Draft objective for per- and polyfluoroalkyl substances in Canadian drinking water: Exposure considerations
PFAS are a family of thousands of substances that contain linked fluorine and carbon atoms. This chemical link results in a very stable molecule that is essentially unreactive and persists in the environment. Because of their unique properties, PFAS have a wide range of uses including as surfactants, lubricants and repellents (for dirt, water and grease). PFAS can also be found in products as diverse as firefighting foams, textiles (for example, carpets, furniture and clothing), cosmetics and food packaging materials.
In Canada, some of the legacy PFAS (that is, PFOA, PFOS and long-chain PFCAs, their salts and their precursors) have been prohibited from manufacture, use and import, with a limited number of exemptions. PFAS primarily enter Canada in products or as constituents of manufactured items. Some PFAS may be used in industrial processes, which may lead to releases from industrial facilities into the environment. Releases can also occur from landfills and wastewater treatment plants, and due to the reuse of biosolids from wastewater treatment plants (Guerra et al., 2014; Hamid et al., 2018).
Many studies have demonstrated that PFAS are transported long distances through the atmosphere, in water bodies and within groundwater. In addition to drinking water, research indicates that Canadians can be exposed to PFAS through food (Tittlemier et al., 2007), dust (De Silva et al., 2012; Eriksson and Kärrman, 2015; Karaskova et al., 2016; Kubwabo et al., 2005; Shoeib et al., 2011) and indoor air (Beesoon et al., 2012; Shoeib et al., 2011).
In Canada, major sources of PFAS contamination of the aquatic environment are associated with both point and non-point sources. Non-point sources of PFAS may include surface runoff from urban areas and wet/dry atmospheric deposition (Lalonde and Garron, 2022). The most common point sources of PFAS contamination are associated with the use of aqueous film-forming foams (AFFFs) to extinguish fuel fires or during firefighting training (for example, at airports and military bases) (D'Agostino and Mabury, 2017; Liu et al., 2021). These AFFFs contain proprietary mixtures of PFAS and other chemicals. A number of PFAS are detected in groundwater at former fire-training areas.
However, PFAS are also reported in ground and surface water at other types of sites (for example, emergency response locations, AFFF lagoons, hangar-related storage tanks, firefighting equipment maintenance areas and pipelines or infrastructure impacted by AFFFs) (Awad et al., 2011; Anderson et al., 2016; Milley et al., 2018). PFAS can migrate long distances through soil and water beyond the point at which they entered the environment.
There are limited data regarding PFAS in Canadian freshwater sources and drinking water. The number and suite of PFAS present in any given drinking water source will vary depending on the source of contamination, environmental conditions as well as new and historical patterns of use.
In a study focused on examining the presence of PFAS in freshwater, 29 sites across Canada were sampled from 2013 to 2020 for 13 different PFAS to determine concentrations and trends. Sampling sites and frequencies varied during the course of the study. Detection limits ranged from 0.4 to 1.6 ng/L. Of the 13 PFAS detected in 566 freshwater samples, the study found PFBA, PFPeA, PFHxA, PFHpA, PFOA and PFOS to have higher detection frequencies than the other PFAS. Within this group of PFAS, concentrations of PFBA and PFPeA increased significantly over the 2013 to 2020 period whereas concentrations of PFHpA, PFOA and PFOS decreased. The highest concentrations were noted to be 138 ng/L for PFBS (although this PFAS had fewer detections than the 6 PFAS identified above) and PFHxA at 137 ng/L. The authors note that this study found a higher frequency of detections of the replacement PFAS, such as PFBA, PFPeA, PFHxA, PFHpA and PFBS, than that seen in older Canadian studies (Lalonde and Garron, 2022).
In Saskatchewan, the Water Security Agency collected drinking water samples (n = 7) from 7 water treatment plants in 2018–2019 to determine levels of PFOA and PFOS in treated drinking water. Neither PFOA nor PFOS were detected (method detection limit [MDL]: 2 ng/L) in the drinking water of 6 out of 7 communities. PFOA was detected in the single sample from 1 drinking water treatment plant at a concentration of 3 ng/L (Saskatchewan Water Security Agency, 2022).
Between 2012 and 2016, the Ontario Ministry of the Environment, Conservation and Parks measured the occurrence and concentrations of 14 PFAS (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnA, PFDoA, PFBS, PFHxS, PFOS, PFDS and PFOSA) in 25 drinking water systems in Ontario (water intakes and treated drinking water). MDLs ranged from 0.5 to 1 ng/L, and results less than the MDL were substituted with a value of half the MDL (Kleywegt et al., 2020). PFUnA, PFDoA, PFDS and PFOSA were not detected in any drinking water samples. The most frequently detected compounds in Ontario drinking water were PFOA (73%; median 1.1 ng/L, maximum 6.6 ng/L), PFBA (67%; median 2.4 ng/L, maximum 10 ng/L), PFHxA (54%; median 1.3 ng/L, maximum 13 ng/L), PFPeA (51%; median 1.0 ng/L, maximum 15 ng/L) and PFOS (50%; median 0.63 ng/L, maximum 5.9 ng/L).
