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.

Keywords: endogenous equivalent concentration; ethylene oxide; exposure contextualization; exposure metrics; exposure science; total equivalent concentration.

Figure 1

Distribution of ambient air EO concentrations in the vicinity of eight EO-emitting industrial facilities and at corresponding representative background locations. Length of box = interquartile range (IQR or P75–P25); horizontal line = P50; large circle = mean; lower whisker = P25 – (1.5 × IQR); upper whisker = P75 + (1.5 × IQR); small circle = potential outlier.

Figure 2

Overall mean (top of box) and SD (whisker) of ambient air EO concentrations across 27 national monitoring locations and across the 27 individual locations aggregated into five background locations for the facilities characterized in this manuscript.

Figure 3

Mean (top of box) and SD (whisker) of ambient air EO concentrations in the vicinity of eight sterilization and other EO-emitting industrial facilities, relative to overall facility-specific background mean EO concentration (0.14 ppb) and endogenous mean EO concentration for the non-smoking U.S. population (2.7 ppb).

Figure 4

Estimated total equivalent exposure to EO in the vicinity of eight sterilization and other EO-emitting industrial facilities relative to that of the 50th, 75th, and 95th percentiles of the non-smoking U.S. population (2.5, 3.2, and 5.5 ppb, respectively). Light gray = [50th percentile endogenous equivalent for the non-smoking U.S. population, or 2.3 ppb] + [50th percentile EO concentration for the facility area from Table 3]. Dark gray = same as light gray, except using 90th percentile EO concentration for the facility area from Table 3.