Ongoing Crisis of PFAS Contamination of Drinking Water Supplies

The reality of PFAS and why the filtration must address this critical water issue now more than ever.

PFAS is the acronym for “per- and polyfluoroalkyl substances.” They are a class of humanmade (anthropogenic) organic chemical compounds that have multiple fluorine atoms attached to an alkyl chain.

A clear and universally accepted definition of what constitutes a PFAS does not now exist. The term “polyfluoro” implies two or more alkyl fluorines anywhere in the molecule. The EPA’s CompTox Chemicals Dashboard contains over 30 PFAS lists, with one list naming more than 11,000 chemicals (doi: 10.3389/fenvs.2022.850019).

These chemicals have been manufactured since the 1950s and are present everywhere: in water, air, soil, food, and now are present in the bodies of virtually all living beings, including people. Because the carbon-fluorine bond is extremely difficult to break, PFAS are considered indestructible and called “forever chemicals.”

Many PFAS are known to bioaccumulate in humans and other animals. Extremely low concentrations (nanograms/liter) of some are suspected to cause health issues. The vast majority of PFAS have not been evaluated for toxicity, but numerous investigations are underway.

This combination of chemical inertness, ubiquitous presence in the environment, and suspected toxicity at low concentrations have earned PFAS the title of the most consequential water contamination issue in our lifetime.

Peter Cartwright entered the water purification and wastewater treatment industry in 1974 and has had his own consulting engineering firm since 1980. He has a degree in Chemical Engineering from the University of Minnesota and is a registered Professional Engineer in that state. Peter has provided consulting services to several hundred clients globally. He has authored over 300 articles, contributed to books, presented at 300+ conference lectures globally, and is the recipient of several patents. He serves the industry as an extensive expert witness, technology educator, and member of many editorial advisory boards and technical review committees. As Technical Consultant for the Canadian Water Quality Association from 2007 until 2018 and the 2016 McEllhiney Distinguished Lecturer for the National Ground Water Research and Educational Foundation, he presented over 35 lectures globally on groundwater contaminant mitigation. Peter is a recipient of the Award of Merit, Lifetime Member Award and Hall of Fame Award from the Water Quality Association and received the 2022 Frank Tiller Award from the American Filtration & Separations Society. Reach him at www. cartwright-consulting.com or peterscartwright@gmail.com

Although PFAS have been in use for many years, concerns about their environmental and health impacts are relatively new, and these water contaminants have only recently attracted the attention of the public.

We currently know very little about PFAS behavior in the environment, their specific health effects, and removal and destruction technologies.

Sources

Environmental sources of PFAS include landfill leachate, biosolids, AFFF (aqueous film forming foam) subsurface plumes, wastewater plant discharge, stormwater runoff, and the air we breathe. The two most commonly encountered compounds are PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonic acid). These compounds are most commonly associated with the manufacturing of Teflon™ and Scotchgard™ products, respectively; however, they have also been used in coatings for paper, cardboard, and leather products, as surfactants, emulsifiers, wetting agents, coatings, and in many other applications.

Examples of common products which have contain PFAS include:

• Cosmetics • Menstrual products

• Electronics • Upholstery

• Nail polish • Toilet paper

• Dental floss • Fast-food wrappers

• Carpeting • Artificial turf

• Fertilizer • Paper drinking straws

Although most U.S. manufacturers are no longer producing PFAS compounds (or plan to phase them out shortly), these compounds are still ubiquitous in the country and are being imported into numerous products.

Chemistry

The molecular structures of PFOA and PFOS are illustrated in Figure 1. From that Figure, note that PFOA has a carboxylic acid “head,” while PFOS has a sulfonic “head.” They are both surfactants and are very water-soluble. The huge number of PFAS compounds encompasses a diverse range of molecular weights and physicochemical properties.

Health Issues

The fact that PFAS can enter the human body via eating, drinking, and breathing contributes to their detrimental health effects. It is estimated that virtually all of us have PFAS in our bodies. They accumulate primarily in the kidney and liver. These compounds are associated with a myriad of health issues, including many cancers, liver, thyroid, and reproductive disorders, pregnancy issues, tooth decay, and the list goes on and on.

p Figure 1.

