THE DIOXIN UN-SCARE -- WHERE'S THE MEDIA?
By Reed Irvine
(Mr. Irvine is chairman of Accuracy in Media Inc., a media watchdog group)
From THE WALL STREET JOURNAL, 6 August 1991, p. A16:3
Dioxin has been described as ``the most potent carcinogen
ever tested.'' An unwanted contaminant in some chemicals and
industrial processes, it has been the target of studies funded by
the government to the tune of $400 million over the past decade.
Claims lodged by individuals who allegedly suffered or even
feared serious damage to their health from exposure to dioxin
have cost businesses and the government additional hundreds of
millions of dollars. Now a high government official tells us
that an inordinate fear of dioxin was just a scientific
misunderstanding.
In 1982, the government ordered the evacuation of the 2,232
residents of Times Beach, Mo., because traces of dioxin were
found in the soil. [Concentrations ranged from undetectable to
almost 0.3 ppm.] At that time, the Centers for Disease Control
believed that ingesting anything containing as much as one part
per billion of dioxin posed a significant risk of [sic] human
health. The Environmental Protection Agency spent $33 million
to buy up the town, and declared it to be a dangerous toxic waste
site. Motorists passing through on Highway 44 were greeted with
signs warning them to keep their windows closed and not to stop
and leave their vehicles.
The government pinned the responsibility for the
contamination of Times Beach and 16 other Missouri sites on
Syntex Corp. One of its subsidiaries had bought a plant that had
once supplied dioxin-tainted waste oil to a contractor who had
sprayed it on the streets of Times Beach and the other sites.
After years of costly litigation, Syntex signed a consent decree
a year ago agreeing to clean up the sites and incinerate some
100,000 cubic yards of contaminated soil. Cost estimates run as
much as $200 million over the next decade.
Soon after the demolition of buildings in Times Beach began
this spring, Dr. Vernon Houk, the CDC official who had
recommended the evacuation in 1982, dropped a bombshell. At an
environmental conference [25th Annual Conference on Trace
Substances in Environmental Health] in Missouri, he said that he
would not be concerned about the levels of dioxin at Times Beach
because scientific studies have shown that low doses of dioxin
pose minimal health risks.
Dr. Houk, who is director of the Center for Environmental
Health and Injury Control at the CDC, told reporters that he now
believes that the evacuation of Times Beach was necessary. Asked
what he would tell the former residents of the town, who
underwent the traumas of being torn from their homes, Dr. Houk
said: ``We should have been more upfront with Times Beach people
and told them `We're doing our best with the estimates of the
risk, but we may be wrong.' I think we never added, `but we may
be wrong.' ''
In debunking the claim that dioxin is a potent human
carcinogen, Dr. Houk attacked the scientific theory and
methodology that had led him and others to what he believes was a
false conclusion. Dr. Houk said that the method used to assess
the risk was based on an assumption that violates a fundamental
rule in toxicology: The dose make the poison. It was assumed
that feeding laboratory animals the maximum dose they could
tolerate would enable scientists to determine whether trace
amounts of a chemical would cause cancer in humans. One obvious
problem with this is that different animals have different
responses to the same chemical. What can be highly toxic to
guinea pigs may have no effect on rats, and what may cause cancer
in mice will not necessarily have the same effect on humans.
But Dr. Houk's attack went beyond this. He added his voice
to that of Bruce Ames, head of the biochemistry department of the
University of California at Berkeley, a leading critic of the
methods used to assess the cancer risk from chemicals. Mr. Ames
contends that the animal tests are fundamentally flawed because
the maximum tolerated doses of the chemicals being tested kill
cells due to the sheer size of the dosage. Mr. Ames argues that
this can cause rapid cell division among the surviving cells,
leading to cancer-causing mutations. This suggests that risks
calculated from animal tests involving maximum tolerated doses
are greatly exaggerated.
Dr. Houk says that most scientists now agree with this. He
cites the dioxin case as ``a good example of why we must use both
animal and human data when evaluating the potential health
effects of chemical exposure for humans.'' The epidemiologic
evidence, he says, shows that ``if dioxin is a human carcinogen,
it is rather a weak one in the population exposed to high doses
... and is not a carcinogen in the population exposed to lower
doses.'' He adds that there are no convincing data that show
that exposure to dioxin causes birth defects, chronic diseases of
the liver or of the immune, cardiovascular, or neurologic
systems.
Skeptics have long noted the glaring inconsistency of the
risk assigned to dioxin based on animal tests and actual human
experience. What has brought scientists such as Dr. Houk around
is the mounting empirical evidence and the growing support for a
theory that explains why humans are far less sensitive to dioxin
than are guinea pigs.
