Submitted to: American Chemical Society Symposium Series
Publication Type: Book / Chapter
Publication Acceptance Date: 3/22/2001
Publication Date: N/A
Interpretive Summary: The use of chemicals by farmers to kill weeds which interfere with their corn/soybean yields is viewed by many as a mixed blessing. These chemicals, known as herbicides, do their job very well but also are a threat to our natural resource base because they sometimes find their way into our streams, and rivers, and even into our groundwater resources. Newer chemicals now available to the farmer are designed to minimize the potential for water contamination. However, we have found that two of these, which are among the most widely used in the cornbelt of the upper Midwest, do find their way into shallow well water when used as prescribed on the product label. Our studies were done on the very high productivity soils of the upper midwestern glacial deposits. This information will be of particular interest to farmers, farm consultants, local conservationists and environmentalists, all of whom will use it to promote improved resource protection practices on the farm. This means that environmental protection programs designed to take into account both agricultural sustainability of the soil resource (more likely, the farmer's primary interest) and natural resource protection (more likely, the general public's primary interst) must provide for detecting and measuring these chemicals in the surface and ground water on which we all are dependent.
Technical Abstract: In a four-year field study carried out on a 96-ha field, we have evaluated the impact on shallow groundwater quality of transition from conventional-till to no-till for two herbicides now commonly used in minimum-till corn/soybean systems. Nicosulfuron and imazethapyr were studied. Well water samples were obtained from shallow piezometers using manual bailers and residue analyses carried out in our laboratory. Methods utilized SPE cartridge chemistry followed by HPLC/MS/MS techniques, providing a 10 part-per-trillion quantitation limit in two liters of filtered groundwater. By January of 1993, ten months following initial application, imazethapyr, nicosulfuron, and one nicosulfuron degradate had been detected in the well water and confirmed by MS/MS. During the 1993 through 1995 sampling seasons, average concentration in the piezometer samples was 131 and 125 part-per-trillion for nicosulfuron and imazethapyr, respectively. The data show that these widely used ALS- inhibiting chemicals are capable of leaching to shallow groundwater during tillage transition.