PFAS Monitoring: Novel Approaches for Air and Water Detection

As the extent of PFAS contamination becomes clearer, Sarit Kaserzon looks at the application of new technologies in revolutionising how we monitor these persistent chemicals

MONITORING of per- and polyfluoroalkyl substances (PFAS) in environmental systems requires approaches that can detect their presence and concentrations to determine risk and prevent human and environmental harm.

A unique feature of PFAS is their amphipathic nature, as they contain both water-attracting and water-repelling properties, allowing them to move easily through both water and air.

As these chemicals continue to infiltrate the environment on a large scale, monitoring methods capable of testing both air and water are needed for accurate PFAS detection. Reflecting this growing need, the global PFAS testing market is projected to expand from US$335.9m in 2023 to US$893.2m by 2034.

Measuring PFAS in water

Testing PFAS in drinking water, surface water, and ground waters helps to identify the PFAS type and the extent of contamination. The comparison of PFAS water levels with health-based guideline values are then made to determine whether action is required to protect human and/or ecological health. The US Environmental Protection Agency (EPA), for example, has set enforceable maximum contaminant levels (MCLs) of 4 parts per trillion for PFOA and PFOS, individually.

To test PFAS in water systems, traditional methods involve the collection of water in a “grab” sampling bottle and analysis using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for detection and measurement of target PFAS of concern (US EPA Method 1633, Method 533, Methods 537/537.1). Differences between the methods are designed to increase performance for certain attributes. For example, emphasis on detection of some shorter-chain PFAS (in method 533) or longer-chain PFAS (in method 573.1).

Typical PFAS analysis method detection limits range from 0.0005–0.10 µg/L (parts per billion) but it will depend on the background impurity levels, amount of water concentrated to produce the final sample for testing, and capabilities of the instruments used. To detect trace levels of PFAS, it is often necessary to extract the chemicals from the water sample using the solid phase extraction (SPE) method. This process ensures more accurate and sensitive detection of PFAS at low concentrations. For samples with significant co-pollutants, the SPE can be used in combination with clean-up procedures (such as the use of specific sorbent phases that remove organic interferences and/or washing with solvents) to improve detection in a sample. This technique can be scaled up to increase the volume of water use and improve limits of detection.

Sampling methodologies and their impact

The representativeness of a single-point-in-time water sample (grab sample) from a natural water body can be uncertain, especially if PFAS concentrations vary over time. This presents challenges in assessing ecological and human risk. If samples are collected during a peak concentration event, or alternatively, during a dilution episode following heavy rain, the resulting concentrations may be over- or under-representative of the risk. To address this, techniques that sample PFAS in-situ have evolved into what are called passive samplers.

Benefits of ‘passively’ sampling PFAS

Passive sampler technologies have evolved from early designs focused on non-polar persistent organic pollutants to now addressing more polar, persistent, and mobile substances like pesticides and pharmaceuticals. Their application in PFAS monitoring is relatively new but has quickly proven to be an effective tool. Modern PFAS passive samplers typically use sorbent phases with a high affinity for PFAS, paired with housing materials that are strategically designed (see Figure 1). These designs are optimised to either achieve rapid equilibrium (for equilibrium sampling) or support slower, time-integrative accumulation (for kinetic sampling), depending on the sampling goals.

Passive sampling techniques provide several key benefits for environmental monitoring. They can be deployed for extended periods – from days to months – without the need for a power supply, making them ideal for remote or challenging locations. Their compact design allows for use in difficult terrain and surface water environments. By accumulating PFAS in situ, they deliver time-weighted average water concentration estimates.

In particular, the ability to adjust sorbent phases in passive sampling devices for PFAS selectivity is extremely advantageous as this allows for adjustment of the sampling regime to target select PFAS chemical groups, including anionic, cationic, and neutral PFAS species as well as future PFAS of concern. An example is the ability of some passive samplers to measure PFAS with >10 carbon chains that are not easily extracted from water using traditional grab water sample methods. Another is their capacity to measure ultra-short chain PFAS (with carbon chains of < 3), that are produced as breakdown or transformation products of longer chain PFAS precursors. The widespread occurrence of ultra-short chain PFAS, such as trifluoroacetic acid (TFA), is prompting concern globally due to their mobility and widespread distribution. However, their measurements can be challenging due to background levels being present in blank samples. Therefore, robust methods for reliable measuring TFA in water and air are paramount.