Innovative problem-solving needed as the true depth of PFAS contamination and its effects on humanity remain up in the air
You may have seen or heard the term per- and poly-fluoroalkyl substances (PFAS) in the press a lot lately. Municipalities throughout the United States and water systems around the globe are finding traces—and in some cases high levels—of PFAS in their water sources.
As testing continues to identify more affected areas, the true scale of contamination is yet to be determined.
Previously held assumptions that drinking water sources are “safe” are proving false, and communities are left scrambling to provide a treatment solution that restores confidence in the drinking water supply. The first story of this kind, that of Parkersburg, West Virginia, and its neighbors, has been turned into the movie Dark Waters, released Friday, November 22.
So, what are these chemicals anyway? In short, PFAS were first invented in the 1930s for use in firefighting foams, and widely used to make water-, grease- and stain-repellant coatings. They are used in a vast array of consumer goods and industrial applications. Need a primer on PFAS? Learn more from my colleague Sasha Richards here.
While the PFAS family encompasses thousands of individual compounds, the most common PFAS are perfluorosulfonic acids (PFSAs) and perfluorocarboxylic acids (PFCAs). These PFAS are comprised of an anionic, functional group head and a carbon tail of varying lengths, saturated with fluorine atoms. The two PFAS chemicals you’re most likely to hear about are PFOS and PFOA—the eight-carbon version of PFSA and PFCA. These two compounds were phased out of production in the US in the 2000s, but manufacturers in other countries still produce these two compounds and export products containing them into the US.
The problem? PFOS and PFOA—and other long-tailed PFAS—have been shown to have higher toxicity—to humans, wildlife, and the environment—than their short-tailed PFAS counterparts. Although PFOS and PFOA are still present in soil and water due to legacy contamination, in many places their environmental concentrations have slowly been decreasing as chemical companies shifted to different compounds. Unfortunately, the toxic effects of these next-generation compounds are not as well understood.
PFOS (left) and PFOA (right), sulfuric and carboxylic heads, respectively.
It is their perfluoronated tail that primarily gives PFAS their unique properties. The carbon-fluorine (C-F) bonds make them incredibly difficult to be degraded or destroyed, leading to their nickname “forever chemicals.” In fact, PFAS are so ubiquitous in the environment that they are detected in remote places such as Arctic polar bears and the depths of the Atlantic Ocean.
Do I need to worry? What is being done?
Because these chemicals have been used in many consumer products for decades, most people have been exposed to them. Studies estimate that 98% of Americans have detectable levels of PFAS in their blood. They can enter our bodies through the packaging surrounding food we eat, like microwave popcorn and in takeout containers, or through bioaccumulation in animal products such as contaminated fish. Some people may inhale PFAS-contaminated air or dust, and some are exposed through contaminated drinking water. While there is a consensus that PFAS contamination carries health impacts, the toxicity of individual compounds, or how that toxicity might change with exposure to multiple compounds, remains a topic of intense research.
Health-based guidance levels are constantly being developed and changed as the impacts of PFAS are better understood. As a water engineer, this can lead to general uncertainty over what level of treatment makes water safe. A search of “PFAS health effects” through my alma mater’s online library shows 70 new peer reviewed articles in the last 3 months alone.
Just this month, the EPA has released a Systematic Review Protocol for five PFAS toxicity assessments for a 45-day comment period. Currently, they have only listed drinking water health advisories for PFOA and PFOS, at a combined 70 nanograms per liter (ng/L). Drinking water health advisories are not directly enforceable, which leaves the decision of whether to regulate up to individual states.
The response has varied significantly among states, with some states proactively lowering the federal advisories or supplementing with additional standards of their own. For example, Minnesota lowered guidance values for PFOS and PFOA to 15 ng/L and 35 ng/L, respectively, and added guidance values for PFHxS, PFBS, and PFBA for a total of 5 regulated PFAS. Texas, following the theme that everything is bigger in Texas, expanded their list to regulate 16 distinct PFAS compounds. Some states choose not to regulate at all, preferring to wait for federal regulation.
The need for a rapid response in Cottage Grove
The Minnesota Department of Health (MDH) issued new, lower health-based recommendations for both PFOA and PFOS in 2017, and with the advent of these newly established hazard indexes, 8 out of 11 wells in the City of Cottage Grove became non-compliant. This left the city of more than 36,000 residents with only three wells that could provide water for the community.
