During 2004, a study to document the occurrence of herbicides and herbicide degradation products was conducted for 10 major Iowa rivers draining to the Missouri and Mississippi Rivers. Seventy-five water-quality samples were collected to measure isoxaflutole, acetamide, and triazine herbicides and their herbicide degradation products. An analytical method to measure isoxaflutole and its degradation products, diketonitrile and benzoic acid, was developed by the U.S. Geological Survey Organic Geochemistry Research Laboratory in Lawrence, Kansas, using vacuum manifold solid-phase extraction and liquid chromatography/mass spectrometry/mass spectrometry and is described in this report.

Isoxaflutole, a low application rate preemergence herbicide for control of annual broadleaf weeds, is used extensively in Iowa. Findings from the study documented in this report indicate that isoxaflutole was designed to degrade quickly to diketonitrile, which appears to be more stable, and then to benzoic acid. Of the 75 samples collected to measure isoxaflutole, there were four detections of isoxaflutole, 53 detections of diketonitrile, and 41 detections of benzoic acid. Also, results of acetamide and triazine water-quality samples correlate with past studies, which indicate that herbicide degradation products are detected more frequently and often at higher concentrations in surface water than their parent compounds.

In addition to analysis of isoxaflutole and its degradation products, samples were analyzed by the USGS National Water-Quality Laboratory schedule 2001 for about 52 pesticides and their degradation products.