Ethylene Oxide (EtO)

What is Ethylene Oxide (EtO)?

Ethylene oxide (commonly referred to as EtO) is a highly versatile, flammable gas used to manufacture a range of consumer products such as plastics, textiles, adhesives, detergents and antifreeze. It is also utilized in the sterilization of medical and dental equipment and plastic devices that cannot be sterilized by steam. According to the Food and Drug Administration (FDA), EtO is used in the production of about 20 billion medical devices every year, which accounts for roughly 50% of all sterile medical devices manufactured. However, the Environmental Protection Agency (EPA) is currently working to reduce EtO emissions, and the FDA is actively searching for alternatives to EtO. Moreover, EtO is also used in the sterilization of some spices and dehydrated vegetables. The Centers for Disease Control and Prevention (CDC) warns that exposure to EtO may also occur through gasoline vehicle exhaust and tobacco smoke.

It is important to note that the Clean Air Act lists EtO as one of the 187 hazardous air pollutants (HAP), commonly referred to as air toxics.

What are the health risks of EtO?

According to the EPA, exposure to high concentrations of EtO over a short period of time can result in various health problems. These may include headache, dizziness, nausea, fatigue, respiratory irritation such as coughing, wheezing and shortness of breath, and in some cases, vomiting and gastrointestinal distress. Studies have shown that inhalation of air containing low concentration levels of EtO over an extended period of time can increase the risk of several cancers of the white blood cells such as Non-Hodgkin lymphoma, myeloma and lymphocytic leukemia. Moreover, long-term exposure to EtO has been linked to an increased risk of breast cancer in women. Given that children's bodies are still growing, they are more susceptible to the toxic effects of EtO, which is mutagenic, meaning it can cause DNA damage. However, it is important to note that risks would decrease with decreased exposure.

It is crucial to acknowledge that each type of cancer has its own set of risk factors, some of which are better understood than others. Cancer development is a complex process, and many factors can affect an individual's cancer risk, including their genetics, overall health and exposure to carcinogens. It is rare to find a specific cause for any particular case of cancer. A review of the South Carolina Cancer Registry data for cancers in the monitored area did not reveal any cancer clusters of the types associated with EtO.

Why is DHEC Addressing EtO?

EPA conducts an assessment of air toxic emissions across the United States annually, called the Air Toxics Screening Assessment (AirToxScreen). The assessment was previously called the National Air Toxics Assessment (NATA) and was conducted about every three years. 

AirToxScreen is EPA's ongoing review of air toxics in the United States. It serves as a screening tool for state, local, and tribal air agencies to help identify which pollutants, emission sources, and/or localized areas should be studied further to better understand possible public health risks. 

AirToxScreen gives a snapshot of outdoor air quality with respect to emissions of air toxics. It calculates air toxics concentrations and long-term health risks into identified areas called “census tracts” or “census blocks.”

The 2014 NATA was compiled and released by EPA in 2018. It included 106 census tracts in the United States with an estimated cancer risk greater than 100 in 1 million, which means there’s a likelihood that 100 in 1 million people (or 1 in 10,000 people) would develop cancer if they breathed air containing the same amount of the same air toxic every day for 70 years. The primary risk in many of these census tracts was driven by emissions of EtO. In South Carolina, the 2014 NATA identified two census tracts with a total cancer risk greater than 100 in 1 million, both in the North Charleston area. 

According to the latest air quality monitoring data, the concentration of harmful air pollutants that are detrimental to health is decreasing across the country. Since the data was last collected for the 2014 NATA, many toxic air emissions have significantly reduced. The most recent AirToxScreen report shows that based on emissions data from 2017, 2018, and 2019 no areas in South Carolina have a cancer risk greater than 100 in 1 million. Moreover, EtO emissions in South Carolina have decreased by about 66% since 2017. Going forward, it is expected that air pollutants in South Carolina will continue to decrease in the long run as new federal and state air quality regulations and standards become effective and regulated facilities adhere to or surpass the requirements.

What Are EPA and DHEC Doing to Reduce EtO Nationally?

EPA regularly reviews Clean Air Act regulations for facilities that emit hazardous air pollutants, including EtO, to ensure that they protect the public from significant risk. EPA’s Miscellaneous Organic Chemical Manufacturing National Emission Standards for Hazardous Air Pollutants (NESHAP) rule (often referred to as the “MON”), requires reduction of hazardous air pollutants, including EtO emissions, nationwide. EPA also regulates air toxics emissions from many commercial sterilizers that use EtO. A proposal to review and amend the Commercial sterilizer standards was proposed on April 11, 2023, and is expected to be finalized in 2024. For the latest information on these EPA rules, please visit EPA’s Actions on Ethylene Oxide webpage.

