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Sampling and Analysis of PFAS

Collecting PFAS Samples for Analysis

 

PFAS is a commonly found substance in a myriad of consumer goods and products, as well as in equipment used by environmental engineers and specialists. Special handling and care are necessary when collecting samples for PFAS analysis to avoid cross-contamination because of the ubiquitous nature and potential presence of PFAS in these common products and in equipment typically used to collect soil, groundwater, surface water, sediment, and drinking water samples, as well as the low parts per trillion screening levels. Extra care is also needed to ensure the level of accuracy and precision required for samples of PFAS.

 

Some guidance documents for reference and a few peer-reviewed studies on the potential for cross-contamination from commonly used sampling equipment and materials (Denly et al. 2019; Rodowa et al. 2020) are available. Most of the guidance documents recommend a conservative approach in implementing measures and controls for prevention of cross-contamination. The United Stated Environmental Protection Agency (EPA) includes sampling protocols in Methods 533 and 537.1  for drinking water sampling. However, there is currently no EPA guidance or requirement for sampling other media.  Although the actual methods of PFAS sampling in many media are similar to those used for other chemical compounds, some special considerations for PFAS sampling include selection of proper personal protective equipment (PPE) and sampling equipment/materials (e.g. tubing, sampling bottles, pumps) that come in contact with the sample, collection of additional and/or more frequent field duplicates, field reagent and equipment blanks and introduction of additional decontamination procedures.

 

A selection of published PFAS sampling guidance documents is listed below. These documents identify materials and equipment that should not be used to collect PFAS samples since they are known or suspected potential sources of PFAS.

Acceptable materials for sampling PFAS

  • High-density polyethylene (HDPE)
  • Polypropylene
  • Silicone
  • Stainless steel
  • Nylon
  • Polyvinyl chloride (PVC)

Unacceptable materials for sampling PFAS

 

Materials that should be avoided include but are not limited to (ITRC, 2020):

  • Polytetrafluoroethylene, Teflon (PTFE)
  • Polyvinylidene fluoride (PVDF)
  • Polychlorotrifluoroethylene (PCTFE)
  • Ethylene tetrafluoroethylene (ETFE)
  • Fluorinated ethylene-propylene (FEP)
  • Low-density polyethylene (LDPE)
  • Pipe thread compounds and tape
  • Waterproof coatings containing PFAS

All Safety Data Sheets (SDS) for the materials to be used for PFAS sampling should be reviewed prior to the sampling. If PFAS are listed on the SDS, it is recommended that the piece of equipment not be utilized. The equipment vendor should be consulted, if necessary, to determine if they have PFAS-free alternatives. Any water used for field sample blanks (e.g. field and equipment blanks) should be supplied by the laboratory performing the analysis with documentation verifying that the water is PFAS-free. Samples should not be filtered since filtration can be a source for contamination (Ahrens L 2009Arp and Goss 2009) or PFAS can be adsorbed by the filter. Sampling equipment should be carefully decontaminated before mobilization and between sample locations. Field sampling equipment such as oil/water interface meters, water level indicators, non-disposable bailers, and other non-dedicated equipment used should be decontaminated between each sampling location. The SDS of detergents or soaps used in decontamination procedures should be reviewed to ensure fluorosurfactants are not listed as ingredients (for example Decon 90®should be avoided) (ITRC, 2020).

 

Aside from the equipment and materials used for sampling and decontamination, the clothing worn, personal care products used, and objects brought to the sampling site should be carefully considered to minimize the potential sample contamination. Some considerations are listed below.

 

PFAS Sampling Tips

  • Wear well laundered (without fabric softener) synthetic or cotton clothing
  • Do not wear or use waterproof, water-repellent, fire-repellant, dirt and/or stain-resistant clothing
  • Do not wear makeup, moisturizers, hand cream, or other cosmetics in the sampling area
  • Do not wear or use sunblock or insect repellents containing PFAS
  • Use powderless nitrile gloves
  • Do not use waterproof logbooks or plastic clipboards
  • Do not bring packaged food or drinks, aluminum foil or adhesive labels on-site
  • Do not use sticky notes, felt tip pens, or permanent markers
  • Do not use chemical ice (such as Blue Ice®)

More detailed information on items allowable and prohibited during PFAS sampling can be found in Michigan Department of Environmental Quality PFAS Sampling Quick Reference Field Guide. (Note that this is not a comprehensive list of products that can or cannot be used. The listing or omission of any product does not imply endorsement nor disapproval of a product. Also, there is no guarantee that these products will remain PFAS-free).

Validated and Published Analytical Methods

 

Currently, only two EPA methods are validated and published for the analysis of PFAS, and they are only for finished drinking (potable) water.

