 Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a host of problems were identified.With the discovery of PCBs' environmental toxicity, and classification as persistent organic pollutants, their production was banned by United States federal law in 1978, and by the Stockholm Convention on Persistent Organic Pollutants in 2001.The International Agency for Research on Cancer (IARC), rendered PCBs as definite carcinogens in humans.