The typical adult male in the US now averages 26 molecules of dioxin in the cells of his body. The 2.5 million carbon compounds are more than all other compounds combined. Compounds with carbon and hydrogen can also form rings. The most infamous carbon ring is benzene, which is a ring of six carbon atoms, each with a hydrogen atom on the outside. Benzene is so important to organic chemistry that it has its own symbol of a ring inside of a hexagon.
Chlorine can replace hydrogen on the outside of the ring.
These principles explain the formation of the very toxic families of PCBs, furans and dioxins. The result is poly-chlorinated biphenyls, knows as PCBs. Their production was banned in the 1970's. Since 2 oxygen atoms bind 2 benzene molecules, the chemical name is dibenzo dioxin. The abbreviation PCDD means polychlorinated dibenzo dioxin, which occurs when chlorine atoms replace hydrogen.