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OCCURRENCE AND USE

Benzene is a clear liquid with a sweet odor, according to the Hazardous Substance Data Bank (HSDB 2005). This aromatic hydrocarbon is used as a solvent; however, its use has declined in many countries because of concerns about carcinogenicity. Benzene occurs naturally but is primarily produced from petroleum products. It is a constituent of gasoline, where it is used to enhance octane rating and as an antiknock agent (Krewski et al. 2000). Uses for benzene are numerous including as an intermediate in the manufacture of several chemicals, such as ethylbenzene, cumene, cyclohexane, and nitrobenzene. Benzene is a precursor in the manufacture of urethanes, chlorobenzene, and maleic anhydride (HSDB 2005).

Benzene can enter the environment during any of the stages involved in its production, storage, use, and transport (Krewski et al. 2000). Vehicular emissions constitute the main source of benzene in the environment. Benzene has been detected in approximately 10% of recent air samples in the space shuttle cabin and in Spacelab at concentrations of 0.01 to 0.1 milligram per cubic meter (mg/m3) (James and Kaplan 1996). In September 2006, an overheating of the oxygen generator in the Russian segment of the International Space Station resulted in elevated concentrations of several aromatic compounds. Samples taken several hours after the incident showed a concentration of benzene in air of 0.5 mg/m3 in the U.S. segment. Benzene is typically not detected in spacecraft water samples. Consumption of benzene in the public water supply is highly unlikely; however, accidental ingestion of water from contaminated streams occurs from leaking gasoline storage tanks, landfills, and other sources (HSDB 2005).

PHARMACOKINETICS AND METABOLISM

Absorption

Acute ingestion of benzene causes gastrointestinal and neurologic toxicity (HSDB). In humans, the lungs rapidly absorb benzene vapor in amounts equivalent to about 50% or less of the doses inhaled over several hours of exposure to concentrations of 50 to 100 ppm (Nomiyama and Nomiyama 1974a,b; Sato and Nakajima 1979; R. Snyder et al. 1981; IARC 1982; James and Kaplan 1996). In men and women exposed to 52 to 62 ppm for 4 h, respiratory uptake was 47% of the original dose, with little difference between the sexes (Nomiyama and Nomiyama 1974a,b; IARC 1982). Absorption was greatest during the first 5 min of exposure and reached a constant level between 15 min (Srbova et al. 1950) and 3 h (Nomiyama and Nomiyama 1974a,b; IARC 1982). Respiratory retention (the difference between respiratory uptake and excretion) was estimated as 30% of the inhaled dose (Nomiyama and Nomiyama 1974a,b; IARC 1982).

Benzene can also be absorbed through the skin, but the rate of absorption is lower than that for inhalation exposure (ATSDR 1989). It has been calculated



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