This review highlights the critical importance of monitoring ethylene oxide (ETO) exposure in the workplace at parts-per-billion (PPB) levels to ensure worker safety. We have advanced the OSHA Method 1010 by achieving reproducible quantification of ETO down to 2 ppb over an 8-hour time-weighted exposure using an SKC passive monitoring badge. Notably, this exact method is now included within the scope of our ISO/IEC 17025:2017 accreditation, ensuring traceability, precision, and regulatory reliability. Our findings underscore a significant regulatory disparity: the EPA’s recently established reference concentration for non-cancer health effects is approximately 10,000 times lower than the current OSHA Permissible Exposure Limit (PEL). This stark contrast strongly supports the need for an urgent revision of OSHA's outdated exposure limit to reflect contemporary toxicological evidence and protect worker health.
EPA's Risk Modeling Approach
The EPA uses a linear no-threshold (LNT) model for ETO, meaning:
· There is no exposure level below which cancer risk is zero.
· Risk increases proportionally with both concentration and exposure time. The EPA calculates cancer risk based on an Inhalation Unit Risk (IUR) value:
· Adult IUR: 3.0 × 10^-3 per µg/m³
· Lifetime IUR (including early life exposure): 5.0 × 10^-3 per µg/m³
Risk Equation: Lifetime Cancer Risk = Concentration (µg/m³) × IUR
Examples
· Low Environmental Exposure (1 µg/m³):
Adult Risk: 0.003 (3 in 1,000)
Lifetime Risk: 0.005 (5 in 1,000)
· OSHA Occupational Limit (1 ppm ≈ 1,800 µg/m³):
Adult Risk: 5.4 (5400 in 1,000) — indicates a lifetime risk exceeding 1 in 1
Supporting Studies
The EPA's risk estimates are grounded in both animal toxicology and large-scale epidemiological studies:
· Steenland et al. (2003, 2004): Evaluated over 17,000 workers at 14 U.S. commercial sterilization facilities from 1987 through 1994. Conducted a retrospective cohort analysis examining mortality and cancer incidence, focusing on breast and hematopoietic cancers. Exposure reconstruction was based on job titles, facility records, and monitoring data.
· Additional cohort studies in chemical production and sterilization plants revealed elevated risks of lymphoid malignancies and breast cancer.
· Animal studies confirmed ETO’s carcinogenicity with increased rates of lymphomas, leukemias, and mammary tumors after inhalation exposure.
Reference Concentration for Non-Cancer Effects
RfC: 0.1 µg/m³ — a level deemed protective for non-cancer health effects.
Regulatory Impact
· The EPA has proposed and implemented rules requiring sterilization facilities to reduce ETO emissions by up to 90%.
· Enhanced monitoring and public transparency efforts are ongoing.
Conclusion
ETO poses a significant cancer risk even at low environmental concentrations. The EPA's rigorous modeling and conservative assumptions reflect the seriousness of chronic exposure. By understanding and applying the EPA's risk formula, stakeholders can assess exposure scenarios and advocate for safer environmental practices. The studies highlight the failure of the current OSHA PEL of 1 PPM to provide a safe workplace.
References
1) U.S. EPA IRIS: Ethylene Oxide https://iris.epa.gov/ChemicalLanding/1025
2) EPA Technical Support Document (2023)
Draft Human Health Risk Assessment for Ethylene Oxide https://www.epa.gov/system/files/documents/2023-04/ETO-draft-human-healh-ra-add.pdf
3) OEHHA ETO Cancer Risk Proposal (California Office of Environmental Health Hazard Assessment) https://oehha.ca.gov/media/downloads/crnr/ETOcanceriurdraft040723.pdf
4) Steenland et al. (2003) – Environmental Health Perspectives https://doi.org/10.1289/ehp.6239
5) Steenland et al. (2004) – American Journal of Epidemiology https://doi.org/10.1093/aje/kwh027
6) ATSDR Toxicological Profile for Ethylene Oxide (Agency for Toxic Substances and Disease Registry) https://www.atsdr.cdc.gov/ToxProfiles/tp137-c7.pdf