Are Household Contaminants Affecting Our Pets?

Flame retardants such as polybrominated diphenyl ethers (PBDEs) are used in construction materials, furniture, textiles, and electrical appliances. These chemicals migrate and stick to household dust, which may be inhaled or consumed in hand-to-mouth activities, accounting for a large percentage of the total body exposure in American adults.^1,2

PBDEs have become ubiquitous environmental contaminants, with troubling environmental persistence and bioaccumulation. Studies have linked PBDEs to lower birth weight, behavioral problems in youths, and reproductive issues. Due to these health concerns, several PBDE mixtures were either banned or voluntarily phased out in the U.S. and E.U. over the past two decades.^1,2

However, PBDEs are not the only culprit; other organohalogens and their hydroxylated metabolites are implicated, including polychlorinated biphenyls (PCB), residues of which are found in commercially available pet foods.³

Replacement non-PBDE flame retardants such as decabromodiphenylethane have also been detected in the home environment⁴ and found to be persistent and bioaccumulative. The extent of their toxicological effects is still yet to be fully understood. The widespread presence of flame retardants, as well as the release of new compounds, requires constant monitoring.

Despite bans and replacement compounds, certain PBDEs and alternatives are still present in numerous household products, and many of us are not the only inhabitants at risk of exposure—our pets must also be considered. So how might these persistent dust contaminants affect them? And what lessons can be taken to better protect both ourselves and our furry friends?

A Link to Feline Hyperthyroidism

In humans, phase I and II enzymes metabolize PBDEs to form hydroxylated compounds. But cats have reduced phase I activity, facilitating higher accumulation of these compounds compared to humans and potentially impacting their endocrine system—in particular, the thyroid.² This may resonate with owners, since cats—especially those who live indoors—are prone to feline hyperthyroidism.⁵

Research published in Environmental Science & Technology in 2017 statistically confirmed the link between house dust and these brominated contaminants in cat blood serum for the first time.¹

Expanding upon studies conducted in other countries and their own previous work,⁶ researchers in Sweden analyzed samples of house dust, cat serum, and cat food from 17 different households. Their findings revealed a strong correlation between the levels of various PBDEs present in house dust—particularly from the living rooms sampled—and the levels present in the cat serum.

The authors report that while their sample size was small and further investigation is necessary, their results support previous hypotheses that cats are routinely exposed to PBDEs via dust—which may be vital in helping to better understand and mitigate exposure pathways for humans, particularly children in early stages of development.

Dogs—Indicators for Human Exposure?

Human exposure is of particular concern, but biomonitoring studies in people have proven difficult. However—and perhaps selfishly—we can use information about our pets’ health to inform our own.

Since dogs are hypothesized to be more similar to us in their response to these environmental contaminants, they may serve as better indicators of human exposures in shared environments compared to cats.⁴ Concentrations of PBDEs in dogs are significantly less than those measured in cats, suggesting that differences of size, dietary exposure, and metabolism exist between the species – and grooming behaviors may also be a differentiating factor.^5,6

There is evidence that dogs can develop chronic diseases that often reflect both histological and clinical aspects of the corresponding human diseases.⁷ One recent study looks at how pet dogs can be used as sentinels for human environmental health studies. The team conducted a comparative pesticide exposure assessment in 30 people and their pet dogs to determine how well silicone wristbands and dog tags predicted urinary pesticide biomarkers of exposure.⁸

The analysis revealed significant and positive correlations between sampler levels of permethrin and N,N-diethyl-meta-toluamide (DEET) with their corresponding urinary metabolites in both species.8 Significantly higher levels of fipronil were also observed in samplers from participants who reported using flea and tick products on their dog. These results suggest that people and their dogs have similar pesticide exposures in a home environment.⁸

For many of us, our pets are our dearest companions. Whether you’re a cat person or a dog person (or both!), it is important to remember that our home environment affects more than just the humans within, and these findings support the need for taking our pets into consideration as well in the ongoing study of environmental exposures and disease.

References

1. Engdahl, J. Norrgran et al. Cats’ Internal Exposure to Selected Brominated Flame Retardants and Organochlorines Correlated to House Dust and Cat Food. Environ. Sci. Technol.2017, 51, 5, 3012–3020
2. Guo, W. et al. Temporal Changes of PBDE Levels in California House Cats and a Link to Cat Hyperthyroidism. Environ. Sci. Technol. 2016, 50, 3, 1510–1518
3. Mizukawa, H. et al. Organohalogen Compounds in Pet Dog and Cat: Do Pets Biotransform Natural Brominated Products in Food to Harmful Hydroxlated Substances? Environ. Sci. Technol. 2016, 50, 1, 444–452
4. Vernier, M. and Hites, R. A. Flame Retardants in the Serum of Pet Dogs and in Their Food. Environ. Sci. Technol. 2011, 45, 10, 4602–4608
5. Dye, J. A,. et al. Elevated PBDE Levels in Pet Cats: Sentinels for Humans? Environ. Sci. Technol. 2007, 41, 18, 6350–6356
6. Norrgran, J. et al. Higher PBDE Serum Concentrations May Be Associated with Feline Hyperthyroidism in Swedish Cats. Environ. Sci. Technol. 2015, 49, 8, 5107–5114
7. Shearin, A.L, and Ostrander, E. A. Leading the way: canine models of genomics and disease. Models Mech. 2010, 3, 27–34
8. Wise, C. F. et al. Comparative Assessment of Pesticide Exposures in Domestic Dogs and Their Owners Using Silicone Passive Samplers and Biomonitoring. Environ. Sci. Technol. 2022, 56, 2, 1149–1161