Ethylene Oxide Exposure in U.S. Populations Residing Near Sterilization and Other Industrial Facilities: Context Based on Endogenous and Total Equivalent Concentration Exposures

Abstract

Given ubiquitous human exposure to ethylene oxide (EO), regardless of occupation or geography, the current risk-specific concentrations (RSCs: 0.0001–0.01 ppb) from the U.S. Environmental Protection Agency (EPA) cancer risk assessment for EO are not useful metrics for managing EO exposures to the general U.S. population. The magnitude of the RSCs for EO are so low, relative to typical endogenous equivalent metabolic concentrations (1.1–5.5 ppb) that contribute ~93% of total exposure, that the RSCs provide little utility in identifying excess environmental exposures that might increase cancer risk. EO monitoring data collected in the vicinity of eight EO-emitting facilities and corresponding background locations were used to characterize potential excess exogenous concentrations. Both 50th and 90th percentile exogenous exposure concentrations were combined with the 50th percentile endogenous exposure concentration for the nonsmoking population, and then compared to percentiles of total equivalent concentration for this population. No potential total exposure concentration for these local populations exceeded the normal total equivalent concentration 95th percentile, indicating that excess facility-related exposures are unlikely to require additional management to protect public health.

Monitored and Modeled Ambient Air Concentrations of Ethylene Oxide: Contextualizing Health Risk for Potentially Exposed Populations in Georgia

“…To better inform risk management decisions, the present study focuses on using this total equivalent exposure metric to provide health-risk context for residential populations near selected emitting facilities in the state of Georgia, relying on publicly available data generated from both monitored and modeled EO concentrations in ambient air. It extends the analyses previously published [ 8 ] by including additional monitoring and modeled concentration data for three sterilization facilities previously evaluated, providing new modeled concentration data for five additional emitting industrial facilities, presenting national historical background EO concentration data and recent national background concentration data, and focusing the exposure analysis on the nearby residential populations to these emitting facilities. Specifically, this study includes the following components: Statistical characterization of ambient air EO concentrations at sites around emitting facilities in Georgia to assess whether they are above those at background sites; Comparison of mean monitored EO concentration at specific sites with mean background concentration to assess the potential contribution from facilities in Georgia; Comparison of monitored and modeled EO concentrations at closely located sites in Georgia to assess consistency between these two types of data; Comparison of U.S. national current and historical background EO concentrations to assess consistency in central tendency measures over time; Assessment of the relative health importance of excess EO concentrations for residential populations near emitting facilities in Georgia by comparing their estimated total EO exposure concentration to the distribution of that for the non-smoking U.S. population.…”

“…Measurable concentrations of ethylene oxide (EO) and its human metabolic precursor, ethylene, are ubiquitously present in the ambient air and are derived from industrial (e.g., stack and/or fugitive emissions) as well as natural (e.g., metabolism of certain plants and microbes and forest fires) and unregulated anthropogenic (e.g., tobacco smoke and fossil fuel combustion) sources [ 1 , 2 , 3 , 4 , 5 , 6 ]. As a result, virtually everyone is exogenously and endogenously exposed daily to some concentration of EO regardless of their occupation and geographic location [ 1 , 3 , 7 , 8 , 9 , 10 ]. Characterizing the potential health significance of environmental EO exposure for U.S. populations residing near emitting industrial facilities, where potential ambient concentrations may be above background levels, is challenging for two primary reasons.…”

“…First, for the general population, ~94.5% of the mean total EO exposure (~2.9 parts per billion (ppb)) is from background endogenous ethylene metabolism rather than from exogenous inhalation of EO [ 3 ]. Second, there is a lack of practical utility of the current U.S. Environmental Protection Agency (EPA)’s inferred risk-specific concentrations (RSCs), which state that 0.0001 to 0.01 ppb is associated with an increase in inhalation cancer risk of 10 −6 to 10 −4 , respectively [ 3 , 8 , 11 ]. Thus, this study evaluates alternative exposure metrics to address the immediate need for additional analytical tools to inform risk management decisions for populations exposed to industrial EO emissions.…”

“…Alternative exposure metrics to evaluate health-risk context associated with EO exposure were initially proposed in Kirman and Hayes [ 7 ] and Kirman et al [ 3 ] (“endogenous equivalent concentration”) and subsequently by Sheehan et al [ 8 ] (“total equivalent concentration”). Total equivalent concentration is the continuous EO exposure concentration extrapolated from hemoglobin adduct levels of 2-hydroxyethylvaline (HEV), a useful biomarker of total EO exposure regardless of exposure source and pathway.…”

“…The conversion of HEV concentrations to equivalent continuous EO exposure concentrations in air is described in Kirman et al [ 3 ]. An initial evaluation of the utility of these alternative equivalent exposure metrics for populations residing near emitting industrial facilities was presented in Sheehan et al [ 8 ]. This initial evaluation was based on 50th and 90th percentile EO concentrations which were based on data collected from monitoring sites generally in proximity to emitting industrial facilities and frequently within the radius of adjacent residential areas.…”