Perfluorooctane sulfonate in the environment: chapter 6
The temporal trends of PFOS have been studied in air, suspended sediment, sediment cores, lake trout and Herring Gull eggs. The majority of temporal trend data is for Lake Ontario; however, Herring Gull eggs were evaluated for PFOS in colonies from each of the five Great Lakes, and Arctic air was assessed for PFOSprecursors. For the most part, levels of PFOS increased markedly until the late 1990s/early 2000s, corresponding to increasing production volumes. However, in recent years, concentration trends varied by media and location. More time may be needed before ongoing shifts in North American and global uses and releases of PFOS and its precursors result in clear trends in various environmental media and locations.
Air: At the Canadian High Arctic station of Alert, Nun., PFOS and its precursors were sampled for with a high-volume air sampler starting in 2006. PFOS was below the detection limit of 0.2 pg/m3 at Alert, Nun., however, PFOSprecursors were detected. One such precursor is methyl perfluorooctane sulfonamidoethanol (MeFOSE) (Figure 3). MeFOSE is easier to detect in air as a result of its higher volatility compared to PFOS. The concentrations of this PFOSprecursor oscillated from below detection to 2.6 pg/m3and are showing general declining trends. Continued measurements are required to examine what factors influence transport of PFOS and its precursors to the Arctic in order to understand the long-range transport ability of these chemicals.
Concentrations of the PFOS precursor compound, methyl perfluorooctane sulfonamidoethanol, in air (pg/m3) at Alert, Nun., between 2006 and 2010.
Suspended Sediment: Suspended sediment has been collected annually, since the 1980s, from Niagara River water flowing into Lake Ontario. The samples were analyzed for PFOS at the Ontario Ministry of the Environment.6 The Niagara River represents the most significant input of water to Lake Ontario, accounting for approximately 80% of the total tributary inflow into the lake. The concentrations of PFOS in suspended sediment increased from the early 1980s (0.47 ng/g dry weight) until 2001, when a peak concentration of 1.1 ng/g dry weight was reached (Figure 4). After this time, PFOS decreased continually to a concentration of 0.48 ng/g dry weight in 2006. The long-term time trends of PFOSin suspended sediment more closely resemble assumed North American production volumes and the timing of the 2002 PFOS production phase-out by the primary supplier, compared to other media. This may not be surprising, considering that suspended sediments were collected from filtered water samples and thus are likely representative of direct loadings into the lake.
Figure 4: Concentrations of PFOS (ng/g dry weight) in Niagara River suspended sediment.
Sediment Core: Three sediment cores were collected from Lake Ontario in 2006, dated using radioisotope methods and analyzed for PFOS at the Ontario Ministry of the Environment.6 Figure 5shows the results of one of these sediment cores. The trends for the other two cores are similar and thus not shown. PFOS increased in the Lake Ontario sediment cores from the start of data collection until 2004, and did not reflect the 2002 phase-out by the primary supplier. This lack of correspondence between the sediment core data with assumed loadings patterns could be a result of the sediment core trend being based on only five measurements dated between 1980 and 2004. This time trend only includes one data point following the 2002 PFOS production phase-out by the primary supplier. It should be noted that better resolution would be difficult to achieve due to the slow rate at which particles are deposited and incorporated into Lake Ontario sediment. Continued monitoring of sediment cores is required, as it may take more years before the reduction in PFOS use is reflected in this media.
Figure 5: Concentrations of PFOS (ng/g dry weight) in a Lake Ontario sediment core sample collected in 2006.
Fish: To provide a long-term perspective of PFOS in Lake Ontario lake trout, annual measurements made by Environment Canada (1997-2010)7 were combined with PFOSconcentrations that Furdui and co-workers24,25 determined in archived lake trout samples (1979-2004). These archived samples were also collected in Lake Ontario by Environment Canada and the Department of Fisheries and Oceans and were analyzed for PFOS by the Ontario Ministry of the Environment. PFOS concentrations in Lake Ontario lake trout showed an overall increase between 1979 and 2000 (Figure 6). However, after this time, concentration trends stabilized, with geometric mean levels oscillating between 44 and 109 ng/g wet weight. These results suggest that although PFOS in Lake Ontario lake trout may have stopped increasing in response to the 2002 PFOSproduction phase-out by the primary supplier, corresponding concentration declines in fish have not been observed. The lack of recent decline may be a result of the large number of processes, in addition to chemical loadings, that affect the accumulation of PFOS in biota such as lake trout. For example, the amount of PFOS in fish is dependent on its diet, the accumulation rate of PFOS and its precursors from water and food, and the rate at which precursors are transformed to PFOS in the fish, its food and the environment. As such, the voluntary and regulatory measures may not be reflected in PFOS concentrations in Lake Ontario lake trout for years to come. In all years, observed concentrations in lake trout were at least an order of magnitude below the draft FEQG for fish tissue (8,300 ng/g wet weight), but were between 1.5- and 27-fold higher than the draft FEQG for wildlife diet. Therefore, although PFOS does not represent a risk to the Lake Ontario lake trout themselves, it is present at levels that are potentially hazardous to the wildlife consumers of the fish.
Figure 6: Geometric mean concentrations of PFOS in Lake Trout (ng/g wet weight) from Lake Ontario, 1979 to 2010. The dashed line represents data reported by Furdui et al. 2007 and 2008, and the solid line represents Environment Canada data. The draft Federal Environmental Quality Guidelines (FEQGs) for fish tissue and for avian and mammalian wildlife diet are shown for comparison (red dotted lines).
Wildlife: Herring Gull eggs were monitored for PFOS in 1990 and in all years between 1997 and 2010 at seven colonies throughout the Great Lakes. The data for gulls collected from the more urbanized regions of southern Ontario are shown in Figure 7. Likewise, Figure 8 shows PFOS levels in gull eggs collected from three more remote colonies in lakes Huron and Superior. The average PFOS concentrations from the more urbanized colonies oscillated between approximately 150 and 930 ng/g egg wet weight. However, consistent with trends found in Lake Ontario lake trout, PFOS levels have not shown consistent declines in response to the 2002 PFOS production phase-out by the primary supplier. PFOS levels in the gull eggs collected from the more remote colonies also varied considerably between years (80-375 ng/g wet weight); however, in contrast to the urbanized colonies, an overall decline was evident. These results show that temporal trend patterns can vary between locations, even for the same media or species. The PFOS concentrations in Herring Gull eggs were below the draft FEQG for bird eggs (1900 ng/g wet weight) in all years and locations; but were 10- to 200-fold higher than the draft FEQG for wildlife diet. Therefore, similar to the case of fish, although PFOS does not represent a risk to the Herring Gull eggs themselves, it is present at levels that are potentially hazardous to the gull’s wildlife predators.
Figure 7: PFOS concentrations in Herring Gull eggs (ng/g wet weight) from Lake Ontario (Leslie Street Spit), Niagara River and Detroit River (Fighting Island), from 1990 to 2010. The draft Federal Environmental Quality Guidelines (FEQGs) for bird eggs and wildlife diet are shown for comparison (red dotted lines).
Figure 8: PFOS concentrations in Herring Gull eggs (ng/g wet weight) from Lake Huron (Channel-Shelter and Chantry Islands) and Lake Superior (Agawa Rocks), from 1997 to 2010. The draft Federal Environmental Quality Guidelines (FEQGs) for bird eggs and wildlife diet are shown for comparison (red dotted lines).
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