Ethylene oxide

Reference Dose for Oral Exposure (RfD) (PDF) (9 pp, 207 K) Last Updated:

Not assessed under the IRIS Program.

Reference Concentration for Inhalation Exposure (RfC) (PDF) (9 pp, 207 K)

Not assessed under the IRIS Program.

Weight of Evidence for Cancer (PDF) (9 pp, 207 K) Last Updated: 12/16/2016

• Under the Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005), ethylene oxide is "carcinogenic to humans" by the inhalation route of exposure, based on (1) strong, but less than conclusive on its own, epidemiological evidence of lymphohematopoietic cancers and breast cancer in EtO exposed workers, (2) extensive evidence of carcinogenicity in laboratory animals, including lymphohematopoietic cancers in rats and mice and mammary carcinomas in mice following inhalation exposure, (3) clear evidence that EtO is genotoxic and sufficient weight of evidence to support a mutagenic mode of action for EtO carcinogenicity, and (4) strong evidence that the key precursor events are anticipated to occur in humans and progress to tumors, including evidence of chromosome damage in humans exposed to EtO.
• This may be a synopsis of the full weight-of-evidence narrative.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure (PDF) (9 pp, 207 K)

Not Assessed under the IRIS Program.

Inhalation Unit Risk: 5 x 10^-3 per µg/m³
Extrapolation Method: Linear extrapolation. Two-piece linear spline model with knot at 1,600 ppm × days for lymphoid cancer. Two-piece linear spline model with knot at 5,750 ppm × days for breast cancer incidence in females. POD of 1% extra risk was used for both cancer types, includes application of age-dependent adjustment factors (ADAFs).
Tumor site(s): Immune, Reproductive
Tumor type(s): Lymphoid cancer, (female) breast cancer (Steenland et al., 2003, 2004)
Note: EPA has concluded that ethylene oxide is carcinogenic by a mutagenic mode of action. Thus, based on the EPA cancer guidelines (2005), the inhalation unit risk (IUR) addressing lifetime exposure includes application of ADAFs. The IUR is recommended for lifetime exposures. EPA has also provided an adult-based cancer unit risk of 3 x 10^-3 per µg/m³. This adult-based cancer unit risk can be used instead of the IUR when assessing cancer risk associated with exposure scenarios that don’t include early life (< 16 years of age) or when other calculations by the user are necessary (e.g., when applying ADAFs to age-specific exposure estimates).