Non-polymer PFAS can build up in blood protein of animals, and is not always removed quickly. This means that predators eating PFAS-contaminated food will have higher levels in their bloodstream, and concentrations can increase up the food chain. Studies suggest that build up of PFAS is similar to those of other Persistent Organic Pollutants such as DDT.PFAS are estimated to be settling in arctic regions at rates of tens to hundreds of kilograms per year (25-850kg per year), depending on the specific PFAS chemical in question. Certain PFAS are released as gases to the environment and are blown a long way by wind and air currents in the atmosphere,. These gas PFAS will over time degrade to more persistent chemicals like PFOS and PFOA. This may be one reason why PFAS of environmental concern have been found in remote regions such as the Arctic as well as near PFAS production sitesPFAS including PFOS and PFOA have been found in air samples around Europe. The chemicals are found in small quantities, but appear in almost all samples tested. PFAS enters the atmosphere both from factories and the air inside our homes. PFAS is found in treated waste water from industrial and domestic sources and has been found in both rivers and groundwater. Conventional drinking water processes will not remove PFAS.PFAS-coated clothes that are thrown away will often end up either incinerated or in landfill. Unless incinerated at very high temperatures (>1000oC), fluorinated polymers could release more harmful PFAS during burning. PFAS of environmental concern have also been found in landfill leachate. Non-polymer PFAS are used in the production of fluorinated polymers. The manufacture of stain-resistant finishes generally releases these PFASs into the environment, both by air and water emissions. They are very hard to remove during water treatment. Workers in textiles factories are some of the population most exposed to these potentially harmful chemicals. Small quantities of PFAS will be removed during wash and wear of products containing PFAS. This includes fluorinated polymers used on stain-resistant coatings, and non-polymers that remain on clothes after production (Lassen et al. 2015).Most UK waste still ends up in landfill, and this includes PFAS-containing products. Studies have shown that the liquid coming from landfills (known as leachate) often contain non-polymer PFAS chemicals. In the USA the total quantities were estimated at 563-638 kg in 2013. To properly break down PFAS chemicals high temperature (1000oC or more) incineration is recommended. Incineration of municipal waste does not necessarily reach these temperatures (min temp. required is 850oC), and the incomplete breakdown could release non-polymer PFAS.Wash and wear of clothing that contains PFAS-based stain-resistant or water repellent finishes release PFAS to the environment. Coatings are thought to lose effectiveness after 20-30 washes. This can include non-polymer PFAS, remnant from production or as a break-down product of side-chain polymers (Lassen et al. 2015). The manufacture of stain-resistant finishes releases PFAS into the environment, both by air and water emissions. PFAS are very hard to remove during water treatment. Industrial emissions are estimated to be the biggest source of these chemicals to the environment.

Environment and Health

PFAS are found in marine animals, seabirds and predators in all parts of the world including polar bears in the remote arctic [1]. They are now ubiquitous in the environment. They have been recorded in our air [2], water [3],[4], sediment [5],[6], plants [7] and wildlife [8]. They are found in rain and snow [9], groundwater [10], tap water [11], rivers [12],[13],[14] lakes [15] and seawater [4],[16],[17].

There are no natural sources of PFAS, they are entirely man-made, however the vast number of consumer goods which utilise PFAS chemistry means they are widely lost into the environment. They can be lost from manufacturing facilities where the chemicals themselves, or the goods that use them, are made (24). They can be lost into wastewater, sewage treatment facilities don’t remove them so they can them be released alongside the treated water or in the sludge that is applied to land (30). They can be lost during use, for example a major localised source is where PFAS-containing firefighting foams are released for fire management or training (31). Wash and wear of clothing that contains PFAS-based stain-resistant or water repellent finishes is also thought to be a source to the environment though likely small compared to other pathways (32). Finally, when we dispose of goods the PFAS chemicals can be lost through landfill leachate (33).   

