Oakland (Calif.) Tribune
January 24, 2006


Rachel's summary: Pesticides and other chemicals can be more potent
when added together. University of California Berkeley professor Tyrone
Hayes has found significant harmful effects on frogs given mixtures of
pesticides commonly found in agricultural runoff -- even though levels of
the individual pesticides were thought to be harmless and were 10 to 100
times below EPA standards.

Studies find pesticides and other chemicals are more potent when added

By Douglas Fischer

Chemical mixtures, such as the soup of pesticides found in
agricultural run-off, 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 greater
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
-- where 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, those frogs that spent the most time in the
water as tadpoles were the largest. But 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

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. "The data are extensive. The exposure is
quite low. It takes really high levels (to see effects)," said James
Lamb, a former regulator who is now consulting for the American
Chemistry Council. "We don't have a lot of data on children, but with
data on adults, we don't see effects."

But what alarms Hayes is that he sees effects in frogs at 0.1 parts
per billion, far below any health threshold. The urine of a farm
worker contains, on average, 2,400 ppb of some of these compounds.
Hayes said he could dilute that urine and effectively castrate 720,000

We don't know 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

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, to dissolve fragrances in cosmetics, and to soften

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 upwards of 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 U.S. 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

But for the tadpole, at least those in pesticide-laced run-off, 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."

Wire services contributed to this report. Contact Douglas Fischer at