herbicide were in the stream, in-stream processes dramatically reduced the herbicide concentrations before exiting the watershed. Best management practices used by herbicide applicators within the watershed are effective in keeping herbicides at the site of application.
Technical Abstract: Herbicide detection in surface water sources has caused concern about contamination of these sources and adverse effects on human health and aquatic life. Understanding surface water herbicide transport from agriculturally intensive watersheds is useful for development of pesticide best management practices to reduce off-site movement. The seasonal occurrence and load of five herbicides exported by a stream were determined for a North Carolina Coastal Plain watershed. Grab samples were collected across the watershed and composite samples were also collected at the watershed outlet using a flow-proportional sampler. Samples were extracted for the herbicides alachlor, ametryn, atrazine, cyanazine, and metolachlor. Herbicides were detected in 15% (n = 415) of the grab samples with atrazine, cyanazine, and metolachlor detected in 3 to 6%, while alachlor and ametryn were detected in 1% of the samples. The mean stream water herbicide concentrations in grab samples were <0.9 ug/L. Herbicides were detected during all four seasons, with most detections occurring during the summer. Total mass of these five herbicides exported from the watershed was small (<0.01% of pesticides applied) suggesting that these compounds have minimally influenced the quality of water exiting this watershed.