Ecological screening assessment report on perfluorooctane sulfonate, salts and precursors: chapter 1

1. Identity, Uses, and Sources of Release

Summary of Critical Information for the Ecological Screening Assessment Report for PFOS, its Salts and its Precursors


The PFOS anion (see Figure 1) has the molecular formula C8F17SO3-. The structural formula is CF3(CF2)7SO3-. While PFOS can exist in anionic, acid and salt forms, the PFOS anion is the most common form at pH values in the environment and in the human body.

PFOS and its precursors all belong to the larger class of fluorochemicals referred to as perfluorinated alkyl compounds. Perfluorinated chemicals such as PFOS contain carbons that are completely saturated by fluorine. It is the strength of the C-F bonds that contributes to the extreme stability and physical-chemical properties of these perfluorochemicals.

This assessment defines PFOS precursors as substances containing the perfluorooctylsulfonyl (C8F17SO2, C8F17SO3 or C8F17SO2N) moiety that have the potential to transform or degrade to PFOS. Appendix 1 lists some compounds considered as PFOS and its precursors (e.g., the PFOS anion; PFOS acid (PFOSH); four PFOS salts; perfluorooctanesulfonyl fluoride (POSF) and four common intermediates for producing PFOS-related chemicals (N-MeFOSA, N-EtFOSA, N-MeFOSE alcohol and N-EtFOSE alcohol) and some other 40 precursors. However, the list is not considered exhaustive as there may be other perfluorinated alkyl compounds that are also PFOS precursors. Appendix 1 was compiled based on information obtained through the Section 71 survey to industry, expert judgement and CATABOL modelling, in which 256 perfluorinated alkyl compounds were examined to determine whether non-fluorinated components of each substance were expected to degrade chemically and/or biochemically and whether the final perfluorinated degradation product was predicted to be PFOS (Mekenyan et al. 2002; Purdy 2002).

The chemistry and identity of fluorochemical products can be complex. For example, compounds produced during the electrochemical fluorination process (e.g., POSF) are not pure chemicals, but mixtures of isomers and homologues. Similarly, POSF-derived fluorochemicals and products do not necessarily produce pure products (US EPA OPPT AR226-0550).Footnote 2 Varying amounts of un-reacted or partially reacted starting materials or intermediates, including PFOS, N-MeFOSA, N-EtFOSA, N-MeFOSE alcohol and N-EtFOSE alcohol, can be carried forward to final products at typical concentrations of 1 to 2% or less (US EPA OPPT AR226-0550). These residuals in final products have the potential to degrade or metabolize to PFOS (US EPA OPPT AR226-0550).

Once PFOS is released to the environment, it is not known to undergo any further chemical, microbial or photolytic degradation and is, therefore, persistent. As well as being commercially produced, PFOS is the final degradation product from POSF-derived fluorochemicals. Key physical/chemical properties of PFOS and some precursors that are useful in predicting its environmental fate are listed in Table 1.

Table 1: Selected Physical and Chemical Properties of PFOS Potassium Salt and Common Intermediates
Substance CAS No. Molecular
Henry’s Law
mol)Footnote a
Log Kow Melting
PFOS (K+) 2795-39-3 538.23 5.19 E-1
to 6.80 E-1
3.31 E-4 3.45 E-4 Not
>400 Not calculable
1691-99-2 571.26 1.51 E-4 5.04 E-1 1.93 E+3 4.4 55-60 N/AFootnote b
N-EtFOSEA 423-82-5 625.30 8.9 E-4 N/A N/A N/A 27-42 150 at 133.3 Pa
24448-09-7 557.23 N/A N/A N/A N/A N/A N/A
N-MeFOSEA 25268-77-3 611.28 N/A N/A N/A 5.6 N/A N/A

Although experimental evidence on the degradation of PFOS precursors to PFOS is very limited, the precursors are expected to degrade through bacterial-mediated degradation pathways. The biodegradation software, CATABOL, which simulates Organization for Economic Co-operation and Development (OECD) 302C 28-day biodegradation tests and which has been designed to accommodate perfluorinated compounds, predicts that the majority of those substances identified as precursors (Appendix 1) will degrade to PFOS (Dimitrov et al. 2004). This degradation has been further supported by expert judgment. It is, therefore, expected that once those substances listed in Appendix 1 are subjected to a biotic or abiotic degradation mechanism, the perfluorinated moiety that remains will be PFOS. The rate of degradation to PFOS is not considered significant, as, over time, these substances are all expected to degrade in the environment to PFOS.