The theory is that for dioxin to have a toxic effect it must
first bind to receptors [e.g. Ah receptor]. There appears to be
a dose, which varies by species, below which the receptors don't
function; therefore there is no risk unless that dose is reached
or exceeded. No one knows just what the level is for humans, but
it is apparently far higher than the maximum acceptable intake
level set by the EPA of 0.006 trillionths of a gram [6
femto-grams (fg)] per kilogram of body weight per day. Canada
and some European countries set acceptable levels 170 to 1,700
times that.
The EPA has yet to recognize that dioxin's dangers have been
greatly exaggerated, but Dr. Houk predicts it will eventually
come around. It plans to begin studying the matter soon, but
acceptance of Dr. Houk's analysis won't come easily. Michael
Gough of the Office of Technology Assessment says that if the EPA
backs off on dioxin, it will open the door to demands for
reassessment of many other chemicals. ``That,'' he says, ``is a
door they will reluctantly open.''
In the meantime, the cleanup of Times Beach proceeds. Dr.
Houk says there is little choice but to go ahead with it,
``because we've got the public so riled up.'' The media that got
people riled up with scare stories about dioxin-tainted Agent
Orange, Times Beach and paper-mill effluent have done little to
``unrile'' them. Dr. Houk's turnabout was reported by the St.
Louis Post-Dispatch [23 May 1991] under a front-page banner
headline, but it got little attention in the East. ABC News
reported it; CBS and NBC did not. The newspapers that influence
those in Washington who could bring the costly Times Beach
boondoggle to a screeching halt buried a small AP story deep on
their inside pages.
The following is not part of the original article.
Dioxins are a group of 75 chemicals. The term ``dioxin'' now
refers to one of these chemicals, TCDD.
DIOXIN [TCDD] LD50 VALUES
[LD50: dose necessary to kill half of a group of test animals]
Animal LD50
micro-gm/kg body weight
Guinea Pig 1
Rat-male 22
Rat-female 45
Monkey <70
Mouse 114
Rabbit 115
Dog >300
Bullfrog >500
Hamster 5,000
(Table 1 in Letts, Roger W.M. DIOXIN IN THE ENVIRONMENT: ITS
EFFECT ON HUMAN HEALTH. New York: American Council on Science
and Health, May 1986.)
More sources....
[Associated Press]. ``U.S. Health Aide Says He Erred on Times
Beach'', THE NEW YORK TIMES, I, 26 May 1991, p. 20:1.
Ames, B.N. and Gold, L.S. ``Carcinogenesis debate'' [letter;
comment] Science 250:1498-9 (1990 Dec 14). Comment on:
SCIENCE 250:743-5 (1990 Nov 9).
Ames, Bruce N. and Gold, Lois Swirsky. ``Chemical.
carcinogenesis: too many rodent carcinogens''. PROC NATL
ACAD SCI U.S.A. 87(19):7772-6 (1990 Oct).
Ames, Bruce N.; Profet, Margie and Gold, Lois Swirsky.
``Nature's chemicals and synthetic chemicals: Comparative
toxicology'', PROC NATL ACAD SCI U.S.A. 87:7782-7786
(October 1990).
``[Dioxin (TCDD) is] one of the most feared industrial
contaminants. TCDD is of great public concern because it is
carcinogenic and teratogenic [birth-defect causing] in
rodents at extremely low doses. The doses humans ingest are,
however, far lower than the lowest doses that have been shown
to cause cancer and reproductive damage in rodents. ...
Alcoholic beverages in humans are a risk factor for cancer as
well as birth defects. A comparison of the carcinogenic
potential for rodents of TCDD with that of alcohol (adjusting
for the potency in rodents) shows that ingesting the TCDD
reference dose [EPA's acceptable dose limit] of 6 fg per kg
per day is equivalent to ingesting one beer every 345 years.
Since the average consumption of alcohol in the United States
is equivalent to more than one beer per person per day, and
since five drinks a day are a carcinogenic risk in humans,
the experimental evidence does not of itself seem to justify
the great concern over TCDD at levels in the range of the
reference dose.'' Note: 1 fg = 1 femto-gram = 1e-15 gm.
Ames, Bruce N. and Gold Lois Swirsky. ``Too many rodente
carcinogens: mitogenesis increases mutagenesis.'' SCIENCE
249:970-1 (1990 Aug 31). (Published erratum appears in
SCIENCE 249:1487 (1990 Sep 28).)
Cohen, Samuel M. and Ellwein, Leon B. ``Cell Proliferation in
Carcinogenesis'', SCIENCE 249:1007-1011 (1990 August 31).
Roberts, Leslie. ``EPA Moves to Reassess the Risk of Dioxin'',
SCIENCE 252:911 (1991 May 17).
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