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PFAS Forensics - Identify the Source of PFAS

Elizabeth Denly & Emily Larson | July 1, 2022

With over 9,000 per- and polyfluoroalkyl substances (PFAS) in the environment, source identification and environmental liability are complicated. One of the major challenges of PFAS is the high cost associated with investigations and clean ups. In the determination of responsible parties, forensics and source identification will be necessary to detect the unique PFAS chemical signatures.

Manufactured since the 1940s, these synthetic compounds are used in a variety of industrial, commercial, and consumer products and processes. While aqueous film-forming foam (AFFF) is one of the major sources of some of the largest and most complex PFAS-contaminated sites, there are numerous other sources of PFAS including metal plating, biosolids, textiles, leather and apparel, plastics, paper and packaging, cleaning products, pesticides and personal care products. As a result of its widespread uses and pervasive presence, many PFAS investigations require the use of forensics or chemical signatures to identify sources and fate and transport scenarios.

Understanding Site and Operational History

The first step in our forensics evaluations includes generating an understanding of the potential sources of PFAS at the site of interest and nearby sites. Forensics is not just about chemistry, but also involves looking into operational history and potential nearby sites or sources that may be affecting the site of interest. Understanding the potential types of industries or products that manufacture and use PFAS is an important part of this evaluation.

Industry or Product How PFAS Used
Fire-fighting Foam Surfactant
Metal Plating Mist suppressant, wetting agent
Textiles, Leather & Apparel Waterproof clothing & shoes, stain-resistant carpeting
Plastics Processing aid
Paper & Packaging Water & oil-resistant paper products
Electronics Magnetic tapes, cables, wires, circuit boards, semiconductors
Photography Film, medical diagnostics
Cleaning Products Alkaline cleaners, car wash products, concrete cleaner
Coatings: waxes, paints, inks, varnish Paints, floor coverings, polishes
Pesticides Surfactant, wetting agent
Medicine X-ray films, stents, contact lenses
Personal Care Products Cosmetics, sunscreen, dental floss
Refrigerants Air conditioners, refrigerators
Building & Construction Concrete mixtures, coatings for buildings & roofs
Explosives Infrared tracking flares, warheads
Oil & Gas Industry Enhance recovery in oil wells, hydraulic oils, gasoline
Mining Enhance metal recovery from ores, mist suppressant

The unique chemical signatures from PFAS mixtures provide forensic markers to help determine the source of a PFAS release. The chemical compositions for the paper and food packaging differ from those for textile and leather, which vary from AFFF, metal plating, and wastewater treatment plants and landfills. With a proprietary analyte comparison mapping tool, TRC can help determine the source of PFAS and chemical trends across large spatial areas.
We Understand Signatures

Looking at chemical signatures is a first step in generating information on different sources. The signatures are used to not only identify various characteristics of the source, but also different fate and transport scenarios. For example, we may see the breakdown of PFAS precursors further downstream in a plume or we may see a change in signatures due to co-mingling of more than one source along the length of a plume.

Therefore, PFAS signatures cannot be evaluated in isolation. TRC uses a multiple lines of evidence approach and provides careful consideration to differentiate complex mixtures of PFAS and distinguish sources of PFAS in environmental media. TRC considers the following:

  • Chemical signatures/fingerprints
  • Hydrogeologic data, site operational history, timing of releases, and other site data
  • Unique fate and transport properties of PFAS
  • Transformation products of precursor PFAS
  • Mixing, dilution and comingled plumes
  • Diagnostic ratios that can help distinguish legacy AFFF from modern fluorotelomer AFFF sources, for example (some diagnostic ratios can be indicative of more than one source)

TRC has nationally recognized PFAS experts who understand the various targeted and non-targeted PFAS analyses as well as laboratory procedures which can greatly impact the final reported data. TRC’s experts can help determine the following at your Site:

  • Appropriate PFAS analyses for site-specific conditions and media
    • PFAS target analyses
    • Total oxidizable precursor (TOP) assay
    • Non-targeted PFAS analyses
    • Total organic fluorine analyses
  • Specific PFAS to select for signature evaluation
    • We are beginning to understand more and more when there are specific PFAS that are indicative of a particular product or industry so we can ensure that the selected list of PFAS for analysis is inclusive of these marker compounds
    • Diagnostic ratios can be determined based on the specific list of PFAS included in the analysis
    • The choice of PFAS selected for signature evaluation must be carefully considered
  • Impact of differences in laboratory methodologies from standard operating procedures
  • Effect of PFAS transformation on chemical concentrations/fingerprints
    • A very large group of transformation intermediates can present a challenge to data interpretation
    • We have used TOP Assay to help us determine the ultimate source of AFFF at airport sites because of the transformation properties of some of the different formulations of AFFF
  • Effect of PFAS sorption to solids on chemical concentrations/fingerprints
    • TRC works with our laboratories to ensure that we understand how samples with elevated levels of particulates or high turbidity samples are handled in the laboratory. Because some of the longer-chain PFAS and more so for the sulfonates like PFOS, can adsorb to solids, the resulting PFAS concentrations and fingerprints can greatly vary depending on how the laboratory prepares these samples, ultimately affecting your forensics interpretation.<?li>

What Can TRC Distinguish on your Site?

TRC has worked on numerous PFAS sites where various sources have been identified. When using the various tools discussed above, trends in the PFAS chemical concentrations can be determined, and based on their spatial relationship to the site of concern, can be differentiated as on-site or off-site sources. Furthermore, hot spots can also be identified at a site and their chemical signatures can be compared to various nearby sources. Finally, our evaluations can help determine if additional information and/or samples need to be gathered to further differentiate site sources and fill data gaps.

Let TRC help you navigate PFAS sources, fate and transport and transformation at your site through thoughtful analyses and expert interpretation to minimize your potential liability.

Elizabeth Denly

Elizabeth Denly serves as TRC’s Vice President, PFAS Initiative Leader. She is also the Quality Assurance & Chemistry Director, responsible for the creation and implementation of the Quality Management Plan and standard operating procedures (SOPs) for field sampling and documentation protocols. Ms. Denly also leads Quality Coordinator networks, which are responsible for the development and communication of quality initiatives within the organization. She is a chemist with 29 years of consulting experience encompassing field and laboratory analyses and audits, QA/QC, data validation, and consulting for regulatory agencies.

Ms. Denly is a leader in ITRC’s PFAS and TPH Risk Work Groups and in TRC’s Center of Research & Expertise (CORE) Emerging Contaminants Team and received the ITRC’s Industry Member of the Year Award in 2017. She is currently focusing on PFAS, specifically the nomenclature, chemistry, sampling procedures, QA/QC, and laboratory analytical methodologies, and has a significant role in educating clients, attorneys, and regulators about PFAS.

As a senior QA specialist at TRC, Ms. Denly is responsible for providing QA/QC oversight in support of a variety of environmental investigations and remediation programs including risk-based soil cleanups, ambient air monitoring, and human health and ecological risk assessments. In this role, she has directed the preparation of QAPPs, coordination with the laboratory, selection of the appropriate analytical methodologies to achieve the desired remedial standards, oversight and performance of the data validation process, and determination of the usability of the data and achievement of data objectives. Ms. Denly has provided this oversight under different regulatory programs.
Read more on Ms. Denly’s bio page. Please contact her at

Emily Larson

Emily Larson has more than 10 years of experience modeling the bioaccumulation of semivolatile compounds and metals in ecological systems, modeling exposure to human and ecological receptors, and preparing human health and ecological risk assessments. She has experience conducting risk assessments with emerging contaminants, specifically per-and polyfluoroalkyl substances (PFAS). In addition, she serves as a technical expert on PFAS within the intermountain region for TRC. She has experience with Superfund (CERCLA) as well as several state-led programs specifically in the Inter Mountain West and Pacific Northwest regions. Emily has worked with several clients in both the private and the public (state and federal) sector. She can be reached at

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