The widespread use of chemicals to control plant pests across the United States has been happening for decades, yet a newly released study shows that only a few herbicides have persisted in well water over the 10 years from 1993 to 2003.
Results for one of the first national studies on the presence of herbicides in groundwater is published by the U.S. Geological Survey in the September-October issue of the "Journal of Environmental Quality."
One goal of the study was to track the retention of various types herbicides and pesticides used over the years.
The study is a part of the National Water Quality Assessment Program, federally funded and conducted by the USGS. It aims to provide an understanding of water quality conditions and how those conditions may vary locally, regionally, and nationally; whether conditions are getting better or worse over time; and how natural features and human activities affect those conditions.
Changes in pesticide detection frequency and concentrations in groundwater might be expected to have occurred on a regional or national basis within the United States during at least the past 10 to 20 years as a result of targeted use restrictions and chemical bans and the introduction of new pesticide compounds.
Each well network was sampled once during 1993-1995 and once during 2001-2003. The networks provide an overview of conditions across a wide range of hydrogeologic settings and in major agricultural areas that vary in dominant crop type and pesticide or herbicide use.
Of about 80 pesticide compounds analyzed, only six compounds were detected in groundwater from at least 10 wells during both sampling events.
Concentrations of these compounds generally were less than 0.12 parts per billion, or more than 10 times lower than applicable EPA drinking water standards.
Sprayed on farm crops, atrazine may wash from soil into streams or groundwater where it will stay for a long time, because breakdown of the chemical is slow in water, according to the federal Agency for Toxic Substances.
Birth defects and liver, kidney, and heart damage have been seen in animals exposed to high levels of atrazine. There are limited human and animal data that suggest that there may be a link between atrazine exposure and various types of cancer, the agency says.
Learning more about these trends is important in determining how quickly ground water systems respond to changes in pesticide use and land management practices, Bexfield wrote, and in identifying compounds that may pose a threat to water quality before large-scale problems occur.