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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

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Fate and Transport of Atrazine at the Plains, Georgia, Ground Water Study Site

by

R. A. Leonard (U.S. Department of Agriculture, Agricultural Research Service, Southeast Watershed Research Laboratory, Tifton, Ga.), L.R. Marti (U.S. Department of Agriculture, Agricultural Research Service, Southeast Watershed Research Laboratory, Tifton, Ga.), D.W. Hicks (U.S. Geological Survey, Water Resources Division, Atlanta, Ga.), and J.B. McConnell (U.S. Geological Survey, Water Resources Division, Atlanta, Ga.)

Abstract

Cooperative research between the U.S. Geological Survey, U.S. Department of Agriculture, Agricultural Research Service, and U.S. Environmental Protection Agency was initiated in 1986 near Plains, Georgia, to define processes that affect movement and fate of agricultural chemicals and to establish a common comprehensive data base for development and testing of mathematical models. Data from one crop cycle (mid-March 1992 to mid-March 1993) are summarized to illustrate the fate and present state of atrazine in the system after four annual treatments at normal application rates for corn. In 1992, parent atrazine dissipated in the root zone with a half-life of about 18 days. The atrazine metabolites, desethylatrazine (DEA) and desisopropylatrazine (DIA) accumulated in the root zone to a maximum 27 days after application; DEA was the primary metabolite. The maximum DEA/atrazine ratio was 0.6 40 days after atrazine application. After crop harvest in mid-July 1992, atrazine, DEA and traces of DIA were detected throughout the unsaturated zone to depths of 8.7 meters. Because the area had been treated with atrazine during the previous 3 years, the atrazine found could not be associated with a particular application. By March 1993, atrazine in the unsaturated zone had decreased from an estimated 360 grams per hectare to 100 grams per hectare. Atrazine and DEA in ground water, at the time of sampling, were at greater concentrations downgradient from the treated area, with the maximum concentrations about 60 meters downgradient from the treated plot boundary. Traces of atrazine and DEA were detected 280 meters downgradient from the plot. DEA/atrazine ratios were slightly higher in ground water compared to the unsaturated zone, possibly indicating continued transformation along the ground-water flow path.

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