 

  1. Method 537.1 Determination of Selected PFAS in Drinking Water by SPE and Liquid Chromatography – Tandem Mass Spectrometry (LC/MS/MS): 18 PFAS compounds (12 perfluoroalkyl acids [PFAAs] and 6 other PFAS, including HFPO-DA [GenX] and ADONA [a PFAS compound used as a PFOA substitute]) can be analyzed. Surrogates analytes are added prior to solid-phase extraction (SPE) to assess for extraction efficiency and analyte loss due to sample preparation. The concentration of each analyte is determined by using the internal standard technique.

 

  1. Method 533 Determination of PFAS in Drinking Water by Isotope Dilution Anion Exchange SPE and LC/MS/MS: 25 PFAS compounds (16 PFAAs and 9 other PFAS, including HFPO-DA and ADONA) can be analyzed. This method targets short chain PFAS (none greater than C12), including perfluorinated acids, sulfonates, fluorotelomers, and poly/perfluorinated ether carboxylic acids. In this method, the concentration of each analyte is calculated using the isotope dilution technique (using isotopically labeled analogues of the method analytes).

Additional Analytical Methods

 

The EPA has also validated, but not published, Method 8327: PFAS Using External Standard Calibration and MRM LC/MS/MS for 24 PFAS compounds in non-potable water (groundwater, surface water, and wastewater). This is a direct injection method, mainly used as a screening method with relatively high reporting limits. Although this method is validated and available for use, it is not yet formally incorporated into the SW-846 Compendium. The EPA is currently collaborating with the U.S. Department of Defense (DoD) for developing an isotope dilution method for non-drinking water aqueous matrices (surface water, groundwater, wastewater influent/effluent, landfill leachate), fish tissues, biosolids, soils, and sediments. Method CWA-1600 is currently undergoing single and multi-lab validation. The EPA anticipates that this method will be finalized in 2021.

 

Currently, the DoD’s Quality Systems Manual (QSM) for Environmental Laboratories, Version 5.3, Appendix B, table B-15 provides the largest number of quality requirements for PFAS analysis. These standards outline specific quality processes for PFAS analysis (sample preparation, instrument calibration, etc.). DoD QSM Table B-15 currently requires isotope dilution quantitation of PFAS analysis which accounts for interferences caused by complex sample matrices and bias introduced by sample preparation and instrument issues (ITRC, 2020).

 

Several other methods have been published for PFAS analysis in non-potable water and solid matrices including:

  • ISO Method 25101
    • A method for the determination of the linear isomers of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) in drinking water, groundwater and surface water.
  • ASTM D7979
    • A direct injection method for determination of PFAS in water, sludge, influent, effluent, and wastewater.
  • ASTM D7968
    • A standard test method for determination of PFAS in soil.

Since both ASTM methods use the external standard technique, which does not account for analyte loss during sample preparation, instrument drift, or matrix effects, they are most suitable for clean matrices with little to no matrix interferences.

Sampling for PFAS in the air

 

Currently, there are no multi-laboratory-validated, published sampling methods for the measurement of PFAS in air emissions and ambient air. Air sampling and analysis have been performed using modifications of existing EPA methods such as:

In January 2021, the EPA issued draft method OTM-45, the first stationary source air emissions test method designed specifically for PFAS. The method is based on SW846 Method 0010 with several changes. In the OTM-45 method, a modified Method 5 sampling train is used to collect PFAS compounds in several fractions which are analyzed separately. Gaseous and particulate bound target pollutants are withdrawn from the gas stream iso-kinetically and collected in the sample probe on a glass fiber or quartz filter on a packed column of adsorbent material and in a series of impingers. The target compounds are extracted from the individual sample collection media. Analysis is conducted using

 

Since there are no EPA-promulgated analytical methods for PFAS other than for finished drinking water, commercial laboratories can also offer proprietary in-house modified methods to analyze non-drinking water matrices (i.e., wastewater, groundwater, soil, sediment, biosolids, leachate, biota, etc.). These modifications may result in variations between the laboratories and potentially inconsistent data.

 

Many of the currently available methodologies for PFAS analysis do not account for all known PFAS. Hence, the full extent of PFAS contamination could be underestimated when analytical methods are used that quantify a discrete list of PFAS compounds. Non-targeted analytical techniques have been developed that measure the total mass of PFAS in multiple matrices. These include:

    • Total Oxidizable Precursors (TOP) Assay
      • The TOP assay (or TOPA) was developed to indirectly quantify the total amount of precursor compounds in a sample through an oxidative digestion by comparing the concentrations of specific s before and after oxidation of the sample by an excess of hydroxyl radicals (Houtz and Sedlak, 2012). This method assumes all non-targeted PFAS can be oxidized and converted to targeted PFAAs. The current TOP assay has not been demonstrated to capture large molecular weight polymer compounds or recently identified per and polyfluoroalkyl ether acids like GenX. This method is commercially available and can be applied both to aqueous and solid samples. TOP assay is helpful in remediation testing to determine the PFAS load but not for site characterization (ITRC, 2020).

