EO sterilization processes are complex and highly regulated

EO is the most widely used gaseous sterilization agent in the world and has been around for nearly 90 years. Today, EO is used to sterilize more than 20 billion medical devices sold in the U.S. every year. There are several regulatory requirements for the EO sterilization process, and Sterigenics maintains collaborative relationships with regulatory agencies.

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Sterigenics operates safely and in compliance with regulatory requirements

Sterigenics consistently complies with environmental permits issued for each of its sterilization facilities. Sterigenics has disclosed its EO emissions for decades in federal and state filings – even when not required and when others in the industry did not – and has a track record of implementing leading safety practices to further perform better than regulatory requirements.

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EO sterilization plants are regulated under the National Emission Standards for Hazardous Air Pollutants (NESHAP).

NESHAP are stationary source standards for hazardous air pollutants. The regulation sets standards for allowable emissions levels, as well as a framework for ongoing compliance and inspection (i.e., reviewing records, inspecting facilities, interviewing personnel).

The medical sterilization industry has been anticipating an update to EO regulation under NESHAP for multiple years. A notice of proposed rulemaking is anticipated during 2022, with a final rule to follow completion of the rulemaking process. Sterigenics is making investments today to best position its EO sterilization facilities for compliance with future regulations.

Controversy Over the Use of EO

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If EO is a longstanding method of medical device sterilization that is essential to the U.S. healthcare system and highly regulated, why is there controversy over its use?

Recent controversy related to EO is ultimately grounded in a study published in December 2016 by EPA’s Integrated Risk Information System program (IRIS). IRIS assessments are a source of information used by EPA, state and local health agencies, other federal agencies, and international health organizations. It is not a safety limit and is not intended to be a regulatory standard.

In 2016, EPA’s IRIS group completed a review and reclassified EO from “Probably Carcinogenic” to “Carcinogenic” and updated its inhalation unit risk estimate. During this multi-year review, EPA’s independent Science Advisory Board (SAB) raised several questions about the basis for these conclusions. The IRIS group’s final report failed to resolve those questions.

The IRIS update gained attention in 2018, when the EPA used it to evaluate nationwide cancer risks as part of its National Air Toxics Assessment (NATA). NATA’s computer-simulated assessment combined the widely disputed IRIS inhalation unit risk estimate with outdated 2014 public emissions data from facilities across the country that are not always reflective of current emission control systems. This flawed analysis implied that 106 census tracts across the country, including the Sterigenics facilities located in Willowbrook, IL, Smyrna, GA, and Santa Teresa, NM, were identified as having an elevated risk of cancer due to EO, including several locations near other medical sterilizers that use EO.

The EPA has recently agreed to reconsider the use of the IRIS value for EO in assessing cancer risk for the source category

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Placing IRIS in perspective.

The IRIS value of 0.1 parts per trillion of EO is an inhalation unit risk estimate, which assumes that inhaling EO 24 hours per day, 7 days per week for 70 years might increase the risk that 1 additional person in 1 million will get cancer.

The IRIS program has been widely questioned in the past by reputable organizations such as the Government Accountability Office and a National Academy of Sciences panel. EO exists naturally at concentrations significantly exceeding the IRIS value, including in the human body.

The State of Texas Commission on Environmental Quality (TCEQ) recently concluded that acceptable EO levels may be more than 2,000 times higher than those suggested by IRIS

IRIS concentration of 0.1 parts per trillion is about the same as:


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Drop of water within...



Olympic size swimming pools


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EPA IRIS Level is Far Lower than Normal EO Exposure from Everyday Sources

Measured in ug/m3


EPA iris chart

Montrose Air Quality Services Measurements of “Everyday Sources” for Ethylene Oxide, October 16, 2019