A new model predicts that atrazine, plus its breakdown product deethylatrazine, has less than a 10 percent chance of exceeding the U.S. Environmental Protection Agency's standard for public drinking-water supplies in shallow groundwater in about 95 percent of the nation's agricultural areas. Atrazine is a commonly used herbicide for weed control in corn and sorghum production.
"With the intensive, widespread use of the herbicide atrazine in agricultural production, some communities will need to carefully monitor the risk to groundwater and human health from this contaminant and its residues," said USGS director Marcia McNutt. "The advantage of this new research is that it reveals the spatial variability of risk for atrazine contamination in groundwater across the United States, allowing communities to make wise decisions on allocating scarce financial resources for water-quality testing."
These findings are based on new statistical models developed from almost 20 years of nation-wide water-quality monitoring data collected by the USGS National Water Quality Assessment Program (NAWQA).
"These models are an improvement over previous models because they predict concentrations rather than detection frequencies. Concentrations can be compared to water-quality standards and guidelines to evaluate potential human-health concerns," said Paul Stackelberg, USGS hydrologist and lead author on the report. "These models are not for regulatory purposes, but can be used to identify areas where concentrations of atrazine are most likely to be of potential concern and also to set priorities among groundwater resources for future monitoring."
EPA's Maximum Contaminant Level (MCL) of 3.0 µg/L for atrazine in public drinking-water supplies is not a regulatory standard for shallow groundwater or domestic supplies, but serves as a benchmark for potential human-health concerns. Predicted concentrations are compared to the MCL for atrazine in order to provide a perspective on potential significance to human health.
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Results of the USGS study "Regression models for estimating concentrations of atrazine plus deethylatrazine in shallow groundwater in agricultural areas of the United States" are published in the Journal of Environmental Quality and are currently available online.
This study is part of the NAWQA Pesticide National Synthesis Project, which is a national-scale assessment of the occurrence and behavior of pesticides in streams and groundwater of the United States and the potential for pesticides to adversely affect drinking-water supplies or aquatic ecosystems.
http://water.usgs.gov/nawqa/pnsp/