When Lulu died tangled in fishing nets in Scotland last year, she was one of the last killer whales in the UK. She was also "one of the most contaminated animals on the planet," Dr. Andrew Brownlow tells the BBC. Brownlow says Lulu's body contained "shocking levels of PCBs." Researchers found 957 milligrams of PCBs per kilogram in the killer whale; it's believed the toxic chemical starts causing health problems for marine mammals at just 9 mg/kg, according to the Guardian. The average concentration of PCBs in killer whales in the northeast Atlantic is 150 mg/kg.
PCBs can hurt the immune system and hamper reproduction, and the latter effect has scientists worried for the future of killer whales in the UK. Despite being at least 20 years old, Lulu doesn't appear to have ever been "reproductively active." If the rest of Lulu's eight-whale pod has similar levels of PCB contamination, it's "increasingly likely" it will go extinct, Brownlow tells USA Today. Scientists haven't seen any killer whale calves born in the waters around the UK in the past 25 years. PCBs were outlawed in the 1970s but don't break down in nature and may still be leaking into the environment from waste storage sites. They work their way up through the food chain stored in the fat of animals; and killer whales are near the top of that chain. (Read more killer whale stories.)