Once these chemicals enter our environment many are highly mobile, meaning they can be found far from their original source. Whilst the distribution pattern of PFAS shows highest concentrations in industrialised or urbanised areas (34), environmental transport means we also find PFAS turning up in the Arctic and in the bodies of polar bears despite no nearby sources. The important implication of this is that if we want to protect ourselves from exposure we need to cut sources worldwide, not just on our doorstep. Moving manufacturing abroad where regulations are weaker is not a solution, we need joined up global regulations to make a genuine impact.  

Some forms can be transported in the air as it circulates round the globe, it can then be deposited at sites far from its source (long-range atmospheric transport) either by settling out (dry deposition) or washed out in rain (wet deposition) (29). Even when harmful PFAS themselves aren’t present in the environment, their precursors may be. Under the right conditions chemicals that don’t themselves cause concern may break down to potentially toxic PFAS (35) 

Chemicals are generally classed as ‘of environmental concern’ if they are P-persistent, B-bioaccumulative and T-toxic (PBT). A number of PFASs have been classified as either PBTs or PB(T)s.  This means they won’t break down in the environment, will build up in the tissue or blood of animals that are exposed to them, and could cause harm to those animals. 

Once sufficient evidence has been collated to prove the above criteria they can put forward to be officially classified as persistent organic pollutants (POPs) under the Stockholm Convention. The Stockholm Convention is an international environmental treaty, signed in 2001 and effective from 2004, that aims to eliminate or restrict the production and use of POPs. PFOA has been classified as a persistent organic pollutant (POP) since 2009 and PFOS is currently on the list of chemicals under consideration 

The fluorinated side-chain polymers, the end-products used on clothing, are themselves generally not considered to be of environmental concern. The molecules are so large that they are not easily taken up by cells and if they can’t be taken up the assumption is they can’t cause direct harm. They persist in the environment, but they are ‘inert’ (unreactive). However, once they are present in the environment they can break down and the side-chains that make up the larger polymer molecule can become detached. When free of the stabilising polymer structure, these smaller non-polymers may be of environmental concern. Fluoropolymers are generally considered very stable under most environmental conditions although certain methods of incineration could theoretically lead to breakdown.  

The PFAS of environmental concern are the non-polymer fluorinated surfactants. Of these there are two groups, the Perfluorinated Carboxylic Acids (PFCAs) and the Perfluorinated Sulfonic Acids (PFSAs) used in the production of textiles. Within these groups the best known and most studied are perfluorooctanoic acid (PFOA) and perfluoroocatanesulfonic acid (PFOS), respectively. Historically these were widely used in the production of fluorinated polymers and textile finishes. However, since the wide-spread recognition of their risks and the introduction of regulations and voluntary phase-outs, many companies have reduced or eliminated their use, often substituting for short-chain varieties of the same chemical group.  

The short-chain PFAS are much less studied than their predecessors so the evidence for their environmental safety is still inconclusive. Whilst some studies have shown they are less toxic and don’t bioaccumulate to the same degree1 there is still concern amongst academic groups that some should still be considered PBTs and be classified as ‘of environmental concern’. The huge range of chemicals that fall within each group makes it extremely difficult to accurately assess the safety of each chemical individually. See below for further information.  

PFAS have been found in the blood serum of the general population, more than 99% of Americans tested had PFOS and PFOA in their blood. Whilst background levels are generally low, occupational exposure or ground-water contamination can raise levels significantly amongst local populations.  

Long-chain PFAS 

Studies have shown that some forms of PFAS can be harmful to animals. There have also been many population studies that have shown associations between PFAS exposure and various adverse effects on humans. Most focus on PFOS and PFOA in blood serum but some have a broader focus, looking at multiple PFAS. Given the cocktail of chemicals we are exposed to in our everyday life, and even specific to PFAS, the multitude of these chemicals we can be exposed to simultaneously, it is extremely difficult to isolate the specific effects of individual chemicals. Whilst the effects on humans are not well understood studies have suggested links to possible growth, learning, or behavioural problems, cancer, immune system disorders, fertility problems and obesity (12,36-38) 

The most commonly studied chemicals within the group, and the focus of regulatory actions across the EU and elsewhere, are PFOS and PFOA. Official classifications include ‘carcinogenic’ (Cat2, suspected human carcinogens), ‘reprotoxic’ (Cat 1B, presumed human reproductive toxicants), ‘Lact’ (may cause harm to breast-fed children), and ‘toxic to specific organs’ (liver) (39). The toxicity of lesser studied forms of PFAS, increasingly used as alternatives to the restricted substances, are still uncertain. 

