Understanding PFAS: The Forever Chemicals in Our Water Supply

Per- and polyfluoroalkyl substances — PFAS — are a family of over 12,000 synthetic chemicals that have been manufactured and used in industry and consumer products since the 1940s. They are in the water supply of communities across the United States. Understanding what they are and why they persist is the first step toward managing the risk they pose.

What Makes PFAS Different

PFAS compounds are built around the carbon-fluorine bond, one of the strongest chemical bonds in organic chemistry. This bond gives PFAS their extraordinary resistance to heat, water, and chemical degradation — properties that made them commercially valuable for applications ranging from non-stick cookware to firefighting foam to waterproof clothing. It also means that once PFAS compounds enter the environment, they do not break down. They accumulate. This is why they are called "forever chemicals."

The most extensively studied PFAS compounds — PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonic acid) — are classified as persistent organic pollutants under the Stockholm Convention and have been largely phased out of manufacturing in the United States. But thousands of structurally similar compounds remain in active use, and legacy contamination from decades of PFOA and PFOS use continues to affect groundwater and surface water sources across the country.

PFAS compounds are also bioaccumulative. They build up in the bodies of animals — including humans — over time, with the highest concentrations found in blood, liver, and kidney tissue. The longer the exposure and the higher the concentration in water, the greater the accumulation in body burden.

Health Effects: What the Science Shows

The epidemiological evidence linking PFAS exposure to human health effects has grown substantially over the past two decades. The most robust findings associate high PFAS exposure with elevated cholesterol levels, reduced antibody responses to vaccines (particularly in children), thyroid hormone disruption, kidney cancer, testicular cancer, and pregnancy-induced hypertension.

The EPA's setting of MCLs at 4 ppt for PFOA and PFOS is based on a determination that there is no safe level of exposure for some of these health outcomes — particularly for sensitive populations including infants, children, pregnant women, and immunocompromised individuals. This represents a significant departure from the conventional risk assessment approach, where MCLs are typically set at levels where lifetime cancer risk is below one in a million.

Emerging PFAS compounds — sometimes called "next-generation" PFAS or regrettable substitutions — are less well studied but often demonstrate similar patterns of persistence and bioaccumulation. GenX chemicals, developed as a replacement for PFOA by Chemours, have been detected in drinking water near manufacturing facilities and appear to cause similar health effects at similar exposures.

Where PFAS Comes From: Sources and Pathways

PFAS contamination in drinking water sources originates from multiple pathways. Industrial discharge is the most common source near manufacturing facilities, particularly those involved in fluorochemical production or in industries that historically used PFOA or PFOS as processing aids. Paper mills, chrome plating facilities, and semiconductor manufacturers have all been identified as PFAS sources in various regions.

Aqueous film-forming foam (AFFF) — the firefighting foam used at military bases, airports, and industrial fire training facilities — is one of the most significant sources of PFAS contamination in groundwater across the United States. The Department of Defense has identified more than 700 military installations with known or suspected PFAS contamination from AFFF use. Civilian airports and fire training facilities present similar contamination patterns.

Agricultural land application of sewage sludge (biosolids) is an increasingly recognized contamination pathway. Biosolids used as fertilizer on farmland can contain elevated PFAS concentrations, which leach into soil and groundwater over time. Sampling programs in New England, Michigan, and the Pacific Northwest have identified PFAS contamination in private wells and public water sources downhill from biosolids-amended fields.

Consumer products — food packaging, stain-resistant coatings, and personal care products — contribute to PFAS loads in wastewater and, eventually, in the biosolids and effluent that wastewater treatment plants discharge. Conventional wastewater treatment does not remove PFAS effectively, meaning treatment plant effluent can elevate PFAS concentrations in receiving waters used as drinking water sources downstream.

The Detection Challenge

Detecting PFAS at the concentrations specified in the EPA's MCLs requires analytical methods with detection limits in the low parts-per-trillion range. Standard water quality testing instruments cannot achieve this sensitivity. Certified laboratory methods — specifically EPA Method 533 and EPA Method 537.1 — use high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), which is expensive and not available at all certified laboratories.

The large and growing number of PFAS compounds creates additional analytical challenges. A laboratory test for PFAS may quantify 40 to 100 specific compounds depending on the method, but there are thousands of PFAS compounds, many of which have limited or no analytical standards available. This means that total PFAS contamination in a water source is almost certainly higher than what any current analytical method can measure.

Continuous in-line monitoring for PFAS is not currently feasible using direct measurement — the analytical sensitivity required cannot be achieved with deployed sensor technology. However, continuous monitoring of correlated parameters — specific conductance, total organic carbon, and certain optical absorbance signatures — can flag conditions indicative of PFAS input, triggering targeted laboratory sampling before routine monitoring would catch the event.

Treatment Options

Several treatment technologies can effectively reduce PFAS in drinking water. Granular activated carbon (GAC) is the most widely deployed option at drinking water treatment plants — it adsorbs PFAS compounds effectively, though capacity varies significantly by compound, contact time, and carbon type. Spent carbon must be either regenerated using high-temperature thermal treatment or disposed of as hazardous waste.

Reverse osmosis (RO) achieves near-complete removal of most PFAS compounds and is typically used in small systems or point-of-use applications where the capital cost of full-scale GAC systems is prohibitive. RO generates a concentrated brine reject stream containing PFAS that must be managed carefully to avoid creating new contamination pathways.

Ion exchange resin systems — particularly single-use anion exchange resins designed specifically for PFAS removal — can achieve better performance than GAC for short-chain PFAS compounds that GAC handles poorly. They are increasingly used as a polishing step following GAC treatment or as the primary treatment in systems with specific short-chain PFAS challenges.

Effective treatment system selection requires a detailed understanding of the specific PFAS compounds present and their concentrations, source water chemistry, and system hydraulics. There is no single solution that works optimally for all contamination profiles — and the 2027 compliance deadline means that system selection decisions must be made now, with installation and commissioning timelines of 18 to 36 months for major treatment upgrades.