Public Health Statement for Chlorinated Dibenzo-p-dioxins (CDDs)
Spanish: Dibenzo-p-dioxinas policloradas
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for Chlorinated Dibenzo-p-dioxins (CDDs). It is
one in a series of Public Health Statements about hazardous
substances and their health effects. A shorter version, the
ToxFAQs™, is also available.
This information is important because this substance may harm
you. The effects of exposure to any hazardous substance depend
on the dose, the duration, how you are exposed, personal traits
and habits, and whether other chemicals are present. For more
information, call the ATSDR Information Center at 1-888-422-8737.
This public health statement tells you
about chlorinated dibenzo-p-dioxins (CDDs) and the effects
The Environmental Protection Agency (EPA)
identifies the most serious hazardous waste sites in the nation.
These sites make up the National Priorities List (NPL) and
are the sites targeted for long-term federal clean-up.
CDDs (all types) have been found in at least 126 of the 1,467
current or former NPL sites. However, it's unknown how
many NPL sites have been evaluated for these substances.
As more sites are evaluated, the number of sites with CDDs
may increase. This is important because exposure to
these substances may harm you and because these sites may
be sources of exposure.
When a substance is released from a large
area, such as an industrial plant, or from a container, such
as a drum or bottle, it enters the environment. This
release does not always lead to exposure. You can be
exposed to a substance only when you come in contact with
it. You may be exposed by breathing, eating, or drinking
the substance or by skin contact.
If you are exposed to CDDs, many factors
determine whether you'll be harmed. These factors include
the dose (how much), the duration (how long), and how you
come in contact with it. You must also consider the
other chemicals you're exposed to and your age, sex, diet,
family traits, lifestyle, and state of health.
What are CDDs?
CDDs are a family of 75 different compounds
commonly referred to as polychlorinated dioxins. These
compounds have varying harmful effects. The CDD family
is divided into eight groups of chemicals based on the number
of chlorine atoms in the compound. The group with one
chlorine atom is called the mono-chlorinated dioxin(s). The
groups with two through eight chlorine atoms are called di-chlorinated
dioxin (DCDD), tri-chlorinated dioxin (TrCDD), tetra-chlorinated
dioxin (TCDD), penta-chlorinated dioxin (PeCDD), hexa-chlorinated
dioxin (HxCDD), hepta-chlorinated dioxin (HpCDD), and octa-chlorinated
dioxin (OCDD). The chlorine atoms can be attached to
the dioxin molecule at any one of eight positions. The name
of each CDD indicates both the number and the positions of
the chlorine atoms. For example, the CDD with four chlorine
atoms at positions 2, 3, 7, and 8 on the dioxin molecule is
called 2,3,7,8-tetrachlorodibenzo-p-dioxin or 2,3,7,8-TCDD.
2,3,7,8-TCDD is one of the most toxic of the CDDs to mammals
and has received the most attention. Thus, 2,3,7,8-TCDD
serves as a prototype for the CDDs. CDDs with toxic
properties similar to 2,3,7,8-TCDD are called "dioxin-like"
In the pure form, CDDs are colorless
solids or crystals. CDDs enter the environment as mixtures
containing a variety of individual components and impurities.
In the environment they tend to be associated with ash, soil,
or any surface with a high organic content, such as plant
leaves. In air and water, a portion of the CDDs may
be found in the vapor or dissolved state, depending on the
amount of particulate matter, temperature, and other environmental
factors. 2,3,7,8-TCDD is odorless. The odors of
the other CDDs are not known. CDDs are known to occur
naturally, and are also produced by human activities.
They are naturally produced from the incomplete combustion
of organic material by forest fires or volcanic activity.
CDDs are not intentionally manufactured by industry, except
in small amounts for research purposes. They are unintentionally
produced by industrial, municipal, and domestic incineration
and combustion processes. Currently, it is believed that CDD
emissions associated with human incineration and combustion
activities are the predominant environmental source.
CDDs (mainly 2,3,7,8-TCDD) may be formed
during the chlorine bleaching process used by pulp and paper
mills. CDDs occur as a contaminant in the manufacturing
process of certain chlorinated organic chemicals, such as
chlorinated phenols. 2,3,7,8-TCDD is a by-product formed during
the manufacture of 2,4,5-trichlorophenol (2,4,5-TCP).
