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, according to a news release from the U.S. Geological Society.

Atrazine is a commonly used herbicide for weed control in corn and sorghum production and has been under fire by activist groups that “pick” a crop protection product and pound away at trying to have it removed from the market come hell or high water.

It would seem that this USGS report helps take water out of the picture as a reason to ban atrazine use in the U.S. The biggest problem with the news is that it includes caveats that reinforce how there is never 100 percent safety or no potential for pollution from atrazine.

A long time ago, I learned that the EPA wouldn’t allow a company to say they have the “safest product on the market,” “safe to the environment” or “safer than competitive products.” Therefore, I’m sure the USGS has limitations on how safe they can announce a product performs.       

“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.”

What McNutt is really saying seems a little disguised to me, although I interpret the quote as suggesting that investing in continuous water-quality testing is probably a waste of money. But starting off with suggesting that “some communities will need to carefully monitor the risk” seems to destroy the second half, positive portion of the quote. 

USGS explained that the findings are based on new statistical models developed from almost 20 years of nation-wide water-quality monitoring data collected by the society’s 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.”

USGS then explained that 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. The USGS then noted, “Predicted concentrations are compared to the MCL for atrazine in order to provide a perspective on potential significance to human health.”

Additional findings from the study provided include: 

  • “Concentrations of atrazine residues (atrazine plus deethylatrazine) in groundwater are strongly influenced by the history of atrazine use in relation to the time period that the sampled groundwater infiltrated through the soil and replenished groundwater supplies.
  • “The highest concentrations of atrazine residues were predicted for recently recharged groundwater in agricultural areas where substantial atrazine use is combined with natural conditions of permeable soils and high groundwater recharge. These conditions readily move water from the land surface to groundwater. Because of these factors, the largest area where elevated concentrations are predicted in shallow groundwater is in eastern Nebraska. 
  • “Concentrations of atrazine residues are predicted to be lower across much of the Corn Belt, even in parts of Iowa, Illinois, and Indiana, where atrazine is known to be applied in the greatest quantities. Soils in these areas tend to be poorly drained and often require artificial drainage through trenches and tile drains that capture soil water and divert it from groundwater to nearby streams.”

USGS’s explanation concluded with this statement, “These statistical models provide a cost-effective means of understanding the chemical quality of the nation’s groundwater resources and for estimating water-quality conditions in unmonitored locations.” 

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 available online

The atrazine 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 U.S. and the potential for pesticides to adversely affect drinking-water supplies or aquatic ecosystems.