Q&A: PFAS Anthropogenic Background

Are PFAS “background” contaminants?

While PFAS are not naturally occurring, they are regarded as anthropogenic “background” contaminants. According to the U.S. Environmental Protection Agency (EPA), anthropogenic background contaminants are substances present in the environment as a result of human activities. PFAS have become widespread in the environment because of their persistence and extensive history of use. Once in the environment, they spread via complex cycling between air, soil, water, and biota. Although soils and oceans across the globe are important long-term PFAS sinks, PFAS retained in soil and sediment can also be long-term sources of water contamination. It is important to note that PFAS comprise a large class of substances—in the thousands to millions of molecules—yet only a couple dozen PFAS are regulated as contaminants by environmental agencies. While still a topic of research, the background concentrations of regulated PFAS are specific to certain environmental media (e.g., shallow soil) and exhibit regional or local differences.

Are PFAS ubiquitous?

PFAS are often described as “ubiquitous” because researchers have detected trace concentrations virtually everywhere they’ve looked, from the Arctic to the Tibetan Plateau. Concentrations that are detectable using commercial laboratory methods (e.g., EPA Method 1633) are not ubiquitous, but are still very common in shallow soil and groundwater in many locations where there is no obvious point source, especially in more populous regions.

Are background concentrations in the range of potential regulatory concerns?

Yes. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two PFAS that have regulatory standards and/or screening levels that approach, or are below, background concentrations. For example, EPA recently published drinking water standards for PFOS and PFOA—4 parts per trillion (ppt) each—that are below average background concentrations that were reported in a global survey of PFAS groundwater concentrations at sites with no known source. Consistent with this survey, Langan has observed apparent PFOS and PFOA background concentrations upward of 10 ppt in shallow groundwater in populous regions of the United States. EPA’s soil screening levels for PFOS and PFOA are also generally within the range of reported background concentrations.

What tools and strategies are available to differentiate background PFAS from site-related sources?

Experienced practitioners can leverage a variety of tools and strategies to differentiate background PFAS from site-related sources. Site-related sources often exhibit PFAS concentration distributions that are distinguishable from regional background. These differences can be analyzed and illustrated using compound ratios and graphical presentations such as bar charts, pie charts, radial diagrams, and color-coded distribution matrices. A variety of specialized laboratory analytical techniques and statistical tools can also be leveraged in more challenging situations. The available techniques and tools are most effectively applied in the context of a detailed conceptual site model incorporating the history and use of PFAS at the site and surrounding area, and relevant environmental transport mechanisms.

What are the regulatory implications of background conditions, and are regulators acknowledging the challenges posed by background PFAS?

In many states, remediation is not required and/or requirements are relaxed for contaminant concentrations that are consistent with background. With that in mind, several states (e.g., Maine, New Hampshire, New Jersey) have commissioned statewide assessments of PFAS background concentrations, intending the results to be used for regulatory decision-making. However, some regulators haven’t fully acknowledged the challenges posed by PFAS background. In some instances, regulators have requested the rapid geographic expansion of PFAS sampling programs seeking to tie all detections with one alleged source without considering background. Some states have also advised or required PFAS concentrations to be screened against (or delineated to) analytical reporting limits, which is impractical in locations affected by regional background.

What is the takeaway regarding PFAS background?

Given the prevalence of PFAS as anthropogenic background and the potential regulatory significance, it is important to consider PFAS background early and throughout site assessment and investigation, with heightened scrutiny when interpreting PFAS sample analytical data.

Adam Hackenberg has 27 years of diverse environmental experience investigating and remediating environmentally distressed sites under various state programs, CERCLA/Superfund, and RCRA. He frequently advises clients regarding chemicals of emerging concern, such as PFAS, and plays an active role in several related regulatory and technical stakeholder processes. His areas of expertise include PFAS chemistry and source analysis, remedial design and action for contaminated sites, contaminated site characterization, conceptual site models, regulatory closures, and hydrogeology and groundwater/contaminant behavior in the subsurface.