The public comment period for listing 9 PFAS as RCRA hazardous constituents ends on 8 April. This covers what that means and how to comment.
The public comment period for the EPA proposal to list 9 PFAS as hazardous constituents under the Resource Conservation and Recovery Act (RCRA) ends on 8 April 2024. You may submit a comment here. The 9 PFAS are PFOA, PFOS, PFBS, HFPO-DA, PFNA, PFHxS, PFDA, PFHxA, and PFBA. This includes the 6 PFAS which were have a proposed maximum contaminant level under the Safe Drinking Water Act: PFOA, PFOS, PFHxS, HFPO-DA, PFNA, and PFBS. It may be helpful to review the article on PFAS nomenclature. The intent of this article is to encourage informed public participation in the rule making process. To that end, I plan on covering what RCRA is, what a hazardous constituent is, what that means, and what I, acting in my own personal capacity not representing my employer, think. Please remember that my views are my own and I do not work in this area!
RCRA Introduction
RCRA was first signed into law 21 October 1976 and had major amendments in 1984, 1992, and 1996. RCRA itself is an amendment to the first federal solid waste statute (the Solid Waste Disposal Act of 1965) which is typically included in the term. RCRA governs solid and hazardous waste disposal in the United States and is known for its “cradle to grave” management framework. This law has multiple subtitles, the most referenced are Subtitles C, D, and I.
RCRA Subtitle C
Subtitle C establishes the cradle to grave framework for hazardous wastes which means from the point of generation through transportation, treatment, storage and disposal hazardous wastes must be tracked, handled, recorded, and stored in specific ways.
RCRA Subtitle D
Subtitle D covers for non-hazardous solid wastes. Among other things it banned open landfills. This section covers sludge from industrial wastes, wastewater treatment plants, and drinking water plants as well. It also excludes small quantity generators from having to follow Subtitle C requirements.
RCRA Subtitle I
covers underground storage tanks (USTs) containing petroleum or other listed hazardous substances and provides technical, monitoring, and reporting standards for them.
A note on RCRA Special Wastes
Several wastes, known as “special wastes,” are industrial wastes which were exempted from Subtitle C and includes oil and gas exploration wastes (such as drill cuttings, produced water, or drilling fluids), coal combustion residuals (fly ash, bottom ash, slag waste and flue-gas desulfurization wastes), mining waste, and cement kiln waste.
What is a Hazardous Constituent?
A hazardous constituent is not a hazardous waste. Instead, it is anything listed in 40 CFR part 261 Appendix VIII. A hazardous constituent listing is a step toward a potential hazardous waste listing. To list a waste as a RCRA hazardous waste under 40 CFR 261.11(a)(3), the waste must contain a hazardous constituent listed on Appendix VIII and determine that it is capable of posing a substantial hazard. Additionally, when a corrective action is required, hazardous constituents are expressly identified for consideration and RCRA section 3004(u) requires that any permit issued to a treatment, storage, or disposal facility after November 8, 1984 requires corrective action for all hazardous waste or constituent releases from solid waste management units at the facility. There are additional regulations surrounding hazardous constituents in parts 261, 264, 265, 268, and 270 however, these are not particularly relevant here. To be listed as a as hazardous constituents under RCRA, a substance must have been shown in scientific studies to have toxic, carcinogenic, mutagenic, or teratogenic effects on humans or other life forms.
Does this affect drinking water?
I do not believe so because hazardous constituents do not make themselves, or the wastes containing them, RCRA hazardous wastes. Only hazardous waste treatment storage or disposal facilities are subject to RCRA corrective actions according to 42 U.S.C. 3004(u)(v). I supposed it is possible that a drinking water plant is a hazardous waste treatment, storage, or disposal facility but that would be novel for me. There’s also a domestic sewage exclusion in 40 CFR 261.4(a)(1), which excludes domestic sewage and any mixture of domestic sewage and other wastes that passes through a sewer system from being considered solid wastes (with some exceptions). However, remember folks I’m not a lawyer and don’t know law.
Why is it important to submit a comment?
Simply put the EPA generally listens if you have a well thought out point and it is important to participate in the laws which govern you.
How to submit a comment
To submit comments, just click the “submit a formal comment” button as shown in the picture below. You can also view all comments submitted. Once the public comment period closes, the EPA reviews all the comments and replies to every one; I’m glad I wasn’t working on this Clean Water Rule which received over 1,000,000 public comments.
What do I think?
I believe that the EPA has shown that the nine PFAS, their salts, and their structural isomers meet the listing criteria for RCRA hazardous constituents because there is plenty of detailed, peer reviewed, well established scientific studies that show that these PFAS have toxic effects on humans or other life forms. I believe that it would have been better if rather than listing individual chemicals a structural definition was provided.
I understand the argument that there may not be enough evidence to show that a structural definition should apply however, to quote:
To be honest, PFAS is starting to resemble Christopher Duntsch, also known as Dr. Death. He is one of the only, if not the only, surgeon to face felony accounts for maiming his patients. This is because every doctor is human and humans make mistakes. The prosecution successfully argued that Duntsch should have known he was likely to hurt others unless he changed his approach, and that his failure to learn from his past mistakes demonstrated that his maimings were intentional. Likewise, with PFAS, I feel that even though we may lack specific studies for all perfluoroalkyl carboxylic acids or perfluoroalkyl sulfonic acids from say C4-C20 but at this point are we learning from similar enough chemicals? Baseball is three strikes and you’re out; this listing includes 5 perfluoroalkyl carboxylic acids, 3 perfluoroalkyl sulfonic acids, and 1 perfluoropolyether carboxylic acids could we not just say perfluoroalkyl carboxylic acids or perfluoroalkyl sulfonic acids at this point? How different does something have to be so we prevent regrettable substitutions?
Conclusions
Even if you don’t agree with me you should participate in your democracy! I plan on submitting a comment agreeing with this, if you don’t agree with it why not submit a comment to balance me out? Don’t worry if you miss this opportunity, there are many opportunities to participate in federal decision-making and occur before a rule is proposed, after a rule is proposed, and even after a rule is finalized as this handy site from Harvard’s Environmental and Energy Law Program shows.
