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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

chlorinated dibenzo-p-dioxins. It is one in a series 

of Public Health Statements about hazardous 

substances and their health effects. A shorter 

version, the ToxFAQsTM 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 of exposure. 

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. 

1.1 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 dichlorinated dioxin (DCDD), tri-chlorinated dioxin 

(TrCDD), tetra-chlorinated dioxin (TCDD), pentachlorinated 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 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

CDDs. CDDs with toxic properties similar to 

2,3,7,8-TCDD are called "dioxin-like" compounds. 

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 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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). 

1.2 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, 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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) and 

milk. 

1.3 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 or water. 

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. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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 CDD contamination. 

Exposure to CDDs can also occur through skin 

contact with chlorinated pesticides and herbicides, 

contaminated soils, or other materials such as PCPtreated 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 hightraffic 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 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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. 

1.4 HOW CAN CDDs ENTER AND LEAVE 

MY BODY? 

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 with 

CDDs. 

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 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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 onehalf 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 the body. 

1.5 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

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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. 

1.6 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 considered. 

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. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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. 

1.7 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 investigate. 

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 

playing. 

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 activities. 

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; 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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. 

1.8 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. 

1.9 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). 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

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 factors. 

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. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, 

please contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

CHLORINATED DIBENZO-P-DIOXINS 

(CDDs) 

Division of Toxicology December 1998 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

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. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

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. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov