Evaluating the EPA's proposed screening-level methodology for 1,3-butadiene exposures in fenceline communities: A case study approach.

As part of the Toxic Substances Control Act (TSCA) Risk Evaluation, the United States Environmental Protection Agency (US EPA) published a proposed screening-level methodology in January 2022 to evaluate potential chemical exposures from air pollutants in fenceline communities. In this work, we investigate the suitability of the proposed methodology for making risk determination decisions by applying its tiers to a case study facility located in Texas, which reports the release of hazardous air pollutants such as 1,3-butadiene. While 1,3-butadiene serves as a suitable example chemical due to its high-priority status under TSCA and the public availability of its emissions and ambient measurements data, the methodology presented here is broadly applicable to any chemical. The EPA's suggested tiered methodology, including its Pre-Screening Integrated Indoor-Outdoor Air Calculator (IIOAC) and its simplified air dispersion model setup (Full-Screening AERMOD), is compared to a more detailed dispersion model setup in AERMOD (Facility-specific AERMOD) following the example provided in the EPA's 2020 Miscellaneous Organic Chemical Manufacturing Residual Risk and Technology Review (MON RTR), for two years (2019 and 2021). Results show that the IIOAC consistently produces the highest output concentrations (10.75 µg/m and 9.69 µg/m for years 2019 and 2021, respectively), followed by the TSCA Full-Screening AERMOD (1.04 µg/m and 0.74 µg/m), with the facility-specific AERMOD run producing the lowest output concentrations (0.44 µg/m and 0.46 µg/m). Ambient air concentrations of 1,3-butadiene measured at various nationwide sites with automated gas chromatography (auto-GC) from 2017 to 2021 are also analyzed. All average concentrations of 1,3-butadiene, with the exception of one Texas site in 2021, are found to be below 1 ppb (2.21 µg/m).: While the TSCA Screening Level Approach provides a necessary initial framework for assessing chemical exposures, incorporating facility-specific modeling and real-world monitoring data can lead to more accurate risk management decisions. This refined approach can ensure that regulatory efforts are both protective of public health and practically feasible for regulated entities.