Per- and polyfluoroalkyl substances (PFAS) are a vast class of thousands of synthetic chemicals manufactured and used globally since the 1940s. These compounds were valued for their unique properties that resist heat, oil, and water. Their widespread incorporation into industrial processes and consumer goods has resulted in their ubiquitous presence across the planet. Among this large chemical family, two compounds—Perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA)—have become the most studied due to their prevalence and potential for long-term harm.
Defining PFOS and PFOA
PFOS and PFOA are fully fluorinated organic compounds, meaning a chain of carbon atoms is completely saturated with fluorine atoms. This structure, which typically involves an eight-carbon chain, is the source of their functionality and persistence. The chemical structure features a hydrophobic (water-repelling) carbon-fluorine tail and a hydrophilic (water-attracting) functional head.
The carbon-fluorine bond is one of the strongest in organic chemistry. This extreme bond strength makes the chemicals highly stable and resistant to typical environmental degradation processes like heat, light, and microbial action. Because they do not break down in nature, they have earned the nickname “forever chemicals.”
While both are eight-carbon-chain PFAS, they differ in their functional head group: PFOA features a carboxylate group, while PFOS is characterized by a sulfonate group. Historically, these compounds were used in a wide range of products, including the processing aid for manufacturing polytetrafluoroethylene (Teflon). They were also the active ingredient in certain aqueous film-forming foams (AFFF) used for fighting liquid hydrocarbon fires. Major manufacturers in the United States began voluntarily phasing out the use of PFOS and PFOA in the early 2000s due to growing environmental and health concerns.
Common Sources of Exposure
Exposure to PFOS and PFOA is now widespread, primarily stemming from the past manufacture, use, and disposal of products containing these chemicals. For the general public, one of the most significant routes of exposure is through contaminated drinking water supplies. This contamination often occurs near industrial manufacturing facilities, chemical plants, or military bases and airports where AFFF firefighting foams were used.
These substances are also present in many consumer products treated for stain, grease, or water resistance. These chemicals can leach out of products and into household dust, air, and the food chain over time. Examples of products include:
- Stain-resistant carpets and fabrics
- Water-resistant clothing
- Certain food packaging materials, such as grease-resistant paper
Occupational exposure represents a particularly high-risk pathway for certain workers. Individuals involved in the manufacturing of these chemicals, as well as firefighters who routinely use AFFF, have shown significantly elevated levels of PFOS and PFOA in their blood.
How These Chemicals Affect the Human Body
The chemical stability that made PFOS and PFOA useful in industry also makes them extremely difficult for the human body to eliminate. Once absorbed, these chemicals resist being broken down or excreted, leading to a process known as bioaccumulation. They can persist in the bloodstream and organs for years.
Exposure to PFOA has been linked to an increased risk of certain cancers, specifically kidney and testicular cancer. Both PFOS and PFOA exposure show correlations with metabolic and endocrine disruption.
Exposure to these compounds is associated with increased cholesterol levels and increased liver enzyme levels, suggesting liver function impairment. Furthermore, there is evidence linking PFOS and PFOA exposure to effects on the immune system. This includes a decreased response to vaccines in children.
For vulnerable populations, especially pregnant individuals and developing fetuses, exposure poses distinct concerns. PFOS and PFOA have been linked to potential developmental effects in infants and children. Exposure to PFOA has also been associated with pregnancy-related issues such as preeclampsia and high blood pressure.
Environmental Persistence and Mitigation Efforts
The same carbon-fluorine bond that prevents PFOS and PFOA from breaking down in the human body also ensures their environmental persistence. Once released, these chemicals contaminate soil, surface water, and groundwater, where they remain intact for extremely long periods. Their high mobility in water allows them to be transported far from their original release sites, resulting in global contamination, even reaching remote areas.
Globally, PFOS and PFOA are listed under the Stockholm Convention on Persistent Organic Pollutants (POPs). This international treaty aims to eliminate or restrict the production and use of the most toxic chemicals. This action recognizes their capacity for long-range environmental transport and their toxicity.
In the United States, the Environmental Protection Agency (EPA) has worked to establish enforceable limits for these compounds in drinking water. The EPA previously issued a Lifetime Health Advisory (LHA) for PFOS and PFOA in drinking water. More recently, the agency established maximum contaminant levels (MCLs) for certain PFAS compounds. These regulatory actions are designed to protect public health by setting standards for water systems and driving cleanup efforts at contaminated sites across the country.