The World Health Organization (WHO) is considering adding PFOA and PFOS into its Guidelines for Drinking Water Quality and is seeking public comment on their background document for development of WHO Guidelines for Drinking Water Quality. This document is undergoing rolling revisions and accepting public comment using the form here sent to gdwq@who.int by 11 November 2022. Guidelines for Drinking Water Quality are essentially the WHO’s version of the US EPA’s Health Advisories however, are 5 orders of magnitude higher with 100 ppt individual guidelines for PFOA and PFOS as well as a 500 ppt total PFAS guideline. This 5 order of magnitude divergence between health agencies is primarily because the US EPA used epidemiological studies to define the reference dose while the WHO primarily relied on toxicology. Relying on toxicology, the “WHO considered that the uncertainties in identifying the key endpoint applicable to human health following exposure to PFOS and/or PFOA are too significant to derive a HBGV with confidence” (page 79) while the US EPA did not have that issue. The intent of this article is to go over what the WHO is, why it publishes drinking water quality guidelines, and the comments I submitted. Please remember that my views are my own and do not reflect my employer’s position!
What is the WHO?
The WHO serves to coordinate and guide public health policy on a global level. It started as the Office International d’Hygiène Publique (OIHP) or The International Office of Public Hygiene of President Wilson’s failed experiment, the League of Nations. After the League of Nations folded on 20 April 1946 many of its functions were eventually rolled into the Untied Nations including the WHO. The WHO has been heavily criticized for decades such as by its former leaders and think tanks. Criticism stepped up sharply during the ongoing corona virus pandemic. Despite all this, the WHO remains virtually the only true global consensus-building public health organization. While its influence has weakened in recent years due to other global public health actors such as the World Bank or the Bill and Melinda Gates Foundation, it still is one of the most broadly recognized and supported organizations dedicated to public health.
Why does the WHO publish drinking water quality guidelines?
The WHO itself has been publishing drinking water quality guidelines since 1958 and in fact the WHO’s grandparents were the International Sanitary Conferences (ISC) first held on 23 June 1851 which were established as a result of a cholera pandemic. The OIHP was initially established to carry out some of the ISC’s recommendations. Cholera is a waterborne disease; a fact made famous by John Snow and the Broad Street Pump. By removing a pump handle Dr. Snow helped deal a blow to the miasma theory of disease and served as a founding father to epidemiology; a subject I have a case study in.
The WHO currently recommends individual provisional guidance values of 100 ppt for PFOS and PFOA as well as 500 ppt for total PFAS. These numbers exactly mirror the EU Drinking Water Directive and are substantially higher than the US EPA recommendations which are 0.004 ppt (or 4 parts per quadrillion) and 0.02 ppt (or 20 parts per quadrillion) for PFOA and PFOS respectively. A key reason why these values are so dramatically different is that the US EPA considered epidemiological studies while the WHO did not.
Throughout the document the WHO uses older thoughts on PFAS and consistently cites the 2016 health advisories. The US EPA has the most current human health toxicity assessments for PFAS however, the WHO consistently lists them last.
On page 63 the WHO states (the numbers in the quote are line numbers for that page) “PFOA exposure is associated with clear 23 evidence of carcinogenic activity in male rats based on the increased incidence of liver 24 adenomas and pancreatic acinar cell tumours.” It is therefore not possible using current evidence 25 to exclude PFOA as a human carcinogen”. This wording reflects the US EPA’s 2016 position; more recent human and animal studies lead the US EPA to conclude that PFOA is a more potent carcinogen than previously thought.
I am not enough of a health scientist to know or provide a meaningful analysis on the health aspects of the document other than the superficial one I just provided pointing out the WHO is using older science. Normally in the debate between epidemiology and toxicology, toxicology points to a more dangerous substance than the epidemiological studies. Here, due to the preferred analysis by these organizations it appears to be flip flopped. I would personally prefer to err on the side of caution; especially since drinking water according to the UN is a fundamental human right.
Why I submitted comments to the WHO
Simply put the WHO generally listens if you have a well thought out valid point which conforms to their purpose. During their last request for comment I (and probably quite a few other people) made quite a few recommendations which were incorporated into this draft document. For example, I recommended they:
Take into account Xiao’s paper which shows that PFAS can be generated during advanced oxidation processes. This also changed their practical considerations on monitoring so was quite a substantial change to the document.
Take out the octanol water partitioning coefficient (Kow) from their table of physicochemical properties because PFOA and PFOS are both hydro- and lithophobic so bifurcate into its own layer between octanol and water. Although some people report values, these values are not reflective of the ground truth since the standard test was not designed for that type of material. They also changed some of the other values such as the boiling point and melting point because the predicted range was larger than the experimental range.
Specify that anion exchange deals with anionic PFAS since there are cationic and neutral PFAS so there were some changes to those sections as a result.
Drop the “s” from the PFAS acronym for plurals because a substance cannot simultaneously be per- and polyfluorinated so the plural is already implied.
Use the OECD definition of PFAS which they updated.
Use updates I provided on page 71 about characterizing EPA methods 533 and 537.1
One of my comments was almost incorporated word for word on page 74 related to chain length and functional group removal efficacy; a conclusion I partially took from this Sörengård et al. paper.
Previous comments which were not accepted
Not all my previous comments were accepted. This goes to reflect that two people can look at the same data and draw different conclusions. Especially when the topic is a matter of policy there is often no “correct” answer although there are often clear cut “incorrect” answers. I am going to use this section to highlight some of the comments I made which were rejected, why I made those comments, and potentially the reason why the comment was rejected.
I recommended against using percent removal as a characterization of process efficiency. You can think of properly designed granular activated carbon or anion exchange beds as towels wiping up liquid (contaminant). When the towel is dry and the spill is small it picks up all of it quickly. A wet towel mopping up a large spill may not clean everything or may not clean it quickly. Try and keep that analogy in mind for a contactor. The photo below shows one mode for thinking of breakthrough. Better ways to characterize the efficiency are to use media usage rate or bed life. I believe that the WHO used percent removal because it makes it easier to compare to membrane filtration although again, I disagree with this characterization.
I provided references which show greater removal percentages for sorption that the WHO quotes. There are many however, the US EPA drinking water treatability database captures many such examples. The WHO is also much more pessimistic on anion exchange than I believe is warranted based on the data. There are both full scale, pilot, and bench studies included. I do not really know why the WHO was cautious there compared to their membrane section where results were more often accepted at face value except potentially that was due to the declining efficacy over bed life which again, is why I suggested percent removal is a bad way to measure sorption process efficiency.
The WHO focuses on source water monitoring. In general, this is a good approach however, I do not agree with it for PFAS. PFAS is not known to and is unlikely to leach or permeate into drinking water supply. Likewise, PFAS can be generated during treatment when advanced oxidation (and potentially advanced reduction) processes are used. If resources are constrained it makes more sense to me to monitor the finished water rather than source water if only one is to be monitored especially since source waters are unlikely to change. The counter argument is that only specific wells could be contaminated, and it would make sense to shut down those wells and not have to treat. If you only monitor finished water, you will miss that level of detail. If resources are constrained and you only monitor the influent, you’ll miss that anyway. To me, this is a good example of two reasonable policy positions based on the same facts with divergent conclusions.