PFASs are either absorbed orally or inhaled, absorption through skin is considered negligible (40). Most persistent organic pollutants build up in the fat tissues of animals, PFAS are different in that they do not easy bind to fats and therefore build up in proteins instead (41). They are mainly found in ‘well-perfused tissues’, these are tissues which have a good blood supply such as the liver, kidneys and spleen, they are found in testes and brains (42-44) 

Short-chain PFAS 

Evidence regarding the safety of short-chain PFAS, increasingly being used as substitutes for long-chain versions as regulations and voluntary phase-outs limit their use, is still extremely lacking. Animal experiments where the subjects are exposed just once or over a short period, have suggested the toxicity of short-chain PFAS is low. However, when exposure is repeated, or larger doses are used, there is evidence to suggest they may cause damage to the liver and kidneys. A general pattern of increasing liver toxicity has been seen as the chain length increases until approximately C9 (45). 

There is also worry regarding the potential of some short-chain PFAS to bioaccumulate, or build up in animal tissue, more than initially thought. One particular short-chain PFAS (PFBA – see below) has shown up in human tissue, including human brains, suggesting it can be more bioaccumulative in humans than some of the experimental animal studies originally concluded (44). There is still a significant volume of unanswered questions regarding how these substances build up in the body, what levels they can reach and what effects they have.   

Specific examples of better-studied short-chain PFAS are listed below:

A type of PFSA similar to PFOS, it contains 6 carbons in its chain (C6). This chemical has a half-life of up to 8.5 years in humans. This means that it takes 8.5 years for half of the chemical to be removed from the human body once it gets in, it takes another 8.5 years for the new amount to half again after that and so on. For reference, the half-life of PFOS is only 5.6 years (46). It has also been suggested to have reproductive toxicity (40) (i.e. it can interfere with normal reproduction either through fertility or development effects on the child) and behavioural disorders such as ADHD (47)

Another replacement for PFOS used by Scotchguard, it contains 4 carbons in its chain (C4). It has a chemical half-life of less than a month in humans but is still thought to persist in the environment. Studies suggest that a dose 50 times higher than the equivalent in PFOS was required to have the same effect on the liver48. Whilst some other health impacts have been noted these often occur at very high doses.  

A type of PFCA, similar to PFOA, it contains 4 carbons in its chain (C4). The half-life for human blood is thought to be approximately 3 ½ days (40). Despite its short half-life in blood, an analysis of Spanish autopsy tissues showed surprisingly high levels of PFBA (100 times higher than PFOS) in lung tissues. PFBA also showed the highest concentration of the measured PFSA in the kidneys and was found in livers and brains (44). PFBA appears to act differently in humans compared to experimental animals so whilst some adverse effects have been detected in animals little is known about the human toxicity (40). 

Another type of PFCA, similar to PFOA, which contains 6 carbons in it chain (C6). The half-life for humans is thought to be approximately 32 days (40). Most biomonitoring studies have found concentrations of PFHxA in human blood serum to be near or below the detection limit with higher levels only really observed near industrial sources (49). Very little is known about the health impacts of PFHxA.

[1] Eggers Pedersen K, Basu N, Letcher R, Greaves AK, Sonne C, Dietz R, Styrishave B. Brain region-specific perfluoroalkylated sulfonate (PFSA) and carboxylic acid (PFCA) accumulation and neurochemical biomarker Responses in east Greenland polar Bears (Ursus maritimus). Environmental Research 2015;138:22-31.