In general, acute health effects of toxic chemicals such as arsenic are much more rapidly identified than the chronic (longterm) effects of chemicals such as PFAS that may bioaccumulate in low doses over many years. The data acquisition and analysis required to determine a risk level necessitate careful, meticulous, and deliberate scientific methods.

• A 2022 study from Harvard Medical School and Sichuan University in China estimated exposure to PFOS may have played a role in the deaths of more than 6 million people in the U.S. between 1999 and 2018. (doi/org/10.1289/EHP10393).

• A May 2024 issue of the International Journal of the Hygiene and Environmental Health describes a Dartmouth study that documents how PFAS can cause the production of breast milk in new mothers to slow or stop altogether within six months of birth (https://doi.org/10.1016/j. ijheh.2024.114359).

• There is evidence that some PFAS can cross the Blood-Brain Barrier and enter the brain.

• A recent Yale University study shows evidence that exposure to high levels of PFOA and PFAS may increase the growth of colorectal cancer.

• The National Academies of Sciences publication, Guidance on PFAS Exposure, Testing, and Clinical Follow-Up (2022) (nap.nationalacademies.org/26156) provides a comprehensive summary of the potential health effects of PFAS. Yet, we know so very little to date. This same publication indicates that the half-life (the time it takes for the blood plasma concentration to decrease by 50%) of the PFAS studied ranges from two to eight years in humans. as 0.000001 mg/L (milligrams per liter). A part per trillion is equivalent to one second in about 32,000 years. EPA Health Advisories are just that – advisories and are not enforceable.

• Since children drink more water, eat more food and breathe more air per pound of body weight than adults, their PFAS exposure is of greater concern. Children are also more likely to be exposed to these chemicals in carpeting, toys, dirt and dust.

Regulatory

On April 10, 2024, the EPA issued a National Primary Drinking Water Regulation Maximum Contaminant Level (MCL) for six PFAS, listed in the Figure 2.

Mixtures of two or more of PFHxS, PFNA, GenX and PFBS (Hazard Index) 1.0 (unitless) 1.0 (unitless) p Figure 2.

• A recent study of 17 of the more widely used PFAS revealed that 15 compounds showed substantial dermal absorption through the skin into the bloodstream of humans. This suggests that, in addition to the routes of ingestion and inhalation, PFAS can also be absorbed through the skin (https:// www.birmingham.ac.uk/news/2024/ new-study-confirms-forever-chemicalsare-absorbed-through-human-skin). The intense research addressing the health effects of PFAS will undoubtedly lead to the discovery of additional concerns.

• In June 2022, the EPA issued a Health Advisory Level for PFOA and PFOS (based on “a robust assessment of the best available science at that time”) of 0.004 ppt for PFOA and 0.02 ppt for PFOS. We lack the ability to analytically measure these tiny concentrations at this time. The measurement “ppt” refers to parts per trillion or nanograms per liter and is mathematically expressed

Both MCLs and MCLGs are expressed in parts per trillion (ppt), which is the same as nanograms per liter (ng/L). The EPA defines MCLG (Maximum Contaminant Level Goal) as the level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable. They are just that – goals.

The EPA defines an MCL as the highest level of contaminant that is allowed in drinking water supplies. MCLs are set as close to MCLG levels as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards. These standards require all public water systems to produce water containing no more than these levels of these contaminants. The public systems must also continuously monitor and inform the public about these levels in their drinking water.

The table includes a statement regarding mixtures of two or more of four PFAS and identifies these as a Hazard Index.

This is not based on concentrations but rather on the ratios of each PFAS relative to its Health-Based Water Concentration. This approach is commonly used for Superfund treatment applications.

Public water systems must monitor for these PFAS, which must be completed by 2027, and provide the results to the public. By 2029, all U.S. public water systems must produce drinking water that meets the listed levels.

The EPA estimates that the cost to affected drinking water treatment plants for testing, installation, and operation of treatment technologies will be $1.5 billion per year; the American Water Works Association (AWWA) states that the figure will be at least twice that.