In the previous document, the WHO referenced replacement chemistries; specifically short chained PFAS. I recommended that esterified replacement chemistries be mentioned as well such as HFPO-DA (also known as GenX chemicals), ADONA, and Nafion byproducts. Instead, the WHO removed references to replacement chemistries. This is a good compromise because there are many replacement chemistries available.
My comments on the current draft
On this new draft the comments I have submitted to the WHO using their form emailing to gdwq@who.int (11 November 2022 deadline) are:
The recommendation on page 70 that PFAS monitoring is only required when there is a reasonable source nearby is not protective of public health or in the best interests of society at large. As this document points out PFAS is capable of long-range transport and deposition. PFAS has been found in the artic and Antarctic as well as other remote areas. Additionally, airports; military sites; landfills; wastewater treatment plants; carpet, upholstery, wax, and paper product manufacturers; or spreading biosolids (composting) are all PFAS sources. Rasstadt, Germany was contaminated with composting from used food containers for example. I do not believe that you can successfully perform a risk assessment given the diverse set of sources, low toxicity thresholds, and long-range transport capabilities.
Page 72 lines 8-9 state (line numbers in parathesis): “Blending or diluting PFAS contaminated source water with uncontaminated water may be a (9) cost-effective and viable option for some water systems.” As there is ultra-low toxicity and PFOA as well as PFOS have been identified as likely carcinogens I do not believe that deliberately exposing people to these contaminants through diluting or blending is an appropriate course of action unless there are no other alternatives such as treatment (this would be an economics question) or source substitution.
Page 76 provides information on PFAS removal through sorptive technologies. I believe, and have provided references above in this article, that significantly lower treatment standards are possible.
On page 16 lines 27-30 it states (line numbers in quotes): “In 2019, the US EPA conducted a broad literature search to evaluate (28) evidence for pathways of human exposure to PFOA and PFOS, and in 2021 released a draft (29) analysis that supports application of a 20 percent relative source contribution for PFOA and (30) PFOS in drinking water (US EPA, 2021b,c).” This seems to overstate the strength of the conclusion the EPA made in those health advisories. As I mention in this article, the EPA’s position was that there was insufficient evidence to deviate from a 20% default value; not that evidence supported a particular value.
On page 4 line 37-39 it states (line number in parentheses): “PFOA remains possible, even where it is no longer (38) manufactured or used due to its legacy uses, degradation of precursors, and extremely high (39) persistence in the environment and the human body.” I believe this is also true for PFOS and that disclaimer should be added to that section as well.
Page 74 lines 45-46 deal with anion exchange resin regeneration. Greater than 95% resin regeneration has been demonstrated in literature here, here, and here although it may not be practical for utilities from a safety and/or cost prospective.
On page 9, the WHO references this Boone et al study; when the study was published the conclusion that only one monitored drinking water plan exceeded the EPA’s HAs was valid however, the HAs were updated. That changes the study conclusion from one drinking water plan exceeding the EPA’s HAs to all quantitatively monitored plants exceeding the HAs, a significantly different conclusion.
Conclusion and Key Take Aways
Over time, scientific consensus points to greater and greater awareness of the dangers PFAS pose. Generally, we thought these chemicals were safer in the past than most scientists do today. The WHO, in its role as a policy leader, has developed a significantly less stringent health recommendation than even the old 2016 US EPA HAs on the dangers of these chemicals by not weighting epidemiological evidence the same way. The WHO standard exactly mirrors the EU standard under the drinking water directive. The WHO is a reasonable organization and solicits public comment and feedback as well as generally listening to it. I highly recommend you share your opinions with the WHO regardless of whether you agree with me and take an active role in global public health.
In general, there are three broad strategies for PFAS analysis:
1. Target analysis
2. Total fluorine (organic fluorine) methods
3. Non-target analysis including suspect screening and the total oxidizable precursor (TOP) assay (TOPA)
PFAS analysis is severely complicated by the prevalence of fluorochemicals in laboratory equipment particularly PTFE. For example, PFAS is widely prevalent in HPLC solvent inlet tubing and PFAS from felt tip permanent markers used to mark containers during sampling campaigns.
Target analysis summary
Target analysis targeted methods typically involve either liquid or gas chromatography (LC or GC) coupled with mass spectrometry (MS) and require a reference standard for quantification. Standards are only available for select PFAS and only these specific substances can be quantified. Target analysis yields accurate concentrations but does not provide the total PFAS load.
Total fluorine methods summary
Fluorine is a sum of its inorganic and organic constituents; this insight forms the basis for quantification attempts by total fluorine methods. As PFAS are organic molecules, inorganic fluorine is typically removed from the analysis and absorbable or extractable organic fluorine is measured. Due to differing chemical properties among PFAS, the extraction method chosen will not be suitable for all PFAS classes. Absorbable organic fluorine relies on choosing a suitable absorbent so suffers from the same difficulties.
Non-target analysis summary
Non-target analysis uses chromatography coupled to a high-resolution mass spectrometer and can identify previously unknown PFAS. These methods tend to rely on quadrupole time-of-flight and linear ion trap-orbitraps which are not common instruments. If reference standards are available, similar detection limits to targeted analysis can be achieved. The TOPA deserves special mention as this method performs targeted analysis then attempts to oxidize all precursor compounds into compound endpoints which have standards then performs targeted analysis again to see the difference and theoretically quantify the precursor load but not the specific precursors. These methods suffer from the high technical capacity and equipment required to employ them.
Targeted Analysis
Targeted analysis is currently the only form of analysis which can support drinking water regulatory action because it is able to quantify extremely low PFAS levels; generally around 4 parts per trillion (ppt). In general, LC-MS/MS or GC-MS/MS is used. Reference standards are only available for select PFAS so only select PFAS may be quantified. Which PFAS have standards is driven both by the ability to synthesize extremely high purity samples, regulatory emphasis, and economic viability for the producers. The main PFAS which have standards are per- and polyfluorinated acids (PFAA) – particularly the carboxylic (PFCA) and sulfonic acids (PFSA) as well as the etherified versions of these. As a quick reminder PFCA end in “O” such as PFOA and PFSA end in “S” such as PFOS. The etherified versions tend to have a less standardized nomenclature structure such as “GenX chemicals” or ADONA.
