The primary route of human exposure to benzene is inhalation of ambient air. Benzene is present in the atmosphere both from natural sources, which include forest fires and oil seeps, and from industrial sources, which include automobile exhaust, industrial emissions, and fuel evaporation from gasoline filling stations.
People are exposed to benzene in 3 ways:
At work / occupational exposures: Workers in industries that make or use benzene may be exposed to high levels of this chemical. These industries include the rubber industry, oil refineries, chemical plants, shoe manufacturers, and gasoline related industries. In 1987, OSHA estimated that about 237,000 workers in the United States were potentially exposed to benzene. It is not known if this number has changed since that time. More about occupational exposures.
General environment exposures: Sources of benzene in the environment include gasoline, automobile exhaust fumes, cigarette smoke, emissions from coke ovens and other industrial processes, and waste water from certain industries. While benzene is commonly found in air in both urban and rural areas, the levels are usually very low. Areas of heavy vehicular traffic, gasoline stations, and areas near industrial sources may have higher air levels.
Cigarettes have been found to release between 50 and 150 micrograms of benzene per cigarette, so smoking and second-hand smoke are important sources of exposure to benzene. Cigarette smoke accounts for about half of the U.S. national exposure to benzene and about 89 percent of benzene exposure among smokers. Secondhand smoke accounts for 10 percent of benzene exposure among nonsmokers. Benzene has also been identified in contaminated water and food.
Benzene evaporates into air very quickly and dissolves slightly in water. Benzene is highly flammable. Most people can begin to smell benzene in air at 1.5-4.7 parts of benzene per million parts (ppm) of air and smell benzene in water at 2 ppm. Most people can begin to taste benzene in water at 0.5-4.5 ppm. One part per million is approximately equal to one drop in 40 gallons. Benzene is found in air, water, ground water, and soil. Benzene comes from both industrial and natural sources.
Benzene consumer products exposures: Some consumer household products, such as glues, cleaning products, detergents, art supplies, paint strippers, and soda pop contain benzene.
The greatest risk for exposure to high doses of benzene occurs from workplace exposures, but the most common exposure to lower doses of benzene occurs in the general environment.
Some trade names or synonyms for benzene used in the home are: Benzol 90, Pyrobenzol, Polystream, Coal naphtha, Phene.
The two routes of exposure to benzene are inhalation and skin absorption. However, since liquid benzene evaporates quickly, skin absorption, which requires contact with a source such as gasoline, is less common. Therefore, inhalation of contaminated air is the primary route of exposure.
Benzene has been measured in outdoor air at various U.S. locations with concentrations ranging from 0.02 in a rural area to 112 ppb in an urban area. Exposure to benzene is highest in areas of heavy vehicle traffic and around gasoline filling stations.
Exposure is greater among people who spend significant time in vehicles in areas of congested traffic. Additionally, pumping gasoline can be a significant source of benzene exposure. The general population also can be exposed to benzene by inhaling air containing tobacco smoke, drinking contaminated water, or eating contaminated food. Approximately half of the total national exposure to benzene comes from cigarette smoke.