On the health side, the EPA estimates that this regulation will save $1.5 billion/ year in health-related costs because fewer people will get cancer, heart attacks and strokes from PFAS in their drinking water.

Not surprisingly, lawsuits have started to appear. Water utilities and chemical companies are targeting the science, cost analysis, and rulemaking process of the EPA. These entities claim that the rule is arbitrary and capricious and based on unsound data.

The U.S. EPA has also designated PFOA and PFOS as “hazardous substances” under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). This designation provides the agency greater authority under the 1980 Superfund Law to investigate and to force polluters to clean up contaminated sites. The EPA has stated that it plans to focus its efforts on companies that manufacture or use PFAS in products, rather than on publicly owned water systems, airports, landfills, or fire departments. The agency has identified over 180 Superfund sites with PFAS contamination.

With such a large number of different PFAS in the environment, it is obvious that this initial set of regulations is only the tip of the iceberg. We have almost no knowledge of the interactions between PFAS and other chemicals in water. Considering this and the fact that PFAS are ubiquitous adds credence to the intense concerns about these contaminants and their prominent place in the media spotlight. So, what can be done?

Eliminate PFAS Introduction

The obvious elimination of manufactured products containing PFAS will ultimately reduce exposure to these compounds; however, given the extensive use of these products by everyone and the erratic pace of voluntary replacements of PFAS in these products, this will likely take many years. Additionally, traces of PFAS are found in soils, oceans, water aquifers, and the air - virtually everywhere. We are in constant contact with them.

In most cases, the industry is trying to replace those products under scrutiny with PFAS-free components. This effort will take time and the replacement solutions are often more expensive. One such example is the development of a PFAS-free aqueous film forming foam (AFFF), a significant source of contamination. The U.S. Department of Defense has spent 10 years developing this product. However, due to the roadblocks of cost (over 20% more expensive), equipment changes, training, and other challenges, officials at the Pentagon are expected to request a two-year extension for implementation, according to a July 16, 2024 post on www.military.com. Additionally, there are some products (semiconductors and certain medical devices) for which alternatives may not be available. Whereas it is possible to minimize the introduction of PFAS into the environment, it may not be possible to eliminate them completely.

Removal

Removal of all PFAS contamination from oceans, soil and air will be extremely difficult, if not impossible; however, remediation of drinking water supplies is feasible and the focus of significant activity at this time.

The regulatory activities mentioned are directed at cleaning up drinking water supplies and we will address the technologies to accomplish this effort.

Treatment of Drinking Water Supplies

The technologies most appropriate for PFAS removal from normal water supplies, both municipal and private wells, are:

1) Granular activated carbon (GAC)

2) Anion exchange resins (IX)

3) Reverse osmosis (RO)

4) Foam Fractionation

In my opinion, GAC will likely be the initial technology of choice for municipalities to meet the new MCL requirements to remove all PFAS from water. GAC technology has a long history of successful use in municipal water treatment applications for removal of various organic contaminants; it is readily available and relatively inexpensive. On the other hand, the raw material source of the activated carbon affects its PFAS adsorption capability, and GAC appears to have limited sorption potential for short-chain PFAS. There is a lack of agreement on the definition of “short-chain;” however, it commonly appears to refer to a carbon skeleton of fewer than 7 carbon atoms. Of course, the technology selection will need to meet several variables, including the specific PFAS and other factors. Piloting these efforts will certainly be required.

1) Activated carbon is typically made from carbonaceous sources (often waste material) such as coconut husks, coal, lignite, peat, wood and petroleum materials. It is physically activated by heating in an inert atmosphere followed by oxidation in the presence of steam or oxygen. This process produces a material with very high porosity and high surface area. One gram of activated carbon has an estimated surface area of over 32,000 ft². Activated carbon removes contaminants from water by a process called adsorption, the attachment of the chemical to the surface of the carbon through Van der Waals forces, often inside its pores. Activated carbon is available in several forms: granular, powdered, colloidal, block, extruded. GAC made from bituminous coal appears to be most effective for PFAS adsorption.