Between 2016 and 2021, Quebec's Ministère de l'Environnement et de la Lutte contre les changements climatiques (MELCC) sampled 41 drinking water treatment systems, testing for 18 PFAS (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnA, PFBS, PFHxS, PFHpS, PFOS, PFDS, FHUEA, FOUEA, 4:2 FTS, 6:2 FTS, 8:2 FTS). Both surface and groundwater systems were included, with groundwater systems added in 2018 (MELCC, 2022). The sampling sites were selected based on previous PFAS detections and/or concerns in those locations, or due to their proximity to known potential point sources of PFAS. Detection limits ranged from 0.5 to 5 ng/L for raw water samples and from 0.3 to 5 ng/L for treated water samples. Among the 18 PFAS analyzed, 6 (PFPeA, PFHxA, PFHpA, PFOA, PFNA and PFOS) were detected in 10% or more of the samples taken. The 2016 data showed a reduction in the maximum concentrations of PFOA and PFOS (6 ng/L and 3 ng/L, respectively) when compared with the maximum surface water concentrations from the same sites sampled in 2007–2008 (66 ng/L for PFOA and 8.8 ng/L for PFOS).
In the St. Lawrence River and other rivers, 5 substances (PFHxA, PFHpA, PFOA, PFNA and PFOS) were detected in at least 30% of the samples. PFOA and PFHxA were detected at the highest frequency (72% and 59%, respectively); both had a maximum concentration of 6 ng/L and a median concentration of 2 ng/L.
In Lake Memphremagog, PFOA (median 1 ng/L, maximum 2 ng/L) and PFHxA (median 1.5 ng/L, maximum 3 ng/L) were detected in raw water; both were also found in treated drinking water at a maximum of 1 ng/L and median of 1 ng/L each. In groundwater sources, PFPeA (median 4 ng/L, maximum 48 ng/L) and PFHxA (median 3 ng/L, maximum 30 ng/L) were found in 14% and 17% of samples respectively, while PFOA (median 2 ng/L, maximum 4 ng/L) and PFOS (median 2 ng/L, maximum 3 ng/L) were found in 6% and 4% of samples (MELCC, 2022).
Similar median concentrations of PFBA, PFPeA, PFHxA, PFOA and PFOS were reported in samples of drinking water sourced from 19 sites around Lake Ontario and the St. Lawrence River (n = 8) and other lakes and small rivers in Canada (n = 11). Maximum concentrations of PFAS ranged from 0.1 ng/L (PFDA) to 4.1 ng/L (PFOS) in the Great Lakes–St. Lawrence samples, and 0.1 ng/L (PFUnA) to 4.9 ng/L (PFOA) for the rest of the Canadian tap water samples. PFHxA was detected in all Canadian tap water samples from this study. Other PFAS that were frequently detected included PFBA (95%), and PFHxS and PFOS (both 89%), while PFPeA, PFHpA, PFOA, PFNA, PFDA and PFBS were detected in at least 84% of the samples. Compounds detected less frequently in Canadian waters included FOSA (53%), 6:2 FTSA (37%) and 5:3 FTCA (11%), as well as PFUnA, PFDoA and 7:3 FTCA, which were each detected in less than 10% of samples. A qualitative screening approach indicated that FBSA, FHxSA, PFECHS and PFPeS were occasionally present in tap water (concentrations ranged from below the limit of detection to 1.2 ng/L), whereas PFEtS, PFPrS and PFPeS were below the limit of detection for all Canadian samples. The limits of detection for tap water ranged from 0.01 to 0.08 ng/L (Kaboré et al., 2018).
In Nova Scotia, as of 2019, municipalities have been required to test the raw and treated drinking water for the presence of PFOA and PFOS. Neither PFOA nor PFOS have been detected (MDL: 20 ng/L) in the 9 systems tested to date (NSECC, 2022).
The U.S. EPA completed drinking water monitoring of 6 PFAS (PFHpA, PFOA, PFNA, PFBS, PFHxS and PFOS) between 2013 and 2015 under the Third Unregulated Contaminant Monitoring Rule (UCMR3). The results showed that 1.6% of the 36 977 samples and 4% of the 4 920 public water systems reported at least 1 detectable PFAS compound (Guelfo and Adamson, 2018).
The minimum reporting levels (MRLs) ranged from 10 to 90 ng/L for the monitored PFAS compounds and were generally higher than the limit of quantitation of most published studies (Hu et al., 2016). PFOA (MRL 20 ng/L) and PFOS (MRL 40 ng/L) were detected most frequently across all system sizes and source types at 1.03% and 0.79%, respectively. The highest maximum concentrations of PFOS (7 000 ng/L), PFHxS (1 600 ng/L), PFHpA (410 ng/L), PFOA (349 ng/L) and PFNA (56 ng/L) were detected in large systems with a groundwater source. PFBS (MRL 90 ng/L) was detected only in large systems, and the highest maximum concentration of 370 ng/L was observed in a large system supplied by a surface water source (Crone et al., 2019).
An analysis of the UCMR3 data found that approximately 50% of samples with PFAS detections contained 2 or more PFAS and 72% of detections occurred in groundwater (Guelfo and Adamson, 2018). Certain activities were significant predictors of PFAS detection frequencies and concentrations in public water supplies (that is, the number of industrial sites that manufacture or use PFAS compounds, the number of military fire training areas and the number of wastewater treatment plants) (Hu et al., 2016).
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