PFAS environmental investigations: how to decide on PFAS analysis and/or analytes

The unique challenges of PFAS

PFAS present unique challenges when investigating their presence in the environment (soil, groundwater, surface water, etc.).

For other common contaminants, the presence of environmental impacts can be determined well before samples are submitted to a laboratory for analysis. For example, petroleum-impacted soil near the phreatic (groundwater) surface is typically stained a greyish color and will present strong odors, while groundwater may have a sheen present; chlorinated solvents can be observed either by odors or via field screening with a photoionization detector (PID); and metals-impacted soil can be field-screened with an x-ray fluorescence (XRF) spectrometer to estimate metals concentrations prior to laboratory analysis.

PFAS impacts, however, are not typically evident by field observations and currently there are no readily available technologies for screening samples in the field. Laboratory analysis is relied on to determine the presence or absence of PFAS and to subsequently make decisions regarding risk communications and remedial options.

There are also analytical challenges associated with PFAS including, but not limited to:

Other analytical challenges include how to select a laboratory method and which PFAS or isomers to analyze for an initial investigation.

PFAS regulatory status

The US Environmental Protection Agency (USEPA) has established a proposed drinking water standard for six PFAS, but no enforceable federal groundwater or soil standards yet exist for any PFAS. As part of their PFAS Strategic Roadmap, USEPA intends to finalize a maximum contaminant level (MCL) for drinking water by the end of 2023.

Given the absence of federal PFAS threshold values, many states in the US have opted to set their own regulatory thresholds for drinking water, groundwater, soil and surface water and the current regulatory thresholds for certain PFAS widely range from 3 ppt to 667,000 ppt in different states for various PFAS substances. The most common PFAS that are regulated include PFOA, PFOS, PFBS, PFBA, PFNA, PFHxS, PFHpA, PFDA, and HFPO-DA (GenX).

Summary of current laboratory methods

USEPA has developed various analytical techniques for quantitating PFAS in drinking water, groundwater, wastewater, surface water, soils, sediments, biota, and biosolids. The analytical techniques for PFAS can be separated into three broad groups:

In 2022, on behalf of the Norwegian Environment Agency, Ramboll, collected and compiled information available for analytical methods for PFAS in products and the environment (see norden.org). The report gave insights into established analytical methods available for the primary matrices in commercial and consumer products, and environmental matrices, along with cost considerations.

Targeted analyses

Targeted methods are well-established methods to quantitate specific target PFAS in various matrices. Targeted methods can use liquid chromatography (LC), coupled with several different types of mass spectrometry (MS) to quantitatively measure PFAS concentrations.

Targeted analysis can accurately quantify individual PFAS, and most methods have a target quantitation limit typically in the range of 1-10 ppt for drinking water, groundwater, wastewater, surface water, soils, sediments, biota, and biosolids.

However, this analytical technique requires laboratories to obtain isotopically labeled analytical standards for each compound of interest, and is therefore limited to quantifying only the PFAS specific to that method. Targeted analysis does not provide an indication of other PFAS that may exist in the sampled media.

A summary of the most common commercially available targeted PFAS analyses is provided in Tables 1 and 2, and below.

USEPA method 537.1: The most common method currently used to quantitate PFAS in drinking water. USEPA method 537, published in 2009 to quantify 14 PFAS analytes, was updated to 537.1 in 2018 to include 18 target PFAS analytes (Table 1) in drinking water only.

USEPA method 537.1 modified (sometimes also referred to as USEPA method 537 modified): A modification of USEPA method 537.1 by the commercial laboratories for the quantification of at least 18, but up to 36, targeted PFAS analytes for all matrices (other than drinking water) provided in Tables 1 and 2. It uses an isotope dilution technique that involves quantitation of targeted PFAS using a labeled isotope of the compound.

USEPA method 533: Published in 2018, this method focuses on determination of PFAS with a chain of fewer than twelve carbon atoms, in drinking water matrices only. It has a target analyte list of 25 PFAS, including 14 of the 18 listed in USEPA method 537.1, with more short chain PFAS (Table 2).

