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Polycyclic Aromatic Hydrocarbons (PAHs)
 What
are polycyclic aromatic hydrocarbons?
Polycyclic
aromatic hydrocarbons (PAHs) are a group of over 100 different
chemicals that are formed during the incomplete burning of coal, oil
and gas, garbage, or other organic substances like tobacco or charbroiled
meat. PAHs are usually found as a mixture containing two or more of
these compounds, such as soot.
Some PAHs are manufactured. These pure PAHs usually exist as colorless,
white, or pale yellow-green solids. PAHs are found in coal tar, crude
oil, creosote, and roofing tar, but a few are used in medicines or to
make dyes, plastics, and pesticides.
What
happens to PAHs when they enter the environment?
PAHs enter the air mostly as releases from volcanoes, forest fires,
burning coal, and automobile exhaust.
PAHs can occur in air attached to dust particles.
Some PAH particles can readily evaporate into the air from soil or
surface waters.
PAHs can break down by reacting with sunlight and other chemicals
in the air, over a period of days to weeks.
PAHs enter water through discharges from industrial and wastewater
treatment plants.
Most PAHs do not dissolve easily in water. They stick to solid particles
and settle to the bottoms of lakes or rivers.
Microorganisms can break down PAHs in soil or water after a period
of weeks to months.
In soils, PAHs are most likely to stick tightly to particles; certain
PAHs move through soil to contaminate underground water.
PAH contents of plants and animals may be much higher than PAH contents
of soil or water in which they live.
How might I be exposed to PAHs?
Breathing air containing PAHs in the workplace of coking, coal-tar,
and asphalt production plants; smokehouses; and municipal trash incineration
facilities.
Breathing air containing PAHs from cigarette smoke, wood smoke, vehicle
exhausts, asphalt roads, or agricultural burn smoke.
Coming in contact with air, water, or soil near hazardous waste sites.
Eating grilled or charred meats; contaminated cereals, flour, bread,
vegetables, fruits, meats; and processed or pickled foods.
Drinking contaminated water or cow's milk.
Nursing infants of mothers living near hazardous waste sites may
be exposed to PAHs through their mother's milk.
How
can PAHs affect my health?
Mice that were fed high levels of one PAH during pregnancy
had difficulty reproducing and so did their offspring. These offspring
also had higher rates of birth defects and lower body weights. It
is not known whether these effects occur in people.
Animal studies have also shown that PAHs can cause harmful effects
on the skin, body fluids, and ability to fight disease after both
short- and long-term exposure. But these effects have
not been seen in people.
How likely are PAHs to cause cancer?
The Department of Health and Human Services (DHHS) has determined
that some PAHs may reasonably be expected to be carcinogens.
Some people who have breathed or touched mixtures of PAHs and other
chemicals for long periods of time have developed cancer. Some
PAHs have caused cancer in laboratory animals when they breathed air
containing them (lung cancer), ingested them in food (stomach cancer),
or had them applied to their skin (skin cancer).
Is
there a medical test to show whether I've been exposed to PAHs?
In the body, PAHs are changed into chemicals that can attach to substances
within the body. There are special tests that can detect PAHs attached
to these substances in body tissues or blood. However, these tests
cannot tell whether any health effects will occur or find out the
extent or source of your exposure to the PAHs. The tests aren't usually
available in your doctor's office because special equipment is needed
to conduct them.
Has
the federal government made recommendations to protect human health?
The Occupational Safety and Health Administration (OSHA) has
set a limit of 0.2 milligrams of PAHs per cubic meter of air (0.2
mg/m3). The OSHA Permissible Exposure Limit (PEL)
for mineral oil mist that contains PAHs is 5 mg/m3 averaged
over an 8-hour exposure period.
The National Institute for Occupational Safety and Health (NIOSH)
recommends that the average workplace air levels for coal tar products
not exceed 0.1 mg/m3 for a 10-hour workday, within a 40-hour
workweek. There are other limits for workplace exposure for things
that contain PAHs, such as coal, coal tar, and mineral oil.
 This
factsheet was adapted from ATSDR.
Last updated September 2002
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