A Benchmark Study on Available Data of Henry's Law Constants and Vapor Pressures for 30 Per- and Polyfluoroalkyl Substances (PFAS) and Considerations for Vapor Intrusion

The United States Environmental Protection Agency (EPA) has established criteria for Henry's law constant (HC ≥10⁻⁵ atm m³/mol or 101 Pa m³/mol) and vapor pressure (VP ≥1 mmHg or 133 Pa) to identify contaminants with sufficient volatility to warrant vapor intrusion (VI) evaluation. Site managers, regulatory agency staff, and industry professionals are making decisions about which per- and polyfluoroalkyl substances (PFAS) pose a VI pathway concern using available HC and VP data. To support VI decision-making, this study generated a comprehensive and extensively curated dataset including 424 HC values and 585 VP values for 30 PFAS spanning seven subclasses. Data were assembled through an iterative process that combined manual and automated retrieval from peer-reviewed literature and major chemical databases (e.g., CompTox and CAS SciFinder), Python-based data expansion and cross validation, and extensive manual validation to resolve inconsistences. Across the dataset, 80% of HC values and 34% of VP values met EPA VI screening criteria, though results varied substantially depending on data source and measurement methods. Model-predicted values were frequently inconsistent with experimental measurements and contributed to uncertainty. These findings show the need for high-quality, experimentally derived physicochemical data when assessing PFAS VI potential and demonstrate the limited reliability of applied modeled values. Finally, rather than arbitrarily treating all values as equal, this study establishes a framework for evaluating data quality for VI conditions, considering data consistency, data sources, and whether the data acquisition method aligns with the VI conceptual site model.