On May 25, 2016, US EPA published a Notice of Availability of Lifetime Health Advisories and Health Effects Support Documents for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS), recommending a 0.07 μg/L combined limit for both compounds in drinking water. PFOA, PFOS, and related compounds, often referred to as perfluorinated chemicals (PFCs), have been of concern to US EPA for more than a decade. As attention to PFCs has increased within the environmental community, the terminology used to refer to this diverse, loosely defined group of fluorinated compounds has been problematic.
Compounds with the prefix “perfluoro” are hydrocarbons wherein all C-H bonds have been replaced by C-F bonds. When it comes to the group of organofluorine compounds rapidly gaining notoriety due to their close relation to PFOA and PFOS, using the term “perfluorinated chemicals” or “PFCs” is inaccurate as both terms lack sufficient definition and exclude polyfluorinated chemicals in which some, but not all, C-H bonds have been replaced by C-F bonds. Further, the acronym PFC was also used for perfluorocarbons in official Kyoto Protocol documents (which have their own environmental concerns such as greenhouse gases). While perfluorocarbons are organofluorine compounds that contain only carbon and fluorine (with the formula CxFy), the group of fluorinated compounds of emerging concern do not have a simply definable chemical formula. They are actually a broad class of perfluoroalkyl substances and polyfluoroalkyl substances (with the common acronym, PFAS) that contain a perfluoroalkyl moiety (CnF2n+1–) and can contain a range of possible functional groups. In addition to PFOS and PFOA, other perfluorinated alkyl acids (PFAAs) have been targeted for environmental monitoring, but are not the only PFASs on the ever-growing list of possible chemicals of environmental concern.
Unlike many other categories of compounds (such as polychlorinated biphenyls [PCBs]) that can be extracted and analyzed from a sample using a single technique; there may not be a single sample preparation and analytical technique that can capture all the PFCs/PFASs of possible concern due to their diverse nature. Several commercial laboratories perform analysis for select PFAAs utilizing liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis by either US EPA drinking water Method 537, or proprietary methodologies. The PFAAs analyzed by LC-MS/MS vary by laboratory, but generally contain the perfluoroalkyl moiety with varying lengths and structures (linear or branched) along with a carboxylic, sulfonic or sulfonamidoacetic acid functional group. Some laboratories only perform analysis strictly by US EPA drinking water Method 537. Other laboratories have modified the US EPA method or developed their own proprietary methodology and can analyze non-aqueous matrices. Even within the PFAA category, laboratories utilizing LC-MS/MS vary in their approach to the identification and quantitation of the possible mixtures of linear and branched PFAA isomers present in environmental matrices (in addition to the many other variables amongst the laboratories offering this analysis).
Other possible PFC/PFASs of interest beyond the typical PFAA list may include perfluorinated and polyfluorinated compounds such as:
- perfluoroalkyl sulfonamido substances
- perfluoroalkyl sulfinic, phosphonic, and/or phosphinic acids
- perfluoroalkane sulfonyl fluorides
- perfluoroalkanoyl halides
- perfluoroalkyl aldehydes and/or aldehyde hydrates
- fluorotelomer carboxylic acids
- fluorotelomer sulfonates/sulfonic acids
- fluorotelomer alcohols
- fluorotelomer phosphates
- polyfluoroalkyl phosphoric acid esters
- polyfluoropolyethers (e.g., ammonium 4,8-dioxa-3H-perfluorononanoate [ADONA])
The possibilities are really too numerous to list. Determining which of the PFCs/PFASs are of interest from an environmental standpoint is in the early stages and complicated by the fact that polyfluoroalkyl substances and larger “precursor” compounds (larger compounds and polymers that contain a perfluoroalkyl functional group) may degrade to PFOA and PFOS or other PFAAs of concern. Furthermore, additional PFC/PFASs may also become of interest for source identification or to help illuminate conceptual site models and degradation pathways. The diverse nature of this group of compounds may lead to the need for multiple, varying extraction and analytical approaches to capture them.
Select commercial laboratories currently only offer analysis for a subset of the PFC/PFASs of possible interest. Some laboratories offer analysis for PFAAs beyond the Unregulated Contaminant Monitoring Rule (UCMR) and US EPA Method 537 target lists. Several commercial laboratories have even expanded the list to include several fluorotelomer sulfonates and/or perfluoroalkyl sulfonamides and sulfonamido ethanols. A few laboratories are also starting to use alternative procedures for some PFC/PFASs such as alternative extraction techniques (e.g., avoiding solid-phase extraction for perfluoroalkyl sulfonamides) or analysis techniques (e.g., high-resolution gas chromatography/mass spectrometry [HRGC/MS] for compounds such as perfluoroalkyl sulfonamide ethanols) for improved qualitative identification or quantitation. There are also analytical techniques being developed for PFC/PFAS analysis in research settings that eventually might be offered in a commercial setting; however, some research involves the use of instruments not typically found at commercial laboratories (e.g., fast atom bombardment mass spectrometry [FAB-MS] and high-resolution quadrupole-time-of-flight mass spectrometry [QTOF-MS] to elucidate chemical formulas for the fluorochemicals in aqueous film-forming foam [AFFF]) mixtures as described in “Identification of Novel Fluorochemicals in Aqueous Film-Forming Foams (AFFF) Used by the US Military,” Environ. Sci. Technol. 2012 Jul 3; 46(13): 7120–7127.). While current LC-MS/MS methods are capable of screening for a wide range of PFCs/PFASs, Environmental Standards will continue to closely monitor for additional analytical developments.
Contact David R. Blye, Principal Chemist, CEAC, or Meg A. Michell, Senior Technical Chemist, M.S., at 610.935.5577 to discuss how Environmental Standards can assist your program needs for PFAS analysis.