Coalition for Responsible Waste Incineration
What are Dioxins and Furans?
The term "dioxin" is commonly used to
describe a family of chemical compounds containing 75
dioxins and 135 furans. A dioxin consists of two benzene
rings connected by two oxygen atoms. A furan consists of two
benzene rings connected by one oxygen atom. Often chlorine
molecules are attached at different positions on the dioxin
compound. The number and position of these chlorine atoms
are very important in the toxicity of dioxins. The 75 dioxin
compounds differ among themselves only by the location and
number of chlorine atoms attached to the molecule.
Dioxin does not dissolve readily in
water, it has a high melting and boiling point and only
slowly evaporates. e.g., from surfaces of soil, water, or
plants. Dioxin binds tightly with other organic compounds
and thus, can readily accumulate in soils and sediments. In
humans and animals, dioxins are stored in fat tissue, slowly
metabolized, and eventually eliminated from the body.
Studies of dioxin levels in humans suggest that an amount of
dioxin stored in fat tissue decreases by one-half every
seven years (Gough 1993).
Why Should I be Concerned about
Scientists have determined that one
dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, often
abbreviated as TCDD) is extremely toxic to guinea pigs and
certain types of mice and will cause chloracne in humans.
Chloracne is an temporary skin condition that appears after
exposure to high levels of dioxin and usually disappears
shortly after the exposure is removed. EPA has classified
dioxins as a probable human carcinogen. The eighth edition
of the National Toxicological Panel Report lists
2,3,7,8-TCDD as "reasonably anticipated to be a human
What is Known about the Toxicity of
There are two key factors in determining
the toxicity of dioxin compounds: the number of chlorine
atoms present and the position of those atoms. Dioxin
compounds with four chlorine atoms in the 2,3,7,8 position
of the dioxin molecule exhibit the greatest toxicity. Dioxin
compounds with less than four chlorine atoms are not toxic
Dioxin compounds that do not have
chlorine atoms in the 2,3,7,8 positions are also not toxic
(EPA, 1994), no matter how many chlorine atoms are present.
In addition, compounds with more than four chlorine atoms
exhibit less toxicity when compared to 2,3,7,8-TCDD (see
The scientific community has developed
and accepted a scheme for comparing the toxicity of
different dioxin compounds, referred to as a toxicity
equivalency factor (TEF). Some of the TEFs (EPA 1998a) are:
Mono-, Di-, and Tri-CDD
A similar scheme is developed for furans, but with lower
TEFs. Thus, as the number of chlorine atoms present on the
molecule increases above four, the toxicity of the
dioxin/furan decreases. Most of the information about dioxin
toxicity is derived from studies of the 2,3,7,8-TCDD and
simple screening tests for the others. Little work has been
done to evaluate the toxicity of the other 74 dioxins and
the validity of the TEF relationships.
An often repeated statement is that TCDD
is "one of the most toxic man-made compounds known." This is
based on the observed effect that very small doses of
2,3,7,8-TCDD are lethal to guinea pigs. However, other
species, including humans, react differently. Humans appear
to be markedly less sensitive, requiring very large doses of
dioxin before any adverse health effect is noted (chloracne).
What are the Health Effects Associated
Some scientist, including those in the
EPA, have alleged a number of adverse health effects such as
reproductive impairment, adverse effects on development of
offspring, changes in some enzymes, onset of diabetes,
endometriosis, and potential disruption of certain
components of the immunological system. However, scientific
evidence to support these allegations has not been found.
The only adverse health effect directly associated with
dioxin exposure for which there is conclusive evidence in
humans is the appearance of chloracne. This effect occurs
only following very large doses, generally resulting from
occupational exposures or accidental releases (Seveso,
Italy). When epidemiological studies of these types of
exposures are evaluated, there is no conclusive evidence of
any association with cancer.
There have been three major human
exposures to dioxin in recent history. Some Vietnam veterans
were exposed to 2,3,7,8-TCDD while handling Agent Orange
(Operation Ranch Hand). A number of residents of Times
Beach, Missouri, were exposed to dioxin when contaminated
oil was sprayed on dirt surfaces to control dust. The third
exposure was to the residents of Seveso, Italy, due to an
accidental explosion and subsequent release of dioxins.
Extensive studies of these three populations have failed to
show any short-term (except chloracne) or long-term health
effects in humans. However, it is clear that dioxins will
have significant impacts on other animals (death in guinea
pigs, endometriosis in Rhesus monkeys).
At What Levels of Dioxin Exposure will
People Experience Health Problems?
Recently, allegations have been made that
the current levels of exposure to dioxin in our air, water
and food exceed levels that cause adverse health effects.
Not all scientists agree with this assessment. Scientists at
the Center for Disease Control have stated that if humans
are likely to respond with a plethora of effects from
exposure to dioxin and related compounds because of current
body burdens, these non-cancer effects should have become
apparent in our population during the past 16 years. If
these levels cause adverse health effects, non-cancer
effects should be apparent throughout our population. The
fact that these effects have not emerged reinforces the
results of human epidemiological studies. The only proven
adverse effect associated with very high concentrations of
dioxin is chloracne.
How are People Exposed to Dioxin?
Dioxin is present in air, soil, water,
and the food chain. However, the amounts of dioxin detected
in our environment are small. Most scientists agree that the
most probable exposure route, other than accidental release,
for the general population is through the food chain.