2,4,5-TCP was used to produce hexachlorophene (used to kill
bacteria) and the herbicide, 2,4,5-trichlorophenoxyacetic
acid (2,4,5-T). Various formulations of 2,4,5-T have
been used extensively for weed control on crops and range
lands, and along roadways throughout the world. 2,4,5-T
was a component of Agent Orange, which was used extensively
by the U.S. military in the Vietnam War. In most industrialized
countries the use of products contaminated with CDDs has been
greatly reduced. Use of hexachlorophene and the herbicide
2,4,5-T is currently restricted in the United States.
Other chlorinated chemicals, like pentachlorophenol (PCP),
used to preserve wood, do contain some of the more highly
chlorinated CDDs (those with more chlorine atoms), but 2,3,7,8-TCDD is not usually found. The use of PCP has been restricted
to certain manufacturing applications.
Currently, CDDs are primarily released
to the environment during combustion of fossil fuels (coal,
oil, and natural gas) and wood, and during incineration processes
(municipal and medical solid waste and hazardous waste incineration).
While incineration may be the primary current source of release
of CDDs into the environment, the levels of CDDs produced
by incineration are extremely low. CDDs are associated
with ash generated in combustion and incineration processes.
Emissions from incinerator sources vary greatly and depend
on management practices and applied technologies. CDDs
also have been detected at low concentrations in cigarette
smoke, home-heating systems, and exhaust from cars running
on leaded gasoline or unleaded gasoline, and diesel fuel.
Burning of many materials that may contain chlorine, such
as plastics, wood treated with pentachlorophenol (PCP), pesticide-treated
wastes, other polychlorinated chemicals (polychlorinated biphenyls
or PCBs), and even bleached paper can produce CDDs.
Although this public health statement
will focus on CDDs, it is important to note that CDDs are
found in the environment together with other structurally
related chlorinated chemicals, such as chlorinated dibenzofurans
(CDFs) and polychlorinated biphenyls (PCBs). Therefore,
people are generally exposed to mixtures of CDDs and other
classes of toxicologically and structurally similar compounds.
2,3,7,8-TCDD is one of the most toxic and extensively studied
of the CDDs and serves as a prototype for the toxicologically
relevant or "dioxin-like CDDs. Based on results from
animal studies, scientists have learned that they can express
the toxicity of dioxin-like CDDs as a fraction of the toxicity
attributed to 2,3,7,8-TCDD. For example, the toxicity
of dioxin-like CDDs can be half or one tenth or any fraction
of that of 2,3,7,8-TCDD. Scientists call that fraction
a Toxic Equivalent Factor (TEF).
What happens to CDDs when they enter the environment?
CDDs are released into the air in emissions
from municipal solid waste and industrial incinerators.
Exhaust from vehicles powered with leaded and unleaded gasoline
and diesel fuel also release CDDs to the air. Other
sources of CDDs in air include: emissions from oil- or coal-fired
power plants, burning of chlorinated compounds such as PCBs,
and cigarette smoke. CDDs formed during combustion processes
are associated with small particles in the air, such as ash.
The larger particles will be deposited close to the emission
source, while very small particles may be transported longer
distances. Some of the lower chlorinated CDDs (DCDD,
TrCDD, and some of the TCDDs) may vaporize from the particles
(and soil or water surfaces) and be transported long distances
in the atmosphere, even around the globe. It has been
estimated that 20 to 60% of 2,3,7,8-TCDD in the air is in
the vapor phase. Sunlight and atmospheric chemicals will break
down a very small portion of the CDDs, but most CDDs will
be deposited on land or water.
CDDs occur as a contaminant in the manufacture
of various chlorinated pesticides and herbicides, and releases
to the environment have occurred during the use of these chemicals.
Because CDDs remain in the environment for a long time, contamination
from past pesticide and herbicide use may still be of concern.
In addition, improper storage or disposal of these pesticides
and waste generated during their production can lead to CDD
contamination of soil and water.
CDDs are released in waste waters from
pulp and paper mills that use chlorine or chlorine-containing
chemicals in the bleaching process. Some of the CDDs
deposited on or near the water surface will be broken down
by sunlight. A very small portion of the total CDDs
in water will evaporate to air. Because CDDs do not
dissolve easily in water, most of the CDDs in water will attach
strongly to small particles of soil or organic matter and
eventually settle to the bottom. CDDs may also attach
to microscopic plants and animals (plankton) which are eaten
by larger animals, that are in turn eaten by even larger animals.
This is called a food chain. Concentrations of chemicals
such as the most toxic, 2,3,7,8-chlorine substituted CDDs,
which are difficult for the animals to break down, usually
increase at each step in the food chain. This process,
called biomagnification, is the reason why undetectable levels
of CDDs in water can result in measurable concentrations in
aquatic animals. The food chain is the main route by
which CDD concentrations build up in larger fish, although
some fish may accumulate CDDs by eating particles containing
CDDs directly off the bottom.
