Analyzing Euthyroid & Hyperthyroid Indoor Cat Exposure to Flame Retardants

Hyperthyroidism in cats has increased since its original description in the 1970s. Environmental exposures are suggested as a potential contributing factor. This research investigated pet cats’ exposure to flame retardant chemicals in the home environment and associations with hyperthyroidism. Silicone collar tags were used as indicators of exposure to two classes of flame retardants: polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs). Though previous studies have documented PBDE exposure among house cats, less is known about exposure to OPEs. Thus, we first evaluated silicone tags as measures of internal exposure to OPEs. Cats wore silicone collar tags for 7 days in their home environment, after which tags were analyzed for flame retardants. Urine samples were collected from 9 cats and analyzed for OPE metabolites. Tris(2-chloroisopropyl) phosphate (TCIPP), was significantly and positively correlated with its urinary metabolites (r≥0.73; p<0.05), and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly and positively correlated with its urinary metabolite (r=0.77; p<0.05). Several other OPEs from tags were correlated with their metabolites in urine, suggesting that tags capture information about cats’ internal exposure; however, correlations were not statistically significant. To evaluate exposure differences by thyroid status, 12 hyperthyroid and 12 euthyroid cats (matched by age and sex) wore tags for 7 days. Tags were analyzed for PBDEs and OPEs. Two PBDEs, BDE-47 and BDE-99, were higher on tags worn by hyperthyroid compared to euthyroid cats (p<0.05). Associations with thyroid status were not significant for OPEs; however, we caution against over-interpretation of these results given our limited sample size. Potential confounders, including diet and activity level, were evaluated; however, no significant differences were found between hyperthyroid and euthyroid cats (p>0.20), suggesting these factors are not likely to confound associations with flame retardant exposures. Cumulatively, results suggest that exposure to PBDE flame retardants is higher among hyperthyroid cats, which is in agreement with previous studies that have reported differences in serum PBDE levels of hyperthyroid and euthyroid cats.