Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/6/1996
Publication Date: N/A
Technical Abstract: Contamination of stream water by soil-applied, pre-emergence herbicides is common in the Midwestern U. S., particularly in the spring when treated fields are most susceptible to herbicide transport by surface runoff. However, the extent of herbicide contamination in northern Missouri streams has never been thoroughly assessed. Grab samples were collected at approximately 140 sites throughout northern MO at pre-plant (March, April) and post-plant (June, July) of 1994 and 1995. The sampling scheme encompassed 95 separate streams ranging in drainage area from 40 to 7880 mi**2. In 1996, 20 gauged streams were sampled at 1-2 week intervals from May through early July to assess the magnitude and duration of herbicide contamination as well as to provide data for estimating herbicide mass flux. Samples were analyzed for atrazine, cyanazine, metolachlor, alachlor, metribuzin, and 5 triazine degradation products. Herbicide contamination in northern MO streams was common at pre-plant and post-plan with atrazine, cyanazine, metolachlor, and triazine degradation products most often detected. At pre-plant, atrazine and its degradation products were most often detected, and atrazine degradation products accounted for 58% of the total atrazine load in the streams. Post-plant herbicide concentrations were greater than pre-plant for all herbicides. At post plant, average herbicide prevalence was 100% for atrazine, 97% for cyanazine, and 68% for metolachlor. Cyanazine exceeded the USEPA drinking water health advisory level of 1 ppb in 56% of the post-plant samples, and atrazine exceeded its maximum contaminant level of 3 ppb in 48% of post plant samples.