In August 2025, the facility initiated a plant-wide shutdown to install new air pollution control equipment and implement additional measures under Rule 1405.
In December 2025, the facility shut down Ethylene Oxide (EtO) operations to complete connections between upgraded air pollution control systems and its existing equipment.
Upcoming Meetings:
Thursday, June 11, 2026: AB 2588 Public Notification Meeting: HRA for Sterigenics Ontario
6:00 p.m. - 8:00 p.m.
Notice of Public Meeting (PDF) - English
Health Risk Assessment Documents:
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March 2022 – Investigation initiated
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September 2022 – Facility designated as high risk
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December 2023 – Rule 1405 strengthened
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2024–2025 – Emission controls installed and upgraded
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March 2026 – Updated Health Risk Assessment approved
South Coast AQMD began investigating facilities that emit EtO in March 2022, following the U.S. Environmental Protection Agency’s (U.S. EPA) updated assessment of EtO potential toxicity. For more information on our overall initiative, please visit: www.aqmd.gov/eto.
Sterigenics conducts sterilization of medical equipment using a gas called EtO. They are located at 687 Wanamaker Avenue. The nearest residential area is about 1.4 miles away and the nearest school is about 0.8 miles away.
Air sampling around the facility identified elevated levels of EtO, and South Coast AQMD took immediate action to identify sources and reduce emissions as quickly as possible, including:
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Air monitoring efforts at the facility
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Issuing a Proposition 65 Notice
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Investigating equipment and permit compliance
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Requiring leak detection and source testing to reduce fugitive emissions
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Strengthening Rule 1405 for sterilization operations
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Designating the facility as a Potentially High Risk Level Facility under Rule 1402, with accelerated timelines to address their emissions.
South Coast AQMD has conducted numerous on-site visits and has responded to breakdowns and other notifications reported by the facility. In 2022 Notices of Violation (NOVs) were issued to Sterigenics Ontario relating to equipment breakdowns. Following an investigation, inspectors determined that the facility failed to maintain equipment in good operating condition, did not report equipment breakdowns in a timely manner, submitted incomplete breakdown reports, and failed to operate equipment as specified in facility permits.
Since 2023, additional NOVs were issued to the facility for modifying equipment without first obtaining a permit, operating equipment contrary to permit conditions, failing to maintain equipment in good operating condition, and other administrative or recordkeeping requirements.
The investigation is ongoing, and additional enforcement actions may be taken as necessary.
On September 29, 2022, the facility was designated as a Potentially High Risk Level Facility, meaning emissions data exceeded or had the potential to exceed cancer risk thresholds (greater than 100 in one million). As a Potentially High Risk Level Facility, Sterigenics is required to:
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Develop an Early Action Reduction Plan (EARP), including measures that can be taken immediately to reduce health risks.
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Submit an Air Toxics Emissions Inventory Report (ATIR)
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Conduct a Health Risk Assessment (HRA)
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Submit a Risk Reduction Plan (RRP)
ATIR: South Coast AQMD identified deficiencies and rejected the ATIR on March 29, 2023. A revised ATIR was not submitted, therefore South Coast AQMD modified the document to fix the deficiencies and approved it on October 5, 2023.
EARP: On December 29, 2023, the facility submitted a request to modify the EARP to update the fenceline monitoring plan and curtailment provisions. The amended EARP was approved on February 22, 2024.
HRA: South Coast AQMD identified deficiencies in the HRA and rejected it on October 31, 2023. A revised HRA was submitted on January 2, 2024; however, it did not address all deficiencies identified in the rejection letter. South Coast AQMD modified the HRA and approved it on April 3, 2026. The results of the HRA exceeded the Rule 1402 notification and risk reduction thresholds. A public notification meeting will be held to inform the public of potential health risks posed by the facility.
RRP: South Coast AQMD required revisions to the RRP to incorporate additional controls installed by the facility and ensure consistency with the amended EARP. A revised RRP was received on March 5, 2026, and is currently under review.
AB 2588 Documents:
South Coast AQMD is required to use methodologies developed by the Office of Environmental Health Hazard Assessment to evaluate health risks. Based on monitoring data estimates, the primary concern is off-site worker exposure.
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2022 estimates: Worker cancer risk as high as 1,750 in one million if they are or have been exposed for long periods (i.e., a 25-year worker exposure).
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2025 estimates: Worker cancer risk reduced to approximately 34 in one million if they are or have been exposed for long periods (i.e., a 25-year worker exposure).
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Regional average lifetime cancer risk from all sources (excluding EtO): ~450 in one million
This significant decrease from 2022 to 2025 is due to emission control measures implemented at the facility. Monitoring data trends collected by the facility also show substantial decreases in average concentrations, supporting the conclusion that potential cancer risks have declined.
