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EPA in Illinois

Sterigenics Willowbrook Facility - Latest Update

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Update December 13, 2018

EPA webinar: Update on Ethylene Oxide Monitoring in Willowbrook, Illinois

The U.S. Environmental Protection Agency will hold a webinar Tuesday, December 18, 2018, to provide updates on ethylene oxide monitoring in Willowbrook, Ill.  For more information on this webinar, please review the details below:

Tuesday, December 18, 2018
Time: 1:00pm -2:00pm (CST)
Meeting Link:
Call in Number: 833-819-8005
Conference ID: 1898022

*Note: A maximum of 500 people may attend the webinar at any one time. EPA plans to record the webinar and post it to the website.


  • Opening remarks
  • Review of ethylene oxide monitoring plan 
  • Recent monitoring results
  • Monitoring next steps     

If you have never attended an Adobe Connect meeting before, test your connection by visiting You may also get a quick overview by visiting

1. Click “Enter as a Guest”
2. Type in your first & last name and organization
3. Click “Enter Room”
4. You will be in the room!

Update December 7, 2018

EPA has posted results for three days of air quality monitoring in Willowbrook: November 13, 16 and 19

  • Monitors detected ethylene oxide in the air at the two sites closest to the Sterigenics facility. 
  • Monitors did not detect ethylene oxide at the six community-oriented sites -- those at schools and in residential areas.
  • It is premature to draw conclusions from the data. EPA plans to continue monitoring in the Willowbrook area for three months and will continue to post data as it becomes available.
  • EPA will conduct a full assessment of risk from ethylene oxide in Willowbrook, which we expect to complete by Spring 2019.
  • On November 21, 2018, EPA announced that it had identified an issue with the analytical method used in previous EPA monitoring. We have changed the analytical method, so that the issue does not affect these results.

Learn more about the monitoring and see the data by location.

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Update November 23, 2018

Background information packet on ethylene oxide for the Willowbrook Community

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Update November 21, 2018

  • Open House and Public Meeting on Ethylene Oxide
    The U.S. EPA will host an open house and community forum to provide updates on the agency’s work to better understand air emissions of ethylene oxide from the Sterigenics facility in Willowbrook, Illinois. Both will be held Thursday, November 29, 2018 at Ashton Place, 341 75th St, Willowbrook, Ill.  Learn more.
  • Potential Issue Regarding Previous Ethylene Oxide Monitoring Results
    U.S. EPA recently discovered an issue with the way ethylene oxide has been measured. As a result of the issue, monitors may have reported higher ambient levels of ethylene oxide than actually exist. More specifically, the chemical Trans-2-butene can be incorrectly identified as ethylene oxide when air quality samples are being analyzed in a laboratory. Trans-2-butene can be released from petrochemical industrial processes and the burning of fossil fuels. EPA discovered the issue as part of its work to improve the analysis method for ethylene oxide.
    • What this Means
      This discovery means that the results of air quality monitoring conducted prior to October 2018 may have shown higher concentrations of ethylene oxide than were actually in the air. This includes air quality monitoring that U.S. EPA’s Region 5 conducted in mid-May 2018 in Willowbrook, Illinois. U.S. EPA cannot fully evaluate the difference between reported and actual ethylene oxide concentrations, as the samples of air collected in mid-May are no longer available for analysis. U.S. EPA has made a change to its analytical method to prevent this issue in the analysis of future air quality samples – including those from monitoring started in November 2018 in the Willowbrook area. U.S. EPA is making the technical information about this change available for other laboratories.
    • Does the monitoring issue change EPA’s conclusions in the National Air Toxics Assessment (NATA)?

      No. U.S. EPA would have been concerned about ethylene oxide in Willowbrook, even without air quality monitoring.  U.S. EPA’s NATA identified census tracts in the Willowbrook area as a potentially higher risk community. NATA is based on air quality modeling: it does not rely on any air monitoring data.

      In addition, in the health consultation conducted for U.S. EPA Region 5, ATSDR relied on both the Region’s modeled estimates of ethylene oxide in the outdoor air in the area near the Sterigenics facility as well as the results of the monitoring the Region conducted in mid-May. 

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Update November 14, 2018

EPA is monitoring the outdoor air near the Sterigenics facility to better understand levels of ethylene oxide (EtO) in the air. The first monitors began collecting air samples on November 13, 2018. Learn more.

Update November 5, 2018

EPA will hold a community meeting on November 29, 2018. We will post more information once we finalize time and location.

Update October 24, 2018

EPA has set up a dedicated email address for inquiries related to ethylene oxide and the Sterigenics facility in Willowbrook, IL. Emails should be sent to

Update October 10, 2018

What is EPA doing to reduce ethylene oxide from the Sterigenics facility?

What has been done to date:

Sterigenics has taken steps to further control ethylene oxide emissions from the Willowbrook facility and estimates that those controls have reduced ethylene oxide by about 92 percent.

On September 20 and 21, 2018, a contractor hired by Sterigenics conducted stack tests to measure the actual emissions from the control devices at the facility. U.S. EPA and Illinois EPA experts were present to observe the tests.

The following links exit the site Exit See the test results from September 20, 2018 and September 21, 2018.

What happens next:

  • Once the final report from the stack test is complete, and delivered to U. S. EPA, the Agency will review the results to confirm how much ethylene oxide the pollution controls are reducing. EPA will that information to estimate current emissions from the Sterigenics facility.
  • U.S. EPA needs the emissions estimates to help the agency determine how far any remaining ethylene oxide emissions will disperse and what the levels of ethylene oxide in the air nearby the facility are likely to be. EPA will determine this using a computer model.
  • The information also will help EPA determine the best places to monitor the air for ethylene oxide in the area. EPA will work with local elected officials in the area as it develops its monitoring plan.
  • Existing monitoring methods are not sensitive enough to detect ethylene oxide at all levels in the outdoor air. Because of this, EPA cannot use monitoring alone to determine the levels of ethylene oxide in the air around the facility.
  • EPA will conduct a risk assessment for the Willowbrook area. This assessment will be more comprehensive than either NATA or the ATSDR analysis. It will be similar to the types of risk assessments EPA conducts when it is reviewing its regulations for industries that emit air toxics to determine whether those rules need to be updated to improve protection of public health.
  • EPA will update this information as this work proceeds on our website at:

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