PFAS, known as per- and polyfluorinated alkyl substances, have come under extensive regulatory scrutiny over the past few years. Due to health and safety concerns, efforts are underway mainly in the European Union (EU) and the U.S. to restrict their use. If successful, the ramifications to lubricant manufacturers and end-users could be significant. 

The purpose of this article is to update readers on current efforts to restrict PFAS use, what test methods are in place to evaluate PFAS, what if any methods have been implemented to safely remove PFAS from the environment, what options have emerged to replace PFAS derivatives that are currently used as lubricants and lubricant additives and how replacing fluoroelastomer seals would impact manufacturing and, as a consequence, the future use of lubricants. 

In providing this update, assistance was obtained from the following four experts with knowledge in at least one of these areas. 
1. Dr. T. Reg Forbus, SantoLubes^® Manufacturing LLC 
2. Dr. John Howell, GHS Resources Inc. 
3. Dr. Khalid Malik, Ontario Power Generation 
4. Chuck Meek, Solve for X, L3C 

PFAS definition 
Obtaining a consensus for the definition of PFAS has been difficult. Chuck Meek, principal at Solve for X, L3C, in Traverse City, Mich., says, “Our recommendation is to use the Environmental Protection Agency (EPA) definition, which can be found in TSCA 8 (a) (7) PFAS Chemicals.”¹ 

EPA states that the definition of PFAS covers chemical substances with at least one of three structures. 
• R-(CF₂)-CF(R’)(R”), where both the CF₂ and CF functionalities are saturated carbons. C is the chemical symbol for carbon. 
• R- (CF₂)-O-CF₂-R’, where R and R’ can either be fluorine (F), oxygen (O) or saturated carbons. 
• CF₃C (CF₃) R’R”, where R’ and R” can be either fluorine or saturated carbons. 

This definition became effective in November 2023. 

Unfortunately, within the U.S., the definition of PFAS at a state-level is not consistent with EPA’s definition. As noted in a recent article,² some states designate PFAS as compounds with one fully fluorinated carbon atom while others consider PFAS to contain two perfluorinated or fully fluorinated carbons in a row. 

No matter the definition, the key requirement is that a PFAS contains carbon-fluorine bonds as shown in Figure 1. 


Figure 1. According to EPA, there are an estimated 15,000 PFAS in the environment which all have a carbon [C], fluorine [F] bond. Figure courtesy of Chemical Solutions.

As described in a recent review article³ co-authored by STLE Immediate Past President Dr. Hong Liang of Texas A&M University, PFAS were discovered through research conducted in the 1930s, with the first known patent published in 1939 that involved the discovery of tetrafluoroethylene polymers. The article states that PFAS became widely used due to their oil-repellent, water-repellent and high thermal stability characteristics. They are able to reduce friction and wear in many applications and are used in lubricants and coatings. 

Health and safety concerns 
STLE Fellow Dr. John Howell, principal at GHS Resources Inc. in Potlatch, Idaho, says, “There are a number of serious health effects that potentially can be traced to PFAS according to the EPA. As noted on EPA’s website,⁴ current peer-reviewed scientific studies have shown that exposure to certain levels of PFAS may lead to the following concerns shown below.” 
1. Reproductive effects such as decreased fertility or increased high blood pressure in pregnant women 
2. Developmental effects or delays in children, including low birth weight, accelerated puberty, bone variations or behavioral changes 
3. Increased risk of some cancers, including prostrate, kidney and testicular cancers 
4. Reduced ability of the body’s immune system to fight infections, including reduced vaccine response 
5. Interference with the body’s natural hormones 
6. Increased cholesterol levels and/or risk of obesity 

Howell points out that these adverse effects can occur with exposure to only very small amounts of PFAS. 

With the ability of PFAS to remain stable for long periods of time if not indefinitely, the chances exist that these substances can be present in all areas of our environment, including within human bodies. Of particular concern is that PFAS has been found in the water supply.  

Water is a very important raw material used for cooling in raw material, lubricant manufacturing and end-user facilities. Some lubricant types such as metalworking fluids also are formulated with water. This leads to the possibility that PFAS may be a contaminant in any manufacturing facility. 

Howell says, “The potential for PFAS to contaminate water is real. There is a real possibility that water contaminated PFAS may be getting into a lubricant manufacturing plant and potentially contaminating lubricants prior to shipment to end-users.” 

