Benzene is commonly used as a solvent and a synthetic intermediate in the chemical and pharmaceutical industries. Over 90% of benzene produced annually is used in chemical synthesis applications, including ethylbenzene (styrene production), cumene (production of phenol and acetone), cyclohexane, and nitrobenzene (production of aniline and resins). Benzene can prevent engine knocking and is added to gasoline (at 1-2% by volume) as a replacement for alkyllead compounds. Combustion of fossil fuels accounts for approximately 82% of benzene released into the atmosphere as automotive exhaust, 14% from industrial activities, 3% from human individual activities, and 0.1% from cigarette smoke. This is in comparison to human exposure sources, which would include 45% from cigarettes, 34% from individual activities, 18% from automobile exhaust, and 3% from industrial activities.
Benzene has been produced commercially from coal since 1849, although petroleum has been used since 1951 and is currently the major source of its production. Benzene is consistently one of the top ten organic chemicals produced annually in the US, with peak benzene production in the US having occurred in 2000, with 8.1 million metric tons (17.8 billion pounds) produced. Estimates of annual benzene releases to the environment is found in the Toxics Release Inventory (TRI) data and listed according to each state in the US. In 2002, it was estimated that 2700 metric tons (6 million pounds) of benzene were released to the atmosphere, suggested to account for 88% of the total released from facilities required to report to TRI. These should be considered underestimates, because not all facilities are required to report releases. Of the prior estimates, approximately 8.6 metric tons (19 000 pounds) of benzene were released to surface water from domestic manufacturing and processing facilities during 2002, accounting for about 0.3% of the estimated total environmental releases. In addition, approximately 4.5 metric tons (100 000 pounds) of benzene were released to soils from these same domestic facilities, representing 0.17% of estimated total releases. Another 314 metric tons (692 000 pounds) were released by underground injection, comprising another 10% of estimated environmental releases.
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