Fortunately, the forms of dioxin detected in various food
groups generally represent the least toxic forms (HeptaCDD
and OctaCDD) of dioxin (Furst et al, 1990). EPA and the U.
S. Department of Agriculture have done a number of "market
basket" surveys and failed to find significant amounts of
dioxins in our food. Thus, your food supply is safe.
EPA has recently begun the use of
indirect risk assessment methodologies to estimate the
levels of dioxin that may be found in particular food
groups. This methodology incorporates several assumptions
about the ability of plants to absorb dioxin from air, the
ability of animals and humans eating these plants to
accumulate dioxin in tissue, and the amount of contaminated
plant and animal tissue that an individual might consume
everyday for 70 years. These assumptions have not been
tested or verified as being accurate. Until these models are
tested against field data, their results should only be used
as a part of an uncertainty analysis.
What is TEQ and how is it Calculated?
TEQ is toxic equivalents. It is a method
developed by scientists and regulators to estimate the
toxicity of all dioxins and furans relative to 2,3,7,8-TCDD.
TEQs are calculated by multiplying the amount of a specific
dioxin times its TEF. Thus, one gram of 2,3,7,8-TCDD is also
one gram TEQ dioxin (because it has a TEF of 1). However, 1
gram of 2,3,5,7,8-PCDD has a TEQ of 0.5 (one gram times 0.5
TEF). The two could be combined into 2 grams of dioxin or
1.5 grams TEQ of dioxin. Both numbers are correct. The two
grams accurately describes the total amount of dioxin
present but does not give any information on the total
toxicity of those two grams. The 1.5 grams accurately
represents the toxicity but does not give any indication on
the total amount of dioxin present.
What are the Major Sources of Dioxin?
Dioxin is not intentionally produced but
is a by-product of many industrial activities and natural
processes. Dioxin can be produced naturally during forest
fires and volcanic eruptions, through chemical and
photochemical reactions occurring in air and water and
during enzymatic reactions in natural organisms.
Anthropogenic sources comprise a broad range of industrial
and residential activities, including motor vehicle use,
industrial processes, incineration of waste material, and
burning of wood and coal.
EPA initially developed a list of sources
of dioxins in 1994 (EPA, 1994). The source list was updated
in 1998 (EPA, 1998a) and the estimated dioxin emissions to
the air for 1995 from these sources are summarized in the
As can be seen from this list, municipal waste incineration,
secondary copper smelting, and medical waste incineration
dominate the total emissions of dioxins to the air.
Surprisingly, forest fires and residential wood burning
produce a substantial amount of the estimated dioxin
emissions. Hazard waste incineration contributes about 0.2%
of the annual estimated dioxins emissions to the atmosphere.
It should be noted that recent EPA rules limiting dioxin
emissions from municipal and medical waste incinerators will
substantially reduce the amount of dioxin emissions from
these facilities over the next five years. Similar emission
restrictions for hazardous waste incinerators are expected
in early 1999.
How do Dioxins get into the Emissions
from Waste Combustors?
There are only a few combustion devices
in the United States that are allowed to burn
dioxin-contaminated waste. To obtain a license to burn
dioxin-contaminated waste, a facility must pass a series of
rigid tests that show that 99.9999% of the dioxins are
destroyed in the process. Since there are only a few
facilities that have this license and the vast majority of
the dioxin is destroyed, most of the dioxin found in the
emissions of waste combustors is newly formed in the air
pollution control devices.
A considerable amount of scientific
research has gone into determining the conditions where new
synthesis of dioxins occurs in combustor air pollution
control devices. If the following conditions are met,
dioxins can be formed: a) temperatures between 400 and 750
°F, b) residence time (time in the air pollution control
device) greater than 2 seconds, c) presence of chlorine, d)
the presence of carbon molecules, and e) the presence of a
catalytic surface. Remove any one of these factors, and
dioxin formation in the air pollution control device is much
slower. Combustors that have dioxin formation problems can
often change their air pollution control operating
parameters and eliminate the problem. Combustors with waste
heat boilers often have to add additional air pollution
control equipment to reduce dioxin concentrations in the
stack gas to levels below concern. There is a good
discussion of the mechanisms of dioxin synthesis in EPA's
trial burn guidance document (EPA, 1998b).
Furst, P., Furst, C. and Groebel, W.
1990. Levels of PCDDs and PCDFs in Food-Stuffs from the
Federal Republic of Germany. Chemosphere 20, Nos. 7-9,
Gough, M. 1993. Dioxin: Perception,
Estimates, and Measures. Phantom Risk: Scientific Inference
and the Law Eds. K.R. Foster. D.E. Bernstein and P W. Hubber.
Cambridge, MA: MIT Press.
U. S. Environmental Protection Agency
(EPA). 1994. Estimating Exposure to Dioxin-Like Compounds,
Volume 1: Executive Summary. EPA/600/6-88/005Ca. June 1994.
EPA. 1998a. The Inventory of Sources of
Dioxin in the United States. EPA/600/P-98/002Aa. April 1998.
EPA. 1998b. Guidance on Collection of
Emissions Data to Support Site-Specific Risk Assessments at
Hazardous Waste Combustion Facilities. EPA530-D-98-002.