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Atrazine: Can You Have Too Much of a Good Thing?

A. Lane Rayburn
Associate Professor
Department of Crop Sciences
(217) 333-4374; arayburn@illinois.edu
A. Lane Rayburn

Atrazine has been and continues to be one of the most important agrochemicals in the Corn Belt. The effectiveness of atrazine, along with its low cost, has made it the herbicide of choice for corn production. Its mode of action is in the disruption of the photosynthetic pathway in plants. However, recent evidence has suggested that atrazine causes chromosome damage in animals. Atrazine has been found in the drinking water supplies of communities such as Springfield and Decatur, at levels above the existing Maximum Contamination Level (MCL) set by the Unites States Environmental Protection Agency. The current MCL is 3 parts per billion (ppb), while a proposed new MCL is 20 ppb.

Chinese Hamster chromosomes used to assess the potential of agrochemicals to damage chromosomes.
Figure 1. Chinese Hamster chromosomes used to assess the potential of agrochemicals to damage chromosomes.

The question that is frequently asked is "Can such a small amount of atrazine really pose a potential problem?" After all, "parts per billion" seems like such a small number. Three parts per billion would be the equivalent of 200 pounds of active ingredient of atrazine in the estimated 8 billion gallons of Lake Decatur. What could such a small amount do?

The MCL set by the U.S. EPA is calculated based on the highest dose of a substance for which no adverse effects are observed based on human or animal studies. For health criteria, the dose is then corrected for consumption and body weight. The MCL also takes into account an uncertainty factor. These levels are therefore set on an equation basis with safety factors built in.

Laboratory results indicate that even these low levels have biological activity to specific genetic endpoints. Does this mean that we should be greatly alarmed by the findings? No: There is as yet no evidence to suggest that a major health problem exists. Should we be concerned? Yes: There are many examples of chemicals that were first reported to have no health problems and then unexpected problems were observed. Of course, any concern would be somewhat moot if atrazine did not find its way into the drinking water supplies, so the question becomes: How does the chemical end up in the water supply?

In Illinois, the most susceptible drinking water supplies to atrazine contamination are surface water supplies whose watersheds drain large areas of agricultural land. According to the U.S.G.S., the average use of active ingredient of atrazine is over 122 pounds per square mile in Illinois. This figure is not restricted to land in corn production but includes all land, both urban and rural.

In 1997, over 10 million pounds of atrazine active ingredient were applied to almost 80 percent of the corn grown in Illinois. The Lake Decatur watershed is approximately 925 square miles, and the overwhelming majority of its land use is for agricultural row crops. Given the figures above, over 113,000 pounds of atrazine are applied in the watershed. To obtain 3 ppb atrazine in Lake Decatur, only a 0.2 percent runoff into the lake is necessary. Due to high volume of use, atrazine becomes a problem.

Atrazine is an important agrochemical and has proven to be an effective and economical herbicide. It is the sheer volume of chemical use that is creating the problem. Any chemical that is used to the virtual elimination of all others and at high levels will eventually end up where it does not belong and create health or environmental concerns. It is critical that we keep this in mind when using agrochemicals. Several chemicals important to agriculture have been lost through overuse. To prevent such losses, it is important to realize that it is not simply the nature of the chemical that we need to be concerned with, but also the use of the chemical. Large-scale use of even the seemingly most benign chemical could have serious environmental consequences.

We should all remember an important lesson of our youth: Too much of anything, even a good thing, can be bad for you.

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