[2] Barber JL, Berger U, Chaemfa C, Huber S, Jahnke A, Temme C, Jones KC. Analysis of per- and polyfluorinated alkyl substances in air samples from Northwest Europe. J Environ Monit 2007;9(6):530-41.

[3] Ahrens L, Gerwinski W, Theobald N, Ebinghaus R. Sources of polyfluoroalkyl compounds in the North Sea, Baltic Sea and Norwegian Sea: Evidence from their spatial distribution in surface water. Marine Pollution Bulletin 2010;60(2):255-260.

[4] Yamashita N, Kannan K, Taniyasu S, Horii Y, Petrick G, Gamo T. A global survey of perfluorinated acids in oceans. Marine Pollution Bulletin 2005;51(8):658-668.

[5] Ahrens L, Felizeter S, Ebinghaus R. Spatial distribution of polyfluoroalkyl compounds in seawater of the German Bight. Chemosphere 2009;76(2):179-184.

[6] Zushi Y, Tamada M, Kanai Y, Masunaga S. Time trends of perfluorinated compounds from the sediment core of Tokyo Bay, Japan (1950s-2004). Environ Pollut 2010;158(3):756-63.

[7] Muller CE, De Silva AO, Small J, Williamson M, Wang X, Morris A, Katz S, Gamberg M, Muir DC. Biomagnification of perfluorinated compounds in a remote terrestrial food chain: Lichen-Caribou-wolf. Environ Sci Technol 2011;45(20):8665-73.

[8] Magali Houde, ‡, Jonathan W. Martin, Robert J. Letcher, Keith R. Solomon a, Derek C. G. Muir*, ‡. Biological Monitoring of Polyfluoroalkyl Substances:  A Review. 2006.

[9] Kim S-K, Kannan K. Perfluorinated Acids in Air, Rain, Snow, Surface Runoff, and Lakes: Relative Importance of Pathways to Contamination of Urban Lakes. 2007.

[10] Melissa M. Schultz, Douglas F. Barofsky a, Jennifer A. Field*, ‡. Quantitative Determination of Fluorotelomer Sulfonates in Groundwater by LC MS/MS. 2004.

[11] Ericson I, Domingo JL, Nadal M, Bigas E, Llebaria X, van Bavel B, Lindstrom G. Levels of perfluorinated chemicals in municipal drinking water from Catalonia, Spain: public health implications. Arch Environ Contam Toxicol 2009;57(4):631-8.

[12] Hansen KJ, Johnson HO, Eldridge JS, Butenhoff JL, Dick LA. Quantitative characterization of trace levels of PFOS and PFOA in the Tennessee River. Environ Sci Technol 2002;36(8):1681-5.

[13] Michael S. McLachlan, Katrin E. Holmström, Margot Reth a, Berger U. Riverine Discharge of Perfluorinated Carboxylates from the European Continent. 2007.

[14] Möller A, Ahrens L, Surm R, Westerveld J, van der Wielen F, Ebinghaus R, de Voogt P. Distribution and sources of polyfluoroalkyl substances (PFAS) in the River Rhine watershed. Environmental Pollution 2010;158(10):3243-3250.

[15] Bryan Boulanger, John Vargo, Jerald L. Schnoor a, Keri C. Hornbuckle*. Detection of Perfluorooctane Surfactants in Great Lakes Water. 2004.

[16] Nobuyoshi Yamashita, Kurunthachalam Kannan, ‡, Sachi Taniyasu, Yuichi Horii, Tsuyoshi Okazawa, Gert Petrick a, Gamo‖ T. Analysis of Perfluorinated Acids at Parts-Per-Quadrillion Levels in Seawater Using Liquid Chromatography-Tandem Mass Spectrometry. 2004.

[17] Yeung LWY, Dassuncao C, Mabury S, Sunderland EM, Zhang X, Lohmann R. Vertical Profiles, Sources, and Transport of PFASs in the Arctic Ocean. Environ Sci Technol 2017;51(12):6735-6744.