U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Determining the Relative Age, Transport,and Three-Dimensional Distribution of Atrazine in a Reservoir Using Immunoassay

Abstract

The age, transport, and distribution of atrazine in a reservoir were determined by enzyme-linked immunosorbent assay. A pulse of stormwater runoff containing atrazine concentrations as much as nine times greater than the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) for drinking water (the MCL for atrazine is based on an annual average concentration of 3.0 micrograms per liter) was monitored as it moved through Perry Lake, northeastern Kansas, during the 1992 growing season. The drainage basin of Perry Lake is the first Pesticide Management Area designated by the State of Kansas. The leading edge of the pulse marked the boundary and mixing zone between atrazine applied in previous years and freshly applied atrazine. Deethylatrazine-to-atrazine ratios (DAR) further defined the relative age of atrazine in the reservoir. Runoff entering the reservoir immediately after herbicide application was identified by its small DAR values (0.095 to 0.134). Water with increasing DAR values (0.135 to 0.254) entered the reservoir as the year progressed and gradually displaced water with smaller DAR values. Four hundred and twenty (420) samples from four detailed reservoir surveys (pre-application, post-application, summer, and autumn) were analyzed by immunoassay to determine the distribution of herbicide concentrations in the reservoir. Also, weekly samples were collected from four fixed sites located upstream, within, and downstream from the reservoir. One hundred (100) of these samples were analyzed by gas chromatography/mass spectrometry to confirm immunoassay results and to determine deethylatrazine and deisopropylatrazine concentrations. A combination of immunoassay and DAR values could prove useful in developing reservoir-release strategies to mitigate atrazine concentrations in reservoirs and their outflows.