2) Ion-exchange (IX) resins are small plastic beads engineered to remove ionic contaminants utilizing an adsorption mechanism similar to that of activated carbon. Anion IX resins are effective in removing most PFAS and are claimed to remove them more rapidly than GAC (faster kinetics).

A recent development involves stripping the adsorbed PFAS off the resins with a specialized solvent-brine solution and recovery of the solvent by distillation (cen.acs.org/environment/persistentpollutants/Getting-PFAS-drinking-water/ 102i20). The “still bottoms” contain PFAS concentrated by a factor as high as 50,000 to facilitate destruction. Since the solvent is currently methanol, the process does not comply with NSF/ ANSI 61 and cannot be used for drinking water applications.

3) Reverse osmosis is a crossflow, pressure-driven membrane separation process, utilizing a semipermeable membrane which is designed to reject ionic contaminants and organic compounds with molecular weights above roughly 150 Daltons. This technology produces two streams: one which passes through the membrane and is purified (permeate), and one that passes across the membrane surface and carries away the contaminants (concentrate). Because the contaminants are continuously removed, this is a continuous process, although the membrane will eventually become fouled and require cleaning or replacement. Reverse osmosis is considered effective for removal of all PFAS.

4) Nanofiltration is another membrane separation technology, very similar to reverse osmosis, but capable of rejecting organic compounds with molecular weights no less than about 300 Daltons.

5) Foam fractionation involves introducing air bubbles into water which rise to the surface carrying PFAS with them. Many PFAS are surfactants with hydrophilic “heads” and hydrophobic “tails.” This characteristic causes them to preferentially accumulate at the air-water interface of the bubbles, and this concentrated surface layer (up to 10,000 times) can then be removed and further treated. Using ozone instead of air has been studied and appears to offer cost savings by producing significantly less foam volume (doi.org/10.1016/j.watres.2024.121300).

Whereas no technology will remove 100% of any contaminant, comprehensive testing of the above technologies has exhibited over 99% PFAS removal. Several of these technologies show promise to concentrate PFAS to improve the operation of the destruction technologies described below.

Treatment of Groundwater Plumes

In applications where PFAS has contaminated a groundwater (aquifer) supply, the following techniques can be employed:

1) Pump and Treat

2) Colloidal Activated Carbon (CAC)

Pump and Treat involves pumping contaminated water out of the aquifer, treating it with one of the above technologies, and then returning it to the aquifer. This process has been used for over 40 years for groundwater remediation, primarily for chlorinated contamination removal. A downside of this process is that some contaminants, especially PFOA and PFOS, adhere to soil solids and resist removal during the pumping process.

Colloidal Activated Carbon consists of finely ground carbon particles (<2μ size). These are injected into the contaminated aquifer and adsorb PFAS in situ. The particles of activated carbon are sorbed onto the soil solids and remain there indefinitely. As the treated water remains in the aquifer, no waste management is required, and human exposure to PFAS is not required. Additional CAC can be reinjected as necessary, and it is reported that total cost of this approach is less than 1/3 of the pump and treat process.

 Figure 3.

PFAS Destruction

It is essential to note that none of the above technologies will break down PFAS into its basic chemical components (e.g., carbon dioxide, fluoride ions, and water); however, intensive research is underway to develop destructive (mineralization) technologies. The challenge is that the carbon-fluorine chemical bond is extremely strong, likely the strongest known (in the range of 485kJ/mol).

Fortunately, humans are very innovative. This challenge is manifesting results in the plethora of new technologies under development and in various phases of commercialization.

Most PFAS are either carboxylic or sulfonic acid-based surfactant species with fluoroalkyl chains of varying lengths. This significant variation translates into challenges regarding the efficacy of specific destruction technologies. Some compounds may not be completely mineralized and just produce shorter chain length PFAS.

The key to complete destruction is to harness and control the necessary energy to accomplish this.

Rather than detailing specific manufacturers, I have chosen to attempt to list the particular technology categories being investigated.

