Orca whales in the waters around Washington state and British Columbia are severely contaminated with PCBs, which can weaken the animals’ immune systems and hamper reproduction, according to a comprehensive, new study by Canadian and American scientists. Researchers took samples from 47 killer whales and found that they are 400 to 500 times more contaminated than humans. “These killer whales can now be considered among the most contaminated marine mammals in the world,” said Peter Ross of the Institute of Ocean Sciences. PCBs, a long-lasting industrial compound, were banned in Canada and the U.S. in the mid-1970s, but are still widely used in developing nations. One of the study authors is drafting a petition to have the orcas listed as threatened or endangered in the U.S.