Targeted analysis is well established for various matrices. For example, USEPA Methods 537.1 and 533 together cover 29 PFAS (537.1 focuses mainly on long chain PFAS and covers 18 while 533 was developed mainly to cover some more short chained PFAS and covers 25 PFAS; there are 14 PFAS which overlap between the standards). The German Institute for Standardization (DIN) has also published standard methods DIN 38407-42 and 38414-14. DINs are not freely available like the American methods so I will not link to a store here however, the DINs are broadly similar to the American methods. All these methods use solid phase extraction (SPE) followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). As these methods rely on solid phase extraction, the method efficacy declines with chain length. In other words, the quantification and detection limits for short chained PFAS are higher than they are for long chained PFAS.
As mentioned in the nomenclature article, PFAS may come in “linear” or “branched” forms. These targeted methods may detect branched forms however, branched standards are not widely available and ignoring these will result in a low bias. Linear to branched isomer ratios can also help to identify the PFAS sources. The USEPA Methods 537.1 and 533 include technical notes for dealing with branched isomers.
The DINs note that these methods can be extended to other PFAA with appropriate standard availability however, volatile fluorotelomers (like fluorotelomer alcohols) cannot be determined using these methods.
Total fluorine methods
Total fluorine (TF) is the sum of Inorganic Fluorine (IF) and Organic Fluorine (OF) sometimes called Total Organic Fluorine (TOF). TOF includes fluorine content of all PFAS and their precursors in the sample. TOF methods cannot however separate out organic fluorine contained in medications or other common uses from PFAS. There have been exceedingly few studies quantifying TOF fractions from PFAS compared to medications or other uses of organofluorine. Additionally, TOF methods have much higher quantification limits than targeted analysis, typically around 100 ppt. These two limitations make TOF methods suitable for screening but not protective enough of public health to seriously be used in drinking water regulation. Remember the interim health advisories (HAs) for the apical effects of PFOA and PFOS were 0.004 and 0.02 ppt respectively, so 100 ppt is 4 or 5 orders of magnitude larger than the level at which no apical effects are expected. Additionally, organic fluorine methods only measure the fluorine while the HAs measure the full molecular weight. For example, PFOA (C8HF15O2) has a molar mass of 414.07 g/mol but the mass of fluorine only weighs approximately 285 g/mol PFOA meaning that only about 69% of each PFOA molecule would be quantified assuming perfect extraction and quantification. The exact ratio of fluorine to the overall molecular weight is species dependent.
Organofluorine analysis requires the organic fluorine to be extracted – Extractable Organic Fluorine (EOF). There will always be some organofluorine which cannot be extracted and some which can be extracted but cannot be quantified. Extraction can be the same as for targeted methods. However, due to the large variability between the PFAS chemical composition, the extraction method will influence the test results. Likewise, similar to targeted methods, there is worse extraction efficiency for shorter chained PFAS and specific substances such as trifluoroacetic acid. A special EOF method is known as absorbable organic fluorine (AOF). During AOF, the sample is typically absorbed to a mixed-mode weak anion exchange SPE; again similar to targeted analysis methods.
The most common total fluorine methods are: combustion ion chromatography (CIC), particle-induced gamma-ray emission spectroscopy (PIGE), instrumental neutron activation analysis (INAA), X-ray photoelectron spectroscopy (XPS), and 19F nuclear magnetic resonance spectroscopy (19F NMR). Other methods are under development including: inductively coupled plasma mass-spectrometry (ICP-MS), continuum source molecular absorption spectrometry (CS-MAS), defluorination with sodium biphenyl (SBP), potentiometric and fluorimetric detection, and reversed phase LC-UV or GC coupled with a flame ionization detector (FID), electron capture detector (ECD), or MS. CIC is currently the most discussed TF method.
Non-targeted Analysis
Non-target analysis for PFAS typically uses chromatography coupled to high-resolution mass spectrometers to identify previously unknown PFAS. These methods tend to rely on quadrupole time-of-flight and linear ion trap-orbitraps observed accurate masses, isotopic fingerprints, and MS/MS fragments. Accurate masses, isotope patterns, and molecular feature fragmentation patterns obtained from high resolution mass spectroscopy (HRMS) are compared to databases with known PFAS, such as the USEPA CompTox Chemistry Dashboard, NORMAN Suspect List Exchange, MetFrag, and STOFF-IDENT. Measured chemical responses are compared across two or more sample groups in a process known as fold-change comparison.
Total Oxidizable Precursor Assay
The Total Oxidizable Precursor (TOP) Assay (TOPA) was developed by Houtz and Sedlak in 2012 to quantify concentrations of difficult-to-measure and unidentified precursors of PFCA and PFSA in urban runoff. Essentially a sample is measured following conventional targeted analysis methods and then samples are exposed to hydroxyl radicals generated by persulfate thermolysis under basic pH conditions and measured following conventional targeted analysis methods again. Comparing pre- and post-oxidation concentrations the PFAA precursor load can be estimated. Unfortunately, oxidation conversion yields are compound dependent and many factors affect the oxidation process. Oxidation completeness can be tracked by adding a 13C mass labelled precursor however, this again is dependent on the specific compound chosen. Additionally, the endpoint compounds selected for targeted analysis affect the results dramatically. Activated persulfate does not generally oxidize PFSA so this can only really provide inference on PFCA precursors. The TOP assay is also labor intensive, requiring twice the number of samples and more than twice the amount of work to produce a single result. The TOP assay does provide an indication of PFAS precursor load without requiring as advanced equipment or training as non-targeted analysis.
Conclusions
Each strategy selected for PFAS analysis carries with it its own unique strengths and drawbacks. Under most current toxicological frameworks employed by regulatory agencies targeted analysis is the only real viable option however, this can miss many PFAS. Total fluorine methods are several orders of magnitude too imprecise to accurately protect public health but capture most PFAS. Non-targeted analysis methods require expensive equipment, much experience, as well as being non-quantified.
Per- and polyfluoroalkyl substances (PFAS) are a ubiquitous emerging public health threat. PFAS terminology can be extremely confusing because it looks like an alphabet soup of similar acronyms. This article is the second of two on PFAS terminology. The first intended to provide an overview of PFAS structure (including what counts as PFAS), this one intends to help demystify PFAS terminology and nomenclature. These are part of a broader series on PFAS including their serendipitous discovery.
Introduction
PFAS are a large chemical class generally produced in industrial processes which do not produce pure substances; often impurities are introduced to the end product. An isomer is a compound with the same chemical composition as another compound but a different chemical structure. In the PFAS world the terms “branched” and “linear” refer to differing isomers. As a short hand, people often mean all isomers of a particular compound when they name it. PFAS can also be cyclic in which case the linear/branched nomenclature breaks down.
