Brominated-Flame Retardants (BFRs) in Cats — Possible Linkage to Feline Hyperthyroidism?

Dye J.A.

Conference Proceedings, (2007). American College of Veterinary Internal Medicine, Seattle:


Coincident with global introduction of BFRs into household consumer products nearly 30 years ago, hyperthyroidism in cats has increased considerably. The etiopathogenesis of feline hyperthyroidism remains unknown. We hypothesized that increasing exposure of pet cats to BFRs such as the polybrominated diphenyl ethers (PBDEs) has, in some manner, contributed to the abrupt increase in and now common occurrence of feline hyperthyroidism. To begin to address this possibility, we assessed whether PBDE levels were detectable in serum from young (n= 5), older non-hyperthyroid (non-HT; n= 7), or hyperthyroid (HT; n= 11) cats.

Serum was analyzed using gas chromatographic mass spectrometry. Data demonstrated that in all cats evaluated, a wide variety of congeners were readily detectable–the most prominent being the tetra- (BDE-47), penta- (BDE-99), nona- (BDE-207), and deca-brominated (BDE-209) congeners. Within each subgroup, however, certain “outlier” cats had cumulative (∑PBDE) serum values that were 4-7-fold higher than the other cats in their group. Hence, the mean ∑PBDE serum concentrations in young, non-HT, and HT cats were not significantly different. In like manner to these cats, in the U.S., certain human beings also exhibit PBDE levels that are >10 times higher than the median level in adults.

Lipid adjusted serum ∑PBDE levels (estimated from published serum lipid values in cats) ranged from a low of  0.5-1.0 ppm (or 500-1,000 ng PBDE/gm lipid) in most young cats and select non-HT and HT cats, to 7-10 ppm in several of the older (> 14 yr) HT as well as non-HT “outlier” cats. These levels are 10- to 400-fold higher than median lipid adjusted serum levels in U.S. men and women (Schecter 2005). Notably, congener profiles in our outlier cats most closely resembled that of the penta-BDE commercial mixture. Although recently banned, the penta-mixture was used extensively in carpet padding, furniture, and mattresses. Residential house dust samples have been shown to contain variable levels of PBDEs; the congener profiles of the most contaminated dusts also resemble that of the penta-mixture (Wilford 2004; Stapleton 2005).

Our finding that pet cats in the U.S. have high PBDE serum levels is in good accord with the most consistently identified risk factor for development of FH, namely indoor living. We further propose that house cats–because of their meticulous grooming behavior–not only come in direct contact with these consumer products, they readily ingest any volatilized PBDE-like material or PBDE-laden dust that deposits on their fur. Future studies are needed to elucidate if and how PBDE bioaccumulation of this magnitude in cats can disrupt maintenance of their thyroid-endocrine-axis. These findings may have public health ramifications. (This abstract does not reflect USEPA policy).