DHEC has the delegation of authority to implement and enforce these federal rules. Air permits are written by DHEC to restrict the amount of EtO emissions facilities subject to these rules can emit. DHEC also conducts unannounced on-site inspections, oversees stack testing, and reviews periodic reports to ensure compliance with these rules.

What is DHEC Doing to Address Concerns About EtO? 

DHEC is working with EPA, communities, and stakeholders to identify and assess sources of EtO emissions. To achieve this goal, DHEC has taken the following steps:

  • Conducted limited sampling from October 2019 to June 2021 at six locations across the state to gather and share preliminary information about the presence of EtO in areas close to and far away from known sources of EtO emissions; 
  • Sampled EtO at the National Air Toxics Trend Site (NATTS) located in rural Chesterfield, South Carolina; 
  • Received Community Scale Air Toxics Monitoring grant funding from EPA to conduct sampling in the North Charleston area. The sampling for this project began in May 2022 and ended in April 2023 (see results below);
  • Continuing to educate and collaborate with local communities to share data and information about EtO and other air pollutants.

Community-Scale Air Toxics Monitoring Grant Award

In September 2020, EPA awarded DHEC a Community-Scale Air Toxics Monitoring Grant for monitoring and characterizing concentrations of EtO in the North Charleston area, including in environmental justice communities. 

Sampling Observations & Uncertainties

Detecting and analyzing extremely low concentrations of EtO in ambient air poses a significant challenge, and EPA is currently working to improve the accuracy of the sampling and analysis methods. It is typical for new methods to require additional development to detect such low concentrations accurately. According to studies, the current recommended method may sometimes generate biased high concentrations, leading to lab results indicating a higher concentration than present in the ambient air. As a result, the reported average concentrations may be a conservative estimate, and the actual average concentrations are likely lower than reported.

Questions Raised from Sampling EtO

What are the sources of EtO being measured away from known point sources of EtO emissions? 

  • This is not well understood.
  • There is naturally occurring EtO in trees and other vegetation.
  • The background levels of EtO in the environment have not been estimated due to the uncertainty in the measurement method.  
  • We cannot measure consistently at such low concentrations. 

Are there better methods or method improvements for measuring EtO?

  • EtO measurements across the U.S. show that sample collection and method improvements are needed.
  • There are several sample collection and analysis methods being evaluated by EPA.
  • The work done by DHEC’s sampling will help EPA as they continue to make improvements.

EtO Sampling at the National Air Toxics Trend Site - Chesterfield, South Carolina

EPA developed the National Air Toxics Trend Site (NATTS) network to fulfill the need for long-term air toxic monitoring data of consistent quality. There are typically over 100 pollutants monitored at each NATTS site, including EtO. More information on the NATTS program can be found on EPA’s website.

Sampling results for the Chesterfield NATTS site can be found on EPA’s Air Quality System website. The results are also included in the sampling results above for the grant project period. 

Even though there are no known point sources of EtO near the Chesterfield NATTS site, EtO was detected at or above the same levels it was detected in North Charleston by sampling near a known point source of EtO.

Environmental Justice & Community Engagement Efforts

At DHEC, we have a strong commitment to promoting environmental justice and involving the communities across South Carolina in identifying and resolving environmental concerns. Our dedication to community engagement and keeping communities informed is demonstrated through our outreach efforts. To ensure that residents of Union Heights, Windsor Place, Five Mile, Liberty Hill Chicora, Cherokee, Accabee, and Rosemont in North Charleston were kept informed during the EtO ambient air sampling project in the Charleston/North Charleston area, we collaborated closely with community partners and organizations such as Lowcountry Alliance for Model Communities (LAMC), Charleston Community Research to Action Board (CCRAB), and the Rosemont Neighborhood Council. These organizations helped us to engage with the community and share information about the sampling project. Our strong partnerships and relationships with these communities and organizations, built over several decades, were crucial in quickly communicating the results of our sampling to the community. DHEC looks forward to continued partnership and community involvement on this and other future initiatives.  

DHEC is committed to staying engaged nationally as EPA works to establish standards for reducing hazardous air pollutant emissions like EtO. DHEC will also continue to work with South Carolina facilities and communities to reduce the potential health risks associated with air toxic emissions as more information about EtO becomes known.


EtO Sampling Data: Connie Turner - Director, Division of Air Quality Analysis
Community Engagement: Monica Taylor - Public Participation Coordinator, Bureau of Air Quality