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Propylene oxide Quickview (CASRN 75-56-9)

Health assessment information on a chemical substance is included in IRIS only after a comprehensive review of toxicity data by U.S. EPA health scientists from several Program Offices, Regional Offices, and the Office of Research and Development.

Disclaimer: This QuickView represents a snapshot of key information. We suggest that you read the IRIS Summary to put this information into complete context.

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Status of Data for Propylene oxide

File First On-Line: 10/01/1990; Last Significant Revision: 11/01/1990

Category (section)
Last Revised
Oral RfD Assessment No
Inhalation RfC Assessment Yes 11/01/1990
Carcinogenicity Assessment Yes 10/01/1990
  • 75-56-9
  • Ad 6 (suspending agent)
  • Caswell No. 713a
  • EPA Pesticide Chemical Code 042501
  • Epoxypropane
  • 1,2-Epoxypropane
  • Ethylene oxide, methyl-
  • HSDB 173
  • Methyl ethylene oxide
  • Methyl oxirane
  • Methyloxirane
  • more...
Propylene oxide Source Documents
Revision History
Date Section Description
04/01/1997 III., IV., V. Drinking Water Health Advisories, EPA Regulatory Actions, Supplementary Data were removed from IRIS on or before April 1997. IRIS users were directed to the appropriate EPA Program Offices for this information.
Chronic Health Hazard Assessments for Noncarcinogenic Effects

Reference Dose for Chronic Oral Exposure (RfD)

Not Assessed under the IRIS Program.

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Reference Concentration for Chronic Inhalation Exposure (RfC)

Critical Effect
Point of Departure*
Nest-like infolds of the nasal respiratory epithelium LOAEL (HEC): 2.9 mg/m3 100 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.

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Carcinogenicity Assessment for Lifetime Exposure
  • Weight-of-Evidence Characterization
    • B2 (Probable human carcinogen - based on sufficient evidence of carcinogenicity in animals)
  • Weight-of-Evidence Narrative:
    • Based on inadequate human data and an increased incidence of benign and malignant tumors at the site of exposure in two species of animals, when exposed by subcutaneous injection, by inhalation, and by gavage. There was also evidence of mutagenicity in a variety of test systems. Propylene oxide is structurally similar to other chemicals that demonstrate carcinogenic activity in animals.
    • This may be a synopsis of the full weight-of-evidence narrative. See IRIS Summary.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure

Oral Slope Factor(s)
Extrapolation Method
2.4 x10-1 per mg/kg-day Linearized multistage procedure, extra risk
Drinking Water Unit Risks
6.8x10-6 per µg/L
Risk Level
E-4 (1 in 10,000) 1x101 µg/L
E-5 (1 in 100,000) 1 µg/L
E-6 (1 in 1,000,000) 1x10-1 µg/L

Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

Inhalation Unit Risk(s)
Extrapolation Method
3.7 x10-6 per µg/m3 Linearized multistage procedure, extra risk

Inhalation Concentrations at Specified Risk Levels

Risk Level
E-4 (1 in 10,000) 3x101 µg/m3
E-5 (1 in 100,000) 3 µg/m3
E-6 (1 in 1,000,000) 3x10-1 µg/m3

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