Testing for polyfluoroalkyl substances (PFAS) is increasing nationwide as multiple states launch investigations into PFAS contaminated areas. But while a handful of these “forever chemicals” are tested and starting to be regulated, the vast majority are not. Much of the difficulty lies in the testing itself; PFAS constitute an extensive class of mostly unknown compounds and are measured in trace amounts, usually parts per trillion. For the last eight years, scientists have used the TOP assay (total oxidizable precursors assay) to determine total PFAS concentrations in environmental matrices. But according to a study released in 2019, the TOP assay may well be underestimating total PFAS contamination and providing a false sense of assurance.
Historically, PFAS testing targeted only certain compounds with documented adverse health effects. Over the last decade concern has grown about the environmental and health impacts of these ubiquitous but understudied chemicals. Currently, there are an estimated 3,000 to 5,000 PFAS substances most of which are relatively unknown. This lack of information makes testing for individual PFAS impractical. However, knowing the total concentration of PFAS in a sample can be useful; the total PFAS amount may illustrate where high concentrations are found, how PFAS infiltrate food systems, and possible points of contamination.
The TOP assay was developed in an attempt to close the data gap of unknown PFAS by assessing total PFAS contamination. The method utilizes oxidization to indirectly measure unknown PFAS that exist in the environment. These unknown PFAS compounds, called “precursors,” naturally degrade into perfluoroalkyl acids (PFAA) over time. The TOP assay accelerates this process using heat and chemical oxidation to convert unknown PFAS into PFAAs. These final products, known as “terminal products”, are subsequently measured using conventional LC-MS/MS techniques. While this process theoretically detects total PFAS levels, a 2019 study discovered that the TOP assay missed an entire subclass of terminal products, PFEAs (per- and polyfluoroalkyl ether acids). When estimating the total PFAS amount, the assay did not include any PFAS precursors to the PFEA subclass. For any sample containing PFEAs, the true amount of PFAS present may be significantly higher than previously thought. While PFEAs can be added to the TOP assay to improve future testing, the study revealed a fundamental flaw in the testing method. The assay can underestimate the true extent of PFAS contamination and provide an inaccurate risk evaluation.
Most labs and research facilities use the TOP assay as the tried and true approach to total PFAS testing despite the possibly inaccurate risk assessment. The oxidation process takes 6-8 hours but is inexpensive and requires no additional PFAS testing equipment. Because the test relies on pre- and post-oxidation analysis via LC/MS/MS it can theoretically measure trace amounts of PFAS in liquid and solid matrices.
Over the last few years, research labs have developed a new approach to evaluating potential PFAS contamination by looking for Total Organic Fluorine (TOF). Using Adsorbable Organic Fluorine (AOF) and Extractable Organic Fluorine (EOF) procedures, whole liquid and solid samples are combusted to convert all available organic fluorine to fluoride. Ion chromatography is subsequently used to measure the fluoride levels to then determine the total PFAS concentration. The TOF provides chemists with a more precise method for detecting all PFAS compounds in a given sample. Especially for substances with high interferences such as landfill leachate or wastewater, TOF has been demonstrated to more accurately provide total PFAS present than the TOP assay. Unfortunately, one drawback of the TOF is that it lacks the sensitivity to provide detections down to the part per trillion, which limits its potential use to more highly contaminated sites.
Most commercial labs do not yet provide TOF analysis due to the lack of an approved method and the substantial upfront investment in new instrumentation lacking established long-term maintenance costs and reliability. The extraction and combustion processes also present unique challenges that many labs lack the training or expertise to address.
Although TOF may prove itself more useful for total PFAS testing, the method requires further research and validation before regulatory agencies like the EPA can endorse it. Additional research into the toxicity of PFAS as a class is also needed. While some PFAS, such as PFOA, are well-documented toxins, a large majority have not been studied for toxicity effects. Within the PFAS that have been studied for toxicity, a wide range of toxicity exists making it difficult to set any type of single limit on PFAS as a class. Because lawmakers lack toxicological information about PFAs, many states have different PFAS notification and response levels and are frequently changing as ongoing research informs us. Certain agencies like the EPA and California Water Board prioritize testing for compounds with known toxicological effects rather than analyzing contaminants as a class. With the legislative and public furor over PFAS, changes to that approach may be coming soon. As states continue to investigate PFAS contamination, some policy and scientific minds predict PFAS will be regulated as a class instead of as individual compounds. TOF testing may offer a practical and accurate method to support such PFAS regulations but before any of that is possible, lawmakers and policy makers need more research concerning the health hazards PFAS pose as a class. And environmental labs need access to widely validated methods and affordable instrumentation.
Babcock Labs prioritizes the sharing of timely topics to ensure our clients have access to all the latest on PFAS research and industry developments. As a DoD, OR ELAP, and CA ELAP certified lab, Babcock is an industry leader for PFAS analysis. For more information about PFAS testing, contact Babcock labs.