1.1 What are polychlorinated biphenyls
(PCBs)? |
1.2 What happens to polychlorinated biphenyls
(PCBs) when they enter the environment? |
1.3 How might I be exposed to polychlorinated
biphenyls (PCBs)? |
1.4 How can polychlorinated biphenyls
(PCBs) enter and leave my body? |
1.5 How can polychlorinated biphenyls
(PCBs) affect my health? |
1.6 How can polychlorinated biphenyls
(PCBs) affect children? |
1.7 How can families reduce their risk
of expsoure to polychlorinated biphenyls (PCBs)? |
1.8 Is there a medical test to determine
whether I have been exposed to polychlorinated biphenyls (PCBs)? |
1.9 What recommendations has the federal
government made to protect human health? |
1.10 Where can I get more information? |
References |
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![](/peth04/20041022103803im_/http://www.atsdr.cdc.gov/toxprofiles/phs17.html) |
![](/peth04/20041022103803im_/http://www.atsdr.cdc.gov/toxprofiles/phs17.html) |
November 2000 |
Public Health Statement |
for |
Polychlorinated Biphenyls (PCBs) |
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for polychlorinated biphenyls (PCBs). 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.
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This public health statement tells you
about polychlorinated biphenyls (PCBs) 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 cleanup activities.
PCBs have been found in at least 500 of the 1,598 current
or former NPL sites. However, the total number of NPL sites
evaluated for PCBs is not known. As more sites are evaluated,
the sites at which PCBs are found may increase. This information
is important because exposure to PCBs 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 are 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 PCBs, 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 them. You must also consider the other
chemicals you're exposed to and your age, sex, diet, family
traits, lifestyle, and state of health.
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1.1
What are polychlorinated biphenyls (PCBs)? |
PCBs are a group of synthetic organic
chemicals that can cause a number of different harmful effects.
There are no known natural sources of PCBs in the environment.
PCBs are either oily liquids or solids and are colorless to
light yellow. Some PCBs are volatile and may exist as a vapor
in air. They have no known smell or taste. PCBs enter the
environment as mixtures containing a variety of individual
chlorinated biphenyl components, known as congeners, as well
as impurities. Because the health effects of environmental
mixtures of PCBs are difficult to evaluate, most of the information
in this toxicological profile is about seven types of PCB
mixtures that were commercially produced. These seven kinds
of PCB mixtures include 35% of all the PCBs commercially produced
and 98% of PCBs sold in the United States since 1970. Some
commercial PCB mixtures are known in the United States by
their industrial trade name, Aroclor. For example, the name
Aroclor 1254 means that the mixture contains approximately
54% chlorine by weight, as indicated by the second two digits
in the name. Because they don't burn easily and are good insulating
materials, PCBs were used widely as coolants and lubricants
in transformers, capacitors, and other electrical equipment.
The manufacture of PCBs stopped in the United States in August
1977 because there was evidence that PCBs build up in the
environment and may cause harmful effects. Consumer products
that may contain PCBs include old fluorescent lighting fixtures,
electrical devices or appliances containing PCB capacitors
made before PCB use was stopped, old microscope oil, and old
hydraulic oil. You can find further information on the physical
properties and uses of PCBs in Chapters 4 and 5 of the toxicological
profile.
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1.2
What happens to polychlorinated biphenyls (PCBs) when they enter
the environment? |
Before 1977, PCBs entered the air, water,
and soil during their manufacture and use in the United States.
Wastes that contained PCBs were generated at that time, and
these wastes were often placed in landfills. PCBs also entered
the environment from accidental spills and leaks during the
transport of the chemicals, or from leaks or fires in transformers,
capacitors, or other products containing PCBs. Today, PCBs
can still be released into the environment from poorly maintained
hazardous waste sites that contain PCBs; illegal or improper
dumping of PCB wastes, such as old transformer fluids; leaks
or releases from electrical transformers containing PCBs;
and disposal of PCB-containing consumer products into municipal
or other landfills not designed to handle hazardous waste.
PCBs may be released into the environment by the burning of
some wastes in municipal and industrial incinerators.
Once in the environment, PCBs do not
readily break down and therefore may remain for very long
periods of time. They can easily cycle between air, water,
and soil. For example, PCBs can enter the air by evaporation
from both soil and water. In air, PCBs can be carried long
distances and have been found in snow and sea water in areas
far away from where they were released into the environment,
such as in the arctic. As a consequence, PCBs are found all
over the world. In general, the lighter the type of PCBs,
the further they may be transported from the source of contamination.
