PFOS and PFOA are the best known perfluorinated (fully fluorinated) organics.These substances are chemically very inert, resistant to high temperatures, they reduce surface tension and are water and dirt repellent and grease proof.Due to their properties, these materials are widely used in surface treatments of carpets, textiles, leather, paper and cardboard, but also as a surfactant in extinguishing foams, mist suppressant in chrome plating and as a surfactant in the mining and oil industries.The very properties that have made these materials into an industrial success, also lead to persistency, bio-accumulation and, in some cases, their toxicity in the environment.The following table summarizes PFOS and PFOA properties.

Abbreviation   Name and CAS number Structural formula
PFOS perfluorooctane sulfonic acid 1763-23-1
in dissociated form called Perfluoroctane sulfonate   
C8F17SO3H Derivatives according to Stockholm Convention:
K, Li, NH4 + -, DEA, TEA and DD-DMA salts and PFOSF
PFOA Perfluorooctanoic 335-67-1 C7F15CO2H

VARIANTS

In addition to PFOS and PFOA there are many variants with longer or shorter carbon chains or polymers which have been frequently used.Perfluorinated compounds are also referred to as PFAS (Per Fluoro alkylated Substances) or PFC (Per Fluoro Chemicals). PFAS concentrations found in environmental research are often dominated by PFOS and PFOA. 

Legislation (e.g. the Stockholm Convention and EU regulations) uses the term PFOS whenever perfluoroctane sulfonic acids are meant, also known as PFOS and PFOS derivatives, often precursors of PFOS.

WHY IS PFOS A PROBLEM?

The substance is very stable, even at high temperatures. It is this quality that makes PFOS a perfect fire-fighting foam. Complete combustion of PFOS requires a combustion temperature of at least 1.100 °C. PFOS has been found worldwide in birds, fish and other fauna, even on the North Pole. In the Netherlands, the substance is found in very low concentrations in drinking water 

Studies show that the substance accumulates in the food chain and that the average residence time in the human body amounts to 5.4 years. For PFOA the average residence time is 4 years.

The main producer of PFOS (3M) has phased out the production of PFOS on a voluntary basis in 2002.In 2006 the European Union proclaimed a ban on the production, trade and use of PFOS and in 2009 PFOS was included in the Stockholm Convention. In 2011, the RIVM has conducted a preliminary investigation into the recovery values in soil and groundwater and in April 2013 PFOS was listed in the Water Framework Directive.

The substance is toxic, it accumulates in the liver and in the blood and it can easily cross the placenta.The mechanism of toxicity is not fully clear.Experiments with animals showed liver toxicity, effects on biochemical parameters related to lipid metabolism, reproductive toxicity and immunological effects.


PFOS PFOA
Molar mass (g / mol) 500.1 414.1
Solubility (mg / l) 370 9500
pKa -3.27 (strong acid, calculated value)     0 - 3.8 (variation in reported pKa values)
Vapour pressure (Pa) 3,31 * 10-4 1,3 * 10-3
Log Kow Formation of three phases cannot be determined
Log Koc (4.2 #) (3.7 #)
Melting point ≥ 400 °C 45-50 °C
Boiling point cannot be determined 188 °C
Henry's Law Constant (atm.m3/mol) 4,34 * 10-7 cannot be determined
Tolerable Daily Intake (TDI, ng / kg body weight)    150 1500
MTR (surface water, ng / L) 0.65 not derived
Provisional restoration value land µg / kg 0.1 to 100 not prepared
Provisional restoration value groundwater
remediation g/l
0.010 to 4.7 not prepared


# Large variations, see the fact sheet 'Behaviour in soil and water'