PFAS regulations and testing recommendations are evolving quickly in the United States. The Environmental Protection Agency (EPA) recently finalized the National Primary Drinking Water Regulation (NPDWR), which sets maximum contaminant levels (MCLs) in the low ng/L (ppt) range for several PFAS compounds. Public water systems must monitor concentrations by 2027 and implement actions to reduce pollution levels by 2029 if the MCLs are exceeded.

When it comes to wastewater and surface water, the EPA recently published Method 1633 (the current version is known as 1633A) for PFAS screening of various environmental matrices, including non-potable water. Following this method is not yet federally mandated, but the agency encourages its use in connection with National Pollutant Discharge Elimination System (NPDES) permits required under the Clean Water Act (CWA).

EPA recommendations are often the main driver for selecting analytical methods for PFAS screening of water samples in the US, especially for regulatory monitoring. However, in cases where following an EPA method is not compulsory, alternative standard methods and in-house methods may give a more comprehensive picture of PFAS contamination, as they often cover a larger set of compounds and can have lower detection limits.

Testing recommendations for drinking water samples

With the introduction of maximum contaminant levels for selected PFAS in drinking water, US-based public drinking water systems must complete initial monitoring of PFAS contamination levels by 2027 and continue with ongoing compliance monitoring after this. Method selection for this purpose is straightforward, as EPA-approved methods (EPA 533 or EPA 537.1) must be used. Both methods are based on solid-phase extraction (SPE) liquid chromatography-tandem mass spectrometry (LC-MS/MS), enabling a reporting limit of approximately 2 ng/L for the compounds subject to monitoring requirements. The scope of target substances is rather limited (18 compounds for Method 537.1 and 25 for Method 533), but this is not an issue, as all compounds for which maximum levels have been set are included in each method.

Organizations wishing to study PFAS levels in drinking water for reasons other than NPDWR compliance may opt for the CEN/TS 15968 standard or in-house methods based on EPA 533 or ISO 21675. The advantage here is a broader set of target substances, with 50 to 60 PFAS compounds often included in extended analysis packages. As in-house methods are typically developed in highly specialized laboratories, it may also be possible to reach a lower detection limit. For example, one of Measurlabs’ partners can measure the concentrations of selected compounds in drinking water with a LOQ of 0.3 ng/L, as compared with the 2 ng/L reporting limit of the official EPA 533 method.

Testing recommendations for wastewater and natural water samples

When PFAS monitoring of wastewater is performed for regulatory purposes, such as obtaining an NPDES permit or monitoring water quality under the CWA, the safest choice is to opt for the EPA 1633 method performed by an accredited laboratory. Although not nationally required as of the time of writing, the EPA recommends using this method and is planning to formally promulgate it through addition to 40 CFR Part 136, which establishes approved test procedures for pollutant analysis.

EPA 1633 covers a relatively extensive scope of 40 target substances with a quantification limit of approximately 1–4 ng/L for most analytes in relatively clean water samples. However, certain target compounds have higher LOQs even in clean samples, and limits tend to be higher across the board for highly contaminated wastewaters.

When an official method is not required, such as in the case of research projects comparing PFAS levels across different bodies of natural water, in-house techniques can again extend the compound scope to around 50–60 PFAS. Laboratories specialized in wastewater analysis can also achieve lower LOQs through optimized in-house workflows. One of Measurlabs’ partner laboratories, for example, has developed a method with a quantification limit of 1–2 ng/l for all 40 PFAS included in Method 1633, plus nine additional compounds.

As a complementary approach to targeted analysis, fluorine analyses can be used to evaluate the overall PFAS contamination level of wastewater and natural water. These can capture the thousands of PFAS compounds not included in targeted analyses, although individual substances are not identified; rather, results are expressed as overall fluorine content, including both PFAS and other fluorine-containing compounds. The most typical approach for water samples is adsorbable organic fluorine (AOF) analysis, where organofluorines are adsorbed to activated carbon and quantified as fluoride using combustion ion chromatography (CIC). The EPA has an official Method 1621 for AOF measurement, but in-house methods are more widely available and produce similarly rigorous results, with quantification limits as low as 0.5 µg/L in some laboratories.