Submitted to: International Congress of Pesticide Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 7, 1998
Publication Date: N/A
Technical Abstract: The contribution of subsurface drainage to herbicide contamination of surface waters is highly dependent on soils, farming systems, and climate. Field studies were conducted from 1992 to 1995 to assess the extent of atrazine and metribuzin leaching to subsurface drains and shallow groundwater at a site in the Walnut Creek watershed in central Iowa. Atrazine losses in subsurface drainage ranged from 0.02 to 2.16 g ha**-1 while metribuzin losses ranged from non-detectable to 1.27 g ha**-1. The greatest atrazine and metribuzin losses occurred during 1993 when rainfall exceeded the annual average by 57%. Monthly flow-weighted average concentrations of atrazine in subsurface drainage water did not exceed the MCL of 3 ug L**-1. Atrazine was much more persistent in surface and subsurface soils than metribuzin. Both atrazine and metribuzin were detected in shallow groundwater, with atrazine detection frequency almost twice that of metribuzin. Atrazine was detected in 26% of the well-water samples from 2.6 m depth, but only 1.4% of the samples contained concentrations above the 3 ug L**-1 MCL. This data suggests that the low usage of atrazine in this farming system will result in decreased risk of contamination exceeding MCL concentrations and lower off-site atrazine loads to stream water and groundwater.