Polychlorinated biphenyls (PCBs) are semivolatile organic compounds used predominantly as dielectric fluids in capacitors and transformers. Most applications used oily or waxy mixtures of different PCBs that differ from each other in the number and location of chlorine atoms around the aromatic carbon rings. More than 1.5 billion pounds of PCBs were manufactured in the United States (mostly by Monsanto) before their production was cancelled in 1977. Studies suggest that some PCBs interfere with mammal and bird reproduction, and may disturb development or cause cancer in humans. Despite efforts to ban the use and reduce the emissions of PCBs, their disappearance from the environment is either slow or nonexistent. PCBs bioaccumulate and have a tendency to travel to distant places through the air as vapors or on dust particles. In fact, surprisingly large concentrations of PCBs are found in places where they were never used. For example, the animals and people living in the Arctic have high body burdens of PCBs due to the process of global distillation that has brought PCBs from the lower latitudes of North America, Europe, and Asia.
2,2'-dichlorobiphenyl contains a chlorine atom in the ortho-position of each aromatic ring. It is one of the smaller PCBs, meaning that it is more volatile and prone to atmospheric transport. However, having only two chlorines, it is also more reactive.
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