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#270 - EPA's Dioxin Reassessment -- Part 2: Dioxin Damages Human Immune System, 28-Jan-1992

U.S. Environmental Protection Agency [EPA] is presently reassessing the
dangers of dioxin, one of the most toxic chemicals ever tested on
laboratory animals. As a result of animal tests, EPA has declared only
exceedingly small amounts of dioxin "safe" for the human food supply.
Americans eat food routinely containing roughly 10 to 100 times more
dioxin than EPA considers safe. [SEE RHWN #269.]

No one makes dioxin intentionally, but many industries create dioxin as
a byproduct of their main activity. Industries that emit dioxin into
the environment (paper, plastics, chemicals, and solid waste
incinerators) are being sued for their emissions by citizens claiming
harm from exposure, and one industry--paper--faces billions of dollars
in lawsuits.

Partly to please the paper industry, and partly because there were new
scientific findings worth considering, EPA chief William Reilly
announced a year-long dioxin reassessment to begin in April, 1991.

Now, nine months into the year-long process, EPA scientists responsible
for parts of the reassessment have begun talking openly about new
findings that make dioxin seem as bad as, or worse than, EPA used to
think.

For two decades dioxin has baffled toxicologists. They are used to
seeing cancer-causing chemicals that predominantly cause cancer in one
organ or another--like asbestos, which chiefly affects the lungs, or
benzene, which chiefly affects the blood-forming cells, causing
leukemia. But dioxin seems to cause cancer in many organs, raising the
general level of cancer in a population without causing a huge increase
in any one type of cancer. In addition, dioxin causes certain toxic
effects in one species and other effects in another species. Likewise,
dioxin at low doses causes one kind of illness, and at higher doses it
causes different illnesses. Only recently have EPA scientists concluded
that this puzzling pattern occurs because dioxin acts like an
"environmental hormone." Hormones are potent natural chemicals that
send messages via the bloodstream, turning on and off chemical switches
throughout the body, creating an array of effects in different organs.
Dioxin behaves this way. Hormones are present in the body in tiny
amounts, yet they can trigger huge changes in various bodily systems.
For example, it is hormones that trigger the different stages of growth
in a fetus, and that cause young humans to go through puberty.

New Information

EPA chief William Reilly was right--there IS new information about
dioxin. But it won't be reassuring to the paper industry. On the
contrary, two studies of workers exposed to dioxin, published during
the past year, have shown unmistakable increases in cancers of several
types. A study of 5172 American workers revealed a cancer rate 46%
above the norm.[1] Likewise, a study of 1583 German workers revealed a
cancer rate 39% above the norm; among German workers 20 years on the
job, the rate was 82% above the norm, and among the most heavily
exposed Germans workers, the cancer rate was three times the norm.[2]
Notably, among female German workers, the risk of breast cancer was
doubled. Whereas a year ago one might have argued whether dioxin had
ever been shown to cause cancer in humans, now such arguments are only
voiced by the kind of people who say it still isn't proven that
cigarettes cause lung cancer.

Linda Birnbaum, one of the scientists conducting EPA's reassessment of
dioxin, says these two studies have convinced her that dioxin causes
cancer in humans, at least at relatively high exposures. But, she told
SCIENCE NEWS (January 11, 1992, pgs. 24-27.), she has an even greater
concern about dioxin: "I'm very concerned that much lower exposure to
dioxin may result in adverse health effects that are very subtle and
difficult to detect." She was talking about dioxin's impact on the
immune system.

The immune system is an exceedingly complex network of organs, cells,
and chemical secretions (hormones) that react to preserve health in the
face of a vast array of hostile microorganisms and toxicants that our
bodies encounter every day. The immune system fights against common
colds, influenza, and the body's own cells that go haywire and start to
multiply uncontrollably (a definition of cancer).

A degraded immune system leaves the body less able to defend itself
against hostile forces in the natural environment. Dioxin attacks the
immune system.

