CAS number
- 1763-23-1 (PFOS)
335-67-1 (PFOA)
Not applicable – Family of 3,000 compounds Molecular formula
- C8HF17O3S (PFOS)
C8HF15O2 (PFOA)
Not applicable – Family of 3,000 compounds
Formula weight
- 500 g/mol (PFOS)
414 g/mol (PFOA)
Not applicable – Family of 3,000 compounds
Family
- Fluorinated Organic Compounds
Perfluorooctane Sulfonic Acid (PFOS) Chemical Structure
F3C-CF2-CF2-CF2-CF2-CF2-CF2-CF2-SO3H
Perfluorooctanoic Acid (PFOA) Chemical Structure
F3C-CF2-CF2-CF2-CF2-CF2-CF2-CO2H
The structure of PFASs consists of a fluorinated carbon chain at the end of which is a functional group. These functional groups are carboxylic acids (-COOH), carboxylates (-COO-), sulphonic acids (-SO3H) or sulphonates (-SO3-).
Per- and Polyfluoroalkyl Substances, known as PFAS, form an emerging and diversified group of interest of synthetic chemical compounds used since the 1950’s for many industrial and commercial applications.
PFAS include more than 3,000 different compounds with very distinct physical and chemical properties. Those substances can be classified in two categories: polymer substances (large molecules formed by the combination of many identical smaller molecules (monomer)) and nonpolymer substances including perfluoroalkylated substances (fully fluorinated carbon-chain molecules) and polyfluoroalkylated substances (partially fluorinated carbon-chain molecules). As the polymer substances are large molecules formed with several smaller molecules (or monomers), polymer substances are considered as potential precursors of the nonpolymer per- and polyfluoroalkylated substances. The breaking of a bond can cause the release of a nonpolymer PFAS.
Perfluoroalkylated Substances
Perfluoroalkylated substances are fully fluorinated carbon-chain molecules which means that fluorine atoms are bonded to all available binding sites along the carbonated chain, except for the last carbon which a functional group is fixed. The main functional groups are the perfluoroalkyl carboxylic acids (-COOH), the perfluoroalkyl carboxylates (-COO-), the perfluoroalkane sulfonic acids (-SO3H) or the perfluroalkane sulfonates (-SO3-). The general chemical formula for these substances is CnF2n+1-R where n corresponds to the number of carbon atoms of the carbonated chain, 2n+1 corresponds to the number of fluorine atoms bonded to the carbon atoms chain and where R represents the functional group linked at one end of the carbonated chain. Perfluoroalkyl substances include perfluoroalkyl acids (PFAA), perfluoroalkyl ether acids (PFESA), perfluoroalkane sulfonyl fluorides (PASF), perfluoroalkane sulfonamide (FASA), perfluoroalkanoyl fluorides (PAF), perfluoroalkyl iodine (PFAI) and perfluoroalkyl aldehydes (PFAL).
Polyfluoroalkylated Substances
Polyfluoroalkylated substances differ from the perfluoroalkylated substances in that they are not fully fluorinated, which means that not all the available bonding sites along the carbonated chain are fluorine atoms. A functional group is also fixed to the end of the carbonated chain. Polyfluoroalkylated substances mainly include fluorotelomers (Ft), perfluoroalkane sulfonamido derivatives, perfluoroalkyl ether carboxylic acids (PFECA) and polyfluoroalkyl ether carboxylic acids (PFESA). Polyfluoroalkyl substances mainly include fluorotelomers (Ft), perfluoroalkane sulfonamido derivatives, perfluoroalkyl ether carboxylic acids (PFECA) and polyfluoroalkyl ether carboxylic acids (PFESA).
These substances can be found as solid (white powder or waxy substance) or liquid phase at ambient temperatures. PFAS may also be present as anionic forms or acids in the environment with distinct physical and chemical properties. Therefore, it is essential to differentiate between anionic forms and acids to understand the behavior of these substances in the environment.
PFAS are mostly amphiphilic molecules which means that they have a hydrophilic part and a hydrophobic and lipophilic part. Therefore, their solubility in the water can vary significantly, depending on their chemical structure, the pH and their functional group.
Properties such as high fluorine electronegativity and small size lead to the strong C-F bond explain the PFAS thermic and chemical stability. Thermic and chemical stability give the PFAS a strong resistance to degradation processes such as hydrolysis as well as oxidation and reduction. For example, the acidic forms of perfluoroalkyl acids (PFAA) degrade at temperatures higher than 400°C while complete mineralization occurs at temperatures higher than 1,000°C.
Examples of PFOA and PFOS physicochemical properties are presented below.
