Chloroacetanilide (acetochlor, alachlor, metolachlor) and chloroacetamide (dimethenamid) herbicides are widely used in corn production as well as lesser use with other crops. Monitoring studies indicate the parent herbicides degrade relatively quickly after field application, with the primary degradation products being the ethane sulfonic acid (ESA) and oxanilic acid (OXA) structures. Studies have shown these degradation products to be very persistent in the environment. Proper assessment of environmental exposure to these herbicides needs to include monitoring of the degradation products in addition to the parent herbicides. A 2-year reconnaissance study was initiated in July 2012 with monthly sampling intervals to assess surface water quality across the state of Iowa. A modified version of EPA 535 was used to extract water samples and test for the parent herbicides (acetochlor, alachlor, dimethenamid, metolachlor) in addition to their respective ESA and OXA degradates. The method allowed detection, quantification, and reporting at concentration levels as low as 0.025 �g/L for each analyte. In this presentation, data will be presented highlighting seasonal fluctuations in the concentrations of the monitored analytes for select watersheds leading to the Mississippi River. Data will be contrasted between watersheds with significant row crop farming (Wapsinicon River, Cedar River, Iowa River, Des Moines River) and a watershed where row crop farming is less intense (Upper Iowa River). Results indicated that the parent herbicides are detected in significant amounts for a two month period (June-July) after application while the ESA and OXA degradation products are detected in significant amounts year round. The persistence of the degradation products is evidenced by detections of alachlor ESA and to a lesser extent alachlor OXA at levels as high as 0.5 �g/L in all five watersheds even though use of this pesticide was greatly reduced in the mid-1990's in support of the registration of acetochlor.

Assessment of chloroacetanilide and chloroacetamide herbicides and their ESA/OXA degradation products in Iowa surface water

248th National Meeting (2014)

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