ARCHIVED - Environmental Screening Assessment Report on Perfluorooctane Sulfonate

Identity, Uses, Sources and Release

Substance Identity

The PFOS anion, shown in 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. This assessment defines PFOS precursors as substances containing the perfluorooctylsulfonyl (C₈F₁₇SO₂) or C₈F₁₇SO₃ moiety that have the potential to transform or degrade to PFOS. Appendix 1 lists some compounds considered as PFOS and its precursors -- namely, 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; for complete chemical names, see Appendix 1), all of which are considered PFOS precursors; and other precursors not in the above-named categories. 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 2002a).

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 unique properties of these perfluorochemicals.

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)². Varying amounts of unreacted 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 1–2% 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. Therefore, 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.

^a 1 atm = 101.3 kPa.
^b N/A = not available.
Source: Hekster et al. (2002)

Natural Sources

Notably, all perfluorinated compounds are of anthropogenic origin, and there are no known natural sources of PFOS (Key et al. 1997). Its presence in the environment is due solely to human activity.

Manufacture and Import

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 587 tonnes of perfluorinated alkyl compounds were imported into Canada during 1997–2000, with PFOS and its precursors accounting for 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 US 3M phase-out plan for POSF-based products issued to the US EPA states that 3M anticipated that the manufacture and import of affected products would have ceased by the end of 2002, although 3M will continue to distribute small volumes of certain previously manufactured products to specific customers (US EPA OPPT AR226-0588).

Use

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.

Release

3M has compiled a preliminary review of fluorochemical use, distribution and release (US EPA OPPT AR226-0550).

Significant PFOS releases to the Canadian environment would be expected from the 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 (e.g., home furnishings and electronic goods) that may contain PFOS or PFOS precursors as part of fabric finishes or coatings. However, PFOS could eventually be released to the Canadian environment from these sources.

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 landfilled 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). While work continues in the United States to validate this release scenario, any potential formation and release of PFOS through incineration would likely be a minor source in Canada, where incineration accounts for only about 5% of waste disposal (Compass Environmental Inc. 1999).

² These Administrative Records are all 3M submissions to the US Environmental Protection Agency's (US EPA) Office of Pollution Prevention and Toxics. Additional information may be found in the reference list.