=======================Electronic Edition========================
RACHEL’S HAZARDOUS WASTE NEWS #173
—March 21, 1990—
News and resources for environmental justice.
——
Environmental Research Foundation
P.O. Box 5036, Annapolis, MD 21403
Fax (410) 263-8944; Internet: erf@igc.apc.org
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DIOXIN–PART 2: GAUGING THE TOXICITY OF DIOXIN.
[Continuing our series on dioxin. Page numbers in parentheses
refer to the ATSDR (the federal Agency for Toxic Substances and
Disease Registry) Toxicological Profile for dioxin, cited in our
last paragraph, below.]
It has become fashionable to pooh-pooh dioxin. We believe there
are two reasons why this is occurring. First, some scientists
have been publishing studies indicating that humans exposed to
dioxin do not have an increased risk of cancer. As we saw in RHWN #171,
some of the most important of these studies have now been
exposed as fraudulent. The second reason is that dioxin is so
toxic that it is difficult to express its potency in normal
terms; therefore the media frequently print scary claims without
offering much evidence, leading some people to conclude
(incorrectly) that there isn’t much substance to any claims about
the extreme toxicity of dioxin.
In this series, we hope to lay the groundwork for an
understanding of dioxin, to help people put dioxin into
perspective. Some of what follows may seem a bit more technical
than you are accustomed to reading in this newsletter; but stick
with it, and you’ll see why we have taken this approach.
The scientific and medical evidence presented by ATSDR forces us
to conclude that dioxin deserves our greatest respect. It seems
to be one of the two or three most toxic chemicals ever
discovered, and it is produced as a byproduct of several
different industrial processes. For years, industry has been
dumping dioxin into the environment in large quantities without
paying attention to the consequences. This does not mean there
have been no consequences; it just means no one has made any
systematic effort to tally them up.
Dioxin is a family of chemicals (75 in all) that does not occur
naturally, nor is it intentionally manufactured by any industry
(pg. 1). The most toxic dioxin is called 2,3,7,8-TCDD. Dioxins
are produced as byproducts of the manufacture of some herbicides
(for example, 2,4,5-T), wood preservatives made from
trichlorophenols, and some germicides (for example,
hexachlorophene). Dioxins are also produced by the manufacture of
pulp and paper, by the combustion of wood in the presence of
chlorine, by fires involving chlorinated benzenes and biphenyls
(e.g., PCBs), by the exhaust of automobiles burning leaded fuel,
and by municipal solid waste incinerators.
ATSDR says, “2,3,7,8-TCDD is highly toxic to all laboratory
animals tested….” (pg. 11). Even the most conservative of
toxicologists says, “TCDD has been called the most toxic
synthetic chemical known to man. If its acute toxicity to the
guinea pig, and even the rat and mouse, is the criterion, the
statement is probably correct…. TCDD is unquestionably a
chemical of supreme toxicity to experimental animals. Moreover,
severe chronic effects from low dosages have also been
demonstrated in experimental animals. Therefore, the concern
about its effects on human health and the environment is
understandable.”[1]
In cases of high exposure of humans through industrial accidents,
2,3,7,8-TCDD causes a severe acne (called chloracne) which is not
just a skin ailment; chloracne is a systemic disease that is more
disfiguring than teenage acne and its effects last for years (in
some cases, decades) after exposure (pgs. 3, 39).
There is “suggestive evidence” that 2,3,7,8-TCDD causes liver
damage in humans (pgs. 3, 52-53). It definitely causes severe
liver damage in animals.
In animals, 2,3,7,8-TCDD is toxic to the immune system; such
effects have not been proven in humans (pgs. 3, 40, 54-56). In
animals, 2,3,7,8-TCDD causes reproductive disorders, including
spontaneous abortions. Monkeys are particuarly sensitive to
reproductive effects from exposure to 2,3,7,8-TCDD. Such effects
have not been proven in humans (pgs. 3, 17, 58-59). In animals,
dioxin causes genetic damage (pgs. 60-61).
Both the U.S. Environmental Protection Agency (EPA) and the
International Agency for Research on Cancer (IARC) have concluded
that dioxin is a “probable human carcinogen” (pgs. 7, 61-68, 94).
As we saw in RHWN #171, scientists within EPA have asked that
this question be reviewed again because some of the key studies
of dioxin and cancer were fraudulent, and EPA has relied on these
fraudulent studies to set current standards.
How can we judge the toxicity of dioxin (or of any chemical, for
that matter)? One way is to look at the standards that have been
set by regulatory agencies.
