Atrazine is one of the most widely used and most controversial herbicides in the world. Farmers, lawn care workers and gardeners use atrazine both to prevent broadleaf weeds from establishing before they emerge from the ground and to kill weeds that have emerged. The chemical is cheap and, because it’s a pre-emergence herbicide, it prevents weeds from competing with crops from the beginning of the growing season. It’s estimated that atrazine can increase crop yields by up to six percent. Atrazine has also been used in conservation tillage systems to control weeds and reduce soil erosion.

As late as 2002, it was estimated that atrazine was the most commonly used herbicide in the world with applications in 80 countries. But studies around that time showed that atrazine was dissolving into water in the fields and was showing up in streams and underground drinking water supplies all over the world.

The European Union banned all use of atrazine in 2004 because of persistent groundwater contamination.

In other areas, atrazine use continued – at least, until the later years of the 2000s. In 2005, Nebraska farmers applied atrazine to 77 percent of the corn acres in the state. That’s the most recent reporting year on file at the Lincoln office of the National Agricultural Statistics Service.

During this same time period, genetically modified organism (GMO) crops have taken over across the American Midwest. According to the USDA, by 2008, 92 percent of the soybeans planted in the U.S. were GMO varieties. Nebraska and South Dakota were the two highest percentage states at 97 percent each. Genetically modified corn was planted in 80 percent of the fields in the U.S. by 2008. Again, sophisticated farmers in the Midwest led the way. Nebraska farmers planted 86 percent GMO corn while South Dakota topped the list of states at 95 percent GMO corn.

The use of GMO crops – particularly RoundUp Ready varieties – may mean that farmers are transitioning from atrazine to Roundup as their primary defense against weeds.

The other pressure against atrazine is that scientific studies are suggesting that the chemical may be dangerous to humans and other species, especially in the area of reproductive health.

In 2003, there were six studies that showed that frogs exposed to atrazine from nearby farm fields were developing sexual abnormalities. Some species developed multiple testes and multiple ovaries. Males in other studies became hermaphrodites.

The Environmental Protection Agency during the Bush administration took note of the studies, weighed them against other studies and declared the herbicide safe for use. But it did require the manufacturer, the Swiss company Syngenta, to monitor water wells in several areas of the country. Those results showed that overall levels of atrazine were low, but in several wells in corn country levels of atrazine spiked during the spring and summer.

Some local officials are aware of the spikes. For instance, water officials in Lincoln, Nebraska, routinely shut down the wells drawing water into the city’s water supply reservoirs every spring when they know farmers are applying atrazine.

In other parts of the country, local officials have not been notified of the spikes in atrazine levels.

After the frog studies raised the issue, other researchers began looking at atrazine and its effects on humans. Epidemiological and animal studies in 2009 suggested that high levels of atrazine during specific periods of pregnancy could result in more birth defects, more low birth weight babies, menstrual problems and even possible susceptibility to cancer for humans later in life.

film_martin_LSo, in 2009, the EPA – under a new administration – decided to conduct a new review of the latest scientific data on the herbicide.

Agronomy professor Alex Martin says atrazine works against broadleaf weeds without killing corn because corn has a natural immunity without genetic modification. “In contrast to 2, 4-D, the reason that Atrazine doesn’t kill a corn plant is not anything to do with the structure of the corn plant,” he says. “But it’s the fact that the corn plant has a biochemical pathway that allows it to detoxify atrazine extremely rapidly.”

In addition, atrazine can be broken down in the environment by microorganisms, but that process can take time. In the meantime, the chemical can wash into streams and aquifers.

Written by Bill Ganzel, the Ganzel Group. First published in 2009. A partial bibliography of sources is here.

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