An epidemic of thyroid disease among pet cats could be caused by toxic flame retardants that are widely found in household dust and some pet food, government scientists reported last week.
The often-lethal disease was rare in cats until the 1980s, when it began appearing widely. A the time, industry started using large volumes of brominated flame retardants in products, including furniture cushions, electronics, mattresses and carpet padding.
Scientists from the Environmental Protection Agency noted a possible connection between hyperthyroidism and flame retardants. The chemicals - known as polybrominated diphenyl ethers, or PBDEs - mimic thyroid hormones, so experts have theorized that high exposure in cats could cause overactive thyroids.
Indoors cats that eat fish-flavored canned food were found to be the most contaminated.
"We know there is an association between indoor living for cats and hyperthyroidism," said Linda Birnbaum, a senior author of the study and the EPA's director of experimental toxicology. "Our paper does show cats are highly exposed and hyperthyroidism may be due to the high PBDEs. More studies are needed to fully determine this."
A major unanswered question is whether cats are the proverbial canaries in the coal mine, signaling health dangers for their owners. Cats and humans are the only mammals with a high rate of hyperthyroidism.
No link has been established between human endocrine disorders and exposure to flame retardants. However, "there is growing concern," the scientists wrote.
"It is clear that house cats may be able to serve as sentinels for indoor exposure to PBDEs for humans who share their houses," said Birnbaum, one of the world's leading experts on hormone-altering chemicals.
Twenty-three cats were tested in the EPA's study, including 11 with hyperthyroidism. The researchers found that the cats with hyperthyroidism had substantially higher levels of a PBDE compound. Symptoms of the disease, which is a leading cause of cat death, include weight loss, rapid heartbeat and irritability.
Myrto Petreas of the California Department of Toxic Substances Control said the cat study was small but that it reaffirmed health concerns not only for cats but humans, too, "especially children, anyone exposed to high levels."
"PBDEs are in consumer products, so we get exposed while we use the products in homes ... . We inhale or ingest dust, mostly from hand-to-mouth transfer," said Petreas, who did not participate in the study.
Much of the exposure - for cats as well as people - comes from dust, not food.
Cats, while sleeping, often come in direct and prolonged contact with upholstery, carpeting and mattress materials that contain flame retardants. "Because of their meticulous grooming behavior, cats would effectively ingest any volatilized PBDEs or PBDE-laden dust that deposited on their fur during such activities," the scientists wrote.
Scientists say toddlers who crawl on floors and put objects in their mouths also can be highly exposed to the chemical-tainted dust, which has been found in most U.S. homes.
Marla Cone writes for the Los Angeles Times.