CDDs deposited on land from combustion
sources or from herbicide or pesticide applications bind strongly
to the soil, and therefore are not likely to contaminate groundwater
by moving deeper into the soil. However, the presence
of other chemical pollutants in contaminated soils, such as
those found at hazardous waste sites or associated with chemical
spills (for example, oil spills), may dissolve CDDs, making
it easier for CDDs to move through the soil. The movement
of chemical waste containing CDDs through soil has resulted
in contamination of groundwater. Soil erosion and surface
runoff can also transport CDDs into surface waters.
A very small amount of CDDs at the soil surface will evaporate
into air. Certain types of soil bacteria and fungus
can break CDDs down, but the process is very slow. In
fact, CDDs can exist in soil for many years. Plants
take up only very small amounts of CDDs by their roots.
Most of the CDDs found on the parts of plants above the ground
probably come from air and dust and/or previous use of CDD-containing
pesticides or herbicides. Animals (such as cattle) feeding
on the plants may accumulate CDDs in their body tissues (meat)
How might I be exposed to CDDs?
CDDs are found at very low levels in
the environment. These levels are measured in nanograms
and picograms. One nanogram (ng) is one billionth of
a gram, and one picogram (pg) is one trillionth of a gram.
In some contaminated soils, concentrations of CDDs are reported
as parts per billion. One part per billion (ppb) is
one part CDD per billion parts of soil. The concentration
of CDDs is often reported as parts per trillion, in samples
of air, water, or soil. One part per trillion (ppt)
is one part CDD per trillion parts of air, water, or soil.
In some rural areas where CDD concentrations are very low
in air or water, measurements are given in parts per quadrillion
(ppq), which means one part CDD per quadrillion parts of air
CDDs are found everywhere in the environment,
and most people are exposed to very small background levels
of CDDs when they breath air, consume food or milk,
or have skin contact with materials contaminated with CDDs.
For the general population, more than 90% of the daily intake
of CDDs, CDFs, and other dioxin-like compounds comes from
food, primarily meat, dairy products, and fish. CDDs
may be present at much lower levels in fruits and vegetables.
The actual intake of CDDs from food for any one person will
depend on the amount and type of food consumed and the level
of contamination. Higher levels may be found in foods
from areas contaminated with chemicals, such as pesticides
or herbicides, containing CDDs as impurities. CDDs have
been measured in human milk, cow's milk, and infant formula,
so infants are known to be exposed to CDDs.
Most surface water in the United States
typically does not contain 2,3,7,8-TCDD and other CDDs at
levels that are high enough to be measured (1 ppq or more).
Municipal drinking water does not usually contain CDDs because
the CDDs do not dissolve in water and primarily stick to particles,
which are usually filtered out of treated drinking water.
This means that using tap water to wash clothes or to bathe
or shower, or swimming in pools or in uncontaminated lakes,
rivers, or at ocean beaches will not expose people to significant
levels of CDDs. Although CDDs are not usually found
in filtered, treated drinking water, they have, on occasion,
been detected in unfiltered groundwater from areas with known
Exposure to CDDs can also occur through
skin contact with chlorinated pesticides and herbicides, contaminated
soils, or other materials such as PCP-treated wood and PCB
transformer fluids. Background levels of CDDs in soil
are higher than background levels in both air and water.
Background levels of CDDs detected in uncontaminated soils
in the United States are generally very low or not detectable.
2,3,7,8-TCDD is not usually found in rural soil, but is typically
found in soil in industrialized areas at levels ranging from
0.001 to 0.01 ppb. However, higher levels of 2,3,7,8-TCDD
may be found in areas where CDDs have contaminated the soil.
For example, contaminated soil at Times Beach, Missouri, had
levels of 2,3,7,8-TCDD ranging from 4.4-317 ppb.
If CDDs are present at all in outdoor
air in rural areas, they are generally present at very low
levels or at concentrations near the detection limits for
testing equipment. In winter, because of the burning
of wood and other fuels for home heating, CDD levels may be
slightly higher than during other seasons. In general,
the background air levels of CDDs in urban areas are higher
than in rural areas. Typical levels of CDDs in outdoor
air in urban areas and industrial areas averaged 2.3 picograms
per meter cubed (pg/m3). 2,3,7,8-TCDD is not usually
found in rural or urban air, but it is found in air near urban
waste incinerators and high-traffic areas. The air around
people who are smoking cigarettes may also have CDDs at levels
above background levels. Although breathing contaminated
air is a minor route of exposure for most people, exposure
may be greater in areas near these CDD sources.