Compound properties list|
| Melting/boiling point | 54/192 (PFOA)
15,2-73,5 / 219-262 °C (PFOS)
| - |
| Relative density | 1,8 g/cm3 (PFOA)
1,84-1,85 g/cm3 (PFOS)
g/cm3 | - |
| Vapour pressure | 0,525 mm Hg (PFOA)
0,002 mm Hg (PFOS)
| Compounds with very little volatility for several PFASs, sometimes volatile for certain compounds such as fluorotelomer alcohols (FTOH). |
| Vapour density | 0 | N/A |
| Solubility in water | 9.5 x 103 mg/L (PFOA)
550 mg/L (24-25°C) (PFOS)
| High solubility in water (PFOA)
|
| Henry's law constant | Non mesurable (PFOA and PFOS) | Not volatile when dissolved. |
| log Koc (Depending on soil or sediment characteristics) | 2,06 (PFOA)
2,57-3,16 (PFOS)
| Adsorption on organic matter. |
These substances can be found in different environmental media (air, soil, sediment, ground water, surface water, biota).
Although in most cases PFAS are not volatile, some of these substances can be present in the air under gaseous phase or associated with particles and aerosols. These substances can be carried over short or long distances in the atmosphere. PFAS are also found in soil and sediment through contact with contaminated media (landfill leachates, amendments, etc.) or through direct discharge (example: using of aqueous film forming foam (AFFF)). PFAS present in the soil vadose zone can reach ground water and surface water through percolation or soil leaching. As PFAS are very stable in the environment, they can potentially migrate over great distances in contaminated ground water. Their mobility as dissolved phase is strongly controlled through sorption on charged mineral particles or organic matter. Sorption mechanisms at these particles are influenced by surface sorption of charged mineral particles and soil organic matter. Long fluorinated- chains PFAS are more strongly adsorbed than short-chained PFAS. Moreover, they tend to accumulate at phases interfaces, as, for example, at the water-air interface at the surface of ground water tables or at the water-oil interface, in the presence of a non-aqueous phase.
Finally, PFAS are bioaccumulates. Unlike other persistent contaminants, PFAS apparently bond more strongly to protein than lipids. Long-chained PFAS are more likely to accumulate in living organisms than short-chained PFAS.
PFAS are present in a large number of consumer goods and end up in the environment during the lifecycle of these products. These substances are persistent and bioaccumulate. Humans are exposed to PFAS through inhalation, as some PFAS are volatile and can be adsorbed to particles and through drinking water or food ingestion. Dermal contact represents a minor exposure pathway to these compounds.
Currently there is limited information available about the risks on human health linked to PFAS. Studies conducted on animals show that high levels of PFAS can cause adverse effects such as liver damage and impact on neurological development. Immune system impairment, infertility and cancer risks increase are additional risks to human health caused by PFAS exposure. These substances could also cause fetal and child development disorders.
Four main PFAS sources are identified:
- Fire fighting training areas (FFTA) and fire fighting areas (use of AFFF), and, generally, any sites where these foams have been used (military base, airports, fire site or burning sites, gas stations, petroleum refineries, bulk storage facilities, rail yards);
- Industrial sites (fluoropolymers production, semiconductors, electroplating, electronics, pharmaceuticals, textiles, paper and packaging production);
- Landfill and wastewater treatment facilities;
- areas of biosolids production and application.
Although additional point sources and diffuse sources for theses substances do exist, those are generally less significant than the above-mentioned.
- A.B. Lindstrom, M.J. Strynar, E.L. Libelo, Polyfluorinated compounds: past, present, and future, Environ. Sci. Technol. 45 (2011) 7954–7961.
- Ross, J. McDonough, J. Miles, P. Storch, P. Thelakkat Kochunarayanan, E. Kalve, J. Hurst, S. Soumitri Dasgupta, J. Burdick, A review of emerging technologies for remediation of PFASs, Remediat. J. 28 (2018) 101–126.
- R.C. Buck, J. Franklin, U. Berger, J.M. Conder, I.T. Cousins, P.D. Voogt, A.A. Jensen, K. Kannan, S.A. Mabury, L. van, Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, Classification, and Origins. Integrated Environmental Assessment and Management. 7-4 (2011) 513-541.
- Interstate Technology Regulatory Council (ITRC). Washington, D.C.: ITRC, Per- and Polyfluoroalkyl Substances (PFAS) Team.
- Charles-Casini, M. (2019). Réalisation d’un Wiki sur la toxicité des PFAS et leurs solutions de traitement. Internship thesis, Institut polytechnique de Bordeaux, Bordeaux). (available in French only, PDF, 1.47 MB)
- Government of Canada. (2019). Water Talk – Perfluoroalkylated substances in drinking water: Perfluoroalkylated substances (PFAS).
- Arcadis, 2016. Environmental fate and effects of poly- and perfluoroalkyl substances (PFAS) [Online]. Brussells: Concave, Environmental science for the european refining industry; June 2016 [cited on March 31, 2020] 107 pages. (PDF, 1.36 MB)
