RACHEL: Dioxin Reassessed, #2 
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 RACHEL: Dioxin Reassessed, #2

=======================Electronic Edition========================

                       ---May 26, 1994---
                    Dioxin Reassessed--Part 2
                Environmental Research Foundation
               P.O. Box 5036, Annapolis, MD  21403

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After three years of study, U.S. Environmental Protection Agency
[EPA] is about to publish a 9-volume draft "scientific
reassessment" of dioxin and other dioxin-like chemicals,
including dibenzofurans and some PCBs [polychlorinated
biphenyls].  PCBs are industrial poisons now banned in the U.S.
because of widespread environmental damage.  Dioxins and furans
are highly toxic byproducts of certain industrial operations
including incineration, tire burning, combustion of coal and oil,
manufacture of paper and some pesticides, metal smelting, and
perhaps diesel engine exhausts [pgs. 6-9].  There are probably
other sources as well.  Dioxins and furans are created when
chlorine combines with other chemicals at high temperatures.

A copy of EPA's summary volume (Chapter 9) was leaked to the
press in mid-May.  We obtained a copy and reported some of its
findings and conclusions last week, focusing on the cancer
hazard.  This week, we bring you more, stressing non-cancer
effects. [Page numbers inside square brackets refer to EPA's
draft of Chapter 9, dated May 2, 1994.]

According to EPA, nature produces only small amounts of dioxin.
The vast majority of dioxin is created by human economic
activities.  Since about 1920, industrial emissions, and
inattention to the potent toxic effects of dioxin-like chemicals,
have allowed the environment to become widely contaminated with
significant quantities of dioxins, furans and PCBs.  As a result,
all Americans eat and breathe small but important amounts of
dioxin every day.

Human exposure to dioxin begins early in life.  A human fetus
lives in the womb enclosed inside a fluid-filled sac called the
placenta, which provides a barrier to many poisons that the
mother might ingest. Unlike many other poisons, dioxin crosses
the placenta and begins affecting the fetus [pg. 23].  The human
body retains dioxin, so a "body burden" begins accumulating in
each of us during our early months in the womb.[1]

In humans and other species, it is the growing embryo or fetus
that is most sensitive to the toxic effects of dioxin-like
chemicals.  EPA: "A general finding in fish, bird, and mammalian
species is that the embryo or fetus is more sensitive to
TCDD-induced mortality than the {*filter*}. [TCDD is a shorthand name
for dioxin.]  Thus the timing of TCDD exposure during the life
history of an animal can greatly influence its susceptibility to
overt dioxin toxicity." [pg. 36]

Growth occurs in two ways: cells multiply, and cells of one type
turn into cells of another type (a process called
differentiation).  Thus some cells become eyes and other cells
become fingers by differentiation.  Dioxin-like chemicals can
disrupt both cell multiplication and cell differentiation.

"Of particular interest to the risk assessment process is the
fact that a wide variety of developmental events, crossing three
vertebrate classes and several species within each class, can be
perturbed, suggesting that dioxin has the potential to disrupt a
large number of critical developmental events at specific
developmental stages.  Not only can these changes lead to
increases in embryo/fetal mortality, but they can disrupt organ
system structure and irreversibly impair organ function." [pgs.
34-35].  In other words, damage that occurs in the womb can last
a lifetime.

After a baby (or animal) is born, rapid growth continues, so
sensitivity to the toxic effects of dioxin continues as well.
Human infants who {*filter*} feed get a particularly high dose of
dioxins.  EPA's report calculates that an infant who {*filter*} feeds
for a year will receive 4% to 12% of his or her full lifetime
dose of dioxin during that one year [pgs. 15, 21].  (Despite the
presence of dioxin-like chemicals in human milk, {*filter*} feeding
is still the best way to nourish an infant; all of the
alternatives are worse.[2])

Although dioxin can presumably interfere with every bodily system
in the growing infant, there is evidence that the developing
immune system is one of the most sensitive to disruption by
low-level exposure to dioxin-like chemicals.  EPA says,
"Furthermore, since TCDD [dioxin] alters the normal
differentiation of immune system cells, the human embryo may be
very susceptible to long-term impairment of immune function from
in utero [in the womb] effects of TCDD on developing immune
tissue." [pg. 39]

EPA points out that, "Impairment of the immune system can be
considered an adverse outcome in its own right, being responsible
for induced pathologies." [pg. 51]  And: "Concern over the
potential toxic effects of chemicals on the immune system arises
from the critical role that the immune system plays in
maintaining health.  It is well recognized that suppressed
immunological function can result in increased incidence and
severity of infectious diseases as well as some types of cancer.
Conversely, the inappropriate enhancement of immune function or
the generation of misdirected immune responses can precipitate or
exacerbate the development of allergic and autoimmune diseases."
[pg. 37]  In other words, there are two ways your immune system
can malfunction: it can be depressed and fail to protect you
against bacteria, parasites, viruses and cancer.  Or it can
become too active and start to attack you; this creates
autoimmune diseases like asthma, diabetes, and lupus.

EPA clearly considers these immune system hazards important; the
report spends considerable time discussing them: "Animal host
resistance models that mimic human disease are available and have
been used to assess the effect of TCDD on altered host resistance
[to disease]. Results from host resistance studies provide
evidence that exposure to TCDD results in increased
susceptibility to bacterial, viral, parasitic, and neoplastic
[cancer] disease. These effects are observed at relatively low
doses and likely result from TCDD-induced suppression of
immunological function." [pg. 38]

The immune system is as complex as the brain and central nervous
system.[3]  Scientists speak of two basic parts of the immune
system: those that work via cells (called "cell-mediated") and
those that work in the {*filter*} stream without entering cells
(called "humoral").

