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Herring gull eggs collected from nests along the Great Lakes contain rising levels of a new contaminant that could be as dangerous as the PCBs banned in the 1970s.

The green-and-brown-flecked herring gull eggs contain growing concentrations of a new family of chemicals known as brominated diphenyl ethers, according to research by the Canadian Wildlife Service of Environment Canada.

Concentrations of the chemical have been in a steep ascent, doubling approximately every three years since the early 1980s.

The chemicals are used mainly as flame retardants in the polyurethane foam in upholstered furniture. Their use is largely unregulated in North America.

Environment Canada has found higher levels of the chemicals in eggs collected from areas influenced by pollutants from cities, such as Toronto and Chicago, than in more rural areas of the Great Lakes.

The structure of brominated compounds closely resembles that of PCBs, prompting scientists to suspect that the two have similar biological effects. "There is no reason to believe that these things will be any different than the PCBs," said Ross Norstrom, an adjunct chemistry professor at Carleton University in Ottawa who has worked on the research project. "They look the same. They've got the same kinds of chemicals in them, and so far most of the research seems to be saying they behave the same."

Birds contaminated with high levels of compounds such as PCBs produce offspring with severe birth defects, including extra limbs, malformed eyes and deformed beaks. Research on children suggests PCBs diminish intelligence.

Brominated chemicals, known by the scientific shorthand of BDE, were discovered in samples from Environment Canada's annual collection of herring gull eggs from nests along the Great Lakes, the world's longest-running research project to track contaminants in wildlife annually.

Scientists don't know how the compounds are getting into the environment and into the eggs of fish-eating birds at the top of the food chain. Speculation ranges from the off-gassing of BDE from furniture to the effluent from manufacturing companies using the chemicals.

Collection of herring gull eggs began in 1974 and since then has been done each spring at 15 sites along the Canadian and U.S. parts of the lakes.

Environment Canada scientists are in the midst of collecting this year's eggs for the project.

The eggs are being gathered at nests, including some in Toronto, where wildlife biologist Chip Weseloh, head of the project, recently collected another 13 samples at the huge bird colony on the Leslie Street Spit.

Levels of the brominated compounds found to date are not considered high enough to harm wildlife. But if current trends continue, the pollutant would become the main contaminant in gull eggs in 10 to 15 years.

Other than BDE, concentrations of pollutants in eggs have generally been falling, a sign that the health of the Great Lakes is improving, Mr. Weseloh said. He sees far fewer birds with gross deformities than when he began working on the project in 1978.

Environment Canada checks the eggs for 70 chemical compounds at a cost up to $1,000 an egg to find out what is in them that shouldn't be.

Areas of Lake Michigan affected by Chicago and Milwaukeein the United States had gull eggs with the highest BDE readings on the Great Lakes, followed by Toronto Harbour. The cleanest eggs were at Port Colbourne, Ont.