The celebrated black-and-white orcas that draw an estimated 70,000 whale-watchers to these scenic waters each year are among the most contaminated marine mammals in the world, according to new research.

Blubber samples from 47 live orcas showed PCB concentrations up to 500 times greater than those found in human beings. "The levels are high enough to represent a tangible risk to these animals," said Peter S. Ross, a research scientist with the Institute of Ocean Sciences in Sidney, British Columbia, and lead author of the study, titled "High PCB Concentrations in Free-Ranging Pacific Killer Whales, Orcinus orca."

The orcas, long-held symbols of the unspoiled, wild beauty of the Northwest, are easily more contaminated than the struggling beluga whale populations of Canada's St. Lawrence River estuary, which drains the heavily industrialized Great Lakes, Ross said. Those endangered belugas have shown a high incidence of contaminant-linked diseases and tumors, as well as reproductive impairment.

Whether recent population declines in Northwest orcas are tied to the high toxicity has not been determined. But the study shows that newborn orcas are likely being blasted with toxins, through the placenta and through the high-fat milk of their nursing mothers. The mothers' own PCB levels decrease during reproductive years. "These calves are bathed in PCB-laden milk at a time when their organ systems are developing and they are at their most sensitive," said Ross.

PCBs--polychlorinated biphenyls--are thick, viscous chemical compounds used in electrical power equipment, electronics and the printing industry. Governments in the United States and Canada banned PCBs in the mid-1970s because of health hazards. They are still widely used in industrialized Third World countries.

Ross speculated that PCBs may be collecting in mid-ocean, from distant industrial sources in Asia. Migratory salmon eaten by resident orca families grow up in these deep ocean waters. Contaminated bottom fish and resident salmon stocks from urban areas may be another source of the toxins.

Long-lived animals high on the food chain accumulate the greatest concentrations of toxins from polluted prey. Killer whales, considered top predators of the ocean, can consume 100 to 300 pounds of food a day, and can live to be 40 to 90 years old.

The Institute of Ocean Sciences study, which will be published in the Marine Pollution Bulletin, is one of the most comprehensive toxicology studies to date on live cetacean populations. Contributors are from the federally funded institute, the University of British Columbia, the Vancouver Aquarium and the Pacific Biological Station in British Columbia.

Researchers used a small pneumatic dart to sample three communities of killer whales that swim inland and in coastal waters around Washington and southern British Columbia. These include the oceangoing transient whales that feed on seals, sea lions, porpoises and other marine mammals, and the southern and northern resident families that dine exclusively on fish, preferably salmon. The majority of resident samples were taken from northern pods because of high boat traffic in southern waters.

PCB levels in the fat of northern resident males averaged 46 parts per million. In the southern pods, which swim the more industrialized waters of southwestern British Columbia and northwestern Washington state, those levels were 146 parts per million. Most contaminated were the transients, with 251 parts per million. By comparison, humans in the United States average 1/2 to 7/10 parts per million.

Documented effects of PCB contamination in various marine mammal species include weakened immune systems, decreased reproduction, tumors and skin disorders. In laboratories, offspring of rats fed PCBs show loss of motor coordination and can't pick up certain low-frequency sounds. "Whales communicate with low-frequency sounds," said Theo Colborn, senior program scientist for the World Wildlife Fund. "You have to wonder what PCBs are doing to their ability to communicate."

Whale researchers say compromised immune systems could leave orcas vulnerable to fatal, rapidly spreading diseases. That could spell extinction in the small southern population, whose numbers have dropped about 15 percent, from 98 to 83, in four years. "With the population so small, they could be wiped out by a virus," said Rich Osborne, science curator at the Whale Museum on San Juan Island.

Osborne is drafting a petition to list killer whales under the Endangered Species Act in the United States. They were listed as a threatened species in Canada in April.

Osborne and others studying the carefully documented, individually identified orcas describe recent population declines as the longest and steadiest in decades. Female orcas are reportedly producing fewer calves, and many newborns and juveniles are not surviving.

"The population trend is downward, with deaths exceeding births in each of the most recent six years," said Ken Balcomb, director of the Center for Whale Research on San Juan Island. "If the lack of viable reproduction is due to PCBs, and something is not done to reduce the rate of their accumulation, then the future does not look favorable."

Promoted around the world as a scenic wonder of the west, orcas have a checkered history with humans in these waters. Less than a century ago, commercial fishermen regularly shot the "nuisance animals" that emptied their nets. During World War II, soldiers used the orcas for target practice, and even 40 years ago, Time magazine characterized killer whales as "savage sea cannibals."

Their numbers were seriously depleted in the 1960s and 1970s, when entrepreneurs captured scores of orcas to sell to marine parks, including calves and youngsters. All but one of the animals died in captivity. "A whole age class of animals was removed that today would be 20 to 30 years old, and could be reproducing," said Naomi Rose, marine mammal specialist for the Humane Society of the United States.

That generational gap could be another piece of the puzzle in population declines. Whale researchers also point to the dwindling supply of salmon and increased stress from boat traffic. Whale watchers crowd around the "Stars of the San Juans" like paparazzi in summer months, cameras clicking.

Few could guess that the black-and-white celebrities they see leaping and porpoising in their viewfinders may be swimming in a toxic soup. "This should be a wake-up call," said Osborne. "It may take orcas dying for people to finally get it."