OCCURRENCE OF ALACHLOR AND ITS SULFONATED METABOLITE IN RIVERS AND RESERVOIRS OF THE MIDWESTERN UNITED-STATES - THE IMPORTANCE OF SULFONATION IN THE TRANSPORT OF CHLOROACETANILIDE HERBICIDES

Alachlor and its metabolite, lphenyl)(methoxymethyl)amino]-2-oxoethane sulfonate (ESA), were identified in 76 reservoirs in the midwestern Un ited States using immunoassay, liquid chromatography, and gas chromato graphy/mass spectrometry. The median concentration of ESA (0.48 mu g/L ) exceeded the med lan concentration of alachlor (0.05 mu g/L), with h ighest values in the upper Midwest. ESA also was detected in the Missi ssippi River from the mouth to the headwaters at concentrations of 0.2 -1.5 mu g/L, exceeding the concentration of alachlor. In a field runof f study, alachlor rapidly formed ESA. It is hypothesized that a glutat hione conjugate forms, which later oxidizes in soil to ESA. The remova l of the chlorine atom lessens the toxicity of the parent compound and increases runoff potential. It is hypothesized further that sulfonic acid metabolites of other chloroacetanilides, including acetochlor, bu tachlor, metolachlor, and propachlor, also occur in surface water.