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Hazardous Air Pollutants: Ethylene Oxide

Frequent Questions: Basic Information About Ethylene Oxide

Basic Information

What is ethylene oxide and what are its uses?

Ethylene oxide (EtO) is a gas at room temperature.

There are two key uses for ethylene oxide: 1) It is used to make other chemicals that produce many everyday products and 2) It is used to sterilize devices that can’t be sterilized using steam, such as some medical and dental equipment.

Ethylene oxide is reacted to make ethylene glycol, which is a key ingredient in a variety of consumer household products. Ethylene oxide is an essential building block for synthetic fibers (e.g., upholstery, carpet), plastics, PVC pipe and cosmetics.

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What is an acceptable/safe level of ethylene oxide?

Ethylene oxide is one of 187 pollutants that Congress classified as “hazardous air pollutants,” also called “air toxics.” The Clean Air Act instructs the U.S. EPA to regulate air toxics by setting limits on the amount of pollution that industrial sources can emit to the air, rather than by setting ambient standards, which are limits on the amount of a pollutant that is allowed in the outdoor air. So, the Agency does not have a “bright line,” or a level for ethylene oxide below which air quality is considered OK. Because there is not a bright line, U.S. EPA is going to conduct a risk assessment in Willowbrook. The Agency will use the results of that risk assessment to determine whether emissions from the Sterigenics facility need to be further reduced.  U.S. EPA expects to complete the risk assessment in early Spring.

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Why have the ethylene oxide results in EPA’s National Air Toxics Assessment (NATA) changed in my area from the previous NATA?

Newer studies show that ethylene oxide is a more potent carcinogen than scientists had thought. We updated our cancer risk calculations to reflect these new data. This means that in the 2014 NATA, more areas show elevated risks driven by ethylene oxide than in the 2011 NATA. This does not mean there is more of this compound in the air in these places than before. Even if emissions in an area are the same—or possibly even if they are lower—the new cancer value often results in a higher risk estimate.

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How long does ethylene oxide stay in the air and how does it leave? What is ethylene oxide's half-life in air?

​Like all air pollutants, ethylene oxide (EtO) disperses in the air, with the speed of dispersal depending on the strength of winds. EtO is a volatile compound, meaning that it does not persist for a very long time in the environment.

Its estimated half-life in the atmosphere is 69 days (during summer months) to 149 days (during winter months). EtO reacts in the air to form formic acid, which is a naturally occurring chemical.

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Since the boiling point of ethylene oxide is approximately 50 degrees Fahrenheit and measurement being done presently in temperatures below the boiling point of ethylene oxide, how is ambient air concentration going to be determined for the winter months?

There is no change in measurement. While temperature may affect the transport of ethylene oxide, the purpose of the sampling is to determine the concentrations at fixed points.

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Has the EPA done studies or are they aware of additional studies pertaining to which plants degrade to ethylene oxide and whether the emissions from these plants are in fact negligible?

EPA has not conducted studies to determine the role that plants play in levels of ethylene oxide emissions. 

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Is ethylene oxide like lead where you can get a blood test to see if you’ve been exposed? Can my doctor test it?

According to the Agency for Toxic Substances and Disease Registry (ATSDR) there are two kinds of tests that can determine if you have been recently exposed to ethylene oxide (EtO). One test measures ethylene oxide in blood and the other test measures it in your breath. However, these tests are not intended for use on individuals that may have been exposed to very low levels of EtO (as these tests are not sensitive enough to detect it) nor can they be used to predict how it will affect a person’s health. Because special equipment is needed, these tests are not usually done in the doctor's office.

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Does rain wash ethylene oxide from the air?

Rain will likely not wash ethylene oxide out of the air. While ethylene oxide does dissolve in water, it can also evaporate from water back to the air. It also doesn't rain frequently enough in the Willowbrook area to have much of an impact.

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I would like to know how exactly ethylene oxide travels in the air/through the wind, and on average, what is the distance/range for which surrounding communities should be concerned of cancer risks as well?

Ethylene oxide can last in the air for weeks and can be transported with prevailing winds.  At higher temperatures, especially above 50 degrees Fahrenheit, and stronger winds, we would expect ethylene oxide to transport farther away from the emission source more effectively.  Our current monitoring plan is designed to gain a better understanding of how much ethylene oxide is in the outdoor air in neighboring communities. The ongoing monitoring and upcoming risk assessment will tell us what ethylene oxide concentrations are in the community.

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What should I do if I smelll ethylene oxide?

People cannot smell ethylene oxide when it is in the air at concentrations U.S. EPA monitors have detected.

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Are there alternatives to ethylene oxide?

Ethylene oxide (EtO) is necessary to assure that some types of medical equipment are sterilized for safe use. EtO is used for items that are sensitive to moisture, heat, or radiation. It can penetrate various materials and safely sterilize the equipment without causing damage.

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