We recently wrote an article for the American Bar Association (ABA) on human health risks from ethylene oxide exposure. The information below is a summary of the article along with some additional conclusions based on recent observations.
Health Impacts, Regulatory Scrutiny, and Evolving Risk Assessment With Ethylene Oxide
Ethylene oxide (EtO) has become a focus of attention due to its potential health impacts, especially concerning community and occupational exposures. Investigations in the 2010s highlighted the risks associated with ambient exposure to this chemical, primarily through emissions from sterilization facilities. EtO is a flammable, sweet-smelling gas widely used as a chemical intermediate in the production of various industrial and consumer goods, including adhesives, personal care products, and lithium-ion batteries. It also serves as a sterilizing agent in healthcare and food applications, with established residue thresholds for its use.
Occupational and Community Exposure
Historically, concerns about EtO (ethylene oxide) exposure focused on occupational settings, where enforceable and recommended exposure thresholds, such as OSHA's Permissible Exposure Limit (PEL) and ACGIH’s Threshold Limit Value (TLV), ensure worker safety. These thresholds guide the use of personal protective equipment (PPE) and safe handling protocols. However, sterilization processes, unlike manufacturing, present unique exposure risks due to the potential for leaks or fugitive emissions.
Community exposures to EtO have gained prominence with reports of ambient air emissions from sterilization facilities. Facilities using EtO for sterilizing medical devices often involve separate fumigation and aeration chambers or combined systems, which may inadvertently release the gas into the environment. Possible sources of these emissions include inadequate industrial hygiene controls, equipment malfunctions, or accidental releases. These emissions raised alarm among regulators, non-governmental organizations (NGOs), and affected communities.
Health Risk Assessment and Regulatory Actions
EtO exposure is associated with several health risks, with chronic inhalation identified as the primary concern. Acute exposure can cause neurotoxicity, but chronic exposure is linked to carcinogenic effects. Regulatory bodies such as the EPA and the International Agency for Research on Cancer (IARC) classify EtO as a human carcinogen. However, assessments vary, with organizations like the Texas Commission on Environmental Quality (TCEQ) labeling it "likely to be carcinogenic." These differences stem from variations in methodologies and interpretations of evidence.
Risk assessments have predominantly focused on ambient exposures in non-occupational settings, employing models to estimate cancer risks for populations living near sterilization facilities. These models often assume continuous exposure over a lifetime, providing conservative risk estimates. However, realistic exposure parameters, such as intermittent presence in high-risk areas and home ventilation systems, may modify these risks.
The EPA's National Air Toxics Assessment (NATA) in the 2010s identified elevated cancer risks in communities near sterilization facilities, prompting additional evaluations. In recent years, regulatory agencies have refined risk assessment models, though disagreements persist regarding the most accurate methods. For example, EPA's Integrated Risk Information System (IRIS) applies a linear risk model, while TCEQ uses alternative approaches, leading to differing conclusions about the population risk.
Ambient Monitoring and Dose Assessment
Reliable ambient monitoring data are critical for assessing EtO exposure. Challenges arise from discrepancies in sampling methods and laboratory analyses, which can affect the interpretation of exposure levels. Dose-response assessments are equally vital, distinguishing between exposure (contact with EtO) and dose (absorbed EtO). Understanding how exposure levels compare to naturally occurring EtO within the body provides context for potential health impacts. Biomonitoring methods, such as ACGIH's Biological Exposure Index (BEI), can help evaluate occupational exposure levels.
Regulatory Developments and Future Directions
In response to community concerns, the EPA has introduced regulatory amendments to curb EtO emissions. The 2024 amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) target commercial sterilizers, aiming to reduce lifetime cancer risk. Similarly, new rules for chemical manufacturing facilities were implemented to limit emissions. While these measures seek to protect public health, they may have unintended consequences, such as potential risks of incomplete sterilization of medical devices or supply chain disruptions.
Final Thoughts and Action Steps
EtO remains a critical component of various industries, but its potential health risks necessitate ongoing scrutiny. Future efforts should aim to refine exposure and risk assessment methodologies, ensuring they reflect realistic scenarios. As regulatory measures evolve, a balanced approach is needed to protect public health while addressing the operational needs of industries reliant on EtO. Robust scientific methods will be essential for answering questions about causal links between exposure and health outcomes, fostering both regulatory and public confidence.
