Chemical mixtures pose more dangers

Oakland Tribune, Jan 25, 2006 by Douglas Fischer, STAFF WRITER

Chemical mixtures, such as the soup of pesticides found in agricultural runoff, can be vastly more toxic to humans and creatures than a single chemical, suggesting current efforts to assess health risks posed by such compounds significantly underestimate their danger, researchers find.

The threat comes not just from pesticides: The plastic lining your soup can, the additives used to keep nail polish from chipping and beach balls from cracking, even the trace amounts of DDT found in your house dust all can have an effect when mixed with others far greaterfrom News 1

than any single chemical alone.

And that means, scientists say, that safety tests used by the U.S. Environmental Protection Agency and the Food and Drug Administration -- in which one compound is tested and regulated in isolation -- miss the real effects of the chemical stew making up our world.

The most recent finding came Tuesday from University of California, Berkeley, professor Tyrone Hayes. His report, published in the online version of the journal Environmental Health Perspectives, found significant harmful effects on frogs given mixtures of pesticides commonly found in agricultural runoff -- even though levels of the individual pesticides were thought not to cause harm and were 10 to 100 times below EPA standards:

-Frogs treated with the mixture were, on average, 10 to 12 percent smaller than the untreated control group.

-Nearly 70 percent of those frogs succumbed to a common pathogen that the control group successfully fought off.

-In the control group, frogs that spent the most time in the water as tadpoles were the largest. But it was reversed for tadpoles swimming in the treated water found the reverse -- the longer they stayed tadpoles, the smaller they were as frogs.

-Treated frogs developed holes, or plaques, in their thymus, an organ crucial for suppressing disease.

-Those frogs also had high levels of corticosterone -- a hormone, similar to one also found in humans, associated with stress and known to decrease growth and retard development.

And in a related paper, also published Tuesday, Hayes showed these chemicals are quite efficient at switching testosterone to estrogen, which means the testes of exposed male frogs don't produce sperm -- they produce eggs.

"Metolachlor" -- a common herbicide -- "doesn't do anything on its own," Hayes said Tuesday. "But mix it with something else and it becomes bad somehow. You add them all up and you get significant effects."

Representatives of CropLife America, a trade group representing pesticide companies, had no comment Tuesday on the new findings. The group has long said, however, that there is insufficient evidence that pesticides harm frogs.

Chemical manufacturers decry any effort to link extremely low levels of their chemicals to harm.

It is unknown what that means for humans, however. But Dr. Shanna Swan, a researcher at the University of Rochester, has found an association between low fertility in men and pesticide concentrations in urine as low as 0.1 ppb.

"All we know is that humans are exposed to large amounts of chemicals," Swan said. "Rodents are exposed to one chemical at a time."

Swan has found similar problems in baby boys born to women with high levels of phthalates (THAAL-ates), a common additive used to make nail polish chip-proof, dissolve fragrances in cosmetics, and soften plastics.

That meshes with research by the U.S. EPA in North Carolina that finds phthalates, when added together at levels known to cause little or no problems individually, somehow afflict more than a quarter of the test animals with permanent reproductive damage.

Levels of those phthalates in the amniotic fluid of the most highly exposed women in the United States are not too far from levels known to cause harm in rats.

And, Hayes notes, a fetus in amniotic fluid is not all that different from a tadpole in a pond.

"It's like pregnancy: The longer you're pregnant, the bigger your baby. The longer the tadpole (stage), the bigger the frog," Hayes said.

But for tadpoles, at least those in pesticide-laced runoff, that is no longer true.

"It's like, the longer she's pregnant, the smaller your baby's going to be," Hayes added. "That says the womb is not a nurturing place."

This newspaper's investigation of our chemical "body burden" can be found on the web at http://www.insidebayarea.com/bodyburden.

Wire services contributed to this report. Contact Douglas Fischer at dfischer@angnewspapers.com.