per- and polyfluoroalkyl substances

per- and polyfluoroalkyl substances are a large class of synthetic organofluorine compounds characterized by carbon-fluorine bonds, one of the strongest in organic chemistry. Their unique properties, including oil and water repellency and thermal stability, led to their widespread industrial and commercial use beginning in the mid-20th century. Due to their extreme environmental persistence and emerging evidence of health risks, they have become a major focus of global environmental regulation and public health concern.

Chemical properties and structure

The defining feature of these compounds is the presence of multiple carbon-fluorine bonds, which confer exceptional chemical and thermal stability. The two most studied subgroups are perfluoroalkyl acids, such as perfluorooctanoic acid and perfluorooctanesulfonic acid, which feature a fully fluorinated carbon chain. The strength of the carbon-fluorine bond, a result of the high electronegativity of fluorine, makes these molecules highly resistant to degradation by heat, water, or most chemical reactions. This structural backbone is responsible for their surfactant properties, allowing them to lower surface tension effectively. The family includes thousands of individual substances with varying chain lengths and functional groups, synthesized by major chemical manufacturers like 3M and DuPont.

Environmental persistence and bioaccumulation

Their extreme stability leads to extraordinary environmental persistence, earning them the colloquial name "forever chemicals." They do not break down naturally in the environment and can be transported long distances through water and air. Major contamination events have been documented globally, notably near industrial sites like those operated by DuPont in West Virginia and from the use of aqueous film-forming foam at military bases such as Naval Air Station Whidbey Island. These substances bioaccumulate in living organisms and biomagnify up the food chain, with high concentrations found in top predators like polar bears in the Arctic and in human blood serum worldwide. They are ubiquitous contaminants in water, soil, and even in remote regions like the Himalayas.

Health effects and toxicology

Epidemiological studies and toxicological research have associated exposure with several adverse health outcomes. Key concerns include links to certain cancers, such as testicular cancer and kidney cancer, as well as impacts on the immune system, liver, and thyroid. Developmental effects, including lowered birth weight and reduced vaccine response in children, have been observed in highly exposed communities, such as those near the Flanders region in Belgium. The primary mechanism of toxicity is not fully understood but is thought to involve disruption of lipid metabolism and cellular communication. The U.S. National Toxicology Program and the International Agency for Research on Cancer have classified specific substances within this group as possibly carcinogenic to humans.

Regulation and remediation efforts

Regulatory approaches vary internationally but are becoming increasingly stringent. In the United States, the Environmental Protection Agency has established health advisories and is moving towards enforceable drinking water standards under the Safe Drinking Water Act. The European Union is considering a broad restriction under REACH. Legal actions have been significant, including a major settlement by 3M with the state of Minnesota and the multidistrict litigation depicted in the film Dark Waters. Remediation technologies are challenging and costly, but methods such as granular activated carbon filtration, ion exchange resins, and advanced destruction techniques are being deployed at contaminated sites like Wurtsmith Air Force Base.

Major uses and applications

Their oil-, water-, and stain-repellent properties led to their incorporation into a vast array of consumer and industrial products. Historically, a major application was in Scotchgard fabric protector and Teflon non-stick cookware. They are critical components in aqueous film-forming foam used for fighting fuel-based fires, particularly by the U.S. Department of Defense and civilian airports. Other common uses include grease-resistant food packaging like microwave popcorn bags, waterproof outdoor apparel from companies like Gore-Tex, stain-resistant carpets and textiles, and certain cosmetics. Their use in semiconductor manufacturing and the aerospace industry also highlights their importance in high-tech sectors.