1.1 What are PAHs? |
1.2 What happens to PAHs when they enter
the environment? |
1.3 How might I be exposed to PAHs? |
1.4 How can PAHs enter and leave my body? |
1.5 How can PAHs affect my health? |
1.6 Is there a medical test to determine
whether I have been exposed to PAHs? |
1.7 What recommendations has the federal
government made to protect human health? |
1.8 Where can I get more information? |
References |
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August 1995 |
Public Health Statement |
for |
Polycyclic Aromatic Hydrocarbons
(PAHs) |
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for polycyclic aromatic hydrocarbons (PAHs). 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 statement was prepared to give you
information about polycyclic aromatic hydrocarbons (PAHs)
and to emphasize the human health effects that may result
from exposure to them. The Environmental Protection Agency
(EPA) has identified 1,408 hazardous waste sites as the most
serious in the nation. These sites make up the National Priorities
List (NPL) and are the sites targeted for long-term federal
clean-up activities. PAHs have been found in at least 600
of the sites on the NPL. However, the number of NPL sites
evaluated for PAHs is not known. As EPA evaluates more sites,
the number of sites at which PAHs are found may increase.
This information is important because exposure to PAHs may
cause harmful health effects and because these sites are potential
or actual sources of human exposure to PAHs.
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 substances containing
the substance or by skin contact with it.
If you are exposed to substances such
as PAHs, many factors will determine whether harmful health
effects will occur and what the type and severity of those
health effects will be. These factors include the dose (how
much), the duration (how long), the route or pathway by which
you are exposed (breathing, eating, drinking, or skin contact),
the other chemicals to which you are exposed, and your individual
characteristics such as age, sex, nutritional status, family
traits, lifestyle, and state of health.
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1.1
What are PAHs? |
PAHs are a group of chemicals that are
formed during the incomplete burning of coal, oil, gas, wood,
garbage, or other organic substances, such as tobacco and
charbroiled meat. There are more than 100 different PAHs.
PAHs generally occur as complex mixtures (for example, as
part of combustion products such as soot), not as single compounds.
PAHs usually occur naturally, but they can be manufactured
as individual compounds for research purposes; however, not
as the mixtures found in combustion products. As pure chemicals,
PAHs generally exist as colorless, white, or pale yellow-green
solids. They can have a faint, pleasant odor. A few PAHs are
used in medicines and to make dyes, plastics, and pesticides.
Others are contained in asphalt used in road construction.
They can also be found in substances such as crude oil, coal,
coal tar pitch, creosote, and roofing tar. They are found
throughout the environment in the air, water, and soil. They
can occur in the air, either attached to dust particles or
as solids in soil or sediment.
Although the health effects of individual
PAHs are not exactly alike, the following 17 PAHs are considered
as a group in this profile:
- acenaphthene
- acenaphthylene
- anthracene
- benz[a]anthracene
- benzo[a]pyrene
- benzo[e]pyrene
- benzo[b]fluoranthene
- benzo[g,h,i]perylene
- benzo[j]fluoranthene
- benzo[k]fluoranthene
- chrysene
- dibenz[a,h]anthracene
- fluoranthene
- fluorene
- indeno[1,2,3-c,d]pyrene
- phenanthrene
- pyrene
These 17 PAHs were chosen to be included
in this profile because (1) more information is available
on these than on the others; (2) they are suspected to be
more harmful than some of the others, and they exhibit harmful
effects that are representative of the PAHs; (3) there is
a greater chance that you will be exposed to these PAHs than
to the others; and (4) of all the PAHs analyzed, these were
the PAHs identified at the highest concentrations at NPL hazardous
waste sites.
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1.2
What happens to PAHs when they enter the environment? |
PAHs enter the environment mostly as
releases to air from volcanoes, forest fires, residential
wood burning, and exhaust from automobiles and trucks. They
can also enter surface water through discharges from industrial
plants and waste water treatment plants, and they can be released
to soils at hazardous waste sites if they escape from storage
containers. The movement of PAHs in the environment depends
on properties such as how easily they dissolve in water, and
how easily they evaporate into the air. PAHs in general do
not easily dissolve in water. They are present in air as vapors
or stuck to the surfaces of small solid particles. They can
travel long distances before they return to earth in rainfall
or particle settling. Some PAHs evaporate into the atmosphere
from surface waters, but most stick to solid particles and
settle to the bottoms of rivers or lakes. In soils, PAHs are
most likely to stick tightly to particles. Some PAHs evaporate
from surface soils to air. Certain PAHs in soils also contaminate
underground water. The PAH content of plants and animals living
on the land or in water can be many times higher than the
content of PAHs in soil or water. PAHs can break down to longer-lasting
products by reacting with sunlight and other chemicals in
the air, generally over a period of days to weeks. Breakdown
in soil and water generally takes weeks to months and is caused
primarily by the actions of microorganisms.
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1.3
How might I be exposed to PAHs? |
PAHs are present throughout the environment,
and you may be exposed to these substances at home, outside,
or at the workplace. Typically, you will not be exposed to
an individual PAH, but to a mixture of PAHs.
