Gardening Columns

Frogs, Ethanol, Herbicides, and Why We Should Care

First published on garden.org on December 4, 2008, by Suzanne DeJohn

Although the authenticity of Chief Seattle's famous "All Things Are Connected" speech is disputed, the underlying principle rings true: Whatever man does to the web of life on Earth, he does to himself. A story I recently read in ScienceNews reminded me of this.

Biologists have been alarmed at declining amphibian populations for several decades, with some species showing bizarre deformities such as extra or missing limbs. Numerous species are near extinction, and scientists can only speculate on how many undiscovered amphibians have already been lost. Conservation groups declared 2008 the Year of the Frog to raise awareness about the problem. Researchers have suspected that farm chemicals, specifically herbicides, might somehow be involved but it wasn't until recently that a direct link was made.

A Decade-Old Dilemma
In the mid 1990s, scientists noted high rates of limb deformities in frogs, which were debilitating if not fatal. Initially, the cause for the sudden increase in these deformities puzzled scientists. Subsequent research pointed to tapeworm infection as the cause, but the reason for higher tapeworm infection rates was unknown.

According to the November 22, 2008 issue of the journal ScienceNews, ponds contaminated with atrazine, the second-most widely used herbicide in American agriculture, contain many more amphibian-infecting flatworms than unaffected waters. At the same time, the chemical appears to diminish the ability of larval frogs to fight off these parasites.

Now add in the results of new studies, which show that phosphate pollution, caused by fertilizer runoff, boosts algae growth, which in turn increases snail populations. These snails serve as intermediate hosts for developing parasitic flatworms, further increasing the parasites' population.

Picture a pond near an agricultural field that's been fertilized with a soluble fertilizer and also treated with atrazine herbicide. Rain washes some of the chemicals into the pond. The fertilizer feeds an algae bloom, which in turn causes the snail population to skyrocket. The snails harbor parasitic larval tapeworms that are released as adults and go on to infect frogs. At the same time, the atrazine is affecting the frogs' immune system, leaving them particularly vulnerable to infection. The frogs don't have a chance.

Because they live both in water and on land, amphibians are especially vulnerable to toxins and changes in their environment. They also breathe and take in water through their very sensitive skin. Many species reproduce in vernal pools -- temporary wetlands that occur in spring -- the occurrence of which is affected by changes in weather patterns.

Why It's Important
Why should we care about a few frogs? Many would argue that we should care about these diminutive denizens just as much as we worry about the more charismatic polar bears and pandas. Frogs and other amphibians are vital parts of the food web and their decline affects the survival of other species. Closer to home, various frog species are the source of chemicals used in human medicines, including pain killers, antibiotics, and treatments for stroke, HIV, and cancer.

Amphibians have been likened to the canary in the coal mine -- species that are particularly vulnerable to environmental toxins. Their alarming decline may serve as an early warning that our health and survival may be in jeopardy, too. Researchers have discovered that atrazine exposure in frogs causes a reduction in male hormones. Atrazine activates an enzyme that converts testosterone to estrogen -- the same enzyme found in humans -- leading to speculation about a connection between atrazine and diseases associated with hormone levels, including breast and prostate cancers. Several studies have shown a possible link between atrazine and cancer; however, the U.S. Environmental Protection Agency disputes these studies and deems atrazine safe when applied properly. (The European Union banned atrazine in 2004.)

Herbicides, Corn, and Ethanol
The herbicide atrazine is widely sprayed on cornfields to control weeds. According to a report by Minnesota Public Radio, each year Minnesota farmers apply just under two million pounds of it. Nationwide, farmers use tens of millions of pounds annually. And now even more land is being converted to corn production to supply new ethanol-producing plants. Ironically, although ethanol produces less pollution than gasoline when burned, farmers growing corn rely heavily on synthetic pesticides. The net result may mean more, not less, pollution.

What's a Gardener To Do?
Atrazine is available only to commercial pesticide applicators, so you aren't using it in your landscape. However, gardeners nationwide apply a staggering amount of lawn and garden chemicals. Consider using eco-friendly techniques to control pests (including weeds) and improve soil health. Also, try to purchase foods from local farmers -- you can ask them about their pest control philosophy and practices. Become an informed citizen so you can make your voice heard when opportunities arise.

For more information visit these Web sites:

Living on Earth:
http://www.loe.org/shows/segments.htm?programID=06-13-00016&segmentID=1

U.S. EPA
http://www.epa.gov/pesticides/reregistration/atrazine/atrazine_update.htm

Syngenta, maker of atrazine:
http://atrazinefacts.com/