983787 - Evaluation Of Theoretical Lifetime Cancer Risks Associated With Ambient Levels Of Ethylene Oxide In The United States

Ethylene oxide (EtO) is a highly reactive chemical used as a sterilizing agent and a feedstock for producing other chemicals. In 2016, the United States Environmental Protection Agency (USEPA) updated the existing Inhalation Unit Risk (IUR), and this unit risk estimate has fueled risk assessments that predict high cancer risks in communities surrounding facilities that emit EtO. While there are few natural sources of EtO in the environment, anthropogenic non-point sources for this chemical include fossil fuel combustion which has resulted in detectable levels of EtO in outdoor air away from any specific point sources. Because of the increased concern associated with this chemical, the USEPA began monitoring for EtO at locations that were part of the National Air Toxics Trends Stations (NATTS) and Urban Air Toxics Monitoring Program (UAMTP) starting in October 2018 in order to characterize ambient levels of EtO in the United States. More recently, monitors have been added that are not a part of those networks in Florida, New York, Maryland and Rhode Island. For this evaluation, the publicly available sampling data from locations that are not near facilities known to emit EtO were summarized and the theoretical lifetime cancer risk for each sampling location was calculated using the 2016 USEPA IUR and an alternate, lower, IUR that was calculated by the Texas Commission on Environmental Quality (TCEQ). Overall, the average air concentration across all 39 sampling locations was 0.41µg/m3 with the lowest average of 0.088 µg/m3 at the Horicon, WI location and the highest average of 1.47 µg/m3 at the Decatur, GA location. The theoretical lifetime cancer risks based on the average air concentration for these sampling locations using the USEPA IUR ranged from 4x10-4 to 7x10-3. Using the alternate TCEQ IUR, these theoretical lifetime cancer risks ranged from 1x10-7 to 2x10-6. Focusing on only the rural sampling locations, the theoretical lifetime cancer risks using the USEPA IUR still range as high as 3x10-3, which is based on data from the sampling location in Smithland, KY. Therefore, given that the estimated lifetime cancer risks even for rural sampling locations are as high as 3 in 1,000, this is an indication that the current USEPA IUR for EtO may be overly conservative.