Feeding Rodents Is No Way To Measure Cancer Risk (D. Avery)

CHURCHVILLE, Va.–One of organic farming’s most widely used pesticides–pyrethrum–has been classified
as a “likely human carcinogen.” An advisory committee to the Environmental Protection Agency made the
classification two years ago, after pyrethrum caused higher-than-normal numbers of tumors in two sets of
laboratory rodents.

The advisory committee’s decision was not made public at the time but recently came to light as the result of
a court suit.

The fact that pyrethrum has been classified as a “likely human carcinogen” does not mean the chemical is a
danger to consumers.

Pyrethrum is a botanical nerve toxin, but it has low toxicity for people, it’s applied at low rates, degrades
quickly in sunlight and leaves little residue.

Pyrethrum is made from flowers (a variety of chrysanthemum) that are grown and picked by the billions in
East Africa, by women and children, who don’t get sick from doing so. In the 19th century, people used the
ground-up flowers as a body powder to kill lice, without setting off a cancer epidemic.

The real significance of the pyrethrum classification is this: Organic farmers have been needlessly frightening
consumers for decades over synthetic pesticides. The regulatory test for human carcinogens is not whether
the pesticide at realistic exposure levels causes cancer in people. Only one approved pesticide has ever
flunked that test: lead arsenate, which hasn’t been used in 40 years.

The official test for a “likely human carcinogen” is whether giving the rats 100,000 times or 200,000 times
the expected human exposure can cause tumors. About half the thousands of chemicals (both natural and
man-made) put through the high-dose rodent tests have triggered extra tumors.

The first rule of toxicology is “the dose makes the poison.” Many poison are actually beneficial to people in
small doses (like iodine and arsenic).

Virtually no substance is as dangerous in low doses as at high ones. That’s why government regulators have
approved a wide variety of pesticides for use at low rates even though these, like pyrethrum, can cause rat
tumors at high doses.

Rotenone, an organic pesticide squeezed from the roots of tropical plants, has produced symptoms like
those of Parkinson’s disease when massive doses are injected directly into rats.

That certainly doesn’t mean eating organic food will cause Parkinson’s disease. “We found you can (reduce)
the cancer-causing impact of one of the most potent carcinogens from 90 percent down to 3 percent just by
cutting rodent caloric intake by 20 percent,” said Ronald Hart, then-director of the National Center on
Toxicological Research in 1990.

“We feed rats ‘all-you-can-eat’ buffets every day, yet we know that caloric intake is the single greatest
contributing cause of cancer,” Hart said. “This means high-dose feeding skews the results.”

In short, the high-dose rodent tests are guaranteed to frighten us. That’s why they’ve been so loved by the
environmental activists and organic farmers all these years.

In 1990, Science magazine editorialized, “The standard carcinogen tests that use rodents are an
obsolescent relic of the ignorance of past decades.” We could make the rat tests more useful, by testing at
some reasonable safety factor beyond the maximum expected human exposure–say, 1,000 times what we
think people will encounter.

Instead, Ron Cummings of the Organic Consumers Association is ready to sacrifice pyrethrum on the altar of
the rodent gods. “If pyrethrum is as dangerous as it sounds, then it shouldn’t be allowed (for organic farms),”
he told me.

The problem is that Cummings and his eco-allies are backing humanity into a tighter and tighter corner on
food production and wildlife habitat preservation, without giving us safer food.

An organic farming couple in Michigan is trying to protect their crops without pesticides, using a shop
vacuum and portable generator carried in a wheelbarrow. The husband spends huge amounts of time trying
to suck the insects off his crops, leaf by leaf. Even that endless stoop labor doesn’t help against fungi or plant
diseases. You can produce food without pesticides, but you can’t produce much.

The other question that pyrethrum’s classification as a “likely human carcinogen” brings to mind is: Why
didn’t the organic industry tell us?

For decades, the organic movement has persecuted the chemical companies for not caring about their
consumers and for risking the health of children by marketing “carcinogenic” pesticides. But when one of
their own pesticides was caught in the same phony trap, they kept it secret for two years.

Copyright © 2001 by Hudson Institute.

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