Ecological screening assessment report on perfluorooctane sulfonate, salts and precursors: synopsis
Perfluorooctane sulfonate (PFOS) is of anthropogenic origin with no known natural sources. In Canada, there is no known manufacture of perfluoroalkyl (PFA) compounds, including PFOS. Approximately 600 tonnes of PFA compounds were imported into Canada between 1997 and 2000. While PFOS represents a very small proportion of this total (< 2 %), PFOS and its precursors accounted for about 43 %. The principal applications for PFOS and its precursors are water, oil, soil and grease repellents for use on surface and paper-based applications, such as rugs and carpets, fabric and upholstery, and food packaging. PFOS and its precursors also have specialized chemical applications, such as fire-fighting foams, hydraulic fluids, carpet spot removers, mining and oil well surfactants and other specialized chemical formulations. Exposure in the Canadian environment would likely result from the release, transformation and movement of PFOS and its precursors in effluents fugitive emissions from manufacturing sites elsewhere in the world, and releases from industrial and municipal wastewater effluents.
PFOS is resistant to hydrolysis, photolysis, microbial degradation, and metabolism by vertebrates. PFOS has been detected in fish, in wildlife worldwide and in the northern hemisphere. This includes Canadian wildlife located far from known sources or manufacturing facilities indicating that PFOS and/or its precursors may undergo long-range transport. Maximum concentrations in liver of biota in remote areas of the Canadian Arctic include: mink (20 µg.kg-1), common loon (26 µg.kg-1), ringed seal (37 µg.kg-1), brook trout (50 µg.kg-1), Arctic fox (1400 µg.kg-1) and polar bear (>4000 µg.kg-1).
Unlike many other persistent organic pollutants, certain perfluorinated substances, such as PFOS, are present as ions in environmental media and partition preferentially to proteins liver and blood rather than to lipids. Therefore, the bioaccumulation potential of PFOS may not be related to the typical mechanisms associated with bioaccumulation in lipid-rich tissues. Discretion is required when applying numeric criteria for bioaccumulation such as those outlined in the Government of Canada’s Toxic Substances Management Policy (TSMP) and in the Persistence and Bioaccumulation Regulations under 1999 when determining whether substances such as PFOS is bioaccumulative. These numeric criteria were derived from bioaccumulation data for aquatic species and for substances which preferentially partition to lipids.
Estimated steady state PFOS bioconcentration factors (BCF) of 1100 (carcass), 5400 (liver) and 4300 (blood) have been reported for juvenile rainbow trout. The corresponding 12-day accumulation ratios were 690 (carcass), 3100 (blood), and 2900 (liver) in juvenile rainbow trout. In fish livers collected from 23 different species in Japan, Bioaccumulation factors (BAFs) were calculated to range from 274 - 41 600. Following an accidental release of fire fighting foam, BAFs were calculated in the range of 6300-125 000. Estimated BCFs for the precursors n-EtFOSEA and n-MeFOSEA were 5543 and 26 000, respectively. Species differences for the elimination half-life of PFOS in biota have been determined to vary significantly: 15 days (fish); 100 days (rats), 200 days (monkeys) and years (humans). Elimination through the gills is an important route for fish which is not available to birds, terrestrial mammals (e.g., mink, polar bear, Arctic foxes) and marine mammals (e.g., seals and whales). There are three studies suggesting that PFOS biomagnifies in the Great Lakes and Arctic food webs. In the study by Kannan et al., (2005a), for the water-algae-zebra mussel-round goby-smallmouth bass-bald eagle or mink food chain, a biomagnification factor (BMF) of 10 to 20 was calculated in mink or bald eagles. In the study by Martin et al., (2004b), a benthic invertebrate/pelagic invertebrate-three forage fish -top predator fish food chain resulted in a multi-trophic level BMF of 5.88. Tomy et al., (2004) suggested that PFOS biomagnifies through the Arctic marine food web. The trophic level BMFs for PFOS included walrus-clam (4.6); narwhal-cod (7.2); beluga-cod (8.4); beluga-redfish (4.0); black-legged kittiwake-cod (5.1); glaucous gull-cod (9.0); and cod-zooplankton (0.4). Whole body aquatic BCFs or BAFs are below 5000. However, the weight of evidence from both laboratory and field-based BCFs and BAFs in conjunction with the field-based BMFs (avian and aquatic) indicates that PFOS is a bioaccumulative substance.
Based on available toxicity tests, estimated no effect levels were determined for fish, birds liver, bird serum, and wildlife (0.491µg.L-1, 0.609 µg.g-1, 0.873 µg.mL-1 and 0.408 µg.g-1, respectively). The resulting risk quotients for fish, a range of bird species (liver), a range of bird species (serum), and wildlife were 0.25, 0.002 to 2.92, 0.43 to 2.54 and 9.2, respectively. Therefore, current levels show some wildlife organisms (e.g. polar bear, bird species) could be near or at effect levels and could be harmed by current exposures to PFOS.
The assessment is based on a weight of evidence approach regarding persistence, bioaccumulation, the widespread occurrence of and concentrations of PFOS in the environment and in biota (including remote areas of Canada), and risk quotient analyses. Based on available data, it is concluded that PFOS, its salts and its precursors are entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. In addition, based on available data, it is concluded that PFOS and its salts is persistent. The weight of evidence is also sufficient to conclude that PFOS and its salts are bioaccumulative.
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