The Ontario facility currently has active permits for nine EtO sterilization chambers, two EtO aeration rooms, an emergency diesel Internal Combustion Engine (ICE), and three pieces of air pollution control equipment which includes a scrubber system and two catalytic oxidizers.
Products are loaded into sealed sterilization chambers where EtO is injected. Emissions from the sterilizers are vented and controlled by the facility’s scrubber system, which includes two wet scrubbers and three dry bed polishing scrubbers. When the sterilization cycle is complete, the chamber is opened and vented to one of the catalytic oxidizers. The two catalytic oxidizers also control any fugitive emissions from the facility’s Permit Total Enclosure (PTE) which includes the receiving area, the preconditioning room, chamber room, the aeration rooms, the EtO storage room, the processing area, and the shipping area.
All control systems are required to:
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Achieve at least 99.99% reduction in EtO emissions, or
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Limit emissions to 0.01 parts per million (ppm) at the stack
In addition, once upgrades are complete, the facility must demonstrate through source testing that:
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Total facility-wide emissions do not exceed 0.015 pounds per hour (lbs/hr) of EtO,
or
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Emissions remain within permitted limits based on EtO usage and control efficiency
Recent Permitting Actions
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October 31, 2023: Applications submitted to modify existing control systems to include a total enclosure with negative air pressure and updates to scrubber exhaust systems
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July 19, 2024: Permits issued to construct modifications, including the total enclosure system
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March 13, 2025: Additional application submitted to further modify the wet scrubber system
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May 30, 2025: Permit issued for installation of an additional wet scrubber followed by dry-bed polishing systems
The facilities’ permits can be accessed through South Coast AQMD’s Facility Information Detail (F.I.N.D.) using the facility address or ID number (126060).
From April 2023 through April 2024, South Coast AQMD conducted local air sampling to determine levels of EtO near the facility and in the surrounding area. Early in this investigation mobile monitoring was conducted to collect data on Volatile Organic Compounds (VOCs) in the area. VOC signals associated with EtO were elevated near the facility; concentrations decreased to near background levels approximately 1,000 ft. downwind. Individual grab samples (an air sample collected at one location at one point in time) were taken to confirm EtO levels (Figure 1), and a monitor was placed nearby to collect 24-hour samples beginning June 16, 2022 (Figures 2 and 3). Sampling conducted by South Coast AQMD adjacent to the facility to evaluate levels of EtO concluded April 18, 2024.
South Coast AQMD worked with the Sterigenics Ontario facility operator to identify potential sources of EtO from their operations and the facility implemented actions to reduce EtO emissions. As part of the facility’s EARP, the facility installed air monitors around the facility adjacent to agency monitors and data collected was compared to ensure accuracy. The facility monitors, along with the strengthened requirements on the facility under the recently amended Rule 1405, led to South Coast AQMD concluding its sampling activities. Sterigenics is responsible for continuing to collect and analyze 24-hour samples near their Ontario facility and provide that data to South Coast AQMD.
The agency will continue to work with Sterigenics Ontario as needed to identify the source(s) of EtO and determine measures to reduce EtO emissions.
Figure 1: Map of grab samples. Concentrations are in parts per billion volume (ppbv).
Figure 2: Map of 24-hour sampling locations
This plot is interactive, individual data points can be viewed with a mouse hover. The view can be reset by selecting the circular arrows to the right of the plot.
Figure 3: Plot of 24-hour time integrated sample concentrations
South Coast AQMD air monitoring data can be found here (PDF).
As part of the facility’s Early Action Reduction Plan the facility has installed three air monitors around the facility (see figure 4) and provides that data to South Coast AQMD.
Data from the air monitors operated by the facility can be found here. (PDF)
Ramboll Sampling Sites
Figure 4. Map of Early Action Reduction Plan
EtO sterilization and aeration facilities are subject to local, state, and federal regulations.
During South Coast AQMD's monitoring efforts at several commercial EtO sterilization facilities, the agency became aware of fugitive emissions from sources that were not previously known. South Coast AQMD’s investigation has identified that existing pollution controls will need to be upgraded and measures will be needed to reduce fugitive emissions.
South Coast AQMD amended Rule 1405 on December 1, 2023 to:
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Strengthen emission control requirements for sterilization and storage facilities
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Upgrade existing or add new pollution controls and measure to monitor and minimize stack and fugitive emissions.
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Require enhanced monitoring and reporting
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Require storage facilities that receive products sterilized by EtO to monitor fenceline emissions.
The updated rule applies to 15 sterilization facilities. More details related to Rule 1405 requirements can be found on the Rule 1405 webpage.