Metolachlor and Its Metabolites in Tile Drain and Stream Runoff in the Canajoharie Creek Watershed

Water samples collected during April−November 1997 from tile drains beneath cultivated fields in central New York indicate that two metabolites of the herbicide metolachlor metolachlor ESA (ethanesulfonic acid) and OA (oxanilic acid) can persist in agricultural soils for 4 or more years after application and that fine-grained soils favor the transport of metolachlor ESA over metolachlor and metolachlor OA. Concentrations of metolachlor ESA from the tile drains ranged from 3.27 to 23.4 μg/L (200−1800 times higher than those of metolachlor), metolachlor OA concentrations ranged from 1.14 to 13.5 μg/L, and metolachlor concentrations ranged from less than 0.01 to 0.1 μg/L. In the receiving stream, concentrations of metolachlor ESA were always below 0.6 μg/L except during a November storm, when concentrations reached 0.85 μg/L. Concentrations of metolachlor ESA in the stream were 2−45 times higher than those of metolachlor, reflecting the greater relative concentrations of metolachlor in surface water runoff than in tile drain runoff. These results are consistent with findings in other studies that acetanilide herbicide degredates are found in much higher concentrations than parent compounds in both surface water and groundwater.