Meek concurs, “A high possibility exists that PFAS are present in water used by an organization manufacturing or using lubricants. Unfortunately, the technology for removing PFAS is not readily available to them.” 

Howell notes that the concern about PFAS contaminating the water supply led EPA to publish a final rule in April 2024 on PFAS in drinking water.⁵ He says, “Maximum contaminant levels (MCL or MCLs) for several PFAS include an MCL of four parts per trillion (ppt) for perfluorooctanoic acid (PFOA) and for perfluorooctylsulfonic acid (PFOS). Municipal water systems have until 2027 to complete initial monitoring and until 2029 to implement solutions to reduce the monitored PFAS to or below specific substance MCLs. If municipal water is used, for example, by a manufacturer of water-miscible metalworking fluids (MWFs), the MWFs produced in that plant, could, as a result of contaminated water, also contain PFAS. Ground water also may be contaminated, and the only way to know for sure is to test.” 

Table 1 lists the five PFAS that are regulated to a final MCL with a final maximum level contaminant goal (MCLG). The sixth substance consists of combinations of two or more PFAS as shown in Table 1. Measurement is done through the use of a hazard index. 


Table 1. EPA’s PFAS regulation published in April 2024 covers six substances shown. Table courtesy of Chemical Solutions.

Concern about PFAS in water is supported by a global study that was published in April 2024.6 The authors report that 31% of the 45,000 groundwater samples tested globally contained PFAS levels potentially harmful to human health even though they were not near any obvious source of contamination. A similar result was found with the 16% of surface water samples tested. 

Companies involved in producing lubricants can take steps to minimize PFAS exposure. Meek says, “Pay attention to the supply chain. Establish a ‘red/yellow/ green light’ triage system to determine what sources are the most likely culprits containing PFAS. Without a resource allocation plan, most or all of us will not have the capacity to effect change. Use the 80-20 rule: 80% of your risk likely resides in 20% of your supply chain.” 

Howell adds, “A lubricant manufacturer should first do an assessment of all possible sources of PFAS contamination from incoming water, from a fire-suppression system and from incoming raw materials. Then implement an action plan.” Fire-suppression is included because PFAS has been found in the past in fire-fighting foam that has leached into ground water. 

Raw materials based on fluorinated substances should be placed under immediate scrutiny by lubricant manufacturers. The best advice is to contact the specific raw material supplier and ask about a particular fluorinated substance. A lubricant manufacturer should ask for a reformulated raw material without fluorine or find a supplier with a viable non-fluorine containing alternative. 

Analytical test methods are available for determining PFAS content at the ppt level in drinking water. Howell says, “Contact laboratories can perform the needed testing using EPA protocols such as EPA Method 537.17 (Determination of Selected PFAS in Drinking Water by SPE and LC/MS/ MS) for drinking water.” 

EPA Method 537.1 can determine the presence of 18 PFAS in drinking water including HFPO-DA. 

Howell points out that no validated method exists for sampling, extracting and analyzing PFAS from a mineral oil or petroleum matrix and from water-based lubricants. He says, “The most likely approach would be to combine the extraction procedure embodied in EPA Method ACB B21-028 followed by analysis using EPA Method 1633 (Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/ MS).⁹ When validated using, for example, an ASTM interlaboratory testing program, this testing strategy should work.” 

Howell indicates that EPA Method 1633 is a good place to start in analyzing water-based lubricants. He says, “Several waterborne lubricant matrices need to be prepared with known treat rates of specific PFAS such as PFOA and evaluated using EPA Method 1633 to determine PFAS content. The challenge is that individual PFAS vary in their water and solvent/oil solubility, and that is why validation of any method chosen for analysis is a must.”  

Methodologies to evaluate specific PFAS use liquid chromatography followed by tandem mass spectroscopic analysis. Howell cautions that both procedures should only be conducted by experienced personnel well versed in using both techniques. Newer methods for determining total organic fluorine are under development but are not yet validated for lubricant matrices. 

Meek considers EPA Method 1633 to be the current gold standard for detecting PFAS. He says, “While there are several laboratories in the U.S. that can measure for PFAS, there is a dearth of capacity relative to growing demand, making it hard to get test results in a timely manner. More laboratories need to become involved in offering PFAS analysis.” 