PCBs are present as solid particles or as a vapor in the atmosphere.
They will eventually return to land and water by settling
as dust or in rain and snow. In water, PCBs may be transported
by currents, attach to bottom sediment or particles in the
water, and evaporate into air. Heavy kinds of PCBs are more
likely to settle into sediments while lighter PCBs are more
likely to evaporate to air. Sediments that contain PCBs can
also release the PCBs into the surrounding water. PCBs stick
strongly to soil and will not usually be carried deep into
the soil with rainwater. They do not readily break down in
soil and may stay in the soil for months or years; generally,
the more chlorine atoms that the PCBs contain, the more slowly
they break down. Evaporation appears to be an important way
by which the lighter PCBs leave soil. As a gas, PCBs can accumulate
in the leaves and above-ground parts of plants and food crops.
PCBs are taken up into the bodies of
small organisms and fish in water. They are also taken up
by other animals that eat these aquatic animals as food. PCBs
especially accumulate in fish and marine mammals (such as
seals and whales) reaching levels that may be many thousands
of times higher than in water. PCB levels are highest in animals
high up in the food chain. You can find more information about
what happens to PCBs in the environment in Chapter 6 of the
toxicological profile.
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1.3
How might I be exposed to polychlorinated biphenyls (PCBs)? |
Although PCBs are no longer made in the
United States, people can still be exposed to them. Many older
transformers and capacitors may still contain PCBs, and this
equipment can be used for 30 years or more. Old fluorescent
lighting fixtures and old electrical devices and appliances,
such as television sets and refrigerators, therefore may contain
PCBs if they were made before PCB use was stopped. When these
electric devices get hot during operation, small amounts of
PCBs may get into the air and raise the level of PCBs in indoor
air. Because devices that contain PCBs can leak with age,
they could also be a source of skin exposure to PCBs.
Small amounts of PCBs can be found in
almost all outdoor and indoor air, soil, sediments, surface
water, and animals. However, PCB levels have generally decreased
since PCB production stopped in 1977. People are exposed to
PCBs primarily from contaminated food and breathing contaminated
air. The major dietary sources of PCBs are fish (especially
sportfish that were caught in contaminated lakes or rivers),
meat, and dairy products. Between 1978 and 1991, the estimated
daily intake of PCBs in adults from dietary sources declined
from about 1.9 nanograms (a nanogram is a billionth part of
a gram) to less than 0.7 nanograms. PCB levels in sportfish
are still high enough so that eating PCB-contaminated fish
may be an important source of exposure for some people. Recent
studies on fish indicate maximum concentrations of PCBs are
a few parts of PCBs in a million parts (ppm) of fish, with
higher levels found in bottom-feeders such as carp. Meat and
dairy products are other important sources of PCBs in food,
with PCB levels in meat and dairy products usually ranging
from less than 1 part in a billion parts (ppb) of food to
a few ppb.
Concentrations of PCBs in subsurface
soil at a Superfund site have been as high as 750 ppm. People
who live near hazardous waste sites may be exposed to PCBs
by consuming PCB-contaminated sportfish and game animals,
by breathing PCBs in air, or by drinking PCB-contaminated
well water. Adults and children may come into contact with
PCBs when swimming in contaminated water and by accidentally
swallowing water during swimming. However, both of these exposures
are far less serious than exposures from ingesting PCB-contaminated
food (particularly sportfish and wildlife) or from breathing
PCB-contaminated air.
Workplace exposure to PCBs can occur
during repair and maintenance of PCB transformers; accidents,
fires, or spills involving PCB transformers and older computers
and instruments; and disposal of PCB materials. In addition
to older electrical instruments and fluorescent lights that
contain PCB-filled capacitors, caulking materials, elastic
sealants, and heat insulation have also been known to contain
PCBs. Contact with PCBs at hazardous waste sites can happen
when workers breathe air and touch soil containing PCBs. Exposure
in the contaminated workplace occurs mostly by breathing air
containing PCBs and by touching substances that contain PCBs.
You can find more information about exposure to PCBs in Chapter 6
of the toxicological profile.
