Environmental professionals are familiar with this story: A new or newly applied substance is found to be the answer to a host of problems. It gets used in a host of applications. Then, new information is discovered – the substance is found to be harmful for human health, the environment or both. So, its use is regulated or banned. Then the hard work begins – investigating and remediating locations where the substance is found.
This story has been played out with a starring role for asbestos, lead, PCBs, chlorinated solvents – and now the class of compounds called Per-and Polyfluoroalkyl Substances, collectively known as PFAS.
PFAS were first developed in the 1940s and have been incorporated into many industrial processes and a wide range of products such non-stick cookware, paints, carpets, firefighting foam, and many others. Some PFAS
have now been linked to cancer, thyroid hormone disruption, damage to the liver, low birth weights and other health issues.
Now, the push is on to clean up sites where PFAS are found. Several aspects of PFAS make them a particularly challenging puzzle for environmental professionals to unlock:
- Many compounds: Due to the many applications and their long history, thousands of PFAS have been developed. Each of them has its own chemical and physical properties that affect its distribution in the environment, half-life and toxicity.
- Many dispersal patterns: Multiple uses of PFAS and different properties between compounds also mean multiple ways that the substances can be released to the environment. Firefighting foams may impact soil and flow down into the groundwater or into surface water; industrial use may lead to leaks, spills or discharges to air or water; PFAS from household products such as frying pans, breathable waterproof apparel and carpets may end up in landfill leachate.
- Widely spread: PFAS may be spread far from their point of origin by water, sediment or wind transport, due to their persistence in the environment.
- Noisy background: Because of their wide use, long-range atmospheric transport and very low laboratory detection limits, just about any location can have measurable background concentrations of PFAS. Those effects must be separated from those of the PFAS that are specific to the site being investigated.
These issues mean that the techniques often used to understand the impacts of more conventional products such as PCBs may not work with PFAS, especially when dealing with multiple sources and transport mechanisms. Accordingly, we have developed a practical, scalable and customisable approach for unlocking the PFAS puzzle.
Why multiple lines of evidence are needed for PFAS
Our methodology takes a multiple lines of evidence (MLE) approach. This approach uses different types of investigation to determine a causal relationship between observed impacts and to develop a site conceptual model. If the evidence from these different investigations converges, it confirms that the findings are robust and accurate. Many of these techniques rely on data typically collected as part of regular PFAS investigations and therefore do not require extra costs.
Our MLE process, as applied to PFAS impacts, involves four main steps:
1. Analyse PFAS types on the site
Even though PFAS are widely spread in the environment, they often have different composition and release mechanisms, depending on the source. We use this knowledge to study the relative concentrations of various PFAS in soil, sediment and water samples, as needed, taken from various parts of the site. This includes examining the PFAS concentrations in the source zones, and whether the composition changes as the compounds move along the primary flow paths, such as through an aquifer.
Many site investigators will focus only on the few PFAS that are regulated, but there is precious information that can be gained for this type of assessment from the other PFAS analysed at no extra cost.
The full PFAS dataset helps us “fingerprint” PFAS as a preliminary step towards determining their origin or source. This approach also assists with understanding transport mechanisms and obtaining early warnings on their migration towards potential receptors.
In very specific cases, when the analysis of the typical PFAS suite is insufficient to obtain good fingerprints, we rely on non-target analysis to screen the samples for a larger number of PFAS and differentiate sources.
2. Determine the total PFAS mass on the site
One of the challenges of PFAS analysis is that while thousands of PFAS have been developed, current commercial laboratory techniques are only able to test for a limited number of compounds. The rest are, in effect, a black box.
One of the strengths of the MLE approach is that we can turn to other methods for clues about what’s inside that black box.
We do this by assessing the total PFAS mass using semi-quantitative methods like Total Oxidizable Precursor (TOP) assay or more quantitative methods like Total Organo-Fluorine (TOF) analysis, which point to the size of the contamination issue and help plan the remediation. By analysing the PFAS signature of the TOP assay results we can also gain insights about the presence of specific PFAS precursors, making this a valuable line of evidence for characterization of PFAS impacts and fingerprinting.
3. Understand composition of branched and linear PFAS isomers
Some PFAS have more than one chemical structure. In some variants they can be a linear molecule, while others may have a branched molecule, perhaps resembling a letter “L” or “T”. It’s the same compound, but each variant has different properties and behaviour. Chromatograms generated during PFAS analysis help us determine the branched versus linear ratio for certain PFAS. This line of evidence further helps us distinguish sources and, in some cases, identify when and by which manufacturing process those PFAS were produced.
4. Understand the chemistry of the site as a whole
Our fourth line of evidence is to characterize the overall chemistry of the soil and groundwater on the site, as it often gives us insights into how the PFAS will behave. We analyse field parameters like pH, specific conductivity, temperature, dissolved oxygen, as well as any co-contaminants that are present.
Just as a detective does not always use all the analytical tools at their disposal, we do not use all these four elements in every PFAS investigation. However, this toolbox helps us come to better grips with understanding and distinguishing PFAS sources, and the behaviour of PFAS in the environment. The MLE approach also gives us reliable data to help design effective remedial strategies.
ABOUT THE AUTHOR
Stefano Marconetto is a Senior Principal Environmental Engineer and Emerging Contaminants Practice Lead based in Ottawa, Canada with almost 20 years of experience in contaminated sites investigation and remediation, and over 10 years of experience with PFAS on projects as well as research and development across North America and overseas. Stefano’s PFAS focus is on strategic advisory services and project technical direction. He has experience with sites portfolio screening and PFAS liability management, detailed site characterization, risk assessment and remediation. He has given lectures and authored guidance documents on PFAS, provided technical training as well as support to clients at hearings and in their liaison with project stakeholders on PFAS related issues.