CDDs have been found in all samples of
adipose tissue and blood (serum lipids) from individuals with
no known previous exposure. This indicates that all
people are exposed to small amounts of CDDs. Levels
of 2,3,7,8-TCDD in serum from the general population typically
range from 3 to 7 ppt (on a lipid basis), and rarely exceed
10 ppt. Typically, lower levels of CDDs are found in less
industrialized countries and in younger people.
The production, use, and disposal of
pesticides and phenoxy herbicides, disposal of production
waste containing 2,3,7,8-TCDD, industrial accidents involving
2,4,5-trichlorophenol (2,3,5-TCP), and the consumption of
CDD-contaminated food, have all led to increased potential
for excess exposure of some groups of people. 2,3,7,8-TCDD
has been detected at 91 of the 126 hazardous waste sites on
the NPL that have been reported to contain CDDs. People
living around these sites may be exposed to above-background
levels of 2,3,7,8-TCDD and other CDDs. Elevated levels
of CDDs have been reported in fish, shellfish, birds, and
mammals collected in areas surrounding various chemical production
facilities, various hazardous waste sites, and pulp and paper
mills using the chlorine bleaching process. Sometimes
these findings have resulted in closure of these areas for
the purpose of fishing. People who eat contaminated
food from these contaminated areas are at risk of increased
exposure to CDDs.
Occupational exposure to CDDs generally
occurs through breathing contaminated air, or through skin
contact with materials containing CDDs. Workers with
the potential to be exposed to above-average levels of CDDs
include those involved in the production or handling of certain
chlorinated phenols (such as 2,4,5-TCP, PCP) or chlorinated
pesticides or herbicides (such as 2,4,5-T, 2,4-D, hexachlorophene,
Silvex®), and those involved in application of chlorinated
pesticides containing CDDs as impurities. Workers
whose jobs involve pressure treatment of wood with PCP and
the handling of PCP-treated wood products, chlorination processes
at pulp and paper mills, or operation of municipal solid waste
or hazardous waste incinerators may have increased exposure
to CDDs. Finally, workers involved in hazardous waste
clean-up or clean-up of PCB transformer and/or capacitor fires
including emergency service personnel like fire fighters and
police who respond to such fires are also at additional risk
of exposure to CDDs. Most of these occupational exposures
have been significantly reduced in recent years.
In general, workers involved in the manufacture
of 2,4,5-TCP and subsequent products were exposed to far greater
levels of 2,3,7,8-TCDD than those involved in the handling
and application of chlorinated pesticides containing CDDs.
Current serum lipid levels of 2,3,7,8-TCDD in a small number
of U.S. Air Force veterans who were directly involved in the
aerial spraying of herbicides (Agent Orange contaminated with
2,3,7,8-TCDD) in Vietnam as part of Operation Ranch Hand,
are up to 3 times higher than the general population.
However, while studies on blood or fatty tissue 2,3,7,8-TCDD
levels in U.S. Army ground combat Vietnam veterans also found
some individuals with 2,3,7,8-TCDD levels higher than those
of the general population, overall, most Vietnam veterans
and Vietnamese living in Vietnam studied to dated have blood
and fatty tissue 2,3,7,8-TCDD levels comparable to members
of the general U.S. population.
How can CDDs enter and leave my
CDDs can enter your body when you breathe
contaminated air, eat contaminated food, or have skin contact
with contaminated soil or other materials. The most
common way CDDs can enter your body is by eating food contaminated
If you breathe air that contains CDDs,
the CDDs can enter your body through your lungs and pass into
the blood stream, but we do not know how fast or how much
of the CDDs will enter the blood stream. If you swallow
food or water containing CDDs, most of the CDDs will enter
your body and pass from the intestines to the blood stream.
Smaller amounts of highly chlorinated CDDs will enter your
body compared to the less chlorinated 2,3,7,8-TCDD.
If you swallow soil containing CDDs, a small amount of the
CDDs will pass through the intestines into the blood stream.
If soil contaminated with CDDs comes into contact with your
skin, some of the CDDs will enter the body but we do not know
how fast they will enter the blood stream.
Once in your body, CDDs can be found
in most tissues with the highest amounts found in the liver
and body fat (adipose tissue). Body fat and possibly
the liver can store CDDs for many years before eliminating
them from the body. CDDs with chlorine atoms in the 2, 3,
7, and 8 positions and highly chlorinated dioxins, such as
OCDD, are generally found in higher concentrations in the
fat than other CDDs.
