Excerpted from the Environmental Impact of Missouri Crop Production report

• Atrazine detects in raw water exceeding the finished water standard of three ppb ranged from zero in 2004 and 2012 to 52 in 2006. All samples were below the observable adverse effect level found in studies on rats.

Of particular interest in Missouri has been the levels of atrazine in drinking water sources. Atrazine is labeled by the U.S. EPA as a restricted-use pesticide. Farmers and private applicators must undergo training and certification on how to safely use, handle, store and dispose of restricted-use pesticides before they can legally purchase and apply them. The U.S. EPA set the safety standard for atrazine in finished drinking water at three parts per billion (ppb). This level was determined by finding the no observable adverse effect level on rats and dividing it by 10 for extrapolation to humans and 10 for human variability in sensitivity. In other words, the observable adverse effect level of 300 ppb in rats was divided by 100 to determine the 3 ppb threshold for humans.

The table below summarizes aggregate data of raw and finished water samples collected and used as part of the U.S. EPA's 2016 reauthorization of atrazine in the United States. Raw samples are from untreated water that has not been through a public drinking water supply treatment facility. Finished samples are from treated water that has been through a public drinking water supply treatment facility.