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#173 - Dioxin - Part 2: Gauging The Toxicity Of Dioxin, 20-Mar-1990

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

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


[1] Fred H. Tschirley, "Dioxin," SCIENTIFIC AMERICAN Vol. 254
(February, 1986), pg. 34."

[2] Agency for Toxic Substances and Disease Registry, TOXICOLOGICAL
PROFILE FOR CADMIUM (Springfield, VA: National Technical Information
Service [NTIS], 5285 Port Royal Rd., Springfield, VA 22161; phone (703)
487-4650), pg. 76.; NTIS number PB89-194476. $21.95.

[3] Agency for Toxic Substances and Disease Registry, TOXICOLOGICAL
PROFILE FOR ARSENIC (Springfield, VA: National Technical Information
Service [NTIS], 5285 Port Royal Rd., Springfield, VA 22161; phone (703)
487-4650), pg. 92.; NTIS number PB89-185706. $21.95.

Get: Agency for Toxic Substances and Disease Registry, TOXICOLOGICAL
National Technical Information Service [NTIS], 5285 Port Royal Rd.,
Springfield, VA 22161; phone (703) 4874650); NTIS number PB89-214522.

Descriptor terms: dioxin; atsdr; herbicides; wood preservatives;
trichlorophenol; hexachlorophene; pulp and paper industry; pcbs; msw;
incineration; skin disorders; liver disease; fda; health effects;
studies; reproductive disorders; miscarriages; genetic disorders;
cancer; risk assessment; chloracne;

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