Polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are "class of more than 100 chemicals composed of up to six benzene rings fused together such that any two adjacent benzene rings share two carbon bonds." Of these, 17 chemicals get the most attention because of harmful health effects. PAHs can come from biogenic, petrogenic, or pyrogenic sources. In other words, they can come from living organisms, geological processes or oil spills, or by high temperature combustion of organic matter (including forest fires, car exhaust, coal tar), respectively. PAHs have been found in sewage sludge. PAH's are in tobacco smoke. They have also been measured in the Gulf of Mexico following the Deepwater Horizon oil spill.

PAHs of Concern
As noted above, seventeen PAHs cause the most concern because they are considered the most harmful to health as well as the most common PAHs that humans are exposed to. These chemicals are:


 * 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

PAHs in the Environment
PAHs typically enter the air from volcanoes, forest fires, burning coal, and vehicle exhaust. They can also enter the environment via effluent from industrial and wastewater treatment plants. They can also evaporate into the air from soil or surface waters.

In the air, PAHs can attach to dust particles. PAHs can break down by reacting with sunlight and chemicals in the air. In water, PAHs tend to stick to solid particles and settle to the bottom of lakes and rivers. In the soil and water, microorganisms can break down PAHs.

PAHs in Sewage Sludge
In the U.S. EPA's Targeted National Sewage Sludge Survey published in January 2009, it tested for four PAHs in 84 samples of sewage sludge from around the country: Fluoranthene, Pyrene, Benzo(a)pyrene, 2-Methylnaphthalene

It found Fluoranthene in 77 samples in concentrations ranging from 45 to 12,000 micrograms per kilogram. Pyrene was found in 72 samples, ranging from 44 to 14,000 micrograms per kilogram. Benzo(a)pyrene was found in 64 samples, ranging from 63 to 4,500 micrograms per kilogram. Last, 2-Methylnaphthalene was only found in 39 samples, ranging from concentrations of 10 to 4,600 micrograms per kilogran.

Human Exposure Health Effects
Humans can be exposed to PAHs through respiration or diet. Common sources of respiratory exposure include occupational sources (coking, coal-tar, and asphalt production plants, smokehouses, and municipal trash incineration facilities), cigarette smoke, wood smoke, vehicle exhaust, and agricultural burn smoke. Contact with air, water, and soil near hazardous waste sites is also a route of exposure. In the diet, humans may be exposed by eating contaminated foods, drinking contaminated water or milk, or by eating grilled or charred meats. Nursing infants can be exposed through their mother's milk.

According to an Oregon State University website: "Occupational exposures to high levels of pollutant mixtures containing PAHs has resulted in symptoms such as eye irritation, nausea, vomiting, diarrhea and confusion. However, it is not known which of the mixture components were causing these effects. Mixtures of PAHs are known to cause skin effects in animals and humans such as irritation and inflammation. Anthracene, benzo(a)pyrene and naphthalene are direct skin irritants while anthracene and benzo(a)pyrene are reported to be skin sensitizers, i.e. cause an allergic skin response in animals and humans."

Related SourceWatch articles

 * Biosolids
 * Sewage sludge
 * Food Rights Network
 * Deepwater Horizon

External resources

 * Oregon State University, Superfund Research Program, "All About PAHs"
 * *Polycyclic Aromatic Hydrocarbons (PAHs), Ospar website