By collecting data from around the world and loading them into population models, the researchers can see that 10 out of 19 populations of killer whales are affected by high levels of PCBs in their body. PCBs particularly affect the reproduction and immune system of the whales. The situation is worst in the oceans around Brazil and the UK where the model predicts that populations have been cut in half over the first decades since the use of PCBs became widespread. Here, the models predict a high risk that the species will disappear within a 30-40-year period. The line indicates median values, while the shaded field shows the variation.