Analysis of EPA air toxics monitoring data and tools for use in general population exposure assessments: Using acrylonitrile as a case study

Acrylonitrile (AN) is a vinyl monomer used in the manufacture of polymers that have a wide variety of applications in the industrial, consumer, and automotive realms. Acrylonitrile was recently proposed to be designated as a high-priority substance for risk evaluation by the U.S. Environmental Protection Agency (EPA) under the Toxic Substances Control Act (TSCA). Past research has characterized worker population's exposure to acrylonitrile; however, there has been limited assessment of the general population's exposure. The objective of this study was to characterize general population exposure to acrylonitrile via the ambient air and to assess the suitability of EPA monitoring and modeled data for use in regulatory risk assessment. This study used EPA's air monitoring data from its Air Quality System (AQS) from the past 11 years and modeled data from EPA's 2020 AirToxScreen assessment. Acrylonitrile was seldom detected in ambient air samples, as only 13% of air samples from 2013 to 2023 detected acrylonitrile. Additionally, only 0.27% of samples exceeded the Agency for Toxic Substances and Disease Registry (ATSDR) Draft Minimal Risk Level (MRL) for acrylonitrile of 0.9 ppb. Most of the samples exceeding the Draft ATSDR MRL were identified as industrial-owned monitors; however, the number of exceedances has been steadily decreasing from 2013 to 2023. EPA's AirToxScreen modeled results were typically orders of magnitude lower than those measured by AQS monitors. Quantitative limitations with the air sampling methods and the potential for non-industrial sources to contribute to ambient air levels, which are not included in the AirToxScreen, may contribute to discrepancies. Given these limitations, some caution may be considered in the use of AirToxScreen exposure estimates for acrylonitrile. Overall, findings from this study suggest that general population exposure to acrylonitrile from the ambient air is low and AQS data is well suited for general population exposure evaluations.<i>Implications:</i> Acrylonitrile was recently proposed to be designated as a high-priority substance for risk evaluation by the U.S. EPA under TSCA. Past research has characterized the health effects of acrylonitrile and the worker population's exposure to it. However, there has been limited assessment of the general population's exposure to acrylonitrile. The objective of this study was to characterize general population exposure to acrylonitrile via the ambient air and to assess the suitability of EPA monitoring and modeled data for use in regulatory risk assessment. Overall, key findings from this study suggest that general population exposure to acrylonitrile from the ambient air is low and EPA's AQS data is well suited for general population exposure evaluations. These results benefit the general public in understanding their potential exposure to acrylonitrile, the EPA in informing their TSCA risk evaluation for acrylonitrile, and other researchers aiming to utilize AQS for general population exposure assessments.