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1.4
How can polychlorinated biphenyls (PCBs) enter and leave my
body? |
If you breathe air that contains PCBs,
they can enter your body through your lungs and pass into
the bloodstream. We do not know how fast or how much of the
PCBs that are breathed will pass into the blood. A common
way for PCBs to enter your body is by eating meat or fish
products or other foods that contain PCBs. Exposure from drinking
water is less than from food. It is also possible that PCBs
can enter your body by breathing indoor air or by skin contact
in buildings that have the kinds of old electrical devices
that contain and can leak PCBs. For people living near waste
sites or processing or storage facilities, and for people
who work with or around PCBs, the most likely ways that PCBs
will enter their bodies are from skin contact with contaminated
soil and from breathing PCB vapors. Once PCBs are in your
body, some may be changed by your body into other related
chemicals called metabolites. Some metabolites of PCBs may
have the potential to be as harmful as some unchanged PCBs.
Some of the metabolites may leave your body in the feces in
a few days, but others may remain in your body fat for months.
Unchanged PCBs may also remain in your body and be stored
for years mainly in the fat and liver, but smaller amounts
can be found in other organs as well. PCBs collect in milk
fat and can enter the bodies of infants through breast-feeding.
For more information on how PCBs can enter and leave your
body, see Chapter 3 of the toxicological profile.
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1.5
How can polychlorinated biphenyls (PCBs) affect my health? |
Many studies have looked at how PCBs
can affect human health. Some of these studies investigated
people exposed in the workplace, and others have examined
members of the general population. Skin conditions, such as
acne and rashes, may occur in people exposed to high levels
of PCBs. These effects on the skin are well documented, but
are not likely to result from exposures in the general population.
Most of the human studies have many shortcomings, which make
it difficult for scientists to establish a clear association
between PCB exposure levels and health effects. Some studies
in workers suggest that exposure to PCBs may also cause irritation
of the nose and lungs, gastrointestinal discomfort, changes
in the blood and liver, and depression and fatigue. Workplace
concentrations of PCBs, such as those in areas where PCB transformers
are repaired and maintained, are higher than levels in other
places, such as air in buildings that have electrical devices
containing PCBs or in outdoor air, including air at hazardous
waste sites. Most of the studies of health effects of PCBs
in the general population examined children of mothers who
were exposed to PCBs. The possible health effects of PCBs
in children are discussed in Section 1.6.
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.
Rats that ate food containing large amounts
of PCBs for short periods of time had mild liver damage, and
some died. Rats, mice, or monkeys that ate smaller amounts
of PCBs in food over several weeks or months developed various
kinds of health effects, including anemia, acne-like skin
conditions, and liver, stomach, and thyroid gland injuries.
Other effects caused by PCBs in animals include reductions
in the immune system function, behavioral alterations, and
impaired reproduction. Some PCBs can mimic or block the action
of hormones from the thyroid and other endocrine glands. Because
hormones influence the normal functioning of many organs,
some of the effects of PCBs may result from endocrine changes.
PCBs are not known to cause birth defects. Only a small amount
of information exists on health effects in animals exposed
to PCBs by skin contact or breathing. This information indicates
that liver, kidney, and skin damage occurred in rabbits following
repeated skin exposures, and that a single exposure to a large
amount of PCBs on the skin caused death in rabbits and mice.
Breathing PCBs over several months also caused liver and kidney
damage in rats and other animals, but the levels necessary
to produce these effects were very high. For more information
on how PCBs can affect your health, see Chapters 2 and 3 of
the toxicological profile.
Studies of workers provide evidence that
PCBs were associated with certain types of cancer in humans,
such as cancer of the liver and biliary tract. Rats that ate
commercial PCB mixtures throughout their lives developed liver
cancer. Based on the evidence for cancer in animals, the Department
of Health and Human Services (DHHS) has stated that PCBs may
reasonably be anticipated to be carcinogens. Both EPA and
the International Agency for Research on Cancer (IARC) have
determined that PCBs are probably carcinogenic to humans.
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1.6
How can polychlorinated biphenyls (PCBs) affect children? |
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans.
Children are exposed to PCBs in the same
way as are adults: by eating contaminated food, breathing
indoor air in buildings that have electrical devices containing
PCBs, and drinking contaminated water. Because of their smaller
weight, children’s intake of PCBs per kilogram of body weight
may be greater than that of adults. In addition, a child’s
diet often differs from that of adults. A Food and Drug Administration
(FDA) study in 1991 estimated dietary intakes of PCBs for
infants (6 months) and toddlers (2 years) of less than 0.001 and
0.002 µg/kg/day. Children who live near hazardous waste
sites may accidentally eat some PCBs through hand-to-mouth
behavior, such as by putting dirty hands or other soil/dirt
covered objects in their mouths, or eating without washing
their hands. Some children also eat dirt on purpose; this
behavior is called pica. Children could also be exposed by
playing with old appliances or electrical devices that contain
PCBs.