Meek considers health and safety concerns for PFAS to consist of three developing technologies: detection, isolation and destruction. He says, “With EPA estimating that there are at least 15,000 PFAS in the environment, isolation technologies are significantly ahead of the other two. This imbalance has created a significant issue in managing PFAS contamination.” 

The problem is that when PFAS are detected, the hazardous material can be readily isolated, but there are no procedures in place to efficiently destroy them according to Meek. He says, “This creates a large stockpile of PFAS contaminated materials that can only be destroyed through the use of processes that are not energy efficient. Individuals and organizations can easily catch PFAS fatigue because of the perception that the destruction problem is too big to solve without draining the treasury or diverting too much attention and resources away from other needs.” 

But it has not happened yet. The EU called for the complete elimination of PFAS. After feedback from representatives of various industries, the EU announced in March 2024 that meetings will be held to discuss whether PFAS should be restricted in metal plating and manufacture of metal products, petroleum and mining.¹⁰ 

Meek says, “The EU approach could become law, but it begs the question: How will it be enforced?” 

Currently there are three approaches for removing PFAS from water used by consumer and industrial users. Meek says, “Organizations can utilize reverse osmosis (RO) to purify water, filter with granular activated carbon or work with ion exchange media.” 

Potential methods for destroying PFAS have focused on existing technologies such as pyrolysis. Meek says, “New techniques, such as carbon re-pyrolization, are under development. For example, TimberChar™, nominally developed to remove phosphorus and other nutrients that cause harmful algal blooms (HABs), turns out to be extraordinarily effective in sequestering PFAS. Re-pyrolyzing the ‘loaded’ char has presented an unexpected option for destruction, an unforeseen benefit.” 

The rapidly changing nature of PFAS regulations has led to confusion as organizations strive to comply. Meek says, “In the U.S., PFAS regulations are mainly controlled by the states and represent a patchwork effort. EPA has started to enact federal rules, but this is occurring at a slow pace.” 

Howell reports that EPA published a final rule on PFAS requiring any person that manufactures (including importing) or has manufactured (including imported) PFAS or PFAS-containing articles in any year since Jan. 1, 2011, to electronically report information regarding PFAS uses, production volumes, disposal, exposures and hazards.¹¹ He says, “At the moment, only PFAS manufacturers or importers are required to report; while processors of PFAS, which may include lubricant manufacturers, are not required to report now, though they should become familiar with this rule.” 

Howell continues, “Additionally, EPA proposed new rules under the Resource Conservation and Recovery Act (RCRA) to list certain PFAS as RCRA hazardous constituents in February 2024.¹² 

Two of the nine PFAS, PFOA and PFOS on the RCRA list also were designated by EPA as hazardous substances under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in April 2024.¹³ This measure requires any organization knowingly releasing PFOA and PFOS into the environment must report it within 24 hours. 

The advice from Meek and Howell is for those U.S.-based organizations to not just check federal regulations but recognize that awareness of different state laws is mandatory in doing business. 

Replacement of PFAS derivatives used as lubricants 
As regulations potentially restrict the use of PFAS derivatives as lubricants, interest in alternatives is increasing, but finding them can be challenging. STLE member Dr. T. Reg Forbus, president and CTO of SantoLubes^® Manufacturing LLC in Spartanburg, S.C., discusses a specific class of fluorinated lubricants currently in use and why this type is so difficult to replace. He says, “The most widely used fluorinated lubricants are perfluoroethers made typically from perfluoroethylene oxide, perfluoropropylene oxide and difluoroformaldehyde or combinations of these three starting materials. The notable performance features of perfluoro fluids are their high to extremely high viscosity indices (VI) and low pour points. Perfluoroethers also display exceptional thermal and oxidative stability, very low vapor pressures, excellent radiation resistance, non-flammability and compatibility with nearly all seal materials.” 

Forbus stated that these beneficial properties of perfluroethers can vary widely with component composition. 

Three specific characteristics make perfluoroethers very difficult to replace. Forbus says, “Their ultra-high temperature thermal and oxidative stabilities (300°C+), radiation stability and ultra-low vapor pressures make them very hard to replace for extreme conditions and harsh environments.” 

