Atrazine danger declining as practices change

Use of a herbicide here that seems to be raising warning signs worldwide that it could pose a danger is declining as farm practices change.

Atrazine is credited with 40 years of effective, low-cost use, but weed resistance coupled with new tillage and management practices are reducing its use.

Kirby Rector, vice-president and agronomist at Ag Service southeast of Hillsboro, said weed resistance to Atrazine, especially from pigweed in this area, means Atrazine isn’t used as the wide-spread pre-plant herbicide it once was.

Instead, farmers use Atrazine in combination mixes with other chemicals-ones that break down much more quickly causing less concern about residues, Rector said. “They break down quicker, and don’t stick around.”

He added that they use the combinations post-plant to knock out the small weeds with lesser amounts, which in turn saves the producers money.

Atrazine use also is reduced, but to a much lesser extent, Rector said, by farmers using more minimum-tillage and no-tillage practices that use the contact herbicide Roundup instead.

Roundup kills non-resistant plants it contacts, and then becomes inert when it hits the ground.

Atrazine use and other practices in the complicated effort at weed control are all what Rector calls “a part of the puzzle.”

Atrazine has especially been used in this region to control weeds on corn and milo, with more limited use with soybeans and on weeds in wheat fields.

Health concerns

Atrazine in the environment has been cited by many groups as a human carcinogen that also can cause vascular and fertility problems.

The herbicide also is accused of being responsible for a worldwide decline of frogs and other amphibians. Physical defects in frogs, such as multiple limbs, are highlighted by environmental groups as some of the more spectacular immediate evidence of danger.

One of the more immediate studies causing some alarm was released by a University of Missouri scientist, Shanna Swan, in 2003, that showed young rural Missouri men with lower fertility levels than urban counterparts.

Swan linked the study to Atrazine.

Syngente, the company that makes the largest amount of Atrazine, suggested Swan was a “left-wing” environmentalist trying to create a link to the herbicide.

The company said the herbicide has been used safely and effectively with no hazards to humans in its decades of use. It said fertility differences in humans have been shown among areas over the last century with many of them down before herbicide use.

How Atrazine works

Atrazine kills weeds by inhibiting photosynthesis in them. Corn and other crops detoxify Atrazine by linking it in metabolic activities to the substance glutathione, according to the U.S. Department of Agriculture.

The agency said several varieties of weeds are adapting to Atrazine by developing processes similar to the one corn uses.

Atrazine causes many of the concerns in its use by the fact that a major portion of it doesn’t break down or stay attached to the soil, according to the U.S. Environmental Protection Agency.

There is some minor breakdown of the herbicide in microbial activity and other chemical reactions and only limited bonding to the soil.

EPA said most of it leaches into the groundwater, or in worst case scenarios can be washed away after spring application in heavy precipitation.

Oddly, when you consider the list of health effects it can create, EPA said Atrazine also isn’t very likely to be taken up into plant and animal tissues.

This remains one of the major concerns to scientists, environmentalists and the farmers who use Atrazine cited in many of their articles.

Everybody understands the herbicide is in the environment, but, except for contentions here and there, nobody seems to know what the resulting long-term effect of the herbicide could be.

EPA determined under the Drinking Water Act of 1974 that a level of three parts per billion, called the Maximum Contaminant Level Goal, or MCLG, of Atrazine in drinking water would be acceptable, but added that this is in part because that level is the one public water systems can reasonable be expected to remove Atrazine to with existing processes.

Water plants use granular activated charcoal to remove the herbicide if water is above the MCLG.

EPA said human health effects in people exposed to levels above the MCLG for Atrazine can include congestion of the heart, lungs and kidneys, low blood pressure, muscle spasms, weight loss and damage to the adrenal glands.

In addition to these, EPA said lifetime exposure to Atrazine can cause cancer, weight loss, cardiovascular damage and retinal and muscle degeneration.

Drinking water supplies

Although EPA said Atrazine mostly causes health problems in manufacturing plants or in actual farm use, it also has been detected at unacceptably high levels in drinking water wells in Kansas, Missouri, Nebraska, Illinois, Indiana, Delaware, Iowa, Michigan and New York.

EPA has been given authority in more recent years to ban use of Atrazine in watersheds where public water systems have above acceptable MCLG.

The U.S. Department of Health and Human Services has added new concerns with studies that suggest pregnant women in high-Atrazine areas may carry babies that grow more slowly, but are born earlier with a higher risk for mortality.

The European Union is initiating a total ban of Atrazine use in its member countries in 2005. Some of the nations in the Union had already banned its use earlier.

Peggy Blackman of Marion, who works with USDA and watersheds to enhance water purity and shoreline stabilization at Marion Reservoir, said no study she has seen has ever shown significant levels of Atrazine that might cause concern at the reservoir.

Instead, she said, the main problems causing concerns are nutrients and sediments moving into the water.

Changing practices?

Other Marion County USDA workers thought Roundup use in no-till and minimum tillage may spread further to reduce Atrazine use even more. They would expect more use of Atrazine in combinations on traditional-tillage fields.

If Atrazine is still used with the reduced-tillage practices, the practices may reduce amounts of the herbicide required, they said. The reduced disturbance of the soil with the practices also may hinder loss of the chemical to water runoff, they said.

Kansas State University scientists-agronomist Daniel Devlin, agronomist David Regehr and agricultural engineer Phililp Barnes-found in their studies that loss of Atrazine being carried from fields by surface waters is perhaps the biggest concern in Kansas.

A study of the Equus Bed Aquifer in South-Central Kansas conducted by scientists of the U.S. Geological Survey seemed to confirm their findings.

The USGS found Atrazine concentrations at four to six feet deep in the soil at less than one ppb. Below six feet, they said Atrazine concentrations ranged from slight to undetectable.

Tips for better application

The K-State scientists said Atrazine can be kept better where it is applied by doing the following:

— incorporating it into the top 2 inches of soil;

— by putting it on in the fall or early spring to avoid heavy rain times;

— by using post-emergence Atrazine premix products;

— by reducing soil-applied Atrazine application rates to lower levels that might still be effective;

— by using split application of Atrazine, say prior to April 15 and again following planting;

— by reducing Atrazine use with adding another herbicide;

— by using non-Atrazine herbicides totally;

— by using Atrazine with other strategies such as rotation or pre-plant tillage;

— by banding herbicide used into the crop row;

— by establishing vegetative and riparian buffer areas;

— by using proper rates and methods;

— by using conservation structures to slow water runoff.

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