The term "dioxin" encompasses a family of 219 different toxic
chemicals, all with similar characteristics but different potencies.
In recent years, the International Agency for Research on Cancer
(IARC), a division of the World Health Organization, has labeled the
most potent dioxin, called TCDD, a known human carcinogen. IARC has
labeled many of the less potent dioxins "probable" human carcinogens.
Low-level exposures to dioxins are also known to interfere with the
immune system, the reproductive system, the endocrine system, and the
early growth and development of humans and animals. In sum, dioxins
are a family of powerful all-purpose poisons.
In the early 1990s, many governments, including the U.S. government,
reported that everyone in the industrialized world is exposed to
substantial quantities of dioxins day in and day out, thus
acknowledging a humiliating failure of the world's public health
In 1991, the U.S. EPA [Environmental Protection Agency] with
considerable fanfare announced it was undertaking a full-blown
scientific re-assessment of dioxin. Nine years later, that re-
assessment has now disappeared from view and may have died, a victim of
politics. (See REHW #390, #391.) The big corporate dioxin dischargers
are also major contributors to federal election campaigns, and the
Clinton/Gore administration at this point in history seems incapable of
even gumming the hand that feeds it. Furthermore, since 1994, the
Republican-dominated Congress has dropped all pretense of acting
independently of its corporate sponsors.
Meanwhile, a meeting of 40 scientists convened in Switzerland last May
by the World Health Organization concluded that dioxin is 2 to 10 times
as toxic as it had seemed in 1990, and a group of German scientists
concluded last April that dioxin may be responsible for 12% of human
cancers in industrialized countries. If this estimate were correct,
it would mean dioxin is responsible for 120,000 cancers each year in
the U.S. This new German estimate is at least 10 times as high as
previous estimates by U.S. government scientists (see REHW #390, #391).
The good news is that the levels of dioxin in the environment have
dropped as much as 50% in the last decade as governments in Europe and
local activists in this country have forced industry to adopt cleaner
technologies. Still, many of the effects of dioxins are delayed by a
decade or more, so health effects from past exposures will continue to
manifest themselves for several decades.
Except as laboratory curiosities, dioxins are never intentionally
produced because they have no commercial value. However, they are
created as unwanted byproducts by most combustion processes; during the
manufacture of many kinds of chemicals, pesticides and wood preserva-
tives; during incineration of medical, municipal and hazard- ous
wastes; in metal smelting; and in the manufacture of paper. An
important pathway for spreading dioxins into the environment is using
sewage sludge as a soil amendment or a fertilizer.
Dioxins are also present in cigarette smoke at about the same
concentration found in the stack of a municipal incinerator, the
difference being that no one draws the smoke from an incinerator into
their lungs undiluted, or exhales incinerator flue gas into an enclosed
room for others to breathe.
Some dioxins are more toxic than others, and the scientific community
has established a way of comparing the toxicities and the quantities of
various mixtures of dioxins. The technique is called TEQ, or toxic
equivalents. The TEQ system takes into account the variations in
toxicity and expresses toxicity in terms of the most toxic dioxin,
which is TCDD.
For example, U.S. EPA estimates that total dioxin emissions in the U.S.
averaged about 3000 grams (3 kilograms, or 6.6 pounds) per year TEQ in
1995. This means that all of the dioxins released into the environment
in 1995 in the U.S. had a total toxicity equal to the toxicity of 3000
grams of TCDD. (EPA acknowledges considerable uncertainty in this
estimate; the true average lies somewhere between 1200 grams and 7900
grams TEQ, EPA says.[6,pg.2-7])
According to EPA, the major sources of dioxins in 1995 were municipal
garbage incinerators (1100 grams, 36% of the national total); medical
waste incinerators (477 grams, 16%); cement kilns burning hazardous
waste (153 grams, 5%); industrial coal combustion (73 grams, 2.4%);
residential wood combustion (63 grams, 2%); industrial wood combustion
(29 grams, 1%); diesel engines (33 grams, 1%); copper smelting (504
grams, 17%); aluminum smelting (17 grams, 0.5%); forest fires (208
grams, 7%); incineration of sewage sludge (6 grams, 0.2%); plus 375
grams (12% of the national total) spread directly into the nation's
soils in sewage sludge.[6,pg.2-13] (The total is not exactly 100%
because of rounding.)