EPA's dioxin reassessment will "focus much greater attention on
toxicological data revealing TCDD's [dioxin's] reproductive,
developmental, and immunotoxic effects," says SCIENCE NEWS. Immunotoxic
means toxic to the immune system. Furthermore, "This document [EPA's
draft reassessment] will also establish TCDD as the first pollutant to
be regulated on the basis of toxicity observed at the cellular level."

This is one reason why the dioxin controversy is being followed so
carefully by industry and by environmentalists. It promises to set
precedents in the way chemicals are regulated in the future. In the
past, chemicals were considered harmless if they caused no "clinical"
damage (damage your family doctor might detect). Now, with the dioxin
reassessment, evidence of chemical changes inside individual cells is
being considered important to a person's well being.

"So far, studies in mice suggest that dioxin's immunotoxic punch occurs
in extremely low doses and may well be more important than cancer in
determining dioxin's primary health risk," says Birnbaum."

To study TCDD's toxicity to the immune system, researchers use mice,
whose immune systems model those of humans. For example, EPA
researchers have measured how well TCDD-treated mice withstand the
influenza virus. Mice pre-treated with TCDD readily die after exposure
to a quantity of virus that rarely kills healthy mice.

Naturally, it would be very difficult to detect such effects in people.
If people exposed to unusually high levels of dioxin, say from a solid
waste incinerator, had damaged immune systems and consequently
experienced various illnesses, no one might ever suspect dioxin as a
cause.

People might question whether some of dioxin's low-level effects
represent real harm to people, but "...few people will contend that
suppression of the immune system is not an adverse health effect,"
Birnbaum told SCIENCE NEWS.

Unlike hormones, which remain in the body only a few hours, dioxin has
a half-life in the body of seven years. At the end of one half-life,
half the initial dioxin remains. What this means is that dioxin has,
relatively, a very long half-life in the body, unlike the hormones that
it mimics, so it stays around to play havoc with the body's chemical
systems year after year. "Thus one TCDD [dioxin] molecule can
continuously disrupt normal cell physiology," says SCIENCE NEWS, citing
work by well-known dioxin researcher Thomas A. Gasiewicz at the
University of Rochester (NY) Medical School. EPA's Birnbaum, and
Michael Holsapple, a well-known di-oxin researcher at the Medical
College of Virginia, say studies of humans at Times Beach, Missouri,
and of Vietnam veterans, were essentially bungled. Holsapple says, "If
I were to take mice and ask the same [research] questions that are
routinely asked of the populations of Times Beach or in the Ranch Hand
study [of Vietnam vets exposed to dioxin-contaminated herbicide], I
would come up with a very nebulous picture [of dioxin's
immunotoxicity]," says Holsapple. "But when we ask different questions
[in mice], we can certainly show very strong effects on the immune
response," he says.

Is there a threshold for dioxin's damage to the human body? Is there a
level of dioxin below which no effects can be observed? George Lucier
of the National Institute of Environmental Health Sciences in Research
Triangle, North Carolina, has been asking this question in his
laboratory. His data show no evidence of any threshold. "My data might
not prove that a threshold doesn't exist," he told SCIENCE NEWS, "but
there's also no evidence of any thresholds." In other words, any amount
of dioxin does some damage, according to Lucier's findings. This means
the only safe amount is zero.

This conclusion is not what the paper industry wanted to hear when its
executives urged William Reilly to initiate EPA's dioxin reassessment.
As the reassessment reaches its draft stages early this summer, we'll
have new measures of the potency not only of dioxin, but also of
industry's muscle in a contest with unwelcome scientific conclusions.

For all of us, much is riding on the outcome.

--Peter Montague

=====

[1] Marilyn Fingerhut and others, "Cancer Mortality in Workers Exposed
to 2,3,7,8-tetrachlorodibenzo-P-dioxin," NEW ENGLAND JOURNAL OF
MEDICINE Vol. 324 (1991), pgs. 212-218.

[2] A. Manz and others, "Cancer Mortality Among Workers in Chemical
Plant Contaminated With Dioxin," THE LANCET Vol. 338 (October 19,
1991), pgs. 959-964.

Descriptor terms: dioxin; dioxin reassessment; immune systems; epa;
cancer; pulp and paper industry; william reilly;