Little is known about CDDs breakdown
in the human body. Studies in animals show that some
of the 2,3,7,8-TCDD from food is slowly broken down.
There is evidence from animals suggesting that the break-down
products are less harmful than the unchanged 2,3,7,8-TCDD.
For people, the average time it takes
to remove one-half of the 2,3,7,8-TCDD from the body is highly
variable and may take from 7 to 12 years. There is less
information on the other CDDs, but what information exists
suggests 5 to 15 years. CDDs are eliminated from the
body primarily in the stool, and only a small amount leaves
the body in the urine. Some CDDs will leave the body
in the breast milk of nursing mothers.
Much less is known about how much other
CDD compounds will enter the body, how much will be stored
in the body and for how long, and how they are removed from
How can CDDs affect my health?
Many studies have looked at how CDDs
can affect human health. Most of these studies examined
workers exposed during the manufacture of chemicals and pesticides
contaminated with 2,3,7,8-TCDD. Other studies have looked
at American Vietnam veterans and Vietnamese populations exposed
to Agent Orange and populations exposed to 2,3,7,8-TCDD as
a result of an accident. The workers and Vietnam veterans
were most likely exposed to 2,3,7,8-TCDD mainly through breathing
and skin contact. People who were accidentally exposed
to 2,3,7,8-TCDD in Seveso, Italy, or Times Beach, Missouri,
were probably exposed through eating and drinking contaminated
food and milk, breathing contaminated particles and dust,
and through skin contact with contaminated soil. Epidemiology
is an inexact science and many of the human studies have many
shortcomings which make it difficult for scientists to establish
an association between 2,3,7,8-TCDD exposure levels and health
effects. A common problem with most of the human studies
is that the people are exposed to a number of chemicals at
the same time. In most human health studies, we do not
know how much 2,3,7,8-TCDD people were exposed to or how long
the exposure lasted. In other studies, the people were
examined many years after they were exposed and some of the
effects may have not have been present at the time of examination
or the effects observed may not have been caused by 2,3,7,8-TCDD.
Some of the more recent studies have measured 2,3,7,8-TCDD
levels in the blood or fat tissue of exposed populations.
The levels of 2,3,7,8-TCDD in the blood or fat tissue can
be used to estimate the extent of past exposures.
A number of effects have been observed
in people exposed to 2,3,7,8-TCDD levels which are at least
10 times higher than background levels. The most obvious
health effect in people exposed to relatively large amounts
of 2,3,7,8-TCDD is chloracne. Chloracne is a severe
skin disease characterized by acne-like lesions. Chloracne
generally occurs on the face and upper body, but may occur
elsewhere on the body. Unlike common acne, severe chloracne
is harder to cure and can be more disfiguring. In milder
cases, the lesions heal several months after exposure ends.
In more severe cases, the lesions may last for many years
after exposure. Most of the chloracne cases have been
attributed to accidental exposure to high doses of 2,3,7,8-TCDD.
Other effects to the skin, such as erythematous or red skin
rashes, discoloration, and excessive body hair, have been
reported to occur in people following exposure to high concentrations
of 2,3,7,8-TCDD. Changes in blood and urine that may
indicate liver damage have been observed in people.
Alterations in the ability of the liver to metabolize (or
breakdown) hemoglobin, lipids, sugar, and protein have been
reported in people exposed to relatively high concentrations
of 2,3,7,8-TCDD. Most of the effects are considered
mild and were reversible. However, in some people these
effects may last for many years. Slight increases in
the risk of diabetes and abnormal glucose tolerance have been
observed in some studies of people exposed to 2,3,7,8-TCDD.
We do not have enough information to know if exposure to 2,3,7,8-TCDD
will result in reproductive or developmental effects in people,
but animal studies suggest that this is a potential health
concern. Several studies of workers exposed to high
levels (more than 50 times higher than background levels)
of 2,3,7,8-TCDD suggest that exposure to 2,3,7,8-TCDD may
increase the risk of cancer in people.
The Department of Health and Human Services
(DHHS) has determined that it is reasonable to expect that
2,3,7,8-TCDD may cause cancer. The International Agency
for Research on Cancer (IARC) has determined that 2,3,7,8-TCDD
can cause cancer in people, but that it is not possible to
classify other CDDs as to their carcinogenicity to humans.
