The article discusses the emergence of polychlorinated biphenyls (PCB). Manufactured from the waste products of the crude oil refining process and a range of chlorinated chemicals, these oily, syrupy liquids had a multitude of uses and have been described as being as near perfect as any industrial chemical can be. PCBs conduct heat but not electricity and they are not water soluble. Although production is now banned under the Stockholm Convention, PCBs continue to pose a risk to human health and the environment because of the wide array of PCB-containing electrical equipment still in use. It is estimated that 66 per cent of all PCBs ever manufactured are still in service somewhere in the world.