It is possible that children could be
exposed to PCBs following transport of the chemical on clothing
from the parent’s workplace to the home. House dust in homes
of workers exposed to PCBs contained higher than average levels
of PCBs. PCBs have also been found on the clothing of firefighters
following transformer fires. The most likely way infants will
be exposed is from breast milk that contains PCBs. Fetuses
in the womb are also exposed from the exposed mother.
In one study of women exposed to relatively
high concentrations of PCBs in the workplace during pregnancy,
their babies weighed slightly less at birth than babies born
to women exposed to lower concentrations of PCBs. Studies
of women who consumed high amounts of fish contaminated with
PCBs and other chemicals also had babies that weighed less
than babies from women who did not eat fish. Similar observations
have been made in some studies of women with no known high
exposure to PCBs, but not all studies have confirmed these
findings. Babies born to women who ate fish contaminated with
PCBs before and during pregnancy showed abnormal responses
to tests of infant behavior. Some of these behaviors, such
as problems with motor skills and a decrease in short-term
memory, persisted for several years. However, in these studies,
the women may have been exposed to other chemicals. Other
studies suggest that the immune system may be affected in
children born to and nursed by mothers exposed to increased
levels of PCBs. There are no reports of structural birth defects
in humans caused by exposure to PCBs or of health effects
of PCBs in older children. It is not known whether PCB exposure
can cause in skin acne and rashes in children as occurs in
some adults, although it is likely that the same effects would
occur at very high PCB exposure levels.
Animal studies have shown harmful effects
in the behavior of very young animals when their mothers were
exposed to PCBs and they were exposed in the womb or by nursing.
In addition, some animal studies suggest that exposure to
PCBs causes an increased incidence of prenatal death and changes
in the immune system, thyroid, and reproductive organs. Studies
in monkeys showed that young animals developed skin effects
from nursing after their mothers were exposed to PCBs. Some
studies indicate that very high doses of PCBs may cause structural
birth defects in animals.
Children can be exposed to PCBs both
prenatally and from breast milk. PCBs are stored in the mother’s
body and can be released during pregnancy, cross the placenta,
and enter fetal tissues. Because PCBs dissolve readily in
fat, they can accumulate in breast milk fat and be transferred
to babies and young children. PCBs have been measured in umbilical
cord blood and in breast milk. Some studies have estimated
that an infant who is breast fed for 6 months may accumulate
in this period 6–12% of the total PCBs that will accumulate
during its lifetime. However, in most cases, the benefits
of breast-feeding outweigh any risks from exposure to PCBs
in mother’s milk. You should consult your health care provider
if you have any concerns about PCBs and breast feeding. Because
the brain, nervous system, immune system, thyroid, and reproductive
organs are still developing in the fetus and child, the effects
of PCBs on these target systems may be more profound after
exposure during the prenatal and neonatal periods, making
fetuses and children more susceptible to PCBs than adults.
More information regarding children’s
health and PCBs can be found in Chapter 3 (Section 3.7) of
the toxicological profile.
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1.7
How can families reduce their risk of expsoure to polychlorinated
biphenyls (PCBs)? |
If your doctor finds that you have been
exposed to significant amounts of polychlorinated biphenyls,
ask whether your children might also be exposed. Your doctor
might need to ask your state health department to investigate.
You and your children may be exposed
to PCBs by eating fish or wildlife caught from contaminated
locations. Certain states, Native American tribes, and U.S.
territories have issued fish and wildlife advisories to warn
people about PCB-contaminated fish and fish-eating wildlife.
These advisories will tell you what types and sizes of fish
and game animals are of concern. An advisory may completely
ban eating fish or game or tell you to limit your meals of
a certain fish or game type. For example, an advisory may
tell you not to eat a certain type of fish or game more than
once a month. The advisory may tell you only to eat certain
parts of the fish or game and how to prepare or cook the fish
or game to decrease your exposure to PCBs. The fish or wildlife
advisory may have special restrictions to protect pregnant
women, nursing mothers, and young children. To reduce your
children’s exposure to PCBs, obey these advisories. Additional
information on fish and wildlife advisories for PCBs, including
states that have advisories, is provided in Chapter 6 (Section 6.7)
and Chapter 8 of the toxicological profile. You can consult
your local and state health departments or state natural resources
department on how to obtain PCB advisories, as well as other
important information, such as types of fish and wildlife
and the locations that the advisories apply to.