Linear and branched non-polymeric PFAS are typically composed of two parts: a hydrophobic as well as lipophobic fluorinated carbon backbone and a typically polar hydrophilic functional group. The suffix philic means an affinity for and phobic means fear or aversion, the prefix hydro means water and lipo is for lipid or fat.
Structural analogues are compounds similar to other compounds but differing in one aspect. Structural analogues are also known as congeners. An example could be homologues. PFAS with the same functional groups differing in the number of carbons and fluorine atoms in the backbone are known as homologue series. For example, perfluoroalkyl carboxylic acids with 4 fully saturated carbons in the backbone to 12 fully saturated carbons in the backbone would form a homologue series. A homologue group includes all linear and branched carboxylic acids with the same number of carbons in the backbone. For example, the C8 carboxylic homologue group includes linear perfluoroalkyloctanoic acid (PFOA), isopropyl-PFOA, and 3-methyl-PFOA; there are 89 total theoretically possible C8 carboxylic homologue congeners although in addition to the linear form. The picture below shows some C8 carboxylic homologue congeners, while technically separate compounds for ease they are often referred to as a singular entity.
Naming Systems
There are 5 main systematic methods currently in use to name fluorinated compounds: the International Union for Pure and Applied Chemistry (IUPAC) nomenclature, the perfluoro nomenclature, code numbers, Chemical Abstract Service (CAS) nomenclature, and F-nomenclature systems. Due to strong similarities, fluorinated organic compounds tend to follow hydrocarbon naming conventions.
Basic Conventions
Many PFAS are acids and may exist as a protonated or anionic form as well as a mixture of both depending on the pH. The pKa values tend to be quite small and scientists generally refer to PFAS with acid functionalities as “acids” rather than carboxylates, sulfonates, or the correct terms even though the dissociated forms may be the only relevant forms. Scientists refer to both the protonated and ionized forms by the same acronyms. Most perfluorinated acids are environmentally anions. Some labs report results in the acidic form, some report anions, and some a mixture. Many times, perfluorinated carboxylic acids are reported as acids (for example perfluorooctanoic acid instead of perfluorooctanoate) and perfluoroalkyl sulfonic acids as anions (for example perfluorooctane sulfonate instead of perfluorooctane sulfonic acid). This has caused confusion. The labs are really measuring the concentration of perfluorinated acid anions present; when the lab reports an acid the lab adjusts for the cation. Most sulfonate standards are prepared from salts and the mass adjusted which is why they are often reported that way. This is especially true for PFHxS, PFOS, ADONA, 9Cl-PF3ONS and 11Cl-PF3OUdS. Section 7.2.3 of EPA Method 537.1 details how to convert to adjust for this.
IUPAC Nomenclature
IUPAC Nomenclature systematically establishes unambiguous, unique, uniform, and consistent compound names based on their chemical structure. IUPAC Nomenclature can be used for all organic compounds and is not specific to PFAS. IUPAC Nomenclature is quite literally a book containing many precedents and steps however, the general simplified steps for IUPAC Nomenclature are:
Identify the longest carbon chain. The longest carbon chain is also known as the “parent chain.”
Identify any groups off the parent chain.
Number the carbons in the parent chain so that the groups off the parent chain have the lowest number.
Number and name the groups just counted.
Put all the name components together in alphabetical order; prefixes such as di- are not used for alphabetical order.
For example, C2F4 is tetrafluoroethene, shown below, is the simplest perfluorinated alkene (fully saturated carbon backbone with no functional groups).
Perfluoro Nomenclature
Perfluoro Nomenclature only applied to perfluoroalkyl substances. It is commonly used to quickly identify fully fluorine saturated carbon compounds. For shorter substances using IUPAC naming conventions is still easy and understandable. Most chemists would immediately understand that hexafluorobenzene (C6F6 – shown below) has a cyclic fully saturated carbon backbone. However, for longer compounds such as pentadecafluorooctanoic acid it is difficult to readily tell which is the motivation for Perfluoro Nomenclature. The proper IUPAC name for that compound is actually: 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoic acid which is fairly cumbersome to use further motivating Perfluoro Nomenclature. The pentadecafluoro refers to the 15 fluorine atoms, octanoic acid refers to a carboxylic acid functional group that is off the 8th carbon in a chain. This compound is pictured under hexafluorobenzene.
Perfluoro Nomenclature uses the prefix perfluoro along with standard hydrocarbon nomenclature. This simplified naming system has been in place since the 1950s and is the most common naming system among practitioners. The acronyms developed from this system follow a simple pattern; they all start with the prefix PF for perfluoro then have a root based on the carbon backbone, and a suffix denoting the functional group. The table below gives the roots for C1-C14 and the two most common functional group abbreviations are A for carboxylic acids as well as S for sulfonic acids.
The acronym itself provides a well-defined structure for the PFAS compound. For instance perfluorobutanesulfonic acid or PFBS is shown below. The front letters PF stand for per-fluoroalkyl, the B stands for but-, -ane shows there are only single bonds in the carbon backbone which is implied, and the S is for sulfonic acid. PFBA, PFHpA, and PFDA are also shown.
Should it be necessary to refer to a specific salt for a perfluorinated compound it is customary to write the salt’s common abbreviation in front of the standard perfluorinated abbreviation then drop the acid from the name. For instance, the ammonium salt of PFOA, ammonium perfluorooctanoate, is often abbreviated APFO. While not strictly included in the perfluorinated system, some polyfluoroalkyl compounds can degrade into perfluorinated compounds. A polyfluoroalkyl compound is one where the carbon backbone is not fully fluorinated. An important subset of polyfluoroalkyl substances are fluorotelomers. Fluorotelomers are substances made from the most common industrial process for perfluorinated compounds, telomerization. In telomerization a transfer agent, known as a telogen, reacts with a polymerizable taxogen (monomer) to produce a telomer. Generally in commercial production, perfluoroethyl (pentafluoroethyl) iodide as a telogen reacts with tetrafluoroethylene oligomers as taxogens, most commonly tetrafluoroethylene, to produce telomer perfluoroalkyl iodide polymers. The perfluoroalkyl iodide polymers are then converted into other substances.
Similar to perfluorinated acids, fluorotelomer substances are typically named for their functional group. Fluorotelomers often are abbreviated FT followed by their functional group. There are often numbers preceding the abbreviation such as 8:2. The first number represents the total perfluorinated carbon atoms and the second number the unsaturated carbons atoms.
