Fall 2022 Special Edition

PFOS

The newest Arctic pollutant

Chaim Christiana Andersen and Geoff Rayner-Canham

A laboratory distillation apparatus.There is one chemical concept which has become of critical importance to northern peoples: distillation. Yet chemistry students think of the principle of distillation only in the context of a chemistry laboratory, such as the separation of two liquids as shown in Fig. 1.

In the distillation process, a compound of lower boiling point (higher vapour pressure) is preferentially vaporized in the hot flask, the molecules in the gas phase passing down the condenser tube where they revert to the liquid phase and are collected in the receiver flask.

FIGURE 1
A laboratory distillation apparatus. Credit: https://en.wikipedia.org/wiki/Distillation

 

The Grasshopper Effect (Global Distillation)

The Earth is a giant distillation apparatus. Unreactive volatile organic molecules vaporize from the warmer tropical and temperate regions and then condense in the cold polar regions. This process is known as the Grasshopper Effect, or more scientifically, Global Distillation1 (Fig. 2).

A schematic of the Grasshopper Effect.FIGURE 2
A schematic of the Grasshopper Effect. Credit: Environment Canada. The Science and the Environment Bulletin. May/June 1998

POPs: The traditional ‘dirty dozen’ and more

So which organic molecules are of concern? Most organic compounds naturally decompose in the environment; however, there are many halogen-containing organic compounds which are resistant to decomposition. These are the persistent organic pollutants, POPs.2 POPs not only persist in the environment but, being of low polarity, when ingested, accumulate in fatty tissues of animals and fish. This phenomenon is known as biomagnification.3 In turn, when humans eat the animals and fish, the pollutants are further concentrated in our fatty tissues, causing health issues. Of particular concern are the levels of these pollutants in the bodies of Inuit women of child-bearing age as these toxic molecules can cause birth defects and can also be transferred through breast milk into their children.4

In the recent past, the 12 most toxic and long-lasting pollutants became known as the ‘dirty dozen’ though more POPs have since been added to the list. The majority of the compounds are pesticides. Molecules of all of these compounds migrate to the Arctic (and, to a much lesser-extent, Antarctic) where they are concentrated at the low temperatures and pass into the food chain. To stop this problem from becoming worse, in 2001, The Stockholm Convention on Persistent Organic Pollutants5 was instituted, banning the production and use of the POPs. Unfortunately, one of the few countries not to ratify the Treaty was the United States, though that country did ban the original ‘dirty dozen’.

PFOS and its relatives: The new hazard

The POPs have infiltrated the environment and been carried to the poles for decades. Now there is a new threat to northern (predominantly Inuit) well-being: the PFOS family. PFOS itself is perfluorooctanesulfonic acid (Fig. 3), formula CF3CF2CF2CF2CF2CF2CF2CF2SO3H.6 The relatives all have the same ‘backbone’ of fluorocarbon groups, but different functional groups on the end.

The ball-and-stick model of perfluorooctanesulfonic acid.FIGURE 3
The ball-and-stick model of perfluorooctanesulfonic acid. Credit:
https://commons.wikimedia.org/wiki/
File:Perfluorooctanesulfonic-acid-
3D-balls.png

Having a long fluorocarbon chain, PFOS and its relatives are extremely hydrophobic (‘water-hating’) organic compounds while the polar -SO3H group on the end adds polarity to the molecule which renders the molecule also repellant to non-polar liquids (oleophobic).

PFOS and its relatives were produced in large quantities and used for over 40 years as a fire-retardant, such as in textiles, upholstery, carpeting and in fire-fighting foams. They were also used as catalysts, insecticides and surfactants. In 2000, the production of chemicals in the PFOS family was estimated to be 4,650 ton.7 These compounds – especially the fluorocarbon chain part – are extremely resistant to decomposition. This stability is reflected, in part, by the strength of the carbon-fluorine bonds at 485 kJ·mol-1, the strongest of any single bond with carbon. In addition, the fluorine atoms are larger than the hydrogen atoms in hydrocarbons, so it is difficult for any other species to get close to the chain to break it. For the same reason, the chain is quite rigid.

In a 1997 review of fluoro-compounds in the biosphere, the PFOS family was dismissed as ‘non-volatile’ and therefore incapable of dispersing widely and of no concern environmentally.8 It was only in 2001 that research showed that molecules of the PFOS family were sufficiently volatile that they had spread throughout the surface of the Earth.9 Extensive research then began, and is continuing, on the levels of the compounds in the Arctic resulting from global distillation. With the belated realization that these compounds were accumulating in the environment, attempts have been made to phase out production but with only partial success so far.

There are no common pathways for decomposition and because of this, PFOS and its relatives will remain in the Arctic environment for hundreds, perhaps thousands of years. Therefore, the phenomenon of global distillation will cause ever-higher levels of PFOS and its relatives to accumulate in the North.