USEPA method 8327: Published in 2019 to quantitate 24 PFAS (16 PFAAs and eight other PFAS) in non-drinking water matrices, this method expands the analyte list with the addition of 10 different analytes in the list compared to USEPA method 537.1. However, it does not include four analytes that are on the method 537.1 list (Table 2). This method uses external standard calibration instead of isotope dilution calibration to quantify the analytes, with resulting elevated quantitation limits, and is rarely used by commercial laboratories.

Draft USEPA method 1633: This is the newly proposed analytical method for quantification of 40 target PFAS analytes in eight different media (wastewater, surface water, groundwater, soil, biosolids, sediments, landfill, and biota). Currently in its fourth draft, final publication is anticipated later in 2023. Many laboratories are participating in the validation of this method and are already approved to start using it. This draft method quantifies 40 PFAS across a wide range of solid and aqueous matrices and can be used by laboratories, regulatory authorities, and interested parties with the understanding that it is subject to revision.

Isomer analysis

Isomers of certain PFAS can be present in the environment in linear or branched forms, with an example shown in Figure 1 below.

When analyzing a sample (using all the USEPA methods described above), unless directed otherwise, laboratories will report only the total sum of a PFAS compound including all isomers. For example, the linear and branched PFOA would be integrated as a single compound to quantify the total concentration of PFOA.

However, for certain laboratories, it is possible to request that the laboratory report-out the estimated concentrations of each isomer. For this analysis, the laboratory uses a quantitative or qualitative reference standard containing mixtures of available linear and branched isomers and compares the instrument response from the reference standard against the response from suspected isomers in the samples. This analysis can be especially useful for forensics purposes when seeking to determine unique signatures from a given potential source of contamination.

Non-targeted PFAS analyses

A summary of two common commercially available non-targeted PFAS analyses is provided below.

Total organic fluorine (TOF) analysis quantifies the concentration of total organic fluorine in a sample and may be used as a surrogate for total PFAS present (including non-targeted PFAS compounds). It should be noted that this method also detects organic fluorine in other organic compounds (such as pharmaceuticals and herbicides), so the TOF results cannot necessarily be interpreted to equal the total PFAS concentration. However, this method can be used as a screening technique to identify whether the sample contains any organic fluorine or not (i.e., if no organic fluorine is detected, then by default, no PFAS is present at levels detectable by the analysis).

This method involves the removal of inorganic fluorine during sample preparation, followed by the use of combustion ion chromatography (CIC) to measure the total fluorine content of a sample, including non-target precursors, other complex PFAS, or fluorine from any organic compound.

TOF does not identify nor quantify individual PFAS, nor does it provide information about the compound that originally contained the fluorine being measured.

USEPA is in the process of adopting standardized analytical procedures for TOF in the draft USEPA method 1621, with the third draft released in December 2022. The procedure has completed the single laboratory validation and is currently under the process of multi-laboratory validation.

Total oxidizable precursors (TOP) are measured in the “TOP assay” analysis, which estimates the PFAS precursor content of a sample by converting non-target compounds to quantifiable compounds using a thermal hydroxyl radical oxidation process.

Through the TOP assay process, precursors (such as a non-target sulfonamido compound) are degraded to target PFAS end products (such as PFOA). TOP assay results can provide an indication of the total mass of PFAS present in a sample and can be useful when considering plume and source area behavior over time.

TOP assay requires the quantification of PFAS in a sample prior to and following the TOP assay digestion so that the difference in quantifiable PFAS mass can be estimated and is therefore a relatively expensive test.

How to select the right PFAS analysis for your project

For drinking water, USEPA method 537.1 is the only USEPA approved method and most, if not all, regulators require this method for drinking water.

