<unk>  <unk>  (conjugate base perfluorooctanoate) — also known colloquially as C8 — is a perfluorinated carboxylic<unk>  produced and used worldwide as an industrial surfactant in chemical processes and as a material feedstock.<unk>  is considered a surfactant, or fluorosurfactant, due to its chemical structure, which consists of a perfluorinated, n-octyl "tail group" and a carboxylate "head group". The head group can be described as hydrophilic while the fluorocarbon tail is both hydrophobic and lipophobic. The tail group is inert and does not interact strongly with polar or non-polar chemical moieties; the head group is reactive and interacts strongly with polar groups, specifically water. The "tail" is hydrophobic due to being non-polar and lipophobic because fluorocarbons are less susceptible to the London dispersion force than hydrocarbons.<unk>  is one of many synthetic organofluorine compounds collectively known as per- and polyfluoroalkyl substances (PFASs).<unk>  is used in several industrial applications, including carpeting, upholstery, apparel, floor wax, textiles, fire fighting foam and sealants.<unk>  serves as a surfactant in the emulsion polymerization of fluoropolymers and as a building block for the synthesis of perfluoroalkyl-substituted compounds, polymers, and polymeric materials.<unk>  has been manufactured since the 1940s in industrial quantities. It is also formed by the degradation of precursors such as some fluorotelomers.<unk>  is used as a surfactant because it can lower the surface tension of water more than hydrocarbon surfactants while having exceptional stability due to having perfluoroalkyl tail group. The stability of<unk>  is desired industrially but is a cause of concern environmentally. A study of workers living near a DuPont Teflon plant found an association between<unk>  exposure and two kinds of cancer as well as four other diseases. A positive exposure-response trend for kidney cancer is supported by many studies.<unk>  has been detected in the blood of more than 98% of the general US population in the low and sub-parts per billion (ppb) range, and levels are higher in chemical plant employees and surrounding subpopulations. How general populations are exposed to<unk>  is not completely understood.<unk>  has been detected in industrial waste, stain-resistant carpets, carpet-cleaning liquids, house dust, microwave popcorn bags, water, food, and Teflon (PTFE) products. As a result of a class-action lawsuit and community settlement with DuPont, three epidemiologists conducted studies on the population surrounding a chemical plant that was exposed to<unk>  at levels greater than in the general population. Studies have found correlation between high<unk>  exposure and six health outcomes: kidney cancer, testicular cancer, ulcerative colitis, thyroid disease, hypercholesterolemia (high cholesterol), and pregnancy-induced hypertension. The primary manufacturer of PFOS, the 3M Company (known as Minnesota Mining and Manufacturing Company from 1902 to 2002), began a production phase-out in 2002 in response to concerns expressed by the United States Environmental Protection Agency (EPA). Eight other companies agreed to gradually phase out the manufacturing of the chemical by 2015. By 2014, EPA had listed<unk>  and perfluorooctanesulfonates (salts of perfluorooctanesulfonic<unk> , PFOS) as emergent contaminants:
Perfluorooctanoic acid
Triphenylbromoethylene
Tetramethyl bisphenol F
Diiodohydroxyquinoline
Beta-Zearalenol
Diatrizoate
Chloroethane
Triphenylchloroethylene