The effect of PFOS accumulation in the Arctic

There are Inuit lands across the Canadian Arctic (Nunangat) from Nunavik and Nunatsiavut in the east, to Nunavut and to Inuvialuit in the west. To access food resources, Inuit depend on their skills of hunting, fishing and gathering. The Inuit rely, in particular, on marine life for survival. Research has shown significant bioaccumulation of PFOS in fish, seabirds and marine mammals.10 Furthermore, PFOS is found in marine organisms across the Canadian Arctic. Fig. 4 shows the concentration of PFOS and its relatives in seal liver near the communities of Nain (Nunatsiavut); Inukjuak (Nunavik); eight communities in Nunavut, and Sachs Harbour (Inuvialuit).11

Using levels of PFOS in seal liver as an indicator was deliberate. Animal liver particularly concentrates PFOS. And it is not just in seals: all food sources, including polar bears, show high levels of PFOS in their livers.12 In this article, it was commented that 

PFOS and its relatives will remain in the Arctic environment for hundreds, perhaps thousands of years.

The high levels of PFOS in liver is of specific worry, for as we will discuss in a future article, liver is a major source of minerals and vitamins in the Inuit diet. And presumably it would selectively concentrate in human livers too.

The health effects of the PFOS family on humans is of extreme concern. The PFOS and its relatives are known to cause cancers, physical development delays, endocrine disruption, neonatal mortality, and low birth size in animals.13 In a recent study, PFOS accumulation has also been linked to reduced female fertility, decreased sperm quality, low birth rate, attention deficit hyperactivity disorder (ADHD), and changes in thyroid hormone levels.14 However, some results are inconsistent and further work is needed to confirm initial findings. There is a sense of helplessness as there is nothing Inuit can do to prevent the accumulation of PFOS in their food supply. The only long-term hope is for the Canadian Government to keep working towards an international agreement to ban the production of PFOS world-wide.

 

Concentrations ofperfluorooctanoic acid derivatives in sealliver near 11 Arctic communitiesFIGURE 4
Concentrations of perfluorooctanoic acid derivatives in seal liver near 11 Arctic communities.
Credit: C.M. Butt et al., Environmental Toxicology and Chemistry 2008, 27 (3), 542-553

The importance of environmental chemistry and biochemistry for Inuit

At this time, Arctic molecular pollution monitoring of POPs, PFOS, mercury (another problem!) and other toxic molecules is largely carried out by visiting environmental scientists from more southern locations, though Inuit participation is increasing.15 It is crucially important that Inuit students become encouraged to study environmental chemistry and biochemistry, particularly analytical methodologies. We hope that in the not-too-distant future, sampling and analysis can be performed by significant numbers of scientifically trained Inuit from across the Inuit regions. And hopefully the analyses can be performed in a large analytical facility in the north, such as in Iqaluit, capital of Nunavut. Perhaps reading our series of articles about Inuit chemistry will provide inspiration to future scientists towards that goal.

References

  1. Wikipedia. Global Distillation. https://en.wikipedia.org/wiki/Global_ distillation.
  2. Wikipedia. Persistent Organic Pollutant. https://en.wikipedia.org/ wiki/Persistent_organic_pollutant.
  3. Wikipedia. Biomagnification. https://en.wikipedia.org/wiki/ Biomagnification.
  4. Audet-Delarge, Y. et al. Persistent Organic Pollutants and Transthyretin- Bound Thyroxin in Plasma of Inuit Women of Childbearing Age. Environmental Science and Technology 2013, 47, 13086-13092.
  5. Wikipedia. Stockholm Convention on Persistent Organic Pollutants. https://en.wikipedia.org/wiki/Stockholm_Convention_on_Persistent_ Organic_Pollutants.
  6. Wikipedia. Perfluorooctanesulfonic acid. https://en.wikipedia.org/ wiki/Perfluorooctanesulfonic_acid.
  7. Emerging contaminants: Inventory on policy and legislation in Europe. PFOS and PFOA: Production, use, sources. www.emergingcontaminants.eu/index.php/background-info/Factsheets- PFOS-intro/Factsheets-PFOS-production.
  8. Blake, B.D.; Howell, R.D.; Criddle, C.S. Fluorinated Organics in the Biosphere. Environmental Science and Technology 1997, 31, 2445-2454.
  9. Giesy, J.P.; Kannan, K. Global Distribution of Perfluorooctane Sulfonate in Wildlife. Environmental Science and Technology 2001, 35, 1339-1342.
  10. Bossi, R. et al. Preliminary screening of perfluorooctane sulfonate (PFOS) and other fluorochemicals in fish, birds and marine mammals from Greenland and the Faroe Islands. Environmental Pollution 2005, 136, 323-329.
  11. Butt, C.M. et al. Levels and trends of poly- and perfluorinated compounds in the Arctic Environment. Science of the Total Environment 2010, 408, 2936-2965.
  12. Greaves, A.K.; Letcher, R.J. Linear and branched perfluorooctane sulfonate (PFOS) isomer patterns differ among several tissues and blood of polar bears. Chemosphere 2013, 93, 574-580.
  13. Betts, K.S. Perfluoroalkyl acids: what is the evidence telling us? Environmental Health Perspectives 2007, 115 (5), A250–A256.
  14. Webster, G. Potential human health effects of perfluorinated chemicals (PFCs). https://www.ncceh.ca/sites/default/files/Health effects_PFCs_Oct_2010.pdf.
  15. Letcher, R.J. et al. Legacy and new halogenated persistent organic pollutants in polar bears from a contamination hotspot in the Arctic, Hudson Bay, Canada. Science of the Total Environment 2018, 610-611, 121-136.
Publisher's note: This article is a reprint from the November 2018 issue of Chem 13 News.

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