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 areas of the USA. Because of its heavy usage, moderate persistence, and mobility in soil, monitoring of atrazine movement under held conditions is essential to assess its potential to contaminate groundwater. Concentrations of atrazine, deisopropylatrazine (DIA), and deethylatrazine (DEA) were measured in subsurface drainage and shallow groundwater beneath 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 concentration 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, concentrations of parent and degradates in solution were atrazine > DEA > DIA. Lesser levels of atrazine were measured in 1991 from Plots 2 and 4; however greater concentrations of atrazine (6.0-8.4 mu g L(-1)) were measured from Plot 5. Throughout the two growing seasons, atrazine concentration 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), respectively, indicating that the degradation products by themselves or in combination 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 residence 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 2.70 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.