Dioxins do not dissolve readily in water, but they do in fat.
Therefore, fat-containing foods tend to be contaminated with dioxins.
Adults in the U.S. take in between one and 10 picograms of dioxin TEQ
per kilogram of body weight per person per day (pg/kg/day).[1,3] (A
kilogram is 1000 grams, or 2.2 pounds; a picogram is a trillionth of a
gram and there are 28 grams in an ounce.) Eighty to 90 percent of our
daily dioxin intake comes from eating milk, meat and fish.
Breast-fed infants take in 70 picograms of dioxin TEQ per kilogram of
body weight per day -- seven to 70 times as much as the average adult.
 Despite this, breast-fed infants are healthier than infants fed
The cancer hazard from routine exposure to dioxin has recently been
estimated by a group of German scientists. They report that, for
adults, the lifetime cancer hazard lies somewhere between one per
hundred and one per thousand for each picogram of dioxin TEQ ingested
per kilogram of body weight per day (pg/- kg/day) Since the daily
ingestion in the U.S. ranges from one to 10 pg/kg/day, we can calculate
that the cancer hazard from environmental exposure to dioxin ranges
between one per thousand and 100 per thousand. The middle of this range
would be 50 per thousand. Because the average person's lifetime chance
of getting cancer is now about 400 per thousand (or four in 10), we can
see that routine exposure to environmental dioxins may be making a
substantial (12%) contribution to the danger of cancer in this country,
if the German estimate holds true. If it holds true, it qualifies as a
public health disaster.
The mechanisms by which dioxin causes cancer remain poorly understood.
In most studies, dioxin seems to be a powerful promoter of cancer,
rather than an initiator. In other words, once a cell has been made
cancer-prone by something else, dioxin may push it over the edge and
turn it into a full-blown cancer. This would explain why dioxin seems
to cause a general increase in many cancers among exposed populations.
However, a study published during 1998 made it clear that dioxin can
cause breast cancer in rats without either initiating it or promoting
it in the traditional sense. As we reported earlier (REHW #630),
researchers in the U.K. exposed pregnant rats to small amounts of
dioxin on the 15th day of pregnancy.
The female offspring of the dioxin-exposed pregnant rats were born
normal, but by the time they were 7 weeks old, their mammary glands had
developed an unusually high number of "terminal end buds" -- the places
in a breast where breast cancers develop. Four studies have shown that
there is a direct correlation between the number of terminal end buds
in a breast and its susceptibility to breast cancer.
The British researchers went on to expose these young rats (and a
control group) to a well-known carcinogenic chemical, dimethylbenz[a]
anthracene. The dioxin-exposed young rats developed many more breast
cancers than did the control group.
Thus a chemical (like dioxin) that, under some circumstances, appears
to protect against breast cancer may, in fact, under other
circumstances, cause it.
Based on non-cancer health effects, the World Health Organization's
meeting on dioxin in May, 1998, recommended that the "tolerable daily
intake" of dioxin should be between 1 and 4 picograms per kilogram of
body weight per day (pg/kg/day). To reach this number, they took the
lowest observed level that caused problems in laboratory animals and
reduced it by a safety factor of 10. Normal practice in such
circumstances would be to apply a safety factor of 100, but, according
to a knowledgable source who asked not to be quoted, if the WHO group
had applied a safety factor of 100 they would have been declaring much
of the food supply in industrial countries dangerously contaminated,
which they were reluctant to do for political reasons.
The middle of the range that they adopted -- one to 4 pg/kg/day --
would be 2.5 pg/kg/day, 4 times as low as the World Health
Organization's 1990 recommendation, which was 10 pg/kg/day as the
tolerable daily intake. Thus the tolerable daily intake recommended at
the May meeting for an adult weighing 70 kg (154 pounds) would be 2.5 x
70 = 175 picograms per day, or 175 x 365 = 63,875 picograms per year.
