Regulatory interest in per- and polyfluoroalkyl substances (PFAS) continues to expand at the state and federal levels. Many of the proposed and enacted regulations include monitoring requirements that will greatly increase the number of samples being collected for PFAS analysis. Promulgation of drinking water and discharge standards and hazardous substance designations will further increase demand on laboratories for PFAS analytical capacity (87 Fed. Reg. 54415; 88 Fed. Reg. 18638; 88 Fed. Reg. 22399). PFAS analytical methods are still being developed, are not yet available for all environmental matrices, and require different instrumentation than commonly used for other organic compounds. Current PFAS analytical demand is overwhelming existing laboratory capacity, and the PFAS analytical demand will continue to increase. As a result, environmental testing laboratories are rushing into this market to support the need and bolster business growth. Unfortunately, not all laboratories have the experience and expertise to accurately and precisely analyze these samples with sufficient quality to meet regulatory requirements. In response, it will be critical for CERCLA project teams to develop appropriate data quality objectives, and for project chemists to work closely with analytical laboratories to ensure these objectives are met.
PFAS analyses represent one of the most challenging analytical problems for commercial laboratories in many years. PFAS are ubiquitous in the laboratory environment and within the instruments themselves. To eliminate the potential for laboratory-introduced contamination, laboratories must set up dedicated sample handling areas, sample preparation and analysis laboratories, equipment, and instruments free of PFAS-containing materials.
For decades, the basic analytical approach for organic chemicals like PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls), and many pesticides has been to extract a sample with solvent and inject a small volume of the extract into a gas chromatograph (GC). Chemicals are separated by volatility as the temperature of the column increases. Detectors range from flame ionization-based, which essentially measures everything passing through the column, to more advanced detectors like mass spectroscopy that fragment the compounds to acquire mass and structure information to confirm compound identification. While the solvent, column packing, temperature profile, and detectors may differ depending on the target compounds, the instruments and skills required to run the analyses are similar and transferrable. With decades of experience and technical refinements, challenges related to instrument tuning, matrix effects, and common interferences are well understood, and commercial laboratories are well stocked with GC equipment and experienced staff to perform the standard organic chemistry analyses.
Because many PFAS are unstable at the high temperatures reached in GC, liquid chromatography (LC) is used to separate the PFASs prior to introduction to the detector. Instead of volatility, LC separates chemicals based on their polarity by varying the mixture of mobile-phase solvents over the course of each run. LC equipment requires highly accurate mixers and micro-pumps capable of high pressure and thus is more complex and expensive than GC systems. Additionally, EPA’s PFAS Methods 533 and 537.1 require the use of double mass spectrometers (MS/MS) for compound detection, further complicating the process. Even in the face of these challenges, environmental testing laboratories are purchasing new instruments to meet the increased demand for PFAS monitoring. The more challenging need to fill is staffing PFAS laboratories with experienced and capable staff.
With the growing awareness of PFAS, analytical needs are ever-changing. The number of individual PFAS compounds of interest continues to increase, and the requested levels of detection continue to decrease. While thousands of compounds meet the definition of a PFAS, individual regulations and analytical methods focus on anywhere from 20 to 70 specific chemicals. For each PFAS compound analyzed, an analogous surrogate compound is needed for instrument calibration and compound quantification. The limited availability of PFAS surrogate compounds presents another analytical challenge to the expansion of the target PFAS analysis list.
Method reporting and detection limits (MRL and MDL) for the priority pollutant organic compounds, such as benzene or naphthalene, are typically in the parts per billion (ug/l) range, while MRLs for PFAS are 1000 times lower in the parts per trillion (ng/l) range. While the UCMR5 (Fifth Unregulated Contaminant Monitoring Rule) Laboratory Approval Program found that most participating laboratories reported MRLs less than 4 ppt, not all commercial laboratories will be able meet these limits.
PFAS are ubiquitous in our daily lives, making it difficult to acquire water samples free of potential interfering contamination. PFAS are present in certain water-resistant clothing, fabric softeners, cosmetics, hand cream, sunscreen, notepads, markers, Teflon, food packaging, and more. Because traditional compounds of interest do not sorb to Teflon, the material is commonly used in sampling and analytical equipment. Field samplers need to be aware of all possible PFAS sources and ensure that none are present during sample collection. Combined with what the field samplers could potentially introduce, the environment in which the sample is collected must also be PFAS-free. The potential for introducing contamination into a sample at the time of collection is a constant challenge considering the trace levels of these proposed MCLs.
Generating high-quality, accurate PFAS data starts with selecting a competent sampling team and an analytical laboratory. And then, at the end of the day, once PFAS data are generated, extensive quality control assessments by analytical chemists knowledgeable in the nuances of the PFAS sample collection and analysis are required to assess the data’s accuracy, precision, and representation to ensure that the data are suitable to support project decisions.
Given the increasing requirements for PFAS analysis and the technical challenges associated with obtaining high-quality data, commercial laboratories may have difficulties keeping up with the demand. Given the challenges of collecting and analyzing environmental samples for PFAS compounds, care and oversight are required to obtain high-quality and accurate data generation. Where possible, staff experienced in PFAS sample collection should be available to oversee sample collection efforts, and laboratories should be audited prior to the initiation of projects. Laboratory-generated data obtained through one’s effort or from other parties should be inspected and validated by trained staff to assess the accuracy and precision of the results.