Benzene Quickview (CASRN 71-43-2)

Status of Data for Benzene

File First On-Line: 03/01/1988; Last Significant Revision: 04/17/2003

Category (section)	Status	Last Revised
Oral RfD Assessment	On-line	04/17/2003
Inhalation RfC Assessment	On-line	04/17/2003
Carcinogenicity Assessment	On-line	01/09/2000

Synonyms

Benzene Coal naphtha Phene Phenyl hydride Polystream

71-43-2 Benzol Cyclohexatriene Pyrobenzol

Chronic Health Hazard Assessments for Noncarcinogenic Effects

Reference Dose for Chronic Oral Exposure (RfD)

Critical Effect	Point of Departure*	UF	MF	RfD
Decreased lymphocyte count	BMDL : 1.2 mg/kg-day	300	1	4.0 x10-3 mg/kg-day

* The Point of Departure listed serves as a basis from which the Oral RfD was derived. See Discussion of Conversion Factors and Assumptions for more details.

• Principal and Supporting Studies (Oral RfD)
  • Human occupational inhalation study, Rothman et. al., 1996
• Confidence in the Oral RfD
  • Study -- Medium
  • Database -- Medium
  • RfD -- Medium

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Reference Concentration for Chronic Inhalation Exposure (RfC)

Critical Effect	Point of Departure*	UF	MF	RfC
Decreased lymphocyte count	BMCL : 8.2 mg/m3	300	1	3x10-2 mg/m3

* The Point of Departure listed serves as a basis from which the Inhalation RfC was derived. See Discussion of Conversion Factors and Assumptions for more details.

• Principal and Supporting Studies (Inhalation RfC)
  • Human occupational inhalation study, Rothman et. al., 1996
• Confidence in the Inhalation RfC
  • Study -- Medium
  • Database -- Medium
  • RfC -- Medium

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Carcinogenicity Assessment for Lifetime Exposure

• Weight-of-Evidence Characterization
  • A (Human carcinogen)
  • Known/likely human carcinogen
• Weight-of-Evidence Narrative:
  • Benzene is classified as a "known" human carcinogen (Category A) under the Risk Assessment Guidelines of 1986. Under the proposed revised Carcinogen Risk Assessment Guidelines (U.S. EPA, 1996), benzene is characterized as a known human carcinogen for all routes of exposure based upon convincing human evidence as well as supporting evidence from animal studies. (U.S. EPA, 1979, 1985, 1998; ATSDR, 1997).
  • This may be a synopsis of the full weight-of-evidence narrative. See IRIS Summary.

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Quantitative Estimate of Carcinogenic Risk from Oral Exposure

Oral Slope Factor(s)	Extrapolation Method
5.5 x10-2 per mg/kg-day 1	Linear extrapolation of human occupational data
1.5 x10-2 per mg/kg-day 1	Linear extrapolation of human occupational data

¹ This is one endpoint in a range of oral slope factors. See Additional Comments (Carcinogenicity, Oral Exposure).

Drinking Water Unit Risks
1.6x10-6 per ug/L2
4.4x10-7 per ug/L2

² This is one endpoint in a range of drinking water unit risks. See Additional Comments (Carcinogenicity, Oral Exposure).

Risk Level	Concentration
E-4 (1 in 10,000)	1x102 ug/L1
E-5 (1 in 100,000)	1x101 ug/L1
E-6 (1 in 1,000,000)	1 ug/L1
E-4 (1 in 10,000)	1x103 ug/L1
E-5 (1 in 100,000)	1x102 ug/L1
E-6 (1 in 1,000,000)	1x101 ug/L1

¹ This is one endpoint in a range of oral slope factors/drinking water unit risks. See Additional Comments (Carcinogenicity, Oral Exposure).

• Dose-Response Data (Carcinogenicity, Oral Exposure)
  • Tumor Type: Leukemia
  • Test Species: Human
  • Route: Inhalation, Occupational exposure
  • Reference: Rinsky et al., 1981, 1987; Paustenbach et al., 1993; Crump, 1994; U. S. EPA, 1998; U.S. EPA, 1999

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Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

Inhalation Unit Risk(s)	Extrapolation Method
2.2 x10-6 per ug/m3 3	Low-dose linearity utilizing maximum likelihood estimates
7.8 x10-6 per ug/m3 3	Low-dose linearity utilizing maximum likelihood estimates

³ This is one endpoint in a range of inhalation unit risks. Additional Comments (Carcinogenicity, Inhalation Exposure).

Inhalation Concentrations at Specified Risk Levels

Risk Level	Concentration
E-4 (1 in 10,000)	1.3x101 ug/m31
E-5 (1 in 100,000)	1.3 ug/m31
E-6 (1 in 1,000,000)	1.3x10-1 ug/m31
E-4 (1 in 10,000)	4.5x101 ug/m31
E-5 (1 in 100,000)	4.5 ug/m31
E-6 (1 in 1,000,000)	4.5x10-1 ug/m31

• Dose-Response Data (Carcinogenicity, Inhalation Exposure)
  • Tumor Type: Leukemia
  • Test Species: Human
  • Route: Inhalation
  • Reference: Rinsky et al., 1981, 1987; Paustenbach et al., 1993; Crump and Allen, 1984; Crump, 1992, 1994; U.S. EPA, 1998