Polycyclic Aromatic Hydrocarbons
All information presented are excerpts from "Mercury Free", by Dr. James Hardy.
Agency for Toxic Substances and Disease Registry
There is no molecular representation since this substance is a mixture of many compounds.
Exposure to polycyclic aromatic hydrocarbons usually occurs by breathing air contaminated by wild fires or coal tar, or by eating foods that have been grilled. PAHs have been found in at least 600 of the 1,430 National Priorities List sites identified by the Environmental Protection Agency (EPA).
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.
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.
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.
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.
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).
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.
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.