In the case of dioxin, EPA has calculated a “safe” dose, taking
into consideration dioxin’s ability to cause cancer. The “safe”
dose is expressed in extremely small units: femtograms. There are
28 grams in an ounce, and one femtogram is 0.000,000,000,000,001
grams, or one quadrillionth of a gram, or 10**-15 (or, 10 raised
to the power of negative 15) grams.
EPA believes that ingesting (eating) 6.4 femtograms (6.4 x
10**-15 grams) of 2,3,7,8-TCDD per kilogram of body weight per
day would cause cancer in one in a million people so exposed (pg.
95). Since an average adult weighs 62 kilograms or 137 pounds
(average men weigh 70 kilograms [154 pounds] and average women
weigh 55 kg [120 pounds]), the EPA is saying that 397 femtograms
of 2,3,7,8-TCDD consumed in food each day would kill
one-in-a-million humans so exposed. Over a year’s time, 397
femtograms per day add up to 145,000 femtograms; over a 70-year
lifetime, this would add up to 10.1 million femtograms, so 10.1
million femtograms (or 0.01 micrograms) is the maximum amount you
could safely get into your body during your entire lifetime, EPA
believes.
How can we express this in terms that people can grasp?
Let’s compare it to one single aspirin tablet. One aspirin tablet
weighs 5 grains (or 325 milligrams, or 325 trillion femtograms),
so to express one “safe” lifetime dose of 2,3,7,8-TCDD, you would
take a single aspirin tablet and divide it into 32 million
(actually 32,172,218) miniscule pieces. Then one of those tiny
pieces would represent one “safe” lifetime dose of 2,3,7,8-TCDD.
Another comparison: A single grain of table salt weighs
approximately 0.1 milligrams or 100 billion femtograms, so to get
an amount of table salt that weighs the same amount as one “safe”
lifetime dose of 2,3,7,8-TCDD, you would divide a single grain of
table salt into 9,900 microscopic pieces. One of those tiny
pieces would represent a “safe” lifetime dose of dioxin.
The U.S. Food and Drug Administration (FDA) has its own way of
calculating the same one-in-a-million cancer risk and they
believe the EPA has overestimated the hazard by a factor of 10.
In other words, FDA believes you could represent a “safe” dose of
2,3,7,8-TCDD by dividing a single grain of table salt into 990
pieces, with one of those pieces representing a safe lifetime
dose. The federal Centers for Disease Control (CDC) in Atlanta
has done its own calculation, concluding that the cancer hazard
from dioxin is about half-way between the EPA’s estimate and the
FDA’s estimate. EPA says 6.4 femtograms per kilogram of body
weight per day is the safe dose; CDC says the correct number is
27.6; FDA says it’s 57.2 (pg. 95). No matter which agency does
the calculation, there’s no escaping the fact that dioxin is
considered supremely toxic.
One other way to understand the toxicity of dioxin is to compare
the dioxin “reference dose” established by EPA to the “reference
dose” they have set for other common toxic materials. The
“reference dose” is the highest amount they believe you could eat
regularly without incurring any disease (not considering cancer).
The reference dose for dioxin is 0.000,000,001 milligrams per
kilogram of body weight per day (mg/kg/day) (pg. 94); the
reference dose for the toxic metal cadmium[2] is 0.001 mg/kg/day
and the “reference dose” for the toxic metal arsenic[3] is the
same as for cadmium.[2] Thus we can see that EPA considers dioxin
in food 1,000,000 times (one million times) more toxic than
cadmium or arsenic[3], not counting the cancer hazard from
dioxin. Yes, dioxin is toxic, no doubt about it.
–Peter Montague, Ph.D.
===============
[1] Fred H. Tschirley, “Dioxin,” SCIENTIFIC AMERICAN Vol. 254
(February, 1986), pg. 34.”
Get: Agency for Toxic Substances and Disease Registry,
TOXICOLOGICAL PROFILE FOR 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN
(Springfield, VA: National Technical Information Service [NTIS],
5285 Port Royal Rd., Springfield, VA 22161; phone (703) 4874650);
NTIS number PB89-214522. $21.95.
Descriptor terms: dioxin; atsdr; herbicides; wood preservatives;
trichlorophenols; hexachlorophene; pulp and paper; pcbs; msw;
incineration; skin disorders; liver; fda; health effects; sudies;
reproductive disorders; miscarriages; genetic disorders; cancers;
risk assessment; chloroacne;