Two potential non-fluorinated lubricant alternatives are silicones and polyphenyl ethers (PPEs). Forbus says, “Silicone fluids can be made with diverse structures due to two branching groups present on the silicon atoms on the silicon-oxygen backbone. They can be made in a wide range of viscosities from the structure diversity and range of molecular weight capabilities. Proper selection of the branching groups allows for tailoring a wide range of properties but not the ability to co-optimize many critical lubricant properties. However, no silicone fluid is capable of matching the exceptional thermal and oxidative stability properties, nor the radiation resistance, of perfluoroether fluids. The best thermally stable silicone is only stable to 271°C (520°F), well below perfluoroethers that are stable to 400°C (750°F).” 

Forbus claims that PPEs are the only fluid technology capable of matching the exceptional thermal and oxidative stability, and the radiation resistance properties of perfluoroether fluids. He says, “PPEs are short strings (three to six typically) of unsubstituted benzene rings connected together by an oxygen. The five-ring PPE is thermally stable to 465°C, which exceeds the best perfluoroether that is stable only up to 400°C prior to thermal breakdown.” 

Applications where PPEs can replace fluorinated lubricants due to their excellent properties include high vacuum applications, electronic connector lubricants, high temperature optical coupling fluids, high temperature heat transfer fluids, oven chain lubricants and high radiation stable fluids. Forbus discusses, “PPEs high temperature stability combined with their extremely low vapor pressures above 445°C makes them exceptional for ultra and very high vacuum applications. They also function as exceptional electronic connector lubricants for protection against insertion damage, fretting wear and environmental corrosion, from their high surface tensions and non-migrating attributes. PPEs are useful as high temperature optical coupling fluids with high refractive and thermos-optic coefficients.” 

In contrast to most lubricants that wet and form a continuous film on surfaces to create a protective layer between two surfaces, PPEs are different and instead lie on a surface not as a continuous film but as a continuous field of microscopically small droplets. Forbus says, “This unusual situation is a result of PPE’s high surface tension (50 dynes/cm range). The whole field of droplets remains where it was applied, even under pressure and even at high temperatures. No other known lubricants have this useful property of positional stability.” 

Forbus discusses one of the initial applications for PPEs and where they are currently in use. He says, “In 1970, when the supersonic SR-71 spy plane was under development, designers faced a significant obstacle; there was no lubricant that could withstand the sustained operating temperature of 316°C (600°F) of the aircraft’s two axial- flow turbojet engines with afterburners. A PPE fluid was found to be able to cleanly withstand this temperature and provide lubrication to keep the engines from destroying themselves.”  

Forbus continues, “Since the 1970s, new uses for PPEs have been turning up in all sorts of unexpected places that endure extreme conditions, adverse environment and challenging applications. As an example, there is a strong probability that a minute amount of PPE is with you right now on the electrical connectors in your cellphone!” 

Seals 
The possibility that PFAS may not be allowed to be used in the future may lead to concerns about what types of seal materials (see Figure 2) will be available and whether they will be compatible with the current lubricant types approved for specific applications. Fluoroelastomers have been found to be one of the materials of choice in seals due to their inertness to lubricants. Before discussing the implications of what will happen if PFAS-based elastomers cannot be used, the types of seals and their compatibility with lubricants is covered. 


Figure 2. There are at least 12 elastomers that are used to make seals. Fluoroelastomers, containing PFAS, exhibit unique performance characteristics in many applications making them difficult to replace. Figure courtesy of Ontario Power Generation.

STLE member Khalid Malik, CLS, OMA I & II, Lead Auditor General, Nuclear Oversight at Ontario Power Generation in Pickering, Ontario, Canada, lists the most common seal types used in machinery below. 
• Static seals 
• Reciprocating seals 
• Oscillating seals 
• Rotary seals 
• Seat seals 
• Pneumatic seals 
• Vacuum seals 

These seals can be prepared with the 12 elastomers listed in Table 2. 


Table 2. The 12 elastomers used to produce seals are listed. Table courtesy of Ontario Power Generation.

In selecting a seal elastomer, care must be taken in determining if the specific material is compatible with any lubricant that may come into contact with it. Malik provides an extensive evaluation of the compatibility of the 12 elastomers with mineral oil products, synthetics/chemicals and water- based lubricants in Table 3. The one elastomer compatible with all three types is tetrafluoroethylene-propylene. 


