These may make you forget PCBs

Within the past two-and-a-half years, a new family of pollutants has been identified that some scientists are warning could be as bad as PCBs (polychlorinated biphenyls), one of the worst pollutants on earth.

The new pollutants are used as flame retardants, and are found in the plastic of television sets, electrical appliances, and computer terminals and circuit boards, in synthetic rugs, draperies, and fabrics, in the interiors of vehicles, in building materials, and in foams and upholsteries for furniture. « They’re everywhere,’’ says John Jake Ryan, senior research scientist on persistent organic pollutants (POPs) at Health Canada.


They are called polybrominated diphenyl ethers (PBDEs), and they account for 5 per cent to 30 per cent by weight of these products.


Unlike some pollutants, they’re not very soluble in water, but like PCBs, they accumulate in fatty tissues — so the higher you go up in the food chain, the greater the accumulation of PBDEs.


What sparked worldwide interest in them was a Swedish study which found that, in the 25 years between 1972 and 1997, the amount of PBDEs in the breast milk of Swedish women had risen exponentially, doubling every five years.


Since then scientists have discovered that some PBDEs act like PCBs: in mice and rats, they interfere with the thyroid hormone, impairing the ability to learn and memorize, inducing hyperactivity, and compromising motor reflexes.


However, as yet there is no proof that PBDEs harm humans. One of the leading Swedish researchers, Per Ola Darnerud, points out that the concentration of PBDEs causing problems in mice and rats is one million times greater than what is found in humans.


Nevertheless, scientists, such as Kim Hooper and Thomas McDonald of California’s Environmental Protection Agency, warn that, « If the trends…continue, PBDEs will replace PCBs and DDT as the major environmental POP over the next 15 to 30 years.’’


So far, no one has pinpointed how PBDEs get into the food chain. It’s believed they are released into the air by incineration, and by products degrading as they age, especially electrical appliances that warm surrounding plastics when they are turned on.


They’re also found in sewage sludge that’s spread on farmers’ fields as fertilizer, so it’s assumed that people excrete some of the quantities that reach their bodies.


PBDEs have turned up in dairy products, and in fish, dolphins, whales, seals, reindeer, and moose. Levels in humans have registered lower (except for reindeer and moose), but they more than doubled for people with non-Hodgkin lymphoma. In some predator species such as pike, eels, ospreys, and cormorants, the readings are fantastically high.


The level of PBDEs in Great Lakes fish makes the lakes among the most contaminated in the world. Lake Michigan is, by far, the worst.


Further information about PBDEs can be found in three issues of Environmental Health Perspectives (Vol. 108, No. 5, May 2000, pages 387-392; Vol. 109, Supplement 1, March 2001, pages 49-68; and Vol. 109, No. 9, Sept. 2001, pages 903-908), and in Science News, Vol. 160, Oct. 13, 2001, pages 238-239.


What struck me most in reading the studies was the lack of any documented proof that PBDEs are a danger to humans, even though there’s plenty of evidence to suggest they may prove to be as injurious as PCBs. All this underlines the inadequacy of risk assessment, now enshrined by the World Trade Organization (WTO) as the test for allowing nations to ban chemicals.


Risk assessment is beloved by corporations, because it requires the public to establish that a chemical is harmful before it can be regulated.


A far better test is contained in the precautionary principle, adopted at the Earth Summit in Rio de Janeiro in 1992. It says that when there is a threat of serious or irreversible damage, nations should be able able to impose restrictions even though scientific proof of harm is lacking.

That’s a far better approach — especially in a case such as this, where PBDEs have a long lifespan, and can take 60 years or more to degrade to negligible levels.

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