Per- & Polyfluorinated Substances (PFAS)

Per- and polyfluorinated substances (PFAS) are organofluorine chemicals that have been in commercial use since the 1950s.  PFAS have been used in many different use categories, including fire-fighting foam, textiles, electroplating, paper packaging, and insecticides.

PFAS have unique physicochemical properties.  Some PFAS are highly stable and unreactive, while retaining the ability to repel both water and oil and reduce surface tension lower than many other surfactants.  The stability of many PFAS is attributed to their chemical structure, particularly the carbon-fluorine bond.

PFAS, including prefluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), are undergoing regulatory scrutiny.  Scientists are studying the data regarding these chemicals in an attempt to make assessments for health advisories, use and disposal practices, and remediation decisions.  Legal and regulatory attention is anticipated to continue in the near and long term.

Gradient has extensive experience in evaluating the potential for PFAS accumulation in humans and ecosystems, source identification, fate and transport in the environment, potential toxicity and risk assessment, and remedial decision-making.  Gradient also has a thorough understanding of the historical state of knowledge of PFAS, including exposure and toxicity, fate and transport, analytical chemistry, and ecological effects.

Related Publication:  Pizzurro, DM; Seeley, M; Kerper, LE; Beck, BD. 2019. “Interspecies differences in perfluoroalkyl substances (PFAS) toxicokinetics and application to health-based criteria.” Regul. Toxicol. Pharmacol. 

Project Examples:

PFAS Fate and Transport Assessment at a Municipal Solid Waste Landfill.  To support an administrative hearing regarding a landfill expansion permit, Gradient evaluated potential impacts to groundwater and surface water quality near the landfill.  We compared chemical concentrations in landfill leachate, groundwater monitoring wells, and nearby surface water with regulatory benchmarks.  We used multiple lines of evidence, including an evaluation of the effectiveness of the landfill liner system and temporal evolution of PFAS concentrations in leachate, to estimate the scale of potential surface water impacts if the landfill was expanded.

PFAS Source Evaluation and Forensics.  Gradient conducted site research and evaluated the composition and extent of PFAS present at multiple locations throughout the US.  Our evaluation included a review of PFAS source characteristics, and fate and transport of PFAS from industrial facilities, landfills, and fire training areas to soil, groundwater, surface water, and sediment.  Gradient also evaluated PFAS synthesis process chemistry, compounds associated with specific processes (e.g., ECF and telomerization), and changes in chemical characteristics due to environmental mechanisms to forensically draw conclusions regarding the sources of PFAS being observed in environmental samples.

PFAS Analytical Chemistry.  Gradient wrote a white paper on the history of analytical method development for the analysis of PFAS in environmental and biological matrices.  The goal was to define the data quality standards relevant for different analytical methods, matrices, and time periods.

Evaluation of Dietary Intake of PFOS and Implications for Drinking Water Limits.  In the context of setting drinking water limits, Gradient evaluated the scientific support for the commonly used default assumption of 10 to 20 percent of exposure being attributable to drinking water (referred to as relative source contribution [RSC]).  We assessed the relative intakes of PFOS from various sources and evaluated the implications of alternative RSC values on PFOS drinking water guidelines.  The analysis was presented at a toxicology conference.

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