The EPA has determined that 2,3,7,8-TCDD is a possible human
carcinogen when considered alone and a probable human carcinogen
when considered in association with phenoxy herbicides and/or
chlorophenols. The EPA has determined also that a mixture
of CDDs with six chlorine atoms (4 of the 6 chlorine atoms
at the 2, 3, 7, and 8 positions) is a probable human carcinogen.
To protect the public from the harmful
effects of toxic chemicals and to find ways to treat people
who have been harmed, scientists use many tests.
One way to see if a chemical will hurt
people is to learn how the chemical is absorbed, used, and
released by the body; for some chemicals, animal testing may
be necessary. Animal testing may also be used to identify
health effects such as cancer or birth defects. Without
laboratory animals, scientists would lose a basic method to
get information needed to make wise decisions to protect public
health. Scientists have the responsibility to treat
research animals with care and compassion. Laws today
protect the welfare of research animals, and scientists must
comply with strict animal care guidelines.
The health effects of some CDDs have
been extensively studied in animals. Some CDDs are much
more toxic than others. 2,3,7,8-TCDD and, to a lesser
extent, CDDs with five (penta) or six (hexa) chlorine atoms
substituted in the 2, 3, 7, and 8 positions, are extremely
toxic to animals. Other CDDs, which do not have chlorine
atoms substituted in the 2, 3, 7, and 8 positions, are considered
relatively less toxic compared to 2,3,7,8-TCDD.
2,3,7,8-TCDD has been the most extensively
studied CDD and it has been shown to cause a large number
of adverse health effects in animals. There are always going
to be some difficulties in using animal data to quantify health
risks in people. In general, the doses used in the animal
studies result in body burdens that are at least 10 times
higher than human background body burdens, often the animal
studies use doses that are over 1,000 times higher than human
background levels. Some animal species are much more
acutely sensitive to 2,3,7,8-TCDD than others. For example,
it takes several thousand times more 2,3,7,8-TCDD to kill
a hamster than a guinea pig. The reason for the difference
in sensitivity among species is currently being investigated.
For other effects, such as reproductive toxicity, there is
very little difference in sensitivity between hamsters and
guinea pigs. Another consideration in using animal data
to predict health effects in people exposed to CDDs in the
environment is the design of the animal studies. In
most of the animal studies, the animals were exposed to only
2,3,7,8-TCDD, the most toxic CDD. 2,3,7,8-TCDD is rarely
the main CDD found in the environment and people are typically
exposed to a number of CDDs and compounds with similar toxic
actions. Until scientists learn more about possible
differences between people and animals, levels recommended
to be of little or no risk to human health are based on the
more sensitive species and the assumption that effects in
animals could occur in people. This approach is further
justified on the basis that humans are likely to exhibit a
wide range of sensitivities to various health effects and
the need to protect the most susceptible individuals.
In certain species, 2,3,7,8-TCDD is especially
harmful and can cause death after a single exposure to small
amounts. Before death, animals may lose as much as 40%
or more of their body weight following a single dose of 2,3,7,8-TCDD.
Exposure to non-lethal levels in food can cause a variety
of adverse effects in animals, such as weight loss, biochemical
and degenerative changes in the liver. Some animals
that were exposed to CDDs in food had effects to the skin
such as hair loss, swelling of the face, and moderate to severe
chloracne. In many species of animals, the immune system
appears to be extremely sensitive to 2,3,7,8-TCDD. At
relatively low levels (approximately 10 times higher than
human background body burdens), 2,3,7,8-TCDD weakens the immune
system and causes a decrease in the system's ability to fight
foreign substances such as bacteria and viruses.
Exposure to 2,3,7,8-TCDD can cause reproductive
damage and birth defects in animals. Decreases in fertility,
altered levels of sex hormones, reduced production of sperm,
and increased rates of miscarriages were found in animals
exposed to 2,3,7,8-TCDD in food. Rats and mice that
were exposed to small amounts of 2,3,7,8-TCDD in food for
a long time developed cancer of the liver and thyroid, and
other types of cancer.
The results of the oral animal studies
suggest that the most sensitive effects (effects that will
occur at the lowest doses) are immune, endocrine, and developmental
effects. It is reasonable to assume that these will
also be the most sensitive effects in humans.
We know less about the ability of other
CDDs to cause adverse health effects. However, it appears
that all CDDs with chlorine in the 2, 3, 7, and 8 positions
have similar effects to 2,3,7,8-TCDD but the effects occur
at higher doses.
Relatively large amounts of 2,3,7,8-TCDD
applied to the skin of some animal species have resulted in
deaths. Smaller amounts have resulted in weight loss, acne-like
sores on the skin, and biochemical and degenerative changes
in the liver. In addition, mice that had 2,3,7,8-TCDD
repeatedly applied to their skin developed skin cancer.
