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Cat thyroid disease linked to chemicals

EPA scientists zero in on flame retardants in some home products and pet
food. There is concern about humans.
By Marla Cone
August 16, 2007

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 Wednesday.

The often-lethal disease was rare in cats until the 1980s, when it began
appearing widely, particularly in California cats. That was at the same time
industry started using large volumes of brominated flame retardants in
consumer 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.

Cats that remain indoors and eat fish-flavored canned food were found to be
the most highly 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 human
beings are the only mammals with a high rate of hyperthyroidism.

So far, 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.

Brominated flame retardants are ubiquitous outdoors and inside homes. The
chemicals have been building up in people and wildlife over the last two
decades, particularly in the United States, where human concentrations have
doubled every few years.

People in the United States have the highest PBDE levels in humans
worldwide, but U.S. cats are even more exposed -- some with levels 100 times
greater, according to the study.

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.

"Our results demonstrated that cats are being consistently exposed to PBDEs,
an endocrine-disrupting environmental contaminant," the research team, led
by Janice Dye and Marta Venier of the EPA's National Health and
Environmental Effects Research Laboratory in North Carolina, wrote in their
study published in the journal Environmental Science & Technology. Because
of this exposure, "cats may be at increased risk for developing thyroid
hyperplastic changes."

Myrto Petreas, branch chief of environmental chemistry at the California
Department of Toxic Substances Control, said that 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 and during the lifetime of the products. We inhale or ingest dust,
mostly from hand-to-mouth transfer," said Petreas, who did not participate
in the study.

The risk to cats that eat dry food and live in homes with average
contamination is minimal, the study said, while "at the other extreme,
maximal PBDE exposure" occurs in cats that eat fish-flavored canned food and
live in houses with highly contaminated dust.

Cats that eat canned food containing whitefish, salmon and other seafood are
exposed to PBDE levels up to 12 times higher than cats that eat dry food,
and five times more than cats that eat poultry or beef canned foods, the
study said. The chemicals build up in oceans and other water bodies and
magnify in food chains.

However, 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.
In addition, they often sit on electronic equipment.

"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.

In people and cats with the highest levels, Petreas said, "it's explained
not by diet, but more contact with contaminated sofas, computers and other
consumer products."

Two pervasive PBDEs, used mostly in foam cushions, mattresses and carpet
padding, have been banned in the United States since 2004. The ban was
spurred by a California law.

However, other brominated flame retardants remain in widespread use.

In June, the California Assembly passed AB 706, written by Assemblyman Mark
Leno (D-San Francisco), which would prohibit brominated and chlorinated
flame retardants in furniture and bedding. The bill, which now goes to the
Senate Appropriations Committee, does not ban their use in electronics.

California has the nation's strictest fire-retardant standards for
furnishings, so PBDE exposure is generally higher than elsewhere. The cat
epidemic showed up first in California and the Great Lakes region -- the
areas with the highest environmental levels of the chemicals.