Code numbers
Systematic names are fantastic in precision but can be difficult to use. Unless you work with compounds frequently, memorizing the prefix structures and extra rules, which were glossed over in this article can represent an annoying time commitment. Additionally, it can be error prone especially to infrequent or new users. Industrial PFAS manufacturers such as ICI Fluoropolymers, ISC, DuPont, and 3M developed inhouse shorthands for PFAS. As the inhouse systems were not meant for the general public this initially caused confusion. In Organofluorine Chemistry dichlorodifluoromethane (CF2Cl2) is used as an example to illustrate this. Dichlorodifluoromethane was known as Freon-12 by DuPont, Arcton-6 by ICI, and Isceon-122 by ISC. By 1957 a standardized code number system based on DuPont’s system was adopted and formalized as The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 34 which was last updated in 2019. DuPont’s system was first developed by Albert Henne, Thomas Midgley, and Robert McNary in 1929.
In the ASHRAE system for pure compounds, a letter designates the primary purpose of the compound, R for refrigerant, P for aerosol propellant, S for solvent, and the numbers are based on the chemical formula. Sometimes the letter is replaced with a trade name such as Freon. For blends, numbers are assigned sequentially based on ASHRAE data review completion date. For an ASHRAE designation, the first digit from the right is the number of fluorine atoms. The second digit from the right is the number of hydrogen atoms plus one. The third digit is the number of carbon atoms minus one; if this is a zero then that number would be omitted. The fourth digit is the number of unsaturated carbon-carbon bonds, in saturated compounds this number is omitted. If an upper-case B or I appears the number immediately following it is the number of bromine or iodine atoms respectively. There are often lowercase letters following the numeric designations. The first appended letter is for substitutions on the central carbon atom, an x represents a chlorine substitution, y for fluorine, and z for hydrogen. The second appended letter designates substitutions on the terminal methylene carbon, =CCl2 is -a, =CClF is -b, =CF2 is -c, =CHCl is -d, =CHF is -e, and =CH2 is -f. Isomers are also designated by a Z or an E appended to the name for “zusammen” or “entgegen” respectively. Zusammen is German for together and entgegen is opposite; they represent cis and trans isomers respectively.
Cyclic compounds (R300 series), ethers, inorganic fluids (R700 series), and miscellaneous organic compounds (R600 series) have additional rules. The series are specified so the 000 series are methane based compounds, 100 are ethane based, 200 are propane based, and 300 are cyclic. The 400 series are zeotropes and 500 are azeotropes. The 600 series are other organic compounds. The 700 series are inorganic refrigerants such as ammonia, also known as R-717. The 1000 series which are unsaturated organic compounds such as the new R-1234yf refrigerant. R-1234yf is used for about half of all automobiles built after 2018 and it breaks down into short chained perfluorinated carboxylic acids; specifically, trifluoroacetic acid.
There are other code systems in use that are more field dependent as well. For instance, chlorofluorocarbons have a numbering system as do halogenated fire extinguishers. The Halon numbering system is in comparison very easy; there are always four numbers and left to right the digits represent carbon, fluorine, chlorine, and bromine atoms present in the molecule. For instance, Halon-1211 (CF2ClBr also known as Freon-12B1) and Halon-1301 (CF3Br which would also be known as R-13B1). On 1 January 1994 the United States banned the import and production of halons 1211 and 1301 under the Clean Air Act to comply with the Montreal Protocol. These halons are still allowed to be used and recycled halons may be purchased. Both Halon 1211 and 1301 have Class A, B, and C ratings. Halon-1211 is a “streaming agent,” and more commonly used in hand-held extinguishers because it discharges mostly as a liquid stream. Halon-1301 is a “flooding agent” and discharges mostly as a gas, allowing it to penetrate tight spaces and behind obstacles making it ideal for enclosed spaces commonly found in aircraft. The United States owns about 40% of global halon-1301 supply and it will likely stay in use for many years worldwide. Halon-1301 is critical as it was formerly the only material usable in enclosed spaces where humans were present.
CAS nomenclature
CAS stands for Chemical Abstract Service (CAS) and it is a division of the American Chemical Society. A CAS number is a unique identifier assigned by CAS to every chemical substance. It includes isotopes, mixtures, alloys, and substances which have unknown or variable composition. CAS numbers do not contain information about the substance structure unlike all previously discussed naming systems, simplified molecular-input line-entry system (SMILES), or the IUPAC International Chemical Identifier (InChI) system.
The same PFAS chemical in different forms will have differing chemical properties because of structural differences. For example, PFOS (perfluorooctanesulfonic acid) in its acid form (C8HF17O3S) has a CAS number of 1763-23-1, its potassium salt (C8F17KO3S) 2795-39-3, and its ammonium salt (C8H4F17NO3S) 29081-56-9.
F-Nomenclature
F-nomenclature was accepted by the American Chemical Society as an alternative to perfluoro nomenclature because some early fluorochemistry pioneers disliked perfluoro nomenclature. JH Simons in particular disliked perfluoro nomenclature. Simons invented the electrochemical fluoridization processes which was the first industrial process for producing perfluorinated compounds.
In F-nomenclature perfluoropentanoic acid (PFPeA – a C5 fully saturated carboxylic acid) would be F-pentanoic acid. As an aside, C5H10O2 which is pentanoic acid, is also known as valeric acid because it is the cause of the unpleasant smell in valerian.
Some elements of this naming system have survived. For instance, the symbol -R which indicates an organic backbone sometimes is written -RF to indicate a perfluoro backbone. Also, placing an F internal to a benzene ring structure is a shorthand saying that all the bonds off the ring not otherwise indicated are fluorine instead of hydrogen. A forerunner to F-nomenclature used a phi (φ) but was generally similar to F-nomenclature.
Other less common nomenclature systems
In the 1970s, J.H. Simons, an early fluorochemistry pioneer, advocated for placing “for” before the final syllable in standard hydrocarbon nomenclature to convey it was perfluorinated. Organofluorine Chemistry gives the following examples: CF4 as methforane and the perfluorinated version of ethene, CF2=CF2 would be ethforene.
Conclusion and Key Take Aways
Most PFAS naming systems are designed to reveal information about the basic chemical structure or function and to facilitate communication. In industrial settings where not many PFAS are used simultaneously it can be easier to use codes to cut down on potential errors common in systematic names. It is important to understand the basic names within your specific use.
This article is one of several on PFAS. You can read about PFAS discovery, structure, or all my articles on PFAS.
Per- and polyfluoroalkyl substances (PFAS) are a ubiquitous emerging public health threat. PFAS terminology can be extremely confusing because it looks like an alphabet soup of similar acronyms. This article is the first of two on PFAS terminology. This one intends to provide an overview of PFAS structure, the second one intends to help demystify PFAS terminology and nomenclature. My previous article on PFAS was on Dr. Roy Plunkett’s discovery of PTFE, a tetrafluoroethylene fluoropolymer.
