Characterization of Background Exposures to Ethylene Oxide in the United States: A Reality Check on Theoretical Health Risks for Potentially Exposed Populations near Industrial Sources

Abstract

Ethylene oxide (EO) is an industrial chemical and sterilant that is released into ambient air from natural and unregulated anthropogenic sources that contribute to background exogenous exposure and from regulated industrial sources that contribute to additional exogenous exposure for near-facility populations. Metabolic processes contribute to substantial background endogenous exposures to EO, complicating the interpretation of the relation between total background exposure and the health significance of added industrial exogenous exposure. In 2021, Kirman and colleagues characterized the total and endogenous equivalent background concentrations for U.S. populations, which are substantially greater than the USEPA 2016 EO cancer reassessment risk-specific concentrations (0.00011-0.011 ppb), suggesting that the consideration of background exposure could be used as a reality check for the utility of the reassessment in managing EO risk for industrially exposed populations. New exposure biomarker data and background ambient concentration data for EO have become available since the 2021 assessment and are used here to refine the estimates of U.S. population total and endogenous equivalent background EO concentrations. Refined equivalent background concentrations as well as total equivalent exposure estimates for U.S. smokers provide context as to the health significance of near-industry population added exposure and a reality check for the utility of USEPA and TCEQ risk-specific concentrations in managing and communicating EO risk.

Keywords: ethylene oxide; managing and communicating risk; risk specific concentrations; total and endogenous equivalent background concentrations.

Figure 2

Total HEV in (A) nonsmokers and (B) smokers [9,12].

Figure 3

Relationship between HEV and occupational exposures to EO; X = data point for HEV in workers with known EO exposure; solid blue line = robust SE linear regression; solid red line = PK model predictions [22]; solid green line = PBPK model predictions [20].

Figure 1

Conceptual model for exposure pathways contributing to total EO exposure based on HEV biomarker burden.

Figure 4

HEV as a function of serum cotinine (NHANES data; 2013–2020); X = data point; solid red line = linear regression; dashed blue line = upper limit for serum cotinine in nonsmokers.

Figure 5

HEV as a function of cigarettes per day (NHANES data; 2013-2020); X = data point; solid blue line = linear regression of NHANES data; solid red line = linear regression prediction from worker HEV data extrapolated from Figure 3; dashed lines = reported relationships for HEV and CPD from the published literature sources. References as cited in main text: Wu et al. 2004 [46], Boogaard et al. 1999 [25], Bader et al. 1995 [47], Bailey et al. 1988 [48], and Tornquist et al. 1986 [49].

Figure 6

Pathway contribution to total HEV burden for (A) nonsmokers and (B) smokers; light gray columns indicate exposures remote from EO facilities; dark gray columns indicate exposures near EO facilities; error bars = standard deviation; percent values indicate the percentage of total exposure attributed to the pathways; blue arrow on the right vertical axis indicates the 1 × 10⁻⁵ risk-specific concentration based on TCEQ cancer potency (2.4 ppb); red arrow on the right vertical axis indicates the 1 × 10⁻⁵ risk-specific concentration based on USEPA cancer potency (0.0011 ppb). Exogenous background exposures (Pathway 2) were characterized using national air monitoring data for remote-facility exposures and using local air monitoring data for near-facility exposures. Exposures attributed to facility-related site release (~0.11 ppb) were estimated using the arithmetic mean for Steriogenics sample locations S6 and S7 in 2021–2022 less the arithmetic mean calculated for the local background.

Figure 7

Near-facility potential total EO continuous exposure concentrations (black dots) are plotted against the 5th, 50th, and 95th percentile total equivalent background exposure concentrations and USEPA and TCEQ 10⁻⁴ risk-specific concentrations.

Figure 8

Historical cigarette sales in the U.S. reflect over 100 years of exogenous exposure to EO from smoking (Pathway 3) (https://ourworldindata.org/smoking; accessed 11 June 2024).