DEGRADATION OF CHLOROACETANILIDE HERBICIDES - THE PREVALENCE OF SULFONIC AND OXANILIC ACID METABOLITES IN IOWA GROUNDWATERS AND SURFACE WATERS

Water samples were collected from 88 municipal wells throughout Iowa d uring the summer and were collected monthly at 12 stream sites in east ern Iowa from March to December 1996 to study the occurrence of the su lfonic and oxanilic metabolites of acetochlor, alachlor, and metolachl or. The sulfonic and oxanilic metabolites were present in almost 75% o f the groundwater samples and were generally present from 3 to 45 time s more frequently than their parent compounds. In groundwater, the med ian value of the summed concentrations of acetochlor, alachlor, and me tolachlor was less than 0.05 mu g/L, and the median value of the summe d concentrations of the six metabolites was 1.2 mu g/L. All surface wa ter samples contained at least one detectable metabolite compound. Ind ividual metabolites were detected from 2 to over 100 times more freque ntly than the parent compounds. In surface water, the median value of the summed concentrations of the three parent compounds was 0.13 mu g/ L, and the median value of the summed concentrations of the six metabo lites was 6.4 mu g/L. These data demonstrate the importance of analyzi ng both parent compounds and metabolites to more fully understand the environmental fate and transport of herbicides in the hydrologic syste m.