Frequent Fliers and Flame Retardants A study in Sweden reveals that flame retardants designed to protect people show up in high levels inside airplane cabins, and in humans-including our columnist.

A recent study released in Sweden about flame retardants showing up in the cabin air inside commercial airliners-and inside passengers, at high levels-may shed light on a mystery that I discovered in 2006.

That year, I happened to be in an airport waiting for a long flight when I got the news that swirling inside my body were levels of flame retardants 12 times higher than average in the U.S., and 100 times higher than levels found in Europeans.

The results were delivered by phone from a specialist on polybrominated diphenyl ethers-P.D.B.E.'s-a type of flame retardant that until recently was added for safety to products ranging from mattresses and clothing to plastics and electronics found in televisions, computers, and on airplanes.

P.D.B.E.'s are mixed into products such as airline tray tables, seats, carpet, and wiring to raise the temperature at which they would otherwise ignite, making them harder to burn. These chemicals save hundreds of lives a year from death by fire, but they also can break loose as gas and particles released into the air, where they attach to dust that people can breath in.

In mice and rats, high doses of P.D.B.E.'s interfere with thyroid and liver function, and cause neurological problems that include impairment of learning and memory. They also have caused problems with neurological development in fetuses and newborns.

P.D.B.E.'s are suspected carcinogens-which has led the European Union to ban them. In the U.S., California has banned some versions of these chemicals, and Washington State has banned them all.

Scientists have found P.D.B.E.'s all over the Earth, in polar bears in the Arctic, cormorants in England, and killer whales in the Pacific.

When I was tested for my levels of this chemical and hundreds of others for an article in National Geographic, I expected to have normal levels of P.D.B.E.'s-until Ike Bergman of Lund University in Sweden phoned from Stockholm. He asked me if I was sitting down and then paused for what seemed like a very long time.

"I hope you are not nervous, but your concentration is very high," Bergman said in a light Swedish accent. My blood level of one particularly toxic P.D.B.E., found primarily in U.S.-made products, is 249 parts per billion-that's 12 times the mean found in a recent Centers for Disease Control study that tested thousands of Americans.

My levels would be high even if I were a worker in a factory making the stuff, Bergman said.

Yikes, I thought, glad that I was sitting down, though Bergman hastily assured me that even my levels were a long way off from being dangerous-as far as anyone knows.

Trying to get to the bottom of why my levels might be so high, Bergman quizzed me: Had I recently bought a mattress or sheets, or a new car? Did I work for many hours near a new computer?

I kept answering no until I got an idea: Could my onboard stash of flame retardants come from airplanes?

"Yah," said Bergman, "do you fly a lot?"

Yes, I said, I log about 200,000 miles a year.

"Interesting," Bergman says, telling me that he has long been curious about P.D.B.E. exposure inside airplanes, whose plastic and fabric interiors are drenched in flame retardants to meet safety standards set by the Federal Aviation Administration and its counterparts overseas.

Since 2004, Boeing and other plane manufacturers say they have been phasing out the worst forms of P.D.B.E.'s, but these chemicals remain on older planes. At the time of the call, Bergman was hoping to run tests of P.D.B.E. concentrations in airplane air, and inside frequent fliers.

Now he and his team at Lund have done just that-although he cautions this is just a preliminary study with a few test subjects.

The study followed nine passengers who traveled on long flights of nine to eleven hours. They took air samples on their flights, and had their levels of P.D.B.E.'s tested in their blood before and after boarding.

The scientists found that the air onboard was thick with P.D.B.E.'s at high levels. The "after" levels in their blood also showed significant increases-though they were still far less than mine. "The findings from this pilot study call for investigations of occupational exposures to P.D.B.E.'s in cabin and cockpit crews," concludes Bergman and his team.

The data I had sent to Bergman comes from the relatively new science of "biomonitoring," which uses new technologies to detect and measure for the first time even tiny levels of chemicals in people and animals. Reports from the Centers for Disease Control have found detectable levels of chemicals ranging from pesticides and dioxins to plastic additives such as Bisphenyl-A inside people.

The dangers of such miniscule levels to people is unknown, though biomonitoring technologies are a crucial first step to finding out if these chemicals that protect us from fire and give us products that are basic to our civilization are causing harm or not.

In most cases, people aren't dropping dead. Even my 249 parts per billion is still far below a threshold that would cause alarm. (One part per billion is like adding a drop or two of red die into an Olympic-size swimming pool). But it's hard to know whether there is subtle, long-term damage such as cancer and neurological deficits.

Last year, the European Parliament passed a new law-called R.E.A.C.H., for Registration, Evaluation, Authorization, and Restriction of Chemicals-that requires new chemicals to be tested for toxicity and proved safe. This standard had not existed before in Europe, and still does not exist in the U.S., where regulators in most cases require testing only if a chemical is suspected to be toxic.

Fortunately, safer flame-retardant materials exist, and are beginning to be used, although products with P.D.B.E.'s will be with us for a very long time-at home and in the air.

This is not something to panic about, nor should it stop you from climbing onboard an airplane, although it should make us all want to find out more. You can also keep the dust down in your house and office, and buy goods from companies that claim to no longer use P.D.B.E.'s. These include Dell, Canon, Hewlett-Packard, Ericsson, Mitsubishi, and Sony.

Personally, I still fly, though occasionally I glance at someone's dusty sneakers as they board and wonder if some of that will end up in my lung, with a bit of P.D.B.E. attached-and what this means.