Polychlorinated Biphenyl (PCB) is a chemical used widely in large electrical installations. But incidents in which the chemical has leaked, causing pollution, the death of wildlife and illness in humans has concerned environmentalists, safety experts and legislators. In Japan a leak of PCB into a rice-packing plant poisoned 15,000 people. In San Francisco a fire involving PCB led to an office block being abandoned for ten months. There have been other incidents in Belfast and Leeds. Sean Maffett investigates these concerns and asks what is being done to minimise risks to the environment. Producer LESLIE ROBINSON