PFAS Now in Ambient Air and a Vapor Intrusion Risk?

Vapor Intrusion (VI) is the process in which contaminants in subsurface soil or water migrate upwards into the ambient air. This poses a risk to indoor air quality in buildings which have been constructed over contaminated sites. The most common VI contaminants are radon, petroleum components such as benzene, toluene, ethylbenzene, and xylenes (BTEX), or cleaning product chemicals such as trichloroethylene (TCE).

The emergence of new information around per-and polyfluoroalkyl substances’ (PFAS) negative health effects and widespread presence in water has brought PFAS into the VI spotlight as a new potential contaminant to watch.  PFAS is a group of chemicals commonly seen in products such as non-stick pans and chemical cleaners due to its non-stick and de-greasing properties.

While PFAS are typically highly soluble and non-volatile, and therefore were not traditionally evaluated as a VI risk, certain PFAS groups such as fluorotelomer alcohols (FTOHs) have recently been shown to be a VI concern due to their high vapor pressure. The United States Environmental Protection Agency (U.S. EPA) has begun research into PFAS as a potential VI risk and has indicated in a November 2023 Site Study the following finding:

“The presence of PFAS in soil, soil gas, and groundwater at the NJ site indicates the potential for but does not confirm VI as an exposure pathway. Concurrent indoor air measurements would be needed to confirm a complete VI pathway. Given the known health risks associated with PFAS exposure and the presence of volatile PFAS in the environment, PFAS VI assessment is warranted at facilities where high PFAS concentrations are present or suspected in shallow soils and groundwater.”

What Does This Mean?

While the U.S. EPA study is purely exploratory, U.S. EPA still seems to err on the side of caution and says PFAS VI analysis is “warranted”. Given this as well as U.S EPA’s crack down of PFAS in other media (proposed water maximum contaminant levels, Toxic Release Inventory reporting requirements, etc.), it can be expected that U.S. EPA and other state regulatory agencies will conduct additional research on the risk of PFAS as a VI contaminant and explore adding a screening threshold, which establishes numerical limits for when additional investigation or mitigation may be necessary.

What Are the Potential Difficulties?

While the addition of a new contaminant considered a VI risk is not unprecedented, PFAS poses a unique set of challenges. For example, sub-slab sampling, which identifies the concentration of chemicals immediately below the building, is subject to sampling difficulties due to limitations of current sampling procedures and methods. For one, there is minimal U.S. EPA guidance on PFAS sampling methods for ambient air. This, combined with the potential contamination from sampling equipment that contain PFAS (Polytetrafluoroethylene [PTFE or Teflon], Low Density Polyethylene [LDPE], aluminum foil, sticky notes, waterproof pens, passive diffusion bags, and more), makes PFAS air sampling a tedious effort that has potential for uncertainty, scrutiny, and false positives.

Additionally, the unique chemical properties of PFAS means that most, if not all, commercially available vapor barriers have yet to be tested for chemical resistance to these types of chemicals. While diffusion testing is still to be done, there is no assurance that currently available membranes will be able to protect against upward diffusion of PFAS into the building space. This potential lack of chemical resistant barriers could pose a material sourcing issue both now and in the near future until a robust body of chemical resistance testing has been completed.

If you can overcome both previous considerations, you still have one more potential to hurdle, indoor air sampling. Indoor air sampling is used as a confirmation of system efficacy by confirming the concentrations of contaminants in the indoor air are below screening levels. Given the abundance of PFAS in construction materials (textile coatings, cleaning products, metal coatings, paints, wood lacquers, caulks, adhesives, etc.), there is an ample amount of background PFAS which could lead to false positives.

What can I do?

As U.S EPA refines their related VI related guidance, there is plenty to do to stay ahead of the curve. Keeping an eye out for ALL4 articles related to PFAS air sampling or VI will keep you up to date on any new developments. ALL4 is always available to help with your VI risk assessment and mitigation design needs. If you have any questions or want to discuss VI strategies or designs or at your site, please contact Evan Mia at emia@all4inc.com.