Table 3. Performance characteristics for the 12 elastomers in mineral oils, synthetics/chemicals and water-based lubricants are shown. Table courtesy of Parker Seals Handbook.

Malik comments on the performance benefits of fluoroelastomer seals. He says, “Some kinds of fluoroelastomers or fluorinated hydrocarbon rubber products have excellent resistance to high temperatures (320°C), high radiation, ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics and many organic solvents and chemicals. Low temperature resistance is normally not favorable and for static applications is limited to approximately -26°C, although certain compounds are suitable down to -46°C. Under dynamic conditions, the lowest service temperature is between -15°C and -18°C. Gas permeability is very low and similar to that of butyl rubber. Special fluorocarbon elastomer compounds exhibit an improved resistance to high radiation, acids and fuels.” 

When asked if any other non-fluorinated seal type has comparable properties to fluoroelastomers, Malik states that no single material exactly performs in a comparable manner to fluoroelastomers. He adds, “The closest option is ethylene propylene rubber (EPDM), which performs well in both high and low temperature situations, though it best functions at a different temperature range than fluoroelastomer, with an effective operating temperature range of -45°C to 145°C. So, while EPDM can withstand colder temperatures than certain kinds of fluoropolymer elastomers, it cannot withstand hotter temperatures than its counterpart. EPDM offers exceptional moisture and chemical resistance and can withstand many diluted acids; however, it’s not suitable for hydrocarbons, such as oils, gasoline, kerosene and mineral oil-based lubricants.” 

As to what will happen if fluoroelastomer seals are banned from use, Malik admits this is a tough question to answer at the present time. He says, “Fluoroelastomers are widely used in nuclear, aerospace and other industries because of their unique properties and enhanced life expectancy. Replacement of elastomeric products for such unique applications could be a big challenge and might need exceptions from the regulators until a suitable alternative is available. Comprehensive research is required to explore new options.”  



Future outlook 
Howell indicates that regulating PFAS around the world is going to continue with different jurisdictions implementing regulations at different speeds, but the trend is clear. He says, “Customers and regulatory bodies will want to know if the lubricants they are using contain PFAS. If they do, the next question will be, why do they contain PFAS?” 

Meek advises, “Better technology will become available to detect and measure PFAS, and scalable technologies will be developed to destroy them. Until then, the best approach for lubricant manufacturers is to focus on what can be controlled: take small steps to address customer concerns and seek answers from suppliers.” 

Malik says, “The potential ban on fluoroelastomer may impact formulation of fuels and lubricants formulation. Base oil and additive compatibility with elastomers and o-ring gaskets are important considerations in the design phase. This area needs to be explored for new alternatives.” 

While research on how extensively PFAS are contaminating the environment is ongoing, and studies are trying to determine the health and safety ramifications of these fluorinated materials, too little is still known. The lubricant and tribology field is still faced with too many questions and not enough answers. Hopefully more information will become available in the future to provide direction on how to deal with PFAS. As stated by contributors to this article, monitoring regulatory developments will be mandatory now and into the future.

REFERENCES
1. https://cdxapps.epa.gov/oms-substance-registry-services/substance-list-details/490
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4. www.epa.gov/pfas/our-current-understanding-human-health-and-environmental-risks-pfas
5. www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas
6. Grunfeld, D., Gilbert, D., Hou, J., Jones, A., Lee, M., Kibbey, T. and O’Carroll, D. (2024), “Underestimated burden of per- and polyfluoroalkyl substances in global surface waters and groundwaters,” Nature Geoscience, 17, pp. 340-346.
7. www.epa.gov/water-research/pfas-analytical-methods-development-and-sampling-research
8. www.epa.gov/system/files/documents/2021-09/epa-pfas-method-in-oil.pdf
9. www.epa.gov/system/files/documents/2024-01/method-1633-final-for-web-posting.pdf
10. www.echa.europa.eu/-/next-steps-for-pfas-restriction-proposal
11. https://epa.gov/assessing-and-managing-chemicals-under-tsca/tsca-section-8a7-reporting-and-recordkeeping
12. www.epa.gov/hw/proposal-list-nine-and-polyfluoroalkyl-compounds-resource-conservation-and-recovery-act
13. www.epa.gov/epcra/designation-pfoa-and-pfos-hazardous-substances-under-cercla-release-reporting-requirements