In the environment, you are most likely
to be exposed to PAH vapors or PAHs that are attached to dust
and other particles in the air. Sources include cigarette
smoke, vehicle exhausts, asphalt roads, coal, coal tar, wildfires,
agricultural burning, residential wood burning, municipal
and industrial waste incineration, and hazardous waste sites.
Background levels of some representative PAHs in the air are
reported to be 0.02–1.2 nanograms per cubic meter (ng/m³;
a nanogram is one-millionth of a milligram) in rural areas
and 0.15–19.3 ng/m³ in urban areas. You may be exposed
to PAHs in soil near areas where coal, wood, gasoline, or
other products have been burned. You may be exposed to PAHs
in the soil at or near hazardous waste sites, such as former
manufactured-gas factory sites and wood-preserving facilities.
PAHs have been found in some drinking water supplies in the
United States. Background levels of PAHs in drinking water
range from 4 to 24 nanograms per liter (ng/L; a liter is slightly
more than a quart).
In the home, PAHs are present in tobacco
smoke, smoke from wood fires, creosote-treated wood products,
cereals, grains, flour, bread, vegetables, fruits, meat, processed
or pickled foods, and contaminated cow's milk or human breast
milk. Food grown in contaminated soil or air may also contain
PAHs. Cooking meat or other food at high temperatures, which
happens during grilling or charring, increases the amount
of PAHs in the food. The level of PAHs in the typical U.S.
diet is less than 2 parts of total PAHs per billion parts
of food (ppb), or less than 2 micrograms per kilogram of food
(µg/kg; a microgram is one-thousandth of a milligram).
The primary sources of exposure to PAHs
for most of the U.S. population are inhalation of the compounds
in tobacco smoke, wood smoke, and ambient air, and consumption
of PAHs in foods. For some people, the primary exposure to
PAHs occurs in the workplace. PAHs have been found in coal
tar production plants, coking plants, bitumen and asphalt
production plants, coal-gasification sites, smoke houses,
aluminum production plants, coal tarring facilities, and municipal
trash incinerators. Workers may be exposed to PAHs by inhaling
engine exhaust and by using products that contain PAHs in
a variety of industries such as mining, oil refining, metalworking,
chemical production, transportation, and the electrical industry.
PAHs have also been found in other facilities where petroleum,
petroleum products, or coal are used or where wood, cellulose,
corn, or oil are burned. People living near waste sites containing
PAHs may be exposed through contact with contaminated air,
water, and soil.
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1.4
How can PAHs enter and leave my body? |
PAHs can enter your body through your
lungs when you breathe air that contains them (usually stuck
to particles or dust). Cigarette smoke, wood smoke, coal smoke,
and smoke from many industrial sites may contain PAHs. People
living near hazardous waste sites can also be exposed by breathing
air containing PAHs. However, it is not known how rapidly
or completely your lungs absorb PAHs. Drinking water and swallowing
food, soil, or dust particles that contain PAHs are other
routes for these chemicals to enter your body, but absorption
is generally slow when PAHs are swallowed. Under normal conditions
of environmental exposure, PAHs could enter your body if your
skin comes into contact with soil that contains high levels
of PAHs (this could occur near a hazardous waste site) or
with used crankcase oil or other products (such as creosote)
that contain PAHs. The rate at which PAHs enter your body
by eating, drinking, or through the skin can be influenced
by the presence of other compounds that you may be exposed
to at the same time with PAHs. PAHs can enter all the tissues
of your body that contain fat. They tend to be stored mostly
in your kidneys, liver, and fat. Smaller amounts are stored
in your spleen, adrenal glands, and ovaries. PAHs are changed
by all tissues in the body into many different substances.
Some of these substances are more harmful and some are less
harmful than the original PAHs. Results from animal studies
show that PAHs do not tend to be stored in your body for a
long time. Most PAHs that enter the body leave within a few
days, primarily in the feces and urine.
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1.5
How can PAHs affect my health? |
PAHs can be harmful to your health under
some circumstances. Several of the PAHs, including benz[a]anthracene,
benzo[a]pyrene, benzo[b]fluoranthene, benzo[j]fluoranthene,
benzo[k]fluoranthene, chrysene, dibenz[a,h]anthracene, and
indeno[1,2,3-c,d]pyrene, have caused tumors in laboratory
animals when they breathed these substances in the air, when
they ate them, or when they had long periods of skin contact
with them. Studies of people show that individuals exposed
by breathing or skin contact for long periods to mixtures
that contain PAHs and other compounds can also develop cancer.
Mice fed high levels of benzo[a]pyrene
during pregnancy had difficulty reproducing and so did their
offspring. The offspring of pregnant mice fed benzo[a]pyrene
also showed other harmful effects, such as birth defects and
decreased body weight. Similar effects could occur in people,
but we have no information to show that these effects do occur.
Studies in animals have also shown that
PAHs can cause harmful effects on skin, body fluids, and the
body's system for fighting disease after both short- and long-term
exposure. These effects have not been reported in people.
