Draft objective for per- and polyfluoroalkyl substances in Canadian drinking water: Health considerations

While many substances and groups within the PFAS class are data poor and exhibit different properties, well-studied PFAS are persistent in the environment and have been detected in humans, wildlife and environmental media worldwide (Wang et al., 2017). Some PFAS biomagnify in food webs and have the potential to adversely affect both wildlife and human health. In humans, some well-studied PFAS, such as the perfluorocarboxylic and sulfonic acids, have been shown to be readily absorbed in the body and bind to proteins in the blood which serve as the primary transport mechanism (Kudo, 2015; Forsthuber et al., 2020).

Once distributed throughout the body, these substances accumulate in the blood and well-perfused tissues such as the liver and kidneys (Kudo, 2015). Some of these substances can cross the placental barrier, resulting in potential in utero exposure to the developing fetus (Mamsen et al., 2019; Wang et al., 2019; Li et al., 2020) and can also be transferred to infants and children via human milk (VanNoy et al., 2018). Available data show that certain PFAS are eliminated very slowly from the body, likely due to their strong protein binding affinity and internal reabsorption processes (Yang et al., 2010; EFSA, 2020). As such, some PFAS (for example, PFOA, PFNA, PFHxS and PFOS) can accumulate and persist in the body for years (ATSDR, 2021). Other shorter chain PFAS (such as PFBA and PFHxA) are eliminated more quickly with estimated half-lives ranging from several days to several weeks (Chang et al., 2008; Russell et al., 2015).

Toxicological (in vitro and in vivo) and epidemiological information is available for only a limited number of PFAS. The most comprehensively studied PFAS are PFOS and PFOA. Limited information exists for several other PFAS (for example ether PFAS and fluorotelomer-based substances), while no data are available on the vast majority of PFAS (Pelch et al., 2021). Based on the available information, it is evident that exposure to certain PFAS has the potential to affect multiple systems and organs (ATSDR, 2021). Further, many PFAS have been shown to affect the same organs and systems. The main targets affected in humans include the liver, immune system, endocrine system (thyroid), fertility, development and metabolism (cholesterol, body weight) (Sanexen, 2021). In addition, testicular and kidney cancers have been specifically linked to exposures to PFOA (IARC, 2017) and the California EPA has added PFOS to its list of chemicals known to cause cancer (OEHHA, 2021).

Many of the effects seen in humans are supported by experimental studies in animal models. New information on well-studied PFAS shows effects at lower levels than previous studies (for example, HFPO-DA and its ammonium salt [U.S. EPA, 2021a]) and key endpoints of concern that were not previously considered as critical effects (Sanexen, 2021). Currently, only a small number of PFAS are monitored in human biomonitoring surveys. These PFAS have been found in the blood (plasma or serum) of the general population in Canada and internationally.

People who live in Canada are exposed to multiple PFAS simultaneously as can be seen from biomonitoring data (Health Canada, 2021a). The hazards of exposure to PFAS mixtures are largely unknown, although antagonistic, synergistic and additive effects have all been observed in a limited number of in vitro and in vivo studies (Ojo et al., 2021). Studies also indicate that, in areas where drinking water is an important exposure source for PFAS, the treatment of drinking water to reduce PFAS levels can reduce serum PFAS levels and possibly adverse health outcomes (Herrick et al., 2017; Waterfield et al., 2020).