These are:

• Thermal

• Supercritical water oxidation (SWCO)

• Hydrothermal Alkaline Treatment (HALT)

• Electrochemical Oxidation

• Photocatalysis

• Plasma

• Sonolysis

• Bioremediation

Thermal Incineration is an energy-intensive process and gaseous toxic compounds can be released into the environment; however, it appears that at temperatures above 1000°C, mineralization of PFAS is possible. In the September 13, 2022 issue of Remediation (doi.org/10.1002/rem.21735), a research article, titled “Thermal destruction of PFAS during full-scale reactivation of PFAS-laden granular activated carbon,” details the utilization of a multi-hearth furnace followed by a thermal oxidizer, spray quench cooler, dry injection scrubber, and baghouse to regenerate granular activated carbon, which has been used to adsorb PFAS from water supplies. The overall destruction efficiency of the targeted compounds (PFOA, PFOS, GenX and PFBS) exceeded 99.99%.

An illustration of two of the heating systems used in the reactivation process in Figure 3. Pyrolysis, the destruction of organic matter by heating in the absence of oxygen, has been investigated for PFAS mineralization; however, it appears to be more applicable for contaminated soil treatment.

Supercritical Water Oxidation (SWCO)

A supercritical fluid is a substance at a temperature and pressure above its critical point. For water, this point is 374°C and 3200 psig respectively. Above this critical point, water is neither a liquid nor a gas, but has properties of both: salts become insoluble and oxygen extremely soluble.

To break down PFAS, an oxidant (air, oxygen, hydrogen peroxide) is added and the resulting hydrofluoric acid is typically neutralized with sodium hydroxide.

Exposure of organic compounds to ultraviolet (UV) radiation wavelengths below 320 nm can result in photolysis, the photodissociation of polymer chains, theoretically breaking the compound down into its basic components.

A 2022 study, under the direction of the EPA Office of Research & Development, evaluated the efficacy of this technology to destroy PFOA and PFOS in dilute aqueous film-forming foam (AFFF). Three providers of SWCO systems were tested. All systems showed a greater than 99% reduction of these compounds (doi. org/10.1061(ASCE)EE.19437870.0001957).

Although this technology has high energy requirements, it appears to destroy PFAS, regardless of chain length, and the reaction time is quite fast. A chart illustrating the chemistry is ilustrated in Figure 4.

Hydrothermal Alkaline Treatment (HALT)

Somewhat related to SWCO, this technology utilizes a high pH (~14) and pressure (~3600 psi) at a temperature of about 350°C to effect PFAS destruction. Under these conditions, the water is considered in a “subcritical” (liquid) state. Some testing performed has indicated that faster reaction times can be achieved by adding a powdered heavy metal, such as iron. A comprehensive explanation of the technology can be found on www. sciencedirect.com/science/article/abs/ pii/S0045653522041741.

 Figure 4.

Electrochemical Oxidation

The EPA defines this technology as “… a water treatment technology that uses electrical currents passed through a solution to oxidize pollutants” (www.epa. gov/research/potential PFAS destruction technology:electrochemical oxidation). It utilizes an anode and cathode with direct current power. The advantages are low energy costs, ambient temperature operation, and no chemical addition. Disadvantages include the potential for incomplete destruction, anode fouling, electrode cost and potential PFAS volatilization issues.

The electrode material of choice appears to be a boron-doped diamond (BDD), with excellent mechanical, chemical, and thermal stability and high electron transfer properties. The exact mechanism of PFAS destruction is not entirely understood, and long-chain compounds are more rapidly broken down, apparently the result of their greater hydrophobicity. ACS EST Water 2023 (doi.org/10.1021/ acsestwater.2c00660). Electrochemical oxidation is illustrated in Figure 5.

Photochemical Oxidation/Photocatalysis

Supercritical Water Oxidation

Exposure of organic compounds to ultraviolet (UV) radiation wavelengths below 320 nm can result in photolysis, the photodissociation of polymer chains, theoretically breaking the compound down into its basic components. The two most commonly tested UV wavelengths are 185 nm and 254 nm, and destruction results from the generation of photons. Competitive organic contaminants such as NOM (natural organic matter), as well as environmental conditions (temperature, pH, etc.), limit the photolysis of PFAS. The addition of oxidants (ozone, hydrogen peroxide, EPA