The Department of Health and Human Services
(DHHS) has determined that benz[a]anthracene, benzo[b]fluoranthene,
benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene,
dibenz[a,h]anthracene, and indeno[1,2,3-c,d]pyrene are known
animal carcinogens. The International Agency for Research
on Cancer (IARC) has determined the following: benz[a]anthracene
and benzo[a]pyrene are probably carcinogenic to humans; benzo[b]fluoranthene,
benzo[j]fluoranthene, benzo[k]fluoranthene, and indeno[1,2,3-c,d]pyrene
are possibly carcinogenic to humans; and anthracene, benzo[g,h,i]perylene,
benzo[e]pyrene, chrysene, fluoranthene, fluorene, phenanthrene,
and pyrene are not classifiable as to their carcinogenicity
to humans. EPA has determined that benz[a]anthracene, benzo[a]pyrene,
benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenz[a,h]anthracene,
and indeno[1,2,3-c,d]pyrene are probable human carcinogens
and that acenaphthylene, anthracene, benzo[g,h,i]perylene,
fluoranthene, fluorene, phenanthrene, and pyrene are not classifiable
as to human carcinogenicity. Acenaphthene has not been classified
for carcinogenic effects by the DHHS, IARC, or EPA.
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1.6
Is there a medical test to determine whether I have been exposed
to PAHs? |
In your body, PAHs are changed into chemicals
that can attach to substances within the body. The presence
of PAHs attached to these substances can then be measured
in body tissues or blood after exposure to PAHs. PAHs or their
metabolites can also be measured in urine, blood, or body
tissues. Although these tests can show that you have been
exposed to PAHs, these tests cannot be used to predict whether
any health effects will occur or to determine the extent or
source of your exposure to the PAHs. It is not known how effective
or informative the tests are after exposure is discontinued.
These tests to identify PAHs or their products are not routinely
available at a doctor's office because special equipment is
required to detect these chemicals.
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1.7
What recommendations has the federal government made to protect
human health? |
The federal government has set regulations
to protect people from the possible health effects of eating,
drinking, or breathing PAHs. EPA has suggested that taking
into your body each day the following amounts of individual
PAHs is not likely to cause any harmful health effects: 0.3
milligrams (mg) of anthracene, 0.06 mg of acenaphthene, 0.04
mg of fluoranthene, 0.04 mg of fluorene, and 0.03 mg of pyrene
per kilogram (kg) of your body weight (one kilogram is equal
to 2.2 pounds). Actual exposure for most of the United States
population occurs from active or passive inhalation of the
compounds in tobacco smoke, wood smoke, and contaminated air,
and from eating the compounds in foods. Skin contact with
contaminated water, soot, tar, and soil may also occur. Estimates
for total exposure in the United States population have been
listed as 3 mg/day.
From what is currently known about benzo[a]pyrene,
the federal government has developed regulatory standards
and guidelines to protect people from the potential health
effects of PAHs in drinking water. EPA has provided estimates
of levels of total cancer-causing PAHs in lakes and streams
associated with a risk of human cancer development. If the
following amounts of individual PAHs are released to the environment
within a 24-hour period, EPA must be notified: 1 pound of
benzo[b]fluoranthene, benzo[a]pyrene, or dibenz[a,h]anthracene;
10 pounds of benz[a]anthracene; 100 pounds of acenaphthene,
chrysene, fluoranthene, or indeno[1,2,3-c,d]pyrene; or 5,000
pounds of acenaphthylene, anthracene, benzo[k]fluoranthene,
benzo[g,h,i]perylene, fluorene, phenanthrene, or pyrene.
PAHs are generally not produced commercially
in the United States except as research chemicals. However,
PAHs are found in coal, coal tar, and in the creosote oils,
oil mists, and pitches formed from the distillation of coal
tars. The National Institute for Occupational Safety and Health
(NIOSH) concluded that occupational exposure to coal products
can increase the risk of lung and skin cancer in workers.
NIOSH established a recommended occupational exposure limit,
time-weighted average (REL-TWA) for coal tar products of 0.1
milligram of PAHs per cubic meter of air (0.1 mg/m³)
for a 10-hour workday, within a 40-hour workweek. The American
Conference of Governmental Industrial Hygienists (ACGIH) recommends
an occupational exposure limit for coal tar products of 0.2
mg/m³ for an 8-hour workday, within a 40-hour workweek.
The Occupational Safety and Health Administration (OSHA) has
established a legally enforceable limit of 0.2 mg/m³
averaged over an 8-hour exposure period.
Mineral oil mists have been given an
IARC classification of 1 (sufficient evidence of carcinogenicity).
The OSHA Permissible Exposure Limit (PEL) for mineral oil
mist is 5 mg/m³ averaged over an 8-hour exposure period.
NIOSH has concurred with this limit, and has established a
recommended occupational exposure limit (REL-TWA) for mineral
oil mists of 5 mg/m³ for a 10-hour work day, 40-hour
work week, with a 10 mg/m³ Short Term Exposure Limit
(STEL).
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1.8 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). 1995. Toxicological
profile for polycyclic aromatic hydrocarbons (PAHs). Atlanta,
GA: U.S. Department of Health and Human Services, Public Health
Service.
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