The Complexity of the Real World: a case study of PFAS in Norwegian Wildlife
In a thorough characterization of wildlife samples across Norway that included over 12 different species of terrestrial mammals (e.g. moose, wolf, fox), marine mammals (e.g. polar bears, mink, otter) and seas birds (e.g. eagles, gulls, eiders) researchers:
identified long chain PFAS in every sample, from polar bear to gulls.
measured short-chain, second generation PFAS compounds in many samples.
demonstrated that PFAS accumulation varied widely from specie to specie, reflecting the complexity of exposure and metabolic processing.
found a significant gap, in some cases as high as 92%, in their ability to identify specific PFAS compounds against measurements of the total organic fluorine burden with a wildlife sample.
In an effort to better understand PFAS exposure to the environment, researchers in Norway analyzed samples collected from mammals and birds. Samples were collected from polar bear, otter, moose, white tailed eagles, eiders and gulls, among others, throughout Norway from Oslo (subarctic) to Svalbard (arctic). Seventy-three named PFASs were quantitated in the samples; extractable organic fluorine (EOF) was also measured. The EOF measurement is designed to provide a total amount of organofluorine in a sample, of which the 73 named PFAS analytes are a subset. The inclusion of EOF data helps researchers understand how much of the PFAS burden critters in known and how much remains a mystery.
It’s useful to think about PFAS compounds in two groups: long chain (Generation 1) PFAS generally have at least 6 perfluorinated carbon atoms. PFOS and PFOA, the most infamous in the long-chain PFAS line up, have eight and seven peflourinated carbons, respectively. Long chain PFAS compounds were commercialized in the mid-1950s and were sold until 2002-2010. By 2008, in most countries, sale of long chain PFAS compounds ended as scientist raised the alarm that these highly persistent, bioaccumulative chemicals were present across human and animal populations globally. The half life of PFOS and PFOA in humans is estimated to be 3.5-5 years. By comparison, the half life of caffeine in humans is about 5 hours.
In response to regulations against long chain PFAS, by 2010, manufacturers had developed short chain PFAS alternatives. Short chain PFAS compounds are generally (but not always) comprised of fewer than 6 perflourinated carbon atoms; while they are less bioaccumulative than their long chain predecessors (PFBS, for example, has a half life of about 44 days versus 4.5 years), they are no less persistent. Now, like the compounds they were designed to replace, the short chain PFAS compounds are widely present in human blood and detectable globally in critters, in airborne dust particles and in rain drops. Although they dont build up in living systems to the same degree as long chain PFAS, short chain PFAS have an even greater degree of bioavailability, moving more easily through the environment.
In characterizing 73 individual PFAS compounds, the work conducted by the research team in Norway was thorough, covering most of the known long- and short-chain PFAS.
In the analysis of specific PFAS compounds, four long chain PFAS, including PFOS, were detected in all species sampled. The world’s largest manufacturer of PFOS stopped producing the compound in the early 2000s, yet PFOS was the dominant PFAS in most samples collected around 2018. Many of the samples collected from different seabirds (e.g. eagles, gulls, eiders) had similar distributions of long chain PFAS compounds, while samples collected from mammals (e.g. otter, mink, wolf, moose) shared a PFAS distribution similar to each other, but different from that characterized in the seabirds. These different profiles underscore the variability in how different PFAS interact with different species, influencing exposure, uptake, retention and, eventually, elimination.
Short chain PFAS were detected sporadically in samples collected from mammals, including polar bears and mink, with higher levels found in land-based critters living closer to industrialized cities.
The contribution of named PFAS to the EOF varied wildly between matrix, collection date and species. Across all samples, the named PFAS compounds accounted for approximately 2-94% of the EOF, indicating that, often, a significant fraction of PFAS present in arctic and subarctic wildlife remains uncharacterized.
Despite decades of research around PFAS compounds in the environment, this study illustrates the gaps that remain in our understanding of PFAS exposure, bioavailability and bioaccumulation and demonstrates the complexity of characterizing PFAS compounds in our global environment.
