Treating Emerging Contaminants: PFOS & PFOA
Emerging contaminants are chemicals or materials that have been found in global drinking water supplies and are perceived as real or potential threats to human health.
By Matthew P. Adomaitis and Jack Adams
Emerging contaminants are chemicals or materials that have been found in global drinking water supplies and are perceived as real or potential threats to human health. While these contaminants may have always been present in drinking water, advances in technology have only recently made it possible to detect them. Contaminants are classified as “emerging” if a new source or direct pathway to humans has been determined. Perfluorinated compounds, such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), have been identified as both persistent and mobile in the atmosphere and aqueous environments, and are therefore considered emerging contaminants of concern.
What are Perfluorinated Compounds?
Perfluorinated compounds, or PFCs, are manmade, fully fluorinated compounds that are not naturally found in the environment and are used in a range of products such as fire-fighting foams and coating additives. PFOS and PFOA are the most commonly produced PFCs.
Why are PFCs harmful?
According to the U.S. Environmental Protection Agency (EPA), studies have found PFOS and PFOA in the blood samples of the general human population and wildlife throughout the United States, indicating that exposure is widespread.
PFOA and PFOS are persistent and itinerant in the atmosphere and aqueous environments due to their high chemical stability and low volatility. In their anionic form, PFCs are water soluble and can easily travel from soil to groundwater, carrying the contaminants long distances. Additionally, animal toxicological reports indicate potential developmental, reproductive, and systemic effects after oral exposure, as PFCs accumulate and absorb in the serum, kidney, and liver. Because PFCs are resistant to direct oxidation, photolytic degradation, biodegradation, and air stripping/vapor extraction, their removal is very difficult.
In 2009, the EPA Office of Water established a provisional health advisory for PFOA to assess the potential risk from short-term exposure to PFCs through drinking water. Since PFCs reflect health-based hazards, the agency believes action should be taken to reduce exposure to the contaminants. Further steps have been taken to investigate PFOAs and related chemicals, as well as steps to reduce their emissions and use in products. Both PFOS and PFOA are on EPA’s Drinking Water Contaminant Candidate List 4 (CCL 4), which lists contaminants that are not currently subject to proposed or promulgated national primary drinking water regulations but are known or anticipated to occur in public water systems.
A strong fluorine-carbon bond and low vapor pressure can make PFOA and PFOS resistant to many municipal and home water treatment technologies, including direct oxidation, biodegradation, air stripping, vapor extraction and direct photolysis (ultraviolet light), making treatment difficult. However, several groundwater treatment options may be applicable:
Membrane Filtration: Membrane filtration, a technique that uses a porous membrane filter to separate particles in fluids, is an option. To be effective, this process may need the addition of other minerals, and waste/byproducts must be managed.
Anion Exchange: A process that separates a substance based on its charge using ion exchange resin, where the resin is coated with negatively charged counter-ions (anions) is a complex treatment option and competition with common ions for binding sites on resins can impact its effectiveness. Additionally, organics, total dissolved solids, and minerals can clog resins and reduce the efficiency of the treatment.
Granular Activated Carbon: Calgon Carbon has been investigating the application of granular activated carbon (GAC) as an effective way to remove PFCs from sources of drinking water. Recent testing has demonstrated GAC filters as effective technologies for reducing perfluorinated compounds from water. Accelerated Column Tests (ACTs) of virgin GAC show successful removal of harmful compounds in groundwater, including PFOA as well as perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPA), perfluorohexanoic acid (PFFHxA), and perfluorodecanoic acid (PFDA). The spent activated carbon, containing adsorbed PFCs, can be thermally reactivated, thereby destroying the contaminants and allowing the activated carbon to be recycled and reused in groundwater treatment applications. Lab testing and field trials have led to activated carbon systems being successfully employed to treat groundwater for PFC removal throughout North America.
About the Author: Matthew P. Adomaitis is the industrial and food business unit marketing manager for Calgon Carbon Corporation. Jack Adams is director of government affairs for Calgon Carbon Corporation and member of the Board of Directors of the Water and Wastewater Equipment Manufacturers Association.