EPA: "Both cell-mediated and hum{*filter*}immune responses are
suppressed following TCDD exposure, suggesting that there are
multiple cellular targets within the immune system that are
altered by TCDD.  Evidence also suggests that the immune system
is indirectly targeted by TCDD-induced changes in nonlymphoid
tissues." [pg. 38]

EPA goes on: "One potentially important indirect mechanism is via
effects on the endocrine system.  Several endocrine hormones have
been shown to regulate immune responses, including
glucocorticoids, sex steroids, thyroxine, growth hormone, and
prolactin.  Importantly, TCDD and other related compounds have
been shown to alter the activity of all of these hormones." [pg.

The EPA's draft report speaks of "a window of sensitivity of
biological processes." [pg. 48]  In other words, there are
certain times during the life of an animal (or human) when it is
more sensitive to dioxin's effects than at other times.  The
perinatal period (shortly before or shortly after birth) is one
such "window of sensitivity."  But there are evidently other such
"windows."  EPA suggests that any time the immune system begins
to respond to a challenge, disruption by dioxin can have
far-reaching effects: "It is important to consider, however, that
if an acute exposure to TCDD even temporarily raises the TCDD
body burden at the time when an immune response is initiated,
there may be a risk of adverse impacts even though the total body
burden may indicate a relatively low average TCDD level." [pgs.
38-39]  Thus even a short-term exposure to dioxin at the wrong
time might cause disease in a person by suppressing the immune
system, even though the person's average lifetime body burden of
dioxin may not be greatly increased.

Dioxin may also cause inheritable genetic changes: "While dioxin
and related compounds are not generally considered to be
'genotoxic' in traditional terms, both empirical data and the
results of modeling efforts suggest that they may be functioning
indirectly to produce irreversible genetic changes in exposed
cells." [pg. 33]

EPA's draft report emphasizes that most people get their daily
dose of dioxin from their cooking.net">food (about 90% from meat, fish and
dairy products) [pg. 12]. However, people who live near sources
of dioxin emissions (listed in our first paragraph, above),
should consider that inhalation may be an important hazard for
them.  EPA says, "The use of incineration as a means of solid and
hazardous waste management results in the emission of
contaminated particles that may contain TCDD and related
compounds into the environment.  Thus, exposure to TCDD and
related compounds may result from inhalation of contaminated fly
ash, dust and soil. Systemic effects occur in animals after
pulmonary exposure to TCDD, suggesting that transpulmonary [lung]
absorption of 2,3,7,8-TCDD does occur.  Further results suggest
that the transpulmonary absorption of 2,3,7,8-TCDD and
2,3,7,8-TBDD was similar to that observed following {*filter*}
exposure.... these data provide support for the inference that
efficient absorption will occur when particles containing dioxin
and related compounds are inhaled by humans." [pgs. 17-18]

How much dioxin is "safe"?  EPA: "The USEPA has frequently
defined a reference dose (RfD) for toxic chemicals to represent a
scientific estimate of the dose below which no appreciable risk
of non-cancer effects is likely to occur following chronic
exposures.  In the case of dioxin and related compounds,
calculation of an RfD based on human and animal data and
including standard uncertainty factors to account for species
differences and sensitive subpopulations would result in a
reference intake levels on the order of 10-100 times below the
current estimates of daily intake in the general population."
[pg. 51]

How much dioxin is "safe"?  EPA's answers: For cancer hazards?
Three hundred to 600 times less than we all now take in every
day.  (See RHWN #390.)  For non-cancer hazards?  Ten to 100 times
less than we all now take in every day.

EPA's "dioxin reasessment" raises one key public policy
question:  How much additional dioxin is acceptable in the
environment?  To us, the answer seems clear: zero.  To protect
public health, no new sources can be allowed, and present
sources must be sharply reduced.
                                         --Peter Montague, Ph.D.
[1] The "half-life" of dioxins in humans is somewhere between 5.8
years and 7 years [pgs. 13, 20].   (The half-life is the time it
takes for half of today's dioxin intake to be excreted.)
Therefore, dioxin builds up in our bodies as we age.

[2] See, for example, Natalie Angier, "Mother's Milk Found to Be
Potent{*filter*}tail of Hormones," N.Y. TIMES May 24, 1994, pgs. C1,

Publication No. 88-529] (Bethesda, Md.: National Institutes of
Health, July, 1988).

Descriptor terms:  epa; dioxin reassessment; studies;
dibenzofurans; furans; pcbs; tire burning; coal; oil; fossil
fuels; paper; pesticides; metal smelting; smelters; diesel;
chlorine; infants; festuses; immune system; immunotoxicity;
asthma; lupus; diabetes; incineration; msw; hazardous waste;
inhalation; air pollution;

Mon, 11 Nov 1996 04:20:27 GMT
 [ 1 post ] 

 Relevant Pages 

1. RACHEL: Dioxin Reassessed, #1


3. Rachel: DIOXIN

4. dioxin human health (was Greenpeace leaked dioxin...)

5. Dioxins and Pregnancy

6. Dioxin and Native Communities

7. Dioxin & PCB Pollution: An Update

8. Dioxin and endometriosis

9. Test for dioxin exposure

10. ARTICLE: DIOXIN linked to health

11. ARTICLE: US Study shows how to eliminate Dioxin

12. Study Of Dioxin-Exposed Humans

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