Per- and polyfluoroalkyl substances (PFCs) are a large group of synthetic chemicals that have been in production and use since the 1940s. These compounds are fluorinated, meaning that multiple fluorine atoms are bonded to a carbon chain. The unique chemical structure of PFCs has made them desirable for numerous industrial and commercial applications due to their ability to repel grease, oil, and water. This stability, however, is the reason they have become a widespread environmental and public health concern. These substances do not degrade naturally in the environment, leading to their persistence in soil, water, and living organisms.
Unique Chemical Identity and Properties
The distinct behavior of PFCs is rooted in the strength of the carbon-fluorine (C-F) bond, which is among the strongest single bonds in organic chemistry. This high bond energy makes the molecules resistant to breakdown from heat, chemical reactions, and biological processes. The presence of fluorine atoms creates a sheath around the carbon backbone, which is responsible for the compounds’ exceptional thermal and chemical stability.
This structure gives PFCs their amphiphilic nature, allowing them to associate with both water and oil, making them highly effective surfactants. The term “perfluoroalkyl” refers to compounds where every hydrogen atom on the carbon chain has been replaced by a fluorine atom. “Polyfluoroalkyl” substances, in contrast, have at least one carbon atom that is not fully saturated with fluorine, retaining a carbon-hydrogen bond.
The difference between these two groups affects their environmental fate, as polyfluoroalkyl substances can sometimes partially degrade into the more persistent perfluoroalkyl forms. This chemical robustness, which was initially valued for performance in extreme conditions, directly translates into their long-term environmental presence.
Primary Sources of Exposure and Contamination
PFCs have been integrated into a wide variety of consumer products, leading to diverse avenues of human exposure and environmental contamination. Industries utilized these compounds to manufacture products that are stain-resistant, waterproof, and non-stick. This includes fabric coatings for carpets, upholstery, and water-repellent clothing.
Contamination pathways often begin with industrial release or the disposal of products containing PFCs, which then leach into the environment. A significant source of contamination has been the use of Aqueous Film-Forming Foams (AFFF) for extinguishing hydrocarbon fires, particularly at military bases and airports. These foams have led to extensive localized groundwater and soil pollution.
The general public is frequently exposed through contaminated drinking water, especially near manufacturing facilities or military sites. Exposure also occurs through the consumption of food packaged in grease-resistant materials containing PFCs. Dust particles containing these chemicals can also be inhaled or ingested within the home environment from treated consumer goods.
Mechanisms of Action in the Human Body
Once PFCs enter the human body, they exhibit a characteristic known as bioaccumulation, meaning they build up over time rather than being quickly metabolized and excreted. These substances have a strong affinity for binding to proteins in the blood, such as serum albumin. This binding mechanism allows them to circulate throughout the body for extended periods.
The long half-lives of the most studied PFCs, such as PFOA and PFOS, are estimated to be between three and eight years in humans, depending on the specific compound. This slow elimination rate means that even low-level, chronic exposure results in a measurable body burden. PFCs accumulate predominantly in the blood, liver, and kidneys, where they can interfere with normal biological processes.
Scientific evidence suggests that these compounds function as endocrine disruptors, interfering with the body’s natural hormone systems. Exposure has been linked to alterations in cholesterol levels and disruption of thyroid function. Furthermore, studies have shown associations between PFC exposure and adverse outcomes like liver damage and suppression of the immune system.
Environmental Persistence and Remediation
The chemical stability of PFCs is so profound that they are often referred to as “forever chemicals,” resisting natural degradation in water and soil for centuries. This extreme persistence is a major factor driving widespread environmental contamination, as the compounds are highly mobile and travel easily through groundwater and surface water. The difficulty in breaking the C-F bond makes traditional environmental cleanup methods ineffective.
Many conventional water treatment techniques, such as standard filtration and biological degradation, are unable to remove PFCs. Current mitigation efforts primarily focus on transferring the chemicals from the water to a solid medium. Granular activated carbon (GAC) filtration and specialized ion exchange resins are the most common and effective methods for removing PFCs from contaminated drinking water sources.
For highly contaminated source areas, such as industrial sites, more advanced and costly destruction technologies are being explored. These include high-temperature incineration and electrochemical oxidation, which aim to finally break the resilient C-F bonds. While these technologies show promise, large-scale removal of PFCs from all affected environmental media remains a complex and ongoing challenge.