Through their milk, the mothers pass a lifetime dose of the compounds into their firstborn calves. Cetaceans are vulnerable to accumulating large quantities of these chemicals. The killer whales apparently are getting the chemicals from salmon and seals. Some of the PCBs clearly come from local waters, where industrial and port operations deposited the chemicals in the years before they were banned. But Asia also is probably contributing to the Pacific Northwest's problem.
Airborne contaminants blow from China to North America in about a week.
Salmon also probably pick PCBs up from Asia when they migrate into the North Pacific. Alaska's killer whales also are highly contaminated, even though there are no local dumps or sources, said Craig Matkin, a scientist with the North Gulf Oceanic Society. In the waters off Seattle and Victoria, killer whales aren't the only top-level feeders. Human beings are, too. People who regularly consume salmon or sole from Puget Sound face several health problems from the PCBs, including an elevated cancer risk.