Ethylene Oxide (EtO) is a colorless, flammable gas with a faintly sweet odor used widely in industrial and medical sectors. EtO’s primary application is as a chemical intermediate in manufacturing products like antifreeze, detergents, and textiles. It is also an effective sterilant for medical equipment, such as plastic syringes, that cannot withstand traditional steam sterilization. The public health concern stems from its classification as a known human carcinogen, raising the question of how much exposure is dangerous.
Primary Sources of Ethylene Oxide Exposure
Exposure to EtO occurs primarily through inhalation in both occupational and environmental settings. The largest industrial sources are chemical manufacturing plants, which produce the gas and are responsible for the majority of EtO emissions into the air. A second major source is the commercial sterilization industry, which uses EtO to sterilize approximately 50% of all medical devices in the United States.
Although these facilities follow safety standards, uncontrolled emissions or venting can release the gas into the ambient air near the facility. Workers in these plants face the highest risk due to direct involvement with the chemical. The general population can also be exposed to residual amounts of EtO on sterilized products, including medical devices, cosmetics, and fumigated spices. Trace amounts of EtO are also found in tobacco smoke. While public exposure levels are generally lower, they are higher for people living or working near industrial sites that release the gas.
Acute and Chronic Health Consequences
The health consequences of EtO exposure vary based on concentration and duration. Acute effects result from short-term exposure to high concentrations, primarily a risk in occupational settings. Symptoms include severe irritation of the eyes, skin, and respiratory tract, headaches, nausea, and vomiting. High-level exposure can also cause central nervous system depression and lung injury.
Chronic exposure involves lower levels over many years and is the main concern for long-term cancer risk. EtO is a genotoxic carcinogen, meaning it directly damages DNA and initiates cancer development. Long-term inhalation exposure is linked to an increased risk of lymphoid cancers, such as non-Hodgkin lymphoma and leukemia. Chronic exposure also increases the risk of breast cancer in women. Non-cancer chronic effects include damage to the brain and nervous system, causing symptoms like memory loss and numbness. Reproductive harm is also a documented concern, with evidence suggesting increased rates of miscarriage in exposed female workers.
Regulatory Definitions of Dangerous Exposure
Defining dangerous exposure to a carcinogen like EtO is complex because no scientifically established safe threshold exists for a genotoxic substance. Regulatory bodies, such as the U.S. Environmental Protection Agency (EPA), quantify risk using “lifetime cancer risk.” This metric estimates the theoretical number of excess cancer cases that might occur from continuous exposure over a 70-year lifespan.
For the general public, the EPA typically aims to reduce lifetime cancer risk to one excess case per million people exposed (1 in 1,000,000). Since EtO is a potent carcinogen, the concentration associated with this minimal risk level is extremely low, often measured in parts per billion (ppb) or parts per trillion. For example, a 2016 EPA assessment indicated that a 1 in a million lifetime cancer risk could be associated with continuous air concentrations as low as 0.00004 ppb.
In occupational settings, risk is managed through workplace exposure limits set by the Occupational Safety and Health Administration (OSHA). The OSHA Permissible Exposure Limit (PEL) for EtO is currently 1 part per million (ppm) averaged over an eight-hour workday. This standard is widely considered outdated and inadequate for protecting against long-term cancer risk. Recent EPA actions aim to establish stricter phased worker exposure limits, lowering the limit to 0.1 ppm by 2035.
Actionable Steps for Risk Mitigation
The most effective way to mitigate EtO risk is to reduce exposure to the lowest practical level.
For the Public
Members of the public living near sterilization facilities or chemical plants should monitor local air quality reports and engage with state environmental agencies. Advocating for stricter industrial controls and fenceline monitoring requirements helps push for lower community exposure. Individuals can also inquire about the sterilization methods used for implantable or long-term medical devices they receive. While alternatives like steam or radiation exist, EtO remains necessary for about 50% of sterile medical devices.
For Workers
For those in occupational roles near sterilization equipment, proper ventilation and the use of approved personal protective equipment, such as respirators, are mandatory to limit high-level exposure.
Regulatory Efforts
The EPA is actively working to reduce EtO emissions from commercial sterilizers by up to 90%. They are also working to ban the use of the gas for certain non-medical items like cosmetics and beekeeping equipment. Supporting these regulatory efforts helps ensure the overall environmental burden of this carcinogen is reduced.