Agency for Toxic Substances and Disease Registry
Case Studies in Environmental Medicine (CSEM) 

Benzene Toxicity
Who is at Risk

Who is at Risk

Workers employed in industries using or producing benzene (i.e., petrochemical companies; petroleum refining and coke and coal chemical manufacturing; rubber tire manufacturing; and companies involved in the storage or transport of benzene and petroleum products containing benzene) have the greatest likelihood of exposure. The Occupational Safety and Health Administration (OSHA) estimates that approximately 238,000 workers in the United States may be exposed to benzene during refining operations; gasoline storage, shipment, and retail operations; chemical manufacturing; and plastics and rubber manufacturing. Of these workers, only 10,000 (4%) were above an 8-hour time-weighted average (TWA) of 1 ppm and only 0.2% were above 10 ppm. Other workers who may be exposed to benzene because of their occupations include steel workers, printers, rubber workers, shoe makers, laboratory technicians, and gas station employees.

Atmospheric benzene levels of up to 6.6 ppm and 6-hour TWAs of 0.1 ppm have been measured during gasoline pumping. This risk has been lowered by installing vapor recapture devices on delivery hoses. These devices, if used properly, significantly reduce exposure. Catalytic converters have significantly reduced the benzene in automobile emissions.

Benzene is converted to toxic metabolites mostly by mixed-function oxidases (MFOs) in the liver and bone marrow. MFO-inducing drugs (e.g., phenobarbital and ethanol) and certain chemicals (e.g., chlordane and parathion) may increase the rate at which toxic metabolites of benzene are formed. It also seems likely that persons who have bone marrow that is metabolically hyperactive (e.g., fetuses, infants and children, and those persons with hemolytic anemia) are at increased risk of benzene toxicity because the cells are rapidly dividing. Persons with compromised hemoglobin, such as those with B-thalassemia or viral hepatitis, may be at increased risk for benzene-induced aplastic anemia. Exposure to benzene may also stimulate specific CYP (or P450) enzymes, which are responsible for oxygenation of benzene and have a propensity to generate oxygen radicals. These radicals are a major cause of benzene toxicity.

• Two to three million U.S. workers are at risk of benzene exposure.
• Alcohol and other drugs that induce the mixed-function oxidase enzymes may potentiate those effects of benzene that depend on metabolism. Although benzene-induced central nervous system (CNS) depression is probably not dependent on metabolism, alcohol and other CNS depressants might act cumulatively.

Challenge

1. Does the patient in the case study have any risk factors for the adverse effects of benzene? Is anyone else in the case at risk of benzene exposure or its adverse effects?

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