US EPA Proposes Roll Back of Ethylene Oxide Emissions Standards

News & Events

March 19, 2026

US EPA’s proposed rule would rescind the risk-based emission standards of the 2024 NESHAP for Ethylene Oxide and reopen core questions about ethylene oxide as a carcinogen.

The US Environmental Protection Agency (US EPA) proposed revocation of the 2024 National Emission Standards for Hazardous Air Pollutants (NESHAP) for Ethylene Oxide (EtO) would rescind the rule’s risk-based emission standards and relax key compliance requirements – reopening core questions about EtO as a carcinogen and the underlying science of the original rule.  US EPA announced formal reconsideration of the 2024 NESHAP for Ethylene Oxide Commercial Sterilization Facilities (40 CFR Part 63, Subpart O).  The 2024 rule significantly tightened EtO emission limits based on a second residual risk review under Clean Air Act (CAA) § 112(f)(2).

Scientific Issues

Central to the proposed rule are uncertainties associated with the 2016 IRIS Evaluation of the Inhalation Carcinogenicity of Ethylene Oxide and, specifically, the carcinogenic potency value (i.e., inhalation unit risk estimate), which served as the basis for the 2024 NESHAP rule that narrowed emissions limits.  US EPA’s proposed rule suggests that it may not be appropriate to rely on the 2016 EtO Integrated Risk Information System (IRIS) value in setting standards due to significant uncertainties.  US EPA is seeking additional information to help understand exposure and toxicity, including, but not limited to, the following:

  • Underlying cancer data, such as epidemiological studies of cancer in humans exposed to EtO or advancements relevant to analyzing the relationship between community and occupational exposure and cancers not yet considered by the agency;
  • Dose-response model selection, including statistical analyses, visual model fit, or biological plausibility; and
  • Human exposure to EtO, background concentrations, and endogenous exposures not yet considered.

There will be a 45-day public comment period and a virtual public hearing 15 days after the proposed rule is published in the Federal Register.  Comments may be submitted to Docket No. EPA-HQ-OAR-2019-0178.

How Gradient Can Help

Gradient has deep expertise in EtO toxicology, risk assessment, air transport modeling, and regulatory developments.  We can assist clients with:

  • Evaluating the EtO IRIS carcinogenic potency value, including analysis of endogenous production, background exposures, and alternative dose-response models;
  • Preparing or reviewing public comments on the proposed rule;
  • Human health risk assessment and EtO exposure analyses for communities and occupational settings;
  • Air emissions and transport modeling; and
  • Technical consulting and testifying support for EtO disputes.