PCBs were used widely in building materials for decades until a global ban was introduced in 2004. Unfortunately, in spite of the ban PCBs still leak into the environment through careless disposal of products containing PCBs and governmental failure to tackle the 14 million tonnes of contaminated material around the world. PCBs build up through the food chain, with highest amounts and the worst effects seen in top predators such as whales and dolphins. PCBs are toxic, they cause sterility and are decimating marine mammal populations. Some affected whale populations are set to die out within a generation.

The PCBs that whales, dolphins and porpoises absorb from their food end up being stored mainly in their fatty tissue (blubber). The levels of PCBs in an animal’s blubber will build up over time as it consumes more and more contaminated fish. In times of stress, when for example food is scarce, whales, dolphins and porpoises tend to break down their stores of blubber to provide them with an energy supply. Breaking down blubber in this way releases a flood of toxic PCBs into their body.

Scientific studies suggest that the metabolism of whales, dolphins and porpoises are particularly ill equipped to deal with large amounts of PCBs. Scientists have found compelling evidence that whales, dolphins and porpoises make few of the enzymes that many other species of animals use to break down dangerous chemicals such as PCBs. (Enzymes are molecules that animals’ bodies use to bring about the chemical reactions they need to stay live).

The PCB burden carried by male and female whales, dolphins and porpoises tends to increase until they reach sexual maturity. After that point, males continue to absorb PCBs from their food. However, the PCB burden carried by female whales, dolphins and porpoises drops off after they have their first calf, because the females pass on most of their PCB burden to their first-born calves. It seems likely that the large amount of PCBs transferred to calves in these ways can sometimes prove fatal. For example, Lulu, an orca who stranded on the Isle of Tiree in Scotland became infamous because her PCB levels were 20 times the safe limit.