PFAS Sampling & Analysis Pre-Method 1633
Over the past few years, the tools available to assess and address the PFAS challenge have advanced at a rapid pace. Less than 3 years ago (prior to August 2021), the U. S. Environmental Protection Agency (EPA) had not yet published a method for PFAS in environmental samples such as groundwater and soils. Up to that time, analyzing such samples for PFAS often carried a “wild west” analogy, with each laboratory developing and implementing its own specialized PFAS analytical methods; the convention of naming these ad hoc methods after the EPA’s drinking water methods (e. g., “537Mod”) further added to the confusion. Confidence in PFAS data was closely tied to trust in the laboratory, even as the laboratories were forced to develop methods independently and with unclear expectations for analyte lists or detection limits. When looking back at that time, and the experiences of writing work plans and preparing sampling events beneath the aura of uncertainty, we (collectively) do not reminisce fondly.
In January 2024, a milestone was reached; the EPA finalized the analytical method for environmental samples (Method 1633). This article provides an overview of the recent advancements in PFAS analytical methods, including Method 1633, and other recent methods developed to address PFAS in multiple matrices, such as on plastics and in the air.
Method 1633: PFAS Sampling & Analysis
The EPA provided the long-awaited analytical method, Method 1633, in draft form in August 2021. Since that time, the EPA has provided several updates, as Method 1633 advanced through the evaluation/validation process. In January 2024, the final multi-laboratory validation steps were completed, and the “draft” status was removed from Method 1633. In terms of PFAS sample matrices, Method 1633 includes the following: groundwater, surface water, wastewater, landfill leachate, soils, sediments, biosolids, and biological tissue. The finalized Method 1633 includes 40 PFAS analytes and may achieve detection limits below 1 nanogram per liter (ng/L) for aqueous samples or below 0. 1 microgram per kilogram (μg/kg) for solids.
Where does Method 1633 fit in among the other U. S. EPA PFAS methods? Two U. S. EPA methods, Method 533 and Method 537. 1, are for drinking water. Method 8327 (finalized July 2021) is intended for environmental aqueous matrices but is generally considered a screening-level method (8327 utilizes direct injection rather than solid phase extraction and does not include isotope dilution). Analyte lists for EPA Methods 533, 537. 1, and 8327 are 25, 18, and 24 constituents, respectively.
The EPA notes that Method 1633 is not yet required for Clean Water Act compliance monitoring, pending its promulgation through rulemaking via 40 CFR Part 136.
Method 1621: Adsorbable Organic Fluorine
Method 1621 applies to aqueous matrices and provides a single result, nominally representing “total PFAS” Adsorbable organic fluorine (AOF) refers to the fact that the method is selective for organic constituents that sorb to granular activated carbon (GAC). The method involves passing the water sample through a GAC column, combustion of the GAC to mineralize organic constituents, adsorption of gaseous fluoride in reagent water, and analysis of the reagent water for free fluoride via ion chromatography (IC).
A key advantage of the method is that it provides data for all PFAS constituents, beyond the 40 included in EPA Method 1633 (with the potential limitation being those PFAS that do not sorb to GAC). However, the method is not selective for PFAS and may also quantify organic fluorine associated with non-PFAS constituents (e. g., fluorocarbons, pharmaceuticals). This is a relatively new method for which large datasets are not yet publicly available; more widespread data collection will assist with understanding and interpreting results. Unlike other methods quantifying individual constituents for comparisons to regulatory limits, Method 1621 yields AOF estimates for which there are no EPA standards.
Plastics: Quantitative Extraction and Analysis of PFAS from Plastic Container Walls with Cut Coupons
In February 2024, the U. S. EPA published a method for analysis of fluorinated plastic containers.
High-density polyethylene (HDPE) containers have been treated with a fluorination process to improve barrier properties and increase resistance to chemical permeation. Although the fluorination process does not directly involve PFAS, the application of fluorine to plastic materials has been observed to create PFAS; subsequently, the PFAS may contaminate the liquids added to the container.
The method involves methanol extraction of PFAS from cut pieces of plastic containers (“coupons”) and subsequent analysis via LC/MS/MS. The analysis includes 32 PFAS and detection limits as low as 2 parts per trillion (nanograms of analyte per kilogram gram of the container). At this time, no specific rules or regulations have been established for PFAS associated with fluorinated HDPE plastic containers.
OTM 50: PFAS in Air
OTM-50 is a draft method for volatile fluorinated compounds (VFCs) released by the EPA in January 2024. While not officially promulgated, the release of OTM-50 reflects EPA’s endorsement of current best practices and promotes consistency in sampling and analyzing VFCs from stationary sources. This draft method is also anticipated to aid in implementing the forthcoming update to the EPA’s PFAS destruction and disposal guidance, as it will enhance understanding of PFAS products produced by incomplete incineration and destruction. Moreover, the release of this draft method signifies a significant step toward regulating PFAS in air emissions as it will streamline data collection and allow for test method refinement.
The draft method reports 30 target VFCs and emphasizes performance-based techniques for reliable data collection and analysis. Also noteworthy, some VFCs included in OTM 50 do not meet standard definitions for PFAS (e. g., fluorocarbons such as carbon tetrafluoride). VFCs may be generated by multiple sources, one of which is the incomplete combustion of PFAS.
Another consideration for OTM-50 is that the method involves the removal of particulate matter, thus providing data limited to volatile (air-phase) VFCs. In terms of total emission monitoring, this may lead to underestimation of PFAS released from sources. Despite an overlap in their application, the EPA doesn’t propose combining OTM-50 with OTM-45, which targets semi-volatile polar PFAS in air emissions, citing minor technical incompatibilities.
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