Although effects in animals following exposure through the
skin have not been as extensively studied as effects following
exposure in food, they appear to be quite similar. The
ability of other CDDs to cause adverse health effects in animals
following exposure to the skin has not been well studied.
How can CDDs affect children?
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans. Potential effects
on children resulting from exposures of the parents are also
Very few studies have looked at how CDDs
can affect children's health. Chloracne has been observed
in children exposed to much higher than current background
levels of 2,3,7,8-TCDD. The children appeared to be
more sensitive (effects occurred at a lower body burden) than
adults. We do not know why children are more sensitive
than adults to this effect. It is likely that children
exposed to higher than background levels will have similar
effects as adults.
We do not know if exposure to CDDs will
result in birth defects or other developmental effects in
people. Birth defects have been observed in animals
exposed to higher than background levels of 2,3,7,8-TCDD.
The developing animal is very sensitive to 2,3,7,8-TCDD.
In some studies, effects were observed at body burdens 10
times higher than human background levels. Offspring
of animals exposed to 2,3,7,8-TCDD in food during pregnancy
often had severe birth defects including bleeding, skeletal
deformities, kidney defects, weakened immune responses, impaired
development of the reproductive system, and learning and behavioral
impairments. Exposure to other CDDs, such as 2,7-DCDD,
1,2,3,7,8-PeCDD, OCDD, and HxCDD, can also result in developmental
effects in animals.
We have no information to suggest that
there are any differences between children and adults in terms
of how much CDDs will enter the body, where CDDs can be found
in the body, and how fast CDDs will leave the body.
CDDs from the mother can enter her unborn baby through the
placenta. It can also be transferred from the mother
to infant through breast milk. Because CDDs have been
measured in human milk, cows milk, and infant formula, nursing
infants are also exposed to CDDs. In most cases the
beneficial aspects (biological and psychological) of breast-feeding
outweigh any risks from exposure to CDDs from mother's milk.
How can families reduce the risk of
exposure to CDDs?
If your doctor finds that you have been
exposed to significant amounts of CDDs, ask your doctor if
children may also be exposed. When necessary your doctor
may need to ask your state Department of Public Health to
Structural material used in building
homes such as chemically treated lumber for decking and plastic
PVC pipes used in water pipes and other conduits can release
CDDs if they are burned as refuse during construction or if
there is a structural fire in your home. To avoid exposures
from some of these sources, construction refuse should not
be burned near your home especially when children are out
Children may be exposed to CDDs from
ingestion of contaminated soil or by contact of contaminated
soil with their skin. However, skin contact with contaminated
soil will result in much less CDDs entering the blood stream
than if they ingest contaminated soil. Also, the amount
of CDDs that will pass to the blood stream after eating contaminated
soil will depend on the type of soil and on how tight the
CDDs are bound to the soil. Children should be restricted
from playing near any known hazardous waste sites. Some
children eat a lot of dirt. Discourage your children
from eating dirt or from putting their toys or other foreign
objects in their mouths that may be contaminated with soil.
Make sure that your children wash their hands frequently,
especially before eating. Discourage your children from
putting their hands in their mouths or other hand-to-mouth
Older children may be exposed to CDDs
if they smoke cigarettes. Younger children and infants
may be exposed by inhaling the second-hand smoke from their
parents or other adult smokers. Parents should talk
to their children about the dangers of smoking cigarettes.
You and your children are likely to be
exposed to very low amounts of CDDs in the diet particularly
when you consume meat, milk, other dairy products, and fish.
This represents the major source of background exposure to
CDDs in most people. Children and adults should eat
a balanced diet preferably containing low to moderate amounts
of animal fats including meat and dairy products, and fish
that contain higher amounts of CDDs and eat larger amounts
of fruits, vegetables and grains.
You or your children may be exposed to
CDDs by eating certain types of fish or wildlife caught in
certain locations. A number of states have advisories
for CDDs in fish and shellfish species; and one state has
a wildlife advisory in effect for wood ducks. Each state,
Native American tribe, or U.S. Territory sets its own criteria
for issuing fish and wildlife advisories. A fish advisory
will specify which waterbodies have restrictions, and a wildlife
advisory will specify which hunting areas have restrictions.
