NIST works to improve confidence in measurements and conducts research on PFAS for better human health and the environment.
Perfluorinated and polyfluorinated alkyl substances (PFAS) constitute a family of compounds that are distinguished by partial or complete fluorination of alkyl hydrocarbons. Dubbed “forever chemicals”, the unique chemistry of PFAS imparts a high level of stability, making the compounds resistant to decomposition in the environment. After the development of the first PFAS in the 1950s, chemists soon realized that the remarkable properties of PFAS made the compounds well suited for a wide variety of applications that have included non-stick coatings, stain and water repellents, fire-fighting foams, and surfactants used in industrial processes (e.g., the pulp and paper production). As commercial production of PFAS increased over time, studies in the late 1990s and early 2000s revealed the global presence of PFAS in environmental samples, wildlife, and humans. Toxicological studies have indicated that exposure to certain PFAS may be detrimental to the immune system, as well as thyroid, liver, kidney, and reproductive organs in humans. In 2022, the EPA recommended drinking water limits for selected PFAS at parts per quadrillion levels (roughly equivalent to a drop of water in an Olympic-sized swimming pool). Over 14700 individual compounds have been categorized as PFAS by the EPA [https://www.epa.gov/pfas], and the analysis of complex samples represents a daunting challenge that is exacerbated by the limits of analytical instrumentation, the lack of analytical standards, and the pervasive presence of PFAS contaminants in the laboratory environment.
PFAS encompass a huge number of diverse chemicals. Identifying and measuring such a wide array of chemicals is a major challenge. NIST tools including reference materials and databases to assist the measurement community in harmonizing PFAS measurements. Because of NIST's deep measurement capabilities, NIST also tackles complex questions arising from PFAS contamination.
For these reasons, researchers at NIST have been developing reference materials and data resources that can be used to increase confidence in PFAS measurements, including the targeted, quantitative measurement and the nontargeted, qualitative identification of PFAS in human and environmental matrices.
Currently, NIST provides eleven reference materials that have measured amounts of PFAS, for the list visit NIST SRM Website. Additional reference materials for unique matrices, like drinking water and technical solutions, are in development.
NIST has advanced PFAS metrology in four key program areas: (1) development of novel analytical methods to eliminate interferences and provide improved measurement accuracy and reliability, (2) production of a suite of PFAS reference materials for use in calibration and as controls, (3) identification of temporal trends of PFAS in the marine environment, and (4) creation of a PFAS database with over 2000 chemical structures to support accurate identification of individual PFAS in samples.
Measurement Science: The metrology of PFAS represents a formidable challenge due to extreme sample complexity and requirements for detection at infinitesimal levels. Because fluorinated polymers are ubiquitous in laboratory environments, background interferences must also be considered in the determination of PFAS in samples. The team worked with industry to identify laboratory sources of PFAS and to minimize contamination during sample preparation, and they refined methods to provide enhanced recovery of PFAS with greatly improved sensitivity and selectivity. This was especially challenging since there were no reference materials available during early method development to validate methods for PFAS. These improvements in PFAS sample cleanup are now incorporated into EPA and FDA standard methods.
Reference Materials: NIST recognized a critical need for certified reference materials (CRMs) to support the PFAS measurement community. Due to the complexity of the measurement challenges posed by PFAS, a series of reference materials were targeted to represent a broad range of sample types that included human blood, fish, firefighting foam, lake sediment, house dust, food, and sewage sludge. The first reference materials were value-assigned in collaboration with CDC. NISTalso has worked to develop new reference materials specifically for PFAS measurements. Two such solution-based calibrant Reference Materials (RMs) have been issued, and four additional RMs based on firefighting foams are currently being added to the SRM catalog. As additional PFAS reference standards have become commercially available, NIST has increased the number of value assigned PFAS in NIST reference materials from 15 PFAS initially to currently over 50 individual PFAS, also establishing measurement capability for volatile PFAS.
Environmental Studies: NIST collaborated with the New York State Department of Health and 3M to establish PFAS measurement capabilities and apply the methods to NIST-archived marine samples. The measurements in time series samples showed temporal trends of PFAS in marine organisms from the East Coast and the US Arctic. The time series data were used by industry to show that elimination of certain PFAS from production corresponded to declines in East Coast marine mammals and by the Arctic Council (an intergovernmental, 8 nation forum) to show that global increases in overall PFAS production resulted in increasing concentrations in Arctic marine organisms.
Data Science: Recent advances in analytical instrumentation permit collection of vast quantities of data during an analysis that can enable the identification of thousands of compounds in a sample without initially specifying the compounds of interest (referred to as “non-targeted analysis” or “NTA”). In collaboration with the DOD and the EPA, NIST developed a database of individual PFAS compounds for use with NTA. The database contains over 2000 chemical structures and facilitates the most accurate identification of most PFAS potentially present in a sample. This database, while new, is already being embraced nationally and internationally as a tool for understanding PFAS sources in the environment.
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