Investigating the Link Between PBDE Exposure and Feline Hyperthyroidism

Photo Credit: SHINYA SASAKI/Aflo/Getty Images

Exposure to flame retardant additives could be a contributing factor to the occurrence of feline hyperthyroidism (FH) in Swedish cats, according to a new study published in the journal Environmental Science and Technology.¹ The authors also suggest that pet cats can be studied as markers of environmental contamination in the home.

FH affects up to 10% of older cats (over 10 years old) causing symptoms such as weight loss, hyperactivity, and vomiting. It is characterized by elevated levels of free circulating thyroid hormones (THs) in blood serum, caused by overactive thyroid glands, but the cause is still not known. Recent research has suggested that environmental factors could be responsible, specifically exposure to polybrominated diphenyl ethers (PBDEs) used in flame-retardants.

Cat grooming behaviours mean that pet cats, especially indoor cats, have a higher level of exposure to house dust (and the chemicals contained within it) than humans. PBDEs are added to commercial products (including plastics and furniture), and leach out into the environment where they can accumulate in housedust that will come into contact with the fur of cats. Researchers in the USA were first to publish a study proposing a link between an increase in the use of PBDEs since the 1970s and an increase in the occurrence of FH in cats.² Lead author of the new study, Jessica Norrgan, told The Column: “Prof. Nils‑Gunnar Lindkvist and Prof. Bernt Jones both veterinarians, were the initiator of this project. Working with cats, they had experienced this increase of FH also in Swedish pet cats and were interested in exploring it further as a collaboration with us at the environmental chemistry unit, ACES, Stockholm University.” She added: “This was something we wanted to build up on, and focus was to do it on individual basis and also look for phenolic compounds such as OH‑PBDEs that have shown even higher potency to disrupt thyroid hormone system than the parent PBDEs.”

Serum samples were taken from pet cats in Sweden - 37 diagnosed with a hyperthyroid and 23 with normal thyroid status. Individual samples were analyzed to detect decabromo-biphenyl (BB-209), PBDEs, hydroxylated PBDEs (OH-PBDEs), and 2,3,6-TBP to determine differences between the exposures of hyperthyroid vs. healthy cats. Gas chromatography coupled with mass spectrometry (GC–MS) was performed to detect brominated compounds, and gas chromatography coupled with an electron capture detector (GC–ECD) was used to detect chlorinated compounds.

The study found that hyperthyroid cats had higher serum concentrations of PBDEs (BDE-99, BDE-153, and BDE-83), and CB-153. Surprising to the authors was the detection of BB-209 in all cat serum samples - its production and application was discontinued in 2000 - but the contaminant was detected while performing pilot analyses of dry cat food samples.

Norrgan told The Column: “This study is now part of my thesis work that not only focuses on determining body burden of brominated chemicals in euthyroid and hyperthyroid cats, but also looks at the cat as a biomarker for exposure to brominated chemicals in the home environment.” - B.D.

References
1. Jessica Norrgran, Bernt Jones, Anders Bignert, Ioannis Athanassiadis, and Åke Bergman, Environ. Sci. Technol.49, 5197–5114 (2015).
2. J.A. Dye, M. Venier, L. Zhu, C.R. Ward, R.A. Hites, and L.S. Birnbaum, Environ. Sci. Technol. 41(18), 6350–6356 (2007).

This article was first published in LCGC's digital magazine, The Column. Click here to view that issue>>