TCS Daily


Frog Fog

By Alex Avery - January 17, 2003 12:00 AM

Is a widely used herbicide causing transgendered frogs?

Ever since a group of Minnesota middle school students found some deformed frogs while on a nature class field trip in 1995, environmental scientists have been intensively looking for the causes of both frog deformations and reported frog population declines in some areas of the world.

It's been a heated debate and some environmental activists have been pointing the finger at farm pesticides since day one.

Recent research by a group at UC Berkeley supposedly shows that trace concentrations of the herbicide atrazine, commonly used while growing corn in the American Midwest, causes hermaphroditism in the North American leopard frog. (Hermaphroditism means the amphibians have physical attributes from both sexes.) In this case, a team led by Dr. Tyrone Hayes - and funded by activist environmental foundations - reports that in a seemingly high percentage of frogs at herbicide-contaminated sites, the developing testicles of male leopard frogs had immature eggs within them, rather than immature sperm. Female frogs developed normally.

The effects were also seen in the laboratory at atrazine concentrations of 25 parts per billion (ppb) and 0.1 ppb. For comparison, 0.1 ppb is equivalent to 1 inch in 160,000 miles. (6.4 times the circumference of planet earth!)

Curiously, the highest rates of hermaphroditism were seen at sites with the lowest atrazine levels. In the laboratory, much higher rates of underdeveloped and egg-containing testes were seen in male frogs exposed to 0.1 ppb than in male frogs exposed to 25 ppb atrazine. In the wild, the team found that 92% of male frogs at one site in Wyoming had what appeared to be immature eggs in their testes. The atrazine levels at this site in July were only 0.2 ppb atrazine.

All of this would be much scarier if hermaphroditism in leopard frogs were rare, if the results were actually consistent and logical, and if leopard frog populations were threatened or endangered. But hermaphroditism in leopard frogs has been well documented for nearly 200 years, the results were not consistent or logical, and leopard frogs appear to be abundant. In fact, the team had absolutely no trouble finding leopard frogs to study at any of the sites in the wild.

As to the inconsistent results, three other sites had similarly low levels of atrazine as the site in Wyoming where the team found the highest rate of abnormalities, but all had different rates of hermaphroditism. At one site, none showed any abnormalities, another showed only 10 percent and the last had roughly 40 percent abnormalities in the male frogs.

Worse for the researchers, the levels of atrazine found in July, when developmentally mature frogs were collected, may be very different than the levels of atrazine in the water when the frogs are actually metamorphosing from larvae to adults.

Nor do the field observations agree with what was seen in the lab. The lab findings indicated underdeveloped testes should be the most frequent abnormality found, yet it was immature eggs in the testes that was most often seen in the field. Only one field site had frogs with underdeveloped testes.

Finally, reports of hermaphroditism in frogs in the wild occurred decades before any atrazine was used on farms.

You might ask why take any chances? Why not just do what some European countries have done and ban atrazine, just to make sure we're not causing any effeminate male frogs? The main reason is, it's a very effective and useful farm input that allows us to grow corn using less fossil fuel and increase yields by keeping down weed competition. More importantly, atrazine is a key herbicide used in no-till corn farming.

No-till farming means no tillage. Tillage is the old, "bare-earth" way of killing weeds. The farmers hoe, plow, or disk several times per year between the rows of corn to bury and kill weeds. The problem is that all of this dirt churning opens the soil to wind and water erosion, meaning a bunch of our precious topsoil gets carried away each year.

Replacing these crude, labor-intensive, and resource-wasteful mechanical weed-killing methods with safe, effective herbicides leaves the soil undisturbed. The residues of crop plants and weeds are left on top of the soil to help protect it, and the organic matter content of the upper soil layers increases under no-till. No-till not only cuts soil erosion rates by 70-95 percent, it leaves the soil in much better shape. Earthworm populations are much higher in no-till fields - it turns out earthworms hate being plowed.

Time will tell if the Berkeley scientists are on to something with this latest research. So far, other science labs have been unable to replicate the team's earlier research. This replication is the real gold standard of science. Until the frog abnormalities are replicated by other research teams, these findings are nothing more than biased speculation.

The author is director of research and education with the Center for Global Food Issues at Hudson Institute.
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