A risk assessment of ethylene oxide release from a sterilization facility into a community

In recent decades, ethylene oxide (EtO) has been a widely used industrial sterilant and chemical intermediate that has faced increasing scrutiny related to its carcinogenic potential. This study evaluated residential and occupational exposure to EtO in a valley surrounding two point-source emissions in close proximity (~11 m apart). Air samples were collected in residential and industrial areas. Eight locations, ranging from 100 to 1,700 m from the center of the point-sources in varying directions, had average concentrations between 0.290 and 3.212 µg/m³ (0.16 to 1.8 ppb) with peak levels reaching 26.4 µg/m³ (15 ppb). Exposure scenarios were developed based on daily activity patterns, long-term residency, and estimates derived from historical emissions data. Under the most conservative assumptions, including 40 years of occupational exposure during the periods of highest recorded emissions around the facility, the maximum estimated cumulative lifetime exposure was 591 ppm-days. When compared with epidemiology studies of EtO-exposed workers from similar facilities (studies used by the Environmental Protection Agency (EPA) and International Agency for Research on Cancer (IARC) in their cancer risk assessments), the highest cumulative exposures observed (13,500+ ppm-days) were at least 23-fold higher than our maximum estimated lifetime exposure value (591 ppm-days). Importantly, these high-exposure groups showed no statistically significant cancer incidence, particularly for breast and lymphohematopoietic cancers. When compared to regulatory values and health-based benchmarks adjusted to cumulative exposures, estimated exposures were substantially below levels associated with increased cancer incidence in epidemiological cohorts for the community surrounding the sterilization facility, even to the most susceptible populations.Implications: This study presents a site-specific, data-driven framework for evaluating long-term human health risks from ethylene oxide (EtO) emissions using ambient monitoring, historical emissions, and conservative EPA-aligned assumptions. Even at one of the highest-emitting U.S. sterilization facilities, estimated exposures were well below levels associated with increased cancer risk. The findings challenge proximity-based risk assumptions and support more proportionate, risk-based air quality policies. The approach offers regulators a transparent, scientifically grounded method for EtO risk characterization under the Clean Air Act, TSCA, and state air toxics programs.