JEFFERSON CITY - Three and a half million pounds of a weed killer that has been shown to "de-sex" male frogs is spread on Missouri cornfields every year.
But are Missouri men being gradually "de-sexed" as well?
At issue is the nation's top-selling herbicide, atrazine. A study at the University of California-Berkeley released in April showed that the chemical disrupted sexual development in frogs at levels 30 times lower than what the Environmental Protection Agency has deemed safe.
Researcher Tyrone Hayes and colleagues found that the presence of the chemical at levels often found in the Midwest could "demasculinize" male tadpoles. The study showed atrazine caused the tadpoles to turn into hermaphrodites, creatures with both male and female characteristics.
Hayes' study also found the herbicide lowered testosterone levels in adult male frogs by 90 percent, leaving them with less of the sex hormone than normal female frogs.
"Atrazine-exposed frogs don't have normal reproductive systems," Hayes was quoted in a press release. "The males have ovaries in their testes and much smaller vocal organs."
The study notes the effect on humans is not nearly as severe as with frogs, since frogs spend their lives in water and the chemical accumulates in their body. However it warns that the result could be an indicator that the herbicide has a more subtle effect on human sexual characteristics.
This may be what another recent study by MU epidemiologist Shanna Swan indicates, which found that mid-Missourians have much lower sperm counts than their urban counterparts.
Swan's study of 512 men found that men in mid-Missouri had as little as 60 percent of the sperm concentration as men in New York, Los Angeles, or Minneapolis. Her study also showed Missourians to have many fewer active or 'motile' sperm.
Swan examined a number of different explanations for the lower sperm counts in Missouri, including weight, smoking, abstinence, occupation, ethnicity, and education. None of them turned out to be significant.
This led her to examine other factors. In Swan's analysis, she hypothesizes that pesticide run-off could be to blame because a significantly higher percentage of land in Boone County was used for farming than in the other three study sites.
The EPA allows atrazine in levels of up to three parts per billion in drinking water in this country.
Hayes' study, published in Proceedings of the National Academy of Science, found that levels as low as 0.1 parts per billion could cause severe hormonal problems in frogs.
At that concentration, Hayes found that some frogs had as many as six testes or both testes and ovaries.
Haye's lab research has been borne out in the wild. In subsequent field research published last month in Nature, Hayes' team found that as many as 92 percent of male frogs in atrazine-contaminated ponds and streams in the Midwest had abnormal gonads.
Scientists disagree on whether the low sperm counts Swan found are due to pesticides or other factors.
Warren Porter, a professor of zoology at the University of Wisconsin, has no doubt that Missouri men are being affected in the same way as the frogs in Hayes study.
He said Hayes' frogs were a canary in the mineshaft, warning of dangers to human reproductive systems that are now showing up.
Porter said this is because atazine alters the effect of the same enzyme, aromatase, in both frogs and humans. This enzyme controls the production of testoterone relative to estrogen, which could account for low sperm production in humans and the development of ovaries in frogs.
In our water?
Bob Broz, a water quality specialist for University Extension, said that there is no problem with atrazine in Columbia's drinking water, but that nearby rural areas, particularly those that get their water from above-ground sources, were more likely to be contaminated.
Swan's study tested men who visited University Physicians in Columbia, which would include men from both Columbia and rural mid-Missouri.
Broz and Bob Lerch, an expert on pesticides in MU's Soil and Atmospheric Science Department, were more hesitant than Porter to attribute the results of Swan's study to atrazine. Lerch said there is no scientifically proven tie between atrazine and low sperm counts, but he notes that the circumstantial evidence is mounting. He said he hopes Swan's study leads to more research in the area.
It's a compelling finding that begs an answer," Lerch said. "It's reasonable to speculate that [atrazine] may be the cause, but at this time there is no direct link."
Lerch, who studies pesticide contamination of drinking water in Missouri, said the most vulnerable area of the state was the Mark Twain Lake watershed.
Lerch said the highest atrazine levels he's recorded were 120 parts per billion, more than 40 times the EPA standard for safe drinking water, in the ironically named Good Water Creek on the border between Boone and Audrain Counties. This poses little threat to humans as long as they don't drink from the creek, but it doesn't bode well for the creek's aquatic life.
Lerch also provided data from a study sponsored by the pesticide maker Novartis, which showed springtime levels in 1999 at the Clarence Cannon water treatment facility in Stoutville to be twice the EPA standard -- even after the drinking water had been treated.
A farmer's friend
Despite questions about its impact on humans and the environment, atrazine is an important aid in modern agriculture.
Reid Smeta, an assistant professor of agronomy at MU, said atrazine is favored by farmers for a number of reasons.
"It's cheap and can control a lot of different weeds," he said. "It's also persistent."
Smeta said that farmers can apply atrazine on corn at a cost of about $4 an acre. Glyphosate, also known as Round-Up, is a much less toxic alternative but costs about $9 to $12 an acre to apply and may need to be applied more frequently, he said.
Smeta added that atrazine has been around since the 1960s, so it is "off-patent" and can be produced by a number of chemical companies.
Syngenta, one of the world's largest atrazine manufacturers, estimates that atrazine is used on roughly two-thirds of all U.S. corn and sorghum, and that it increases yields by 4 to 6 percent.
Missouri Agricultural Statistics Service in the state's Agriculture Department estimates show that atrazine use was up by nearly a half million pounds statewide last year over 2000. They also show that it is by far the most popular corn herbicide in the state, with more than three times as much atrazine applied as the next most commonly used weed killer.
Swan has sent urine from the men tested in her study to be analyzed by the Centers for Disease Control for traces of atrazine and other pesticides, and plans to publish the results in the coming months.
The results could have important consequences, since the EPA is studying whether to lower the level of atrazine considered safe in drinking water.
Many Europeans have already decided that the herbicide is not worth the risk. Farmers are banned from using atrazine in France, Germany, Italy, Sweden, and Belgium because of concerns it disrupts production of sex hormones.
Swan said a more comprehensive and focused study of sperm counts in men in high atrazine areas could produce better results.
"I'd love to do it," she said. "But I've got to find the research money first."