Chloroacetanilide Herbicide Metabolites in Wisconsin Groundwater

Abstract: In this study, 27 monitoring wells, 22 private drinking water wells, and 23 municipal wells in Wisconsin were sampled for alachlor, metolachlor, acetochlor, and their ethane sulfonic acid (ESA) and oxanillic acid (OA) metabolites. The wells sampled for the study were not randomly chosen. Wells were selected based on previous detections of pesticides or proximity to agricultural fields to increase the likelihood of exposure to the compounds of interest. Alachlor, metolachlor, and acetochlor are chloroacetanilide herbicides that are commonly used on corn and other crops in Wisconsin. With the exception of alachlor ESA, no groundwater occurrence data exists for these metabolites in Wisconsin groundwater because laboratory methods have not been available. Sample results showed over 80 percent of the monitoring wells and drinking water wells contained the ESA and OA metabolites of alachlor and metolachlor. The metabolites of acetochlor, which has only been used since 1994, showed a lower frequency of detection. Concentrations of the metabolites in groundwater ranged from near the level of detection to 42 ug/l. The monitoring wells and private drinking water wells showed higher detection frequencies and concentrations than the deeper municipal wells, but the municipal wells did show significant impacts. Fifty-two percent of the municipal wells had a detection of at least one of the compounds of interest. However, no municipal well studied contained pesticide levels that exceeded an enforcement standard.