Toxicity Profiles

RAGs A Format for Benzene - CAS Number 71432

Benzene is widely used in the United States; it ranks in the top 20 chemicals for production volume. Benzene is a colorless organic liquid with a sweet odor. It evaporates into the air very quickly and dissolves slightly in water. It is highly flammable and is formed from both natural processes and human activities. Benzene. Benzene is used primarily in the production of other chemicals such as ethylbenzene, cumene, and cyclohexane. Benzene has also been used as a solvent, but this use is declining, coincidental with the replacement of benzene with other organic solvents. Benzene is emitted into the workplace and the environment from industrial and other manmade sources, including gasoline from filling stations, smoking tobacco products, and auto exhaust.

Because of benzene's high vapor pressure, inhalation is the most likely route of exposure to the chemical, particularly in the workplace. Benzene is absorbed via ingestion, inhalation, and skin application. Experimental data indicate that humans can absorb up to 80% of inhaled benzene (after 5 minutes of exposure). Lethal oral doses of benzene are estimated to be 10 mL in humans. Nonlethal oral doses of benzene can impact the nervous, hematological, and immunological systems. Ingested and inhaled benzene produces symptoms of neurotoxicity at acute doses of 2 mL for humans. Inhalation of benzene vapor concentrations of 20,000 ppm for 5-10 minutes can be fatal to humans; death results from central nervous system depression.

Benzene is carcinogenic in humans by inhalation and in animals by the oral route of exposure. Occupational exposure to benzene has been associated mainly with increased incidences of acute myeloblastic or erythroblastic leukemias and chronic myeloid and lymphoid leukemias among workers. Studies in animals have demonstrated an association between oral and inhalation exposure to benzene and the development of a variety of tumors, including lymphoma and carcinomas of the Zymbal gland, oral cavity, mammary gland, ovaries, lung, and skin. Benzene has been placed in the EPA weight-of-evidence classification A, human carcinogen.

The following is a presentation of the toxicity information associated with Benzene:

• The Oral Chronic Reference Dose is 4.00E-03 (mg/kg-day).
• The Oral Chronic Reference Dose has a modifying factor of 1.
• The Oral Chronic Reference Dose has an uncertainty factor of 300.
• The Oral Chronic Reference Dose is based on the Rothman et. al. study from 1996.
• The Oral Chronic Reference Dose study critical effect is decreased lymphocyte count.
• The Oral Chronic Reference Dose is based on human study.
• The overall confidence in the Oral Chronic Reference Dose is medium.
• The Inhalation Chronic Reference Concentration is 3.00E-02 (mg/m³).
• The Inhalation Chronic Reference Concentration has a modifying factor of 1.
• The Inhalation Chronic Reference Concentration has an uncertainty factor of 300.
• The Inhalation Chronic Reference Concentration is based on the Rothman et. al. study from 1996.
• The Inhalation Chronic Reference Concentration study critical effects is decreased lymphocyte count.
• The Inhalation Chronic Reference Concentration is based on human study.
• The overall confidence in the Inhalation Chronic Reference Concentration is medium.
• The Inhalation Chronic Reference Dose (converted from the RfC) is 8.57E-03 (mg/kg-day).
• The Dermal Chronic Reference Dose is 3.88E-03 (mg/kg-day).
• The Dermal Chronic Reference Dose is based on a gastrointestinal absorption factor of 0.97.

• The Oral Slope Factor is 5.50E-02 (mg/kg-day)^-1.
• The Oral Slope Factor study target organ is blood.
• The Oral Slope Factor study cancer type is leukemia.
• The Oral Slope Factor is based on the U.S. EPA study from 1999.

• The Inhalation Unit Risk is 7.8E-03 (mg/m³)^-1.
• The Inhalation Unit Risk study target organ is blood.
• The Inhalation Unit Risk study cancer type is Leukemia.
• The Inhalation Unit Risk is based on the U.S. EPA study from 1998.
• The Inhalation Slope Factor (converted from the IUR) is 2.73E-02 (mg/kg-day)^-1.

• The Dermal Slope Factor is 5.67E-02 (mg/kg-day)^-1.
• The Dermal Slope Factor is based on a gastrointestinal absorption factor of 0.9700.