Scope
The EPA’s comptox database lists over 9,252 PFAS; this is too large a class to name on individual bases. A systematic naming convention has evolved so that much information is conveyed with just the name. There are 5 main ways to name fluorinated compounds: the perfluoro nomenclature, F-nomenclature, code numbers, the International Union for Pure and Applied Chemistry (IUPAC) nomenclature, and Chemical Abstract Service (CAS) nomenclature systems. Additionally, fluorine chemistry as a field has existed long before those five systems were created and naming was not really standardized until Buck et al tried to harmonize conventions in 2011. The idea of this article is to provide an overview of common PFAS groupings, the second article will go into the five naming conventions.
Introduction
PFAS is a general nonspecific name encompassing a group of substances. There is no clear agreed upon definition of what exactly counts as PFAS. The Organization of Economically Developed Countries (OECD), the United States Environmental Protection Agency (EPA), and the World Health Organization (WHO) have all used various definitions. In the paper meant to harmonize conventions, Buck defined PFAS as “highly fluorinated aliphatic substances that contain 1 or more carbon atoms on which all the hydrogen substituents (present in the nonfluorinated analogues from which they are notionally derived) have been replaced by F atoms, in such a manner that they contain the perfluoroalkyl moiety CnF2n+1–.” This definition was the first clear PFAS definition. A moiety means part of a molecule. The OECD/United Nations Environment Program (UNEP) pointed out that Buck’s definition left out many substances commonly recognized as PFAS such as perfluorodicarboxylic acids and recommended the –CnF2n– moiety instead, although there is still debate surrounding this. Buck’s definition was updated by Glüge et al and informed the OECD/UNEP definition. Glüge’s definition expands Buck’s to cover perfluorocarbon chains with functional groups on both ends, aromatic substances with perfluoroalkyl moieties on side chains, and fluorinated cycloaliphatic substances.
Historical Note
As mentioned in the PFAS discovery article, PFAS were initially investigated to replace sulfur dioxide, methyl chloride, ammonia, and other extremely dangerous early refrigerants. This may jog your memory; the first major public PFAS concerns were mainly focused on perfluorocarbons under the 1987 Montreal and 1997 Kyoto Protocols. The Montreal Protocol aimed to limit chlorofluorocarbons. The Kyoto Protocol aimed to limit 7 greenhouse gas (GHG) categories and stated that climate change is real and driven by anthropogenic emissions. The GHG categories included perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs).
Unfortunately, early 2000 environmental scientists adopted the PFC acronym for PFAS instead of the perfluorocarbons identified in the Kyoto Protocol. There is still quite some confusion caused by this. While PFC is used in turn of the millennium PFAS literature it should be avoided now.
General Organofluorine Concepts
Carbon (C) bonded to fluorine (F) is the class basis for PFAS. The C-F bond is extremely persistent and the key factor for the problems PFAS causes as well as its desirable technical properties. Carbon can form up to 4 bonds with other atoms. The first broad distinction is between polymers and non-polymers. A polymer is a molecule made up of repeating subunits called monomers. Polymers often serve as the feedstock to produce other PFAS chemicals, the most widely recognized fluoropolymer is polytetrafluoroethylene (PTFE) which Dr. Roy Plunkett discovered on 6 April 1938.
Functional groups often serve as the basis for classification systems. A functional group is a moiety made of a specific structure which causes characteristic chemical reactions which are similar no matter what the rest of the molecular composition is. PFAS chemicals can also exist in multiple states such as acids, anions, cations, and salts which have important implications for their physical and chemical properties. Anionic forms are the environmentally prevalent form and the general form most authors refer to. Some legislation, particularly European Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH), defines substance to include impurities and stabilizers of the main PFAS compound.
Broad non-polymeric structure
Non-polymeric PFAS include perfluorinated and polyfluorinated substances. When carbon is bound only to fluorine except for functional groups it is called perfluorinated and the compound is saturated with F. When some carbon bonds include things other than functional groups or fluorine it is called polyfluorinated and is considered unsaturated with respect to F; hydrogen is the most common other bond. As PFAS stands for “per- and polyfluoroalkyl substances” and no single compound can be both unsaturated and saturated with respect to fluorine simultaneously “PFAS” is by default a plural acronym. Both per- and poly-fluoroalkyl substances are subdivided into classes where the functional groups behave relatively similarly. Two large classes are fluoroalkyl acids and fluoroalkane sulfonamides. These large classes are then subdivided again based on functional groups/moieties. For example, perfluoroalkyl acids are further subdivided into carboxylic, sulfonic, sulfinic, phosphoric, phosphinic, and other acid types. There are about 425 common moiety-based subdivisions within PFAS.
In 2017, Wang et al published an iconic chart covering the number of papers published on various PFAS groups reproduced below.
Conclusion and Key Take Aways
There is no clear definition on what PFAS encompass, even within regulatory organizations. There are about 9,252 PFAS substances which are broadly divided into polymeric and non-polymeric substances. Non-polymeric PFAS subclasses are based on carbon chain saturation with fluorine into full saturated (perfluoroalkyl) or non-fully saturated (polyfluoroalkyl) groups. Those groups are subdivided based on moieties/functional groups so that compounds which behave similarly are classified together. An upcoming article will cover the five common classification systems for individual compounds.
Per- and polyfluoroalkyl substances (PFAS) are a widely used class of chemicals. You’re probably familiar with some of the popular brand names employing these chemicals such as Teflon, Gortex, and Dockers Stain Defender. As our understanding of PFAS has evolved it is becoming an emergent public health threat. This article is the first in a series serving to provide information on PFAS and it will cover their discovery. Other articles in the series will cover concern, regulation, treatment, environmental fate, contaminated sites, consumer protection, uses and provide sources for further information.
Introduction
Per- and polyfluoroalkyls substances (PFAS) are a family of synthetic substances covering over 4,700 chemicals which have a number of deleterious health effects attributed to them. As of 7 June 2020 California, Connecticut, Colorado, Minnesota, North Carolina, New Hampshire, New Jersey, and Vermont all have state health guidelines for some PFAS. New Jersey’s limits just recently started on 1 June 2020. The US Environmental Protection Agency (EPA) has established a health advisory of 70 parts per trillion of combined PFAS. While PFAS is not directly regulated under the Toxic Substances Control Act (TSCA) it is monitored under the Significant New Use Rule (SNUR). On 20 February 2020 the EPA proposed a supplemental SNUR for PFAS.