The advisory will tell you what types and sizes of fish or
game are of concern. The advisory may completely ban
eating fish or game or recommend that you limit the number
of meals you eat of a certain species. For example,
an advisory may tell you to eat a certain type of fish no
more than once a month. The advisory may also tell you
only to eat certain parts of the fish or game animal and how
to prepare or cook the fish or game to decrease your exposure
to CDDs. Fish and wildlife advisories are often stricter
for pregnant women, nursing mothers, and young children.
To reduce your children's exposure to CDDs, obey all fish
and wildlife advisories. Information on Fish and Wildlife
Advisories in your state is available from your state Public
Health Department, or state Natural Resources Department and
signs may be posted in certain fishing and hunting areas.
Is there a medical test to determine
whether I have been exposed to CDDs?
Specific tests exist to measure CDD levels
in samples of body fat, blood, and breast milk, but these
tests are not routinely available. All people now have
some levels of CDDs in their body fat and blood. Levels
of 2,3,7,8-TCDD on a lipid basis are generally below 10 pg/g
of lipid (ppt) in the blood and fatty tissue of the general
population of the United States, and usually range from 3
to 7 ppt. Levels higher than these indicate past exposure
to above-normal levels of 2,3,7,8-TCDD. Although CDDs
stay in the body fat for a long time (see Section
1.4), tests are not used to determine when exposure occurred,
but can be used to estimate dose of the exposure if the time
of exposure is known.
Although exposure to 2,3,7,8-TCDD has
been associated with adverse health effects in people, no
one effect is specifically related to exposure to CDDs.
There are laboratory tests which can indicate whether you
have been exposed to CDDs, but these are costly and take weeks
to perform and they cannot be used to predict whether you
will develop harmful health effects.
What recommendations has the federal
government made to protect human health?
The federal government develops regulations
and recommendations to protect public health. Regulations
can be enforced by law. Federal agencies that
develop regulations for toxic substances include the Environmental
Protection Agency (EPA), the Occupational Safety and Health
Administration (OSHA), and the Food and Drug Administration
(FDA). Recommendations provide valuable guidelines to
protect public health but cannot be enforced by law.
Federal organizations that develop recommendations for toxic
substances include the Agency for Toxic Substances and Disease
Registry (ATSDR) and the National Institute for Occupational
Safety and Health (NIOSH).
Regulations and recommendations can be
expressed in not-to-exceed levels in air, water, soil, or
food that are usually based on levels that affect animals,
then they are adjusted to help protect people. Sometimes
these not-to-exceed levels differ among federal organizations
because of different exposure times (an 8-hour workday or
a 24-hour day), the use of different animal studies, or other
Recommendations and regulations are also
periodically updated as more information becomes available.
For the most current information, check with the federal agency
or organization that provides it. Some regulations and
recommendations for CDDs include the following:
The government has developed regulations
and guidelines for 2,3,7,8-TCDD. These are designed
to protect the public from the potential adverse health effects
of the chemical. The Food and Drug Administration (FDA)
recommends against consuming fish and shellfish with 2,3,7,8-TCDD
levels greater than 50 ppt. Such levels have resulted
in the closing of several commercial fishing areas.
In addition, EPA has issued guidance to states on how to evaluate
health risks to recreational and subsistence fishers, and
how to issue fish consumption advisories when concentrations
of CDDs in fish and shellfish pose a risk to these populations.
Currently, 66 health advisories have been issued by 21 states
restricting consumption of fish and wildlife contaminated
with CDDs. EPA also has recommended limits on how much
2,3,7,8-TCDD can be present in drinking water. EPA advises
that children should not have more than 1 nanogram 2,3,7,8-TCDD
per liter of water (ng/L) (ppt) in 1 day, or more than 0.01
ng/L per day for long-term exposure. For long-term exposure
in adults, EPA recommends that there should not be more than
0.04 ng/L (ppt) in drinking water.
Human milk can contain higher levels of CDDs than cow's milk. Therefore, breast-fed infants can be exposed to higher levels of CDDs on a body weight basis than adults. The World Health Organization (WHO) has concluded that this risk to infants does not outweigh the positive biological and psychological benefits of breast-feeding at general population levels of dioxins. However, the specific concentration at which CDD levels in human milk would lead to harmful health effects in infants has not yet been determined.
Regulation of many of the sources of CDDs appears to have been successful in reducing the amount of CDDs entering the ecosystem and in decreasing the potential for human exposure. EPA considers 2,3,7,8-TCDD to be a hazardous waste. Many regulations govern its destruction and disposal.
Agency for Toxic Substances and Disease Registry (ATSDR). 1998. Toxicological profile for Chlorinated Dibenzo-p-dioxins (CDDs). Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.