For other non-drinking water environmental media (soil, groundwater, etc.), in many cases, the decision is not quite as simple. Based on Ramboll’s experience, the most common analysis currently used in the US is USEPA method 537.1 (modified), however it is likely that USEPA method 1633 will become the default method as soon as it is finalized by the USEPA.

The TOP assay and TOF method are typically only utilized if required by a regulator, or to further characterize the nature and extent of PFAS on sites that have already had an initial investigation completed.

USEPA method 8327 is generally not used by commercial laboratories for PFAS due to the high detection limits.

In some cases, regulators require a specific method to be utilized, so before proceeding with analysis, verify if any local requirements are applicable. For example, New York state requires using draft USEPA method 1633 to analyze PFAS in all non-drinking water environmental media. However, given that USEPA method 1633 is still in draft, it is likely that other regulators may not want to see this method utilized until it is finalized.

In some cases, the cost of analysis may also be a consideration in method selection, given that the cost of PFAS analysis is higher than most other contaminants. The cost of analyzing samples for targeted PFAS is expensive because it requires an intensive extraction process, reference standards and isotopes. To put this into context, below is a summary of the range of costs that were provided to Ramboll by three well-known laboratories in the US: Eurofins Scientific, SGS Analytics and Pace Analytical Services.

If desired, when running one of the targeted analyses above, the laboratory can report out fewer analytes than their full list. For example, if only a few PFAS are regulated in a particular state, it is possible to request that the laboratory only report the results for those regulated compounds, if this would be useful for decision-making purposes. In many cases, this results in lower analytical costs as the use of isotopically labeled standards is reduced and instrument time decreases. If it is later desired to know the concentrations of the other analytes and if all of the performance criteria for the additional compounds were met, the laboratory can typically provide data for the full list, potentially for a small fee.

Ramboll’s experience

The decision to sample for PFAS can often be complicated, given the evolving status of PFAS regulations at the state and federal levels, and the evolving applicable threshold concentrations. In our experience, it is common to address PFAS sampling differently depending on varying factors including, but not limited to:

Ramboll was tasked with assessing the potential for a source of PFAS to exist at an industrial site located close to a public drinking water supply well with PFAS impacts that were below the applicable drinking water regulations.

Ramboll designed an investigation to collect representative groundwater samples for PFAS analysis around the perimeter of the industrial facility. In this situation, only the six PFAS currently regulated by the state were analyzed by the laboratory, utilizing USEPA method 537.1 (modified).

The strategy was to focus only on regulated compounds and to not analyze for the other compounds as those data were not considered useful at the time for decision-making purposes.

Based on the results of sampling, the PFAS data demonstrated to regulators that the site was not the source of PFAS related to the public drinking water supply well.

For a different industrial site also located close a public drinking water supply well with elevated PFAS contamination above the applicable drinking water regulations, Ramboll was tasked with investigating potential sources of PFAS and the nature and extent of contamination.

Ramboll designed an investigation to collect representative soil/groundwater samples for PFAS analysis. A total of 18 PFAS were analyzed by the laboratory, utilizing USEPA method 537.1 (modified). In addition, we requested that the laboratory provide concentrations for PFOA isomers (both linear and branched).

Through the analytical data collected, the following conclusions were made which significantly reduced our client’s responsibility for additional investigation/remediation:

Final recommendations

Before collecting PFAS samples, significant thought should be put into how the samples will be collected and analyzed, as the analytical strategy is a key component in determining the nature and extent of PFAS.

Factors that should be taken into consideration include the environmental setting, the presence or absence of nearby sensitive receptors, the regulatory setting, cost of analysis, and the risk tolerance of the party conducting the work.

Typically, a phased approach makes strategic sense where the first round of data collection involves a narrow scope of work and, depending on the results, further testing is performed.

It is also recommended that, in certain cases, legal counsel be consulted to develop a strategy before proceeding with PFAS sampling.

In summary, environmental investigation of sites for PFAS can be challenging and expensive, making the selection of analytical methodology as part of the early strategic planning phase critical.