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Great Tit and Eurasian Blue Tit Eggs Contained Different Mixes of PFOS Isomers

Great tit eggs in a moss-lined nest inside a wooden nest box
Research · Other research

Eggs from great tits (Parus major) and Eurasian blue tits (Cyanistes caeruleus) contained different mixtures of PFOS isomers near a contaminated industrial site in Belgium. Researchers analysed 41 eggs, and the analysis supported a clear difference in the PFOS isomer profiles of the two species. This concerns the mixture of PFOS forms, not evidence by itself that one species had a higher total PFOS concentration.

PFAS are a large group of highly persistent fluorinated chemicals, and PFOS is one specific PFAS compound. PFAS compounds can occur as structural isomers: molecules with the same chemical formula but different arrangements of their atoms. Some have a straight carbon chain, while others are branched. These forms can have different physicochemical properties, which can affect how they move through the environment, accumulate in organisms and contribute to toxicity.

To distinguish these closely related forms, the researchers combined liquid chromatography, ion mobility and high-resolution mass spectrometry. The method resolved 41 linear and 39 branched PFAS congeners in reference material. When it was applied to the bird eggs, the team detected 20 linear and 34 branched PFAS isomer features.

The species differed in PFOS profile, not necessarily total PFOS

The clearest biological difference concerned PFOS. Great tit and Eurasian blue tit eggs had clearly different PFOS isomer mixtures. The study did not establish why. The authors suggest that differences in foraging behaviour and species-specific accumulation may contribute to the pattern.

Isomer-level analysis reveals differences hidden by a total concentration

The result shows why total concentrations of a named PFAS compound do not always describe the full exposure pattern. Isomer-resolved analysis can reveal structural forms that would otherwise be grouped together. The authors argue that this gives environmental biomonitoring and exposure assessment a more detailed chemical picture, especially when pure standards for individual branched isomers are unavailable.

Sources and image credit

  1. Zhao, L., Cappelli, F., Belova, L., Buytaert, J., Groffen, T., Yin, S., Liu, W., Bervoets, L., & Covaci, A. (2026). Identification and Characterization of Per- and Polyfluoroalkyl Substances Isomers in Bird Eggs by Liquid Chromatography-Ion Mobility-High-Resolution Mass Spectrometry.Primary peer-reviewed article published online 25 July 2026. Analysed 41 great tit and Eurasian blue tit egg samples from a contaminated industrial site in Belgium and found a significant species difference in PFOS isomer profiles.
  2. PubMed record: PMID 42503770.Bibliographic record and abstract confirming the study design, 20 linear and 34 branched PFAS isomer features in the egg samples, and the species difference in PFOS isomer profiles.

Image: Great tit (Parus major) eggs in a nest box, photographed 5 November 2011. Photo: Neozoon / Wikimedia Commons. Representative image for this story; not presented as eggs from the reported study. · CC BY-SA 3.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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SPECIES IN THIS STORY

Species in this story

Great Tit Parus major Explore species Eurasian Blue Tit Cyanistes caeruleus Explore species

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