OCCURRENCE OF ATRAZINE AND DEGRADATES AS CONTAMINANTS OF SUBSURFACE DRAINAGE AND SHALLOW GROUNDWATER

Atrazine is a commonly used herbicide in corn (Zea mays L.) growing ar eas of the USA. Because of its heavy usage, moderate persistence, and mobility in soil, monitoring of atrazine movement under held condition s is essential to assess its potential to contaminate groundwater. Con centrations of atrazine, deisopropylatrazine (DIA), and deethylatrazin e (DEA) were measured in subsurface drainage and shallow groundwater b eneath continuous, no-till corn. Water samples were collected from the subsurface drain (tile) outlets and suction lysimeters in the growing seasons of 1990 and 1991, and analyzed for atrazine and two principle degradates using solid-phase extraction and HPLC. In 1990, atrazine c oncentration ranged from 1.3 to 5.1 mu g L(-1) in tile-drain water and from 0.5 to 20.5 mu g L(-1) in lysimeter water. In general, concentra tions of parent and degradates in solution were atrazine > DEA > DIA. Lesser levels of atrazine were measured in 1991 from Plots 2 and 4; ho wever greater concentrations of atrazine (6.0-8.4 mu g L(-1)) were mea sured from Plot 5. Throughout the two growing seasons, atrazine concen tration in Plot 5 the-drain water was greater than that of Plots 2 and 4, suggesting a preferential movement of atrazine. Concentrations of DIA and DEA ranged from 0.1 to 2.2 and 0.9 to 3.2 mu g L(-1), respecti vely, indicating that the degradation products by themselves or in com bination with parent atrazine can exceed the maximum contaminant Level (mel) of 3 mu g L(-1) even though atrazine by itself may be <3 mu g L (-1). The deethylatrazine-to-atrazine ratio (DAR) is an indicator of r esidence time in soil during transport of atrazine to groundwater. In Plots 2 and 4, DAR values for tile-drain water ranged from 0.43 to 2.7 0 and 0.50 to 2.66, respectively By comparison, a DAR of 0.38 to 0.60 was observed in Plot 5, suggesting less residence time in the soil.