     

    • Particle Induced Gamma Emission (PIGE)
      • PIGE is a well-established, non-destructive nuclear analytical technique that is sensitive to fluorine atoms in any solid matrix. PIGE uses accelerated particles to excite the 19F nucleus, which then emits characteristic gamma-rays that can be measured to give quantitative and unambiguous identification of all fluorine atoms present in a sample. PIGE has primarily been used for solid-phase samples such as textiles, paper, personal care products and food packaging (Lang et al. 2016, Robel et al. 2017, Schaider et al.2017). PIGE is a rapid screening technique to measure fluoride, PFAS, and other fluorine containing compounds in the samples. This method is not compound specific and does not differentiate between inorganic fluorine and organic fluorine (ITRC, 2020).

     

    • Combustion ion chromatography (CIC) methods
      • Combustion ion chromatography mineralizes and then measures organic fluorine from the extractable organic fluorine (EOF) and adsorbable organic fluorine (AOF) assay. Samples are combusted at high temperatures to convert organic fluorine to hydrofluoric acid, which is then absorbed into solution of sodium hydroxide (McDonough et al. 2018). The total concentration of the fluoride is then quantified by ion chromatography (IC). This method is not specific to PFAS. If a sample contains relatively high concentrations of non-PFAS that contain fluorine, like some pharmaceuticals, then the fluorine may be falsely attributed to PFAS and bias total PFAS concentrations higher (ITRC, 2020).

     

     

PFAS analytical methods are still evolving and in development. This blog will be periodically updated to provide the most recent information about PFAS sampling and analysis.

References

 

Ahrens, L., S. Felizeter, R. Sturm, Z. Xie, and R. Ebinghaus. 2009. Polyfluorinated compounds in wastewater treatment plant effluents and surface waters along the River Elbe, Germany. Marine Pollution Bulletin 58.

 

Arp, Hans Peter H., and Kai-Uwe Goss. 2009. Irreversible sorption of trace concentrations of perfluorocarboxylic acids to fiber filters used for air sampling. Atmospheric Environment 43:3654-3655. doi: 10.1016/j.atmosenv.2009.03.001.

 

Denly, Elizabeth, Jim Occhialini, Phil Bassignani, Michael Eberle, and Nidal Rabah. 2019. Per- and polyfluoroalkyl substances in environmental sampling products: Fact or fiction? Remediation Journal 29 (4):65-76.

 

Houtz, Erika F., and David L. Sedlak. 2012. Oxidative Conversion as a Means of Detecting Precursors to Perfluoroalkyl Acids in Urban Runoff. Environmental Science & Technology 46 (17):9342-934

 

Interstate Technology and Regulatory Council (ITRC), 2020. PFAS Technical and Regulatory Guidance Document and Fact Sheets, PFAS-1. PFAS Team, Washington, DC

 

Lang, Johnsie R., B. McKay Allred, Graham F. Peaslee, Jennifer A. Field, and Morton A. Barlaz. 2016. Release of Per- and Polyfluoroalkyl Substances (PFASs) from Carpet and Clothing in Model Anaerobic Landfill Reactors. Environmental Science & Technology 50 (10):5024-5032.

 

McDonough, C. A.; Guelfo, J. L.; Higgins, C. P. 2018. Measuring total PFASs in water: The tradeoff between selectivity and inclusivity. Current Opinion in Environmental Science & Health. 7, 13-18

 

Robel, Alix E., Kristin Marshall, Margaret Dickinson, David Lunderberg, Craig Butt, Graham Peaslee, Heather M. Stapleton, and Jennifer A. Field. 2017. “Closing the Mass Balance on Fluorine on Papers and Textiles.” Environmental Science & Technology 51 (16):9022-9032.

 

Rodowa, Alix E., Emerson Christie, Jane Sedlak, Graham F. Peaslee, Dorin Bogdan, Bill DiGuiseppi, and Jennifer A. Field. 2020. Field Sampling Materials Unlikely Source of Contamination for Perfluoroalkyl and Polyfluoroalkyl Substances in Field Samples. Environmental Science & Technology Letters 7 (3):156-163.

 

Schaider, Laurel A., Simona A. Balan, Arlene Blum, David Q. Andrews, Mark J. Strynar, Margaret E. Dickinson, David M. Lunderberg, Johnsie R. Lang, and Graham F. Peaslee. 2017. “Fluorinated Compounds in U.S. Fast Food Packaging.” Environmental Science & Technology Letters 4 (3):105-111.