About PFAS

What are PFAS?

PFAS stands for per- and polyfluoroalkyl substances. The U.S. Environmental Protection Agency (EPA) describes them as “a group of manufactured chemicals that have been used in industry and consumer products since the 1940s because of their useful properties.” ^[1] The National Institute of Environmental Health Sciences (NIEHS) calls them “a large, complex group of synthetic chemicals.” ^[2]

Scientists also define PFAS by their structure. In 2021 the Organisation for Economic Co-operation and Development (OECD) defined PFAS as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom, which in practice means almost any chemical with a -CF3 or -CF2- group. ^[3]

How many PFAS are there?

There is no single agreed number. EPA says “there are thousands of different PFAS, some of which have been more widely used and studied than others.” ^[1] EPA’s CompTox Chemicals Dashboard lists 21,028 PFAS structures in its August 2022 list, which counts only substances with a defined structure. ^[4] The U.S. Geological Survey puts the number at more than 12,000 types. ^[5]

Why PFAS last so long

PFAS molecules have a chain of linked carbon and fluorine atoms. As NIEHS explains, “because the carbon-fluorine bond is one of the strongest, these chemicals do not degrade easily in the environment.” ^[2] That is why EPA notes that PFAS are “also known as ‘forever chemicals’.” ^[6]

EPA describes the main concern this way: “many break down very slowly and can build up in people, animals, and the environment over time.” ^[1]

The PFAS family

Legacy PFAS: PFOA and PFOS

PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) are the most widely studied PFAS. The OECD refers to them as “well-studied legacy PFASs.” ^[7]

• 3M voluntarily phased out PFOS, and related chemicals, between 2000 and 2002. ^[8]
• In 2006 EPA’s PFOA Stewardship Program asked eight major companies to cut PFOA from emissions and products by 95 percent by 2010 and to work toward eliminating it by 2015. All of them state that they met those goals. ^[9]
• According to ATSDR, “PFOA and PFOS have been phased out of production in the U.S. Other countries may still manufacture and use them.” ^[10]

Replacement PFAS

EPA notes that “PFOA and PFOS have been replaced in the United States with other PFAS in recent years.” ^[1] One example is GenX, a trade name for a technology that makes fluoropolymers without PFOA; HFPO dimer acid and its ammonium salt are known as “GenX chemicals.” ^[11] The OECD notes that many replacements for long-chain PFAS are themselves PFAS, including short-chain compounds. ^[3]

ATSDR cautions that “there are very few scientific studies on new PFAS, so more research is necessary to discover whether they may be a health concern.” ^[10]

Long-chain and short-chain PFAS

Scientists often group PFAS by chain length. Under the OECD’s usage, long-chain carboxylic acids have seven or more fully fluorinated carbons and long-chain sulfonic acids have six or more, though definitions can differ between countries. ^[3] Short-chain PFAS are generally believed to build up in the body less, but the OECD notes that “this belief is being challenged.” ^[7]

Why individual PFAS differ

Each PFAS has its own chemical properties. EPA puts it plainly: “There are thousands of PFAS with potentially varying effects and toxicity levels, yet most studies focus on a limited number of better known PFAS compounds.” ^[1] This is why regulators often address specific PFAS, or small groups of them, rather than the whole family at once.