Natural Sources

There are no known natural sources of PFOS (Key et al. 1997). Its presence in the environment is due solely to anthropogenic activity.

Uses, Manufacturing and Imports

Results from the Section 71 Notice indicated that PFOS and its precursors are not manufactured in Canada but rather are imported as chemicals or products from the United States for Canadian uses. They may also be components in imported manufactured articles. Approximately 600 tonnes of perfluorinated alkyl compounds were imported into Canada during 1997-2000, with PFOS and its precursors accounting for about 43% of imported perfluorinated alkyl compounds. PFOS alone accounted for <2% of imported perfluorinated alkyl compounds (Environment Canada 2001). The most significant Canadian imports of PFOS itself were in the form of the potassium salt, used for fire-fighting foams.

As PFOS production has also been identified in Italy, Japan, Belgium, Germany and Asia, PFOS-containing consumer products could also be imported into Canada from non-US sources. It is not known whether foreign companies are phasing out of PFOS manufacturing. Therefore, the potential remains for PFOS-containing products/materials manufactured elsewhere to continue being imported into Canada. However, these quantities are unknown.

Since 2000, 3M has been phasing out its use of the perfluorooctanyl chemicals and products containing PFOS. Survey data indicated an overall decline in imports from 1997 to 2000. The 3M phase-out plan for PFOS production was completed in 2002 (

It is estimated that the majority of all perfluorinated alkyl compounds imported into Canada were used in applications involving water, oil, soil and grease repellents for fabric, packaging and rugs and carpets; and surfactants/detergents, emulsifiers, wetting agents, dispersants and fire-fighting foams. It is expected that PFOS and its precursors are present in many of these use applications.

Sources of Release

Significant PFOS releases to the Canadian environment may result from major use applications involving water, oil, soil and grease repellents for packaging (Environment Canada 2001). Currently, there are no data available to reflect potential Canadian releases from the use and final disposal of a vast variety of imported finished consumer products that may contain PFOS or its precursors.

Environmental releases from surface treatments for rugs and carpets are expected during use and may involve discharges to process wastewater and air during initial applications (e.g., to uncut carpets) (US EPA OPPT AR226-0550). Additional wastes occur from cutting, shearing or packaging operations and are generally land filled or recycled. As well, end use of consumer articles will create losses (e.g., it is estimated that vacuuming and cleaning of carpets create releases; final disposal of treated carpets is generally to landfills) (US EPA OPPT AR226-0550). Industry Canada (2002) statistics indicate that approximately 22 active carpet and rug mills were operating in Canada in 1999. This number does not account for those establishments classified as “non-employers” or where carpet manufacturing is not the primary activity. In the case of fire-fighting foams, final disposal would primarily be to sewers (wastewater treatment), although uncontrolled releases to surface waters or land may occur (US EPA OPPT AR226-0550).

It has been suggested that PFOSH (PFOS acid) may be released to the environment from incomplete combustion during incineration of PFOS-containing products (US EPA 2002). A laboratory-scale incineration study of PFOS and C8 perfluorosulfonamides determined that a properly operating full-scale (high temperature) incineration system can adequately dispose of PFOS and C8 perfluorosulfonamides (US EPA OPPT AR226-136). The study also indicated that incineration of these substances is not likely to be a significant source of PFOS into the environment. The C-S bond was completely destroyed indicating that transformation of any combustion products to form PFOS was also highly unlikely. Any potential formation and release of PFOS through incomplete incineration is not considered a significant source in Canada, where incineration accounts for only about 5% of waste disposal (Compass Environmental Inc. 1999).

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