Recent peer reviewed studies have explored the potential for some per-and polyfluoroalkyl substances (PFAS) to volatilize from groundwater and soil and enter indoor air via the vapor intrusion (VI) pathway. This research is in its early stages, emphasizing the need for further investigation to determine the conditions under which PFAS become volatile and the implications for indoor air quality.

The Complexity of Vapor Intrusion

Evaluating whether a VI pathway is complete for a building overlying or adjacent to a subsurface vapor-forming compound entails using a multiple-lines-of-evidence evaluation and can be complicated when there are confounding sources present in the building. Identifying and evaluating contributions from confounding sources compared to a complete VI pathway could include an exhaustive search of sources, including consumer products, in a building. Understanding the full scope of potential sources is critical before considering indoor air sampling for PFAS.

Prioritizing Research and Methodical Evaluation

Before responding to a potential request to collect and analyze indoor air samples for PFAS, or even consider PFAS as a potential concern, it is imperative to focus on the research; understand how to evaluate the pathway and potential risk from inhalation of PFAS; and develop an approach protective of human health from significant PFAS sources.

Research to date highlights:

1) Specific subsurface environmental conditions need to exist for PFAS to be at a volatile concentration that poses a concern.

2) The VI pathway is influenced by multiple potential PFAS sources that may be present within buildings or ambient air.

3) More research is needed to assess when subsurface PFAS levels in the subsurface necessitate VI evaluations in occupied buildings.

For example, Kapuscinski (2024) and Schumacher et al. (2024) state that research is needed to better understand the following before conducting a VI assessment:

• The subsurface conditions (e.g., aerobic, pH) associated with PFAS volatility.
• Henry’s law constants—based on a comparison of modeled values to those measured at multiple sites—to evaluate what PFAS may be volatile.
• The concentration of those volatile PFAS in the subsurface (i.e., groundwater, soil, soil vapor) that would warrant evaluating indoor air.
• The PFAS concentrations that could pose an inhalation risk to building occupants.

Note the Schumacher et al. 2024 study does not evaluate other sources of PFAS (e.g. building materials including the concrete slab) that could be off-gassing and impacting the soil vapor.

What Next? Consult with Experts

Some PFAS may be volatile in some subsurface environmental conditions and when present at high enough concentrations could migrate into an overlying building. However, the conditions at which PFAS could pose an inhalation health risk via the VI pathway are unknown.

Given the complexities and emerging nature of PFAS volatility and vapor intrusion, professional guidance is indispensable. Scientists and engineers are available to support you in developing and implementing a strategic approach to evaluate whether PFAS in the subsurface at your site may pose an inhalation risk to building occupants.

References:

Kapuscinski, R.A. (2024). Research needs regarding the vapor intrusion potential of volatile per- and polyfluoroalkyl substances. Environ. Sci. & Technol. 58(9):4056–4059. (https://doi.org/10.1021/acs.est.3c06227)

Schumacher B.A., J. Zimmerman, A. Williams, C. Lutes, C. Holton, E. Escobar, H. Hayes, and R. Warrier. (2024). Distribution of select per- and polyfluoroalkyl substances at a chemical manufacturing plant. Journal of Hazardous Materials 464:133025. doi: 10.1016/j.jhazmat.2023.133025.