Within eight days of receiving the news of revised levels, our Stantec team developed an MDH-approved blending schedule and a concept to build two water-treatment facilities. We then put into motion a solution that involved blending water and implementing a highly specialized, fast-tracked design and construction schedule that delivered interim treatment systems to remove PFAS from water supplies at two critical wells, all within 90 days of receiving the news of the revised guidance. The result? The public now has renewed confidence in its drinking water supply. And an action plan was established with an interim solution to resolve the City’s water quality concerns for five years, thus allowing for a permanent solution to be developed. This project was an American Public Works Association—Minnesota Chapter Project of the Year winner.
The granular activated carbon treatment system above was designed and construction expedited as an interim solution for providing drinking water compliant with Health Based Values in Minnesota while a long-term solution is created and implemented.
Treatments are changing just as quickly as health guidance
The traditional treatment solution for removing PFAS contamination from drinking water has been adsorption using granular activated carbon (GAC) media, which is what was implemented at the City of Cottage Grove. Activated carbon has an incredibly high surface area, on the order of 1,000 m2 per gram. Because of this, as contaminated water flows through and among the activated carbon granules, the hydrophobic, non-stick, tail of the PFAS compounds tend to cling to it rather than stay in the water. This process, called adsorption, is driven by Van der Waals forces, and takes the PFAS out of the drinking water stream.
However, the process is far from perfect.
_q_tweetable:Emerging contaminants carry, by definition, an element of uncertainty. This is one of the reasons they can be so scary._q_PFAS with short-carbon tails have smaller hydrophobic areas, making for decreased removal by GAC. Additionally, competition from other compounds in the water, such as dissolved organic carbon, can quickly exhaust the adsorption capacity of the GAC, necessitating frequent and costly media replacement. Disposal of exhausted GAC is also challenging due to the high quantities of PFAS trapped on the surface. Incineration is a standard method of disposal—as the extremely high temperatures are assumed to break the C-F bond within the PFAS, destroying them outright. Unfortunately, few incineration facilities are certified to carry out this process. For some, these drawbacks have opened the door to GAC being viewed as an interim style treatment, doing the job until a better technology becomes available.
Just as in most fields, better technologies are on the horizon.
Some communities can utilize reverse osmosis to remove PFAS from the drinking water stream, and research on novel technologies to destroy PFAS outright is progressing almost daily. Additionally, improved medias have hit the national stage. One family of improved medias, known as ion exchange (IX) resins, are specifically designed to remove compounds such as PFAS and other contaminants of emerging concern.
These have the potential to provide more bang-for-your-buck than traditional GAC media. IX resins do not rely solely on targeting the hydrophobic PFAS tail, but target the functional group head, which for PFSAs and PFCAs can take on a negative charge. These resins often use another negatively charged ion, such as chloride (Cl-), as a placeholder on the positively charged resin. When the negatively charged PFAS comes close, chloride is displaced by the charged PFAS head and the PFAS molecule takes its place on the resin, hence the name ion exchange. This process is shown below. IX resins also remove PFAS through adsorption, but ionic forces are stronger than adsorptive Van der Waals forces, and are what give the IX resins a leg up on traditional GAC media.
Anion exchange resin for removal of PFSAs and PFCAs.
Revisiting Cottage Grove’s interim solution, our design team, the City, and the Minnesota Pollution Control Agency are looking to demonstrate IX as a viable treatment alternative for PFAS. To do this, Stantec will operate a pilot plant at the City of Cottage Grove to directly compare IX and GAC media and demonstrate the key operational parameters needed to achieve effective IX performance. Analysis during the pilot will be supported by the Johns Hopkins University Bloomberg School of Public Health.
What does the future look like?
Emerging contaminants carry, by definition, an element of uncertainty. This is one of the reasons they can be so scary.
While PFAS are clearly ubiquitous in the environment, no one knows for sure how many people are affected by PFAS contaminated drinking water, or the long-term health impacts. In Minnesota, throughout the country, and across the globe, many communities are still waiting for a long-term treatment solution.
It is clear is that as an industry we need to move quickly; communities and families drinking PFAS contaminated water deserve the best we have to offer. Along with our partners and collaborators, Stantec is working hard to improve PFAS treatment of drinking water. Through our expedited interim solution, ongoing IX pilot in Minnesota, and PFAS work around the country, we are bringing PFAS resiliency to our clients and their customers so they are protected today and will be ready to continue that protection into the future as the science on this topic evolves.
About the AuthorMore Content by Henry Croll