Now that we know that a picogram of dioxin has some public health
significance, we are in a better position to appreciate that 3000 grams
of dioxin emitted each year by industrial sources in the U.S. is a very
substantial quantity. If we multiply 3000 grams by a trillion to turn
it into picograms, then divide by the U.S. population (260 million), we
can see that 3000 grams of dioxin TEQ represents 11 million picograms
of dioxin TEQ for each man, woman and child in the U.S. each year.
Scientists at the May, 1998, World Health Organization meeting
concluded that, based on animal experiments, the following effects
might be expected in humans: decreased sperm counts might be expected
in humans who have a daily dioxin intake of 14 pg/kg/day; learning
disabilities and endometriosis might be expected in humans with a
dioxin intake of 21 pg/kg/day; suppression of the immune system might
be expected in offspring of humans with an intake of 37 pg/kg/day.
[3,pg.25] The May, 1998 WHO meeting "recognized that subtle effects may
already occur in the general population in developed countries at
current background levels, 2 to 6 pg/kg body weight. They therefore
recommended that every effort should be made to reduce [dioxin]
exposure to the lowest possible level," according to a statement
released by the World Health Organization.
All together, not very reassuring news from Europe about dioxin, we
--Peter Montague (National Writers Union, UAW Local 1981/AFL-CIO)
 Jean A. Grassman and others, "Animal Models of Human Response to
Dioxins," ENVIRONMENTAL HEALTH PERSPECTIVES Vol. 106, Supplement 2
(April 1998), pgs. 761-775. There are 75 polychlorinated dibenzodioxins
(PCDDs), the most potent of which is TCDD; plus 135 polychlorinated
dibenzofurans (PCDFs), plus 9 PCBs (polychlorinated biphenyls) that are
structurally similar to PCDDs and PCDFs.
 Douglas B. McGregor and others, "An IARC Evaluation of
Polychlorinated Dibenzo-P-dioxins and Polychlorinated Dibenzofurans as
Risk Factors in Human Carcinogenesis," ENVIRONMENTAL HEALTH
PERSPECTIVES Vol. 106, Supplement 2 (April 1998), pgs. 755-760.
 "Executive Summary; Assessment of the health risk of dioxins: re-
evaluation of the Tolerable Daily Intake (TDI); WHO Consultation, May
25-29 1998, Geneva, Switzerland." World Health Organization, WHO
European Centre for Environment and Health, International Programme on
Chemical Safety, Final December, 1998. This paper is marked as follows:
"This report does not constitute a formal WHO publication. It should
not be quoted or cited and is for personal use only!" However, see
http://www.who.org/inf- pr-1998/en/pr98-45.html, a WHO press release
announcing the results of the May meeting. We can send the WHO paper
free as an Adobe acrobat file to anyone who requests is by E-mail. If
you want the paper by U.S. mail, please send $3.00 to cover postage and
handling to Rachel's, P.O. Box 5036, Annapolis, MD 21403 with a note
saying what you want.
 Heiko Becher, Karen Steindorf, and Dieter Flesch-Janys,
"Quantitative Cancer Risk Assessment for Dioxins Using an Occupational
Cohort," ENVIRONMENTAL HEALTH PERSPECTIVES Vol. 106, Supplement 2
(April 1998), pgs. 663-670.
 H. Muto and Y. Takizawa, "Dioxins in Cigarette Smoke," ARCHIVES OF
ENVIRONMENTAL HEALTH Vol. 44, No. 3 (May/June 1989), pgs. 171-174.
 U.S. Environmental Protection Agency, THE INVENTORY OF SOURCES OF
DIOXIN IN THE UNITED STATES [EPA/600/P-98/002Aa External Review Draft]
(Washington, D.C.: U.S. Environmental Protection Agency, April, 1998).
 Nadine M. Brown and others, "Prenatal TCDD and predisposition to
mammary cancer in rats," CARCINOGENESIS Vol. 19, No. 9 (1998), pgs.
Descriptor terms: dioxin; who; epa; standards; tolerable daily intake;
tdi; pcbs; tobacco; cigarettes; iarc; carcinogens; cancer;
endometriosis; sperm counts; immunotoxins; immune system;