Children should be told that they should
not play with old appliances, electrical equipment, or transformers,
since they may contain PCBs. Children who live near hazardous
waste sites should be discouraged from playing in the dirt
near these sites and should not play in areas where there
was a transformer fire. In addition, children should be discouraged
from eating dirt, and careful handwashing practices should
be followed.
As mentioned in Section 1.3 of the profile,
workplace exposure to PCBs can still occur during repair and
maintenance of old PCB transformers; accidents, fires, or
spills involving these transformers or other PCB-containing
items; and disposal of PCB materials. If you are exposed to
PCBs in the workplace, it may be possible to carry them home
from work. Your occupational health and safety officer at
work can tell you whether the chemicals you work with may
contain PCBs and are likely to be carried home on your clothes,
body, or tools. If this is the case, you should shower and
change clothing before leaving work, and your work clothes
should be kept separate from other clothes and laundered separately.
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1.8
Is there a medical test to determine whether I have been exposed
to polychlorinated biphenyls (PCBs)? |
Levels of PCBs in the environment were
zero before PCBs were manufactured. Now, all people in industrial
countries have some PCBs in their bodies. There are tests
to determine whether PCBs are in the blood, body fat, and
breast milk. These are not regular or routine clinical tests,
such as the one for cholesterol, but could be ordered by a
doctor to detect PCBs in people exposed to them in the environment
and at work. If your PCB levels are higher than the background
levels, this will show that you have been exposed to high
levels of PCBs. However, these measurements cannot determine
the exact amount or type of PCBs that you have been exposed
to, or how long you have been exposed. Although these tests
can indicate whether you have been exposed to PCBs to a greater
extent than the general population, they do not predict whether
you will develop harmful health effects. Blood tests are the
easiest, safest, and probably the best method for detecting
recent exposures to large amounts of PCBs. Results of such
tests should be reviewed and carefully interpreted by physicians
with a background in environmental and occupational medicine.
Nearly everyone has been exposed to PCBs because they are
found throughout the environment, and people are likely to
have detectable amounts of PCBs in their blood, fat, and breast
milk. Recent studies have shown that PCB levels in tissues
from United States population are now declining. Additional
information on tests used to determine whether you have been
exposed to PCBs can be found in Chapter 3 (Section 3.11) and
Chapter 7 (Section 7.1) of the toxicological profile.
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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).
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 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
PCBs include the following:
The EPA standard for PCBs in drinking
water is 0.5 parts of PCBs per billion parts (ppb) of water.
For the protection of human health from the possible effects
of drinking the water or eating the fish or shellfish from
lakes and streams that are contaminated with PCBs, the EPA
regulates that the level of PCBs in these waters be no greater
than 0.17 parts of PCBs per trillion parts (ppt) of water.
States with fish and wildlife consumption advisories for PCBs
are identified in Chapter 6 (Section 6.7) and Chapter 8 of
the toxicological profile.
The FDA has set residue limits for PCBs
in various foods to protect from harmful health effects. FDA
required limits include 0.2 parts of PCBs per million parts
(ppm) in infant and junior foods, 0.3 ppm in eggs, 1.5 ppm
in milk and other dairy products (fat basis), 2 ppm in fish
and shellfish (edible portions), and 3 ppm in poultry and
red meat (fat basis).
OSHA regulates that workers not be exposed
by inhalation over a period of 8 hours for 5 days per week
to more than 1 milligram per cubic meter of air (mg/m³)
for 42% chlorine PCBs, or to 0.5 mg/m³ for 54%
chlorine PCBs.
NIOSH recommends that workers not breathe
air containing 42 or 54% chlorine PCB levels higher than 1 microgram
per cubic meter of air (µg/m³) for a 10-hour
workday, 40-hour workweek.
EPA requires that companies that transport,
store, or dispose of PCBs follow the rules and regulations
of the federal hazardous waste management program. EPA also
limits the amount of PCBs put into publicly owned waste water
treatment plants. To minimize exposure of people to PCBs,
EPA requires that industry tell the National Response Center
each time 1 pound or more of PCBs have been released to the
environment.
For more information on federal and state
regulations and guidelines for PCBs, see Chapter 8 of the
toxicological profile.
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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
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 |
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References |
Agency for Toxic Substances and Disease
Registry (ATSDR). 2000. Toxicological
profile for polychlorinated biphenyls (PCBs). Atlanta,
GA: U.S. Department of Health and Human Services, Public Health
Service.
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