Like most things, an exact beginning is hard to quantify. PFAS’ story could start in a letter dated 26 August 1812 when André-Marie Ampère wrote to Humphry Davy postulating the existence of fluorine, or in 1869 when Dmitri Mendelvee positioned fluorine in the periodic table. An equally rational choice would be 1886 when Henri Moissan first isolated elemental fluorine in France leading to his award of the 1906 Nobel Prize in chemistry. Another serious contender would be Thomas Midgley and A. L. Henne’s 1928 invention of Freon and other chlorofluorocarbons (CFCs) in their Fridgidaire laboratory, which at the time was a General Motor’s subsidiary. I am choosing to start PFAS’ story with Roy Plunkett’s 1938 discovery of Teflon and the birth of fluoropolymers.
Discovery
On 6 April 1938 at the Chemours Jackson Laboratory in New Jersey Dr. Roy Plunkett discovered polytetrafluoroethylene (PTFE) by accident while researching new CFC refrigerants. While CFCs are now banned for their deleterious atmospheric effects under the Montreal Protocol, at the time they were used to replace ammonia and sulfur dioxide refrigerants which killed dozens of workers annually. PTFE is better known by its brand name: Teflon. Although CFCs are perfluorinated compounds, PTFE was the first discovered chemical in the class of Per- and polyfluoroalkyl substances.
After work on 5 April 1938, Dr. Plunkett and his assistant Jack Rebok reacted tetrafluoroethylene (TFE) with hydrochloric acid then compressed the mixture into metal cylinders and froze it overnight. The next morning on the 6th of April, Jack Rebok placed one of the cylinders onto a balance then opened the stop valve. Only 990 grams of TFE came out of a supposedly 1 kg container. Puzzled by the mass balance, Dr. Plunkett tipped the cylinder over and a white powder fell out. Then Dr. Plunkett stuck a metal wire to try and get more of the substance out. He was unable to get much out that way so eventually Jack Rebok suggested to cut the flask open.
In Dr. Plunkett’s article The History of Polytetrafluoroethylene: Discovery and Development he wrote:
On the morning of April 6, 1938, Jack Rebok, my assistant, selected one of the TFE (tetrafluoroethylene) cylinders that we had been using the previous day and set up the apparatus ready to go. When he opened the valve — to let the TFE gas flow under its own pressure from the cylinder — nothing happened…We were in a quandary. I couldn’t think of anything else to do under the circumstances, so we unscrewed the valve from the cylinder. By this time it was pretty clear that there wasn’t any gas left. I carefully tipped the cylinder upside down, and out came a whitish powder down onto the lab bench. We scraped around some with the wire inside the cylinder…to get some more of the powder. What I got out that way certainly didn’t add up, so I knew there must be more, inside. Finally…we decided to cut open the cylinder. When we did, we found more of the powder packed onto the bottom and lower sides of the cylinder.
Instead of ignoring the powder Dr. Plunkett started experimenting on it and discovered PTFE is highly resistant to corrosive acids, has excellent performance in extreme temperatures, and does not dissolve in solvents. This along with its slippery nature lead to DuPont sending PTFE to its central research department. However, no real commercially viable use was found for PTFE.
Ironically, World War II saved Teflon from oblivion. On its own PTFE, what Dr. Plunkett discovered, is a relatively useless polymer. It melts at around 327°C (≈620°F) and under that temperature sits in a ball of nonflowing gel. PTFE does not dissolve in anything and does not react with acids, bases, or solvents and at the time cost about $100 per pound (about $1,820 per pound or $4.02 per gram in 2020 dollars) to manufacture.
The Manhattan Project was the US effort to develop the atomic bomb and the savior of PTFE. The Manhattan Project needed corrosion resistant materials to separate U-235 from U-238 using differential diffusion of UF6. After Lieutenant General Leslie Groves heard of PTFE’s inertness, he verified it could separate U-235 from U-238. Then following LTG Groves’ request, the US Patent Office placed PTFE under a “Secrecy Order” and it was referred to only as “K-416.” Following military interest, DuPont patented PTFE in 1941 and registered the trade name Teflon in 1944. The secrecy order lasted until 1946; by that time the Manhattan Project had paid for a great deal of research that otherwise would not have been carried out on the polymer and its manufacturing cost dropped tremendously.
Dr. Plunkett is also famous for leading DuPont’s team which added tetraethyllead (CH3CH2)4Pb to gasoline (which was phased out under the Clean Air Act) and for significant improvements to freon (a CFC refrigerant).
Brief PFAS Use Examples
The examples of PFAS extend across all facets of human life, from everyday household cookware to aerospace and electronics. PFAS’ widespread use takes advantage of its beneficial properties: chemical resistance, thermal stability, cryogenic properties, low friction coefficients, low surface energies, low dielectric constants, high volume and surface resistivities, and flame resistance. Once it was used to separate U-235 from U-238, the Manhattan Project immediately started finding other uses for PTFE. For example, PTFE was also used in the Manhattan Project in the antenna cap of proximity fuses thanks to its electrical insulating property and invisibility to Doppler radar. Fuel tank coatings used PTFE because of its resistance to low temperatures. After World War II, Teflon was turned to human well-being and started being used in catheters because of its low friction coefficient. PTFE was also used as insulation for wires and cables. It was even used during the Statue of Liberty’s renovations. PTFE often serves as a precursor for other PFAS chemicals which were ubiquitous until their dangers were realized. PFAS are used in fire fighting foams, ski wax, stain-resistant materials (rugs, clothing, furniture, sprayable stain protectors), cookware, outdoor gear, cosmetics, shaving cream, sunscreen, shampoo, and myriad other applications.
Conclusion
While it may seem easy to villainize Dr. Plunkett for his discovery’s degradation of the environment and damage to human health it is critical to remember Dr. Plunkett in the context of this time. Early refrigerants included sulfur dioxide and ammonia; both regularly poisoned people. His contributions to tetraethyllead boosted octane levels enabling, among other things, advanced plane flight and jets. His work introduced numerous new products and processes which are widely used in medicine, refrigeration, aerosol, electronic, plastics, and aerospace. Several of his innovations are of critical importance to national defense. There was also less awareness of the dangers of persistent chemicals to humans and the environment.
Further References
The EPA has designated Lahne Mattas-Curry as a point of contact and can be reached at mattas-curry.lahne@epa.gov
For more on the history and discovery of PFAS:
Plunkett R.J. (1986) The History of Polytetrafluoroethylene: Discovery and Development. In: Seymour R.B., Kirshenbaum G.S. (eds) High Performance Polymers: Their Origin and Development. Springer, Dordrecht https://doi.org/10.1007/978-94-011-7073-4_25
PFASproject.com – a group of faculty, post-doctoral scholars, graduate students, and undergraduates affiliated with the Social Science Environmental Health Research Institute at Northeastern University operating on an NSF grant