Photochemical Degradation of Chloro-biphenyls (PCBs)*

Polychlorinated biphenyls (PCBs) are stable towards oxidation, hydrolysis and other chemical reactions which conceivably occur in the environment. Although there is little direct evidence available, it is generally assumed that PCBs, particularly those with a high chlorine content, are also quite resistant to metabolic change. Over the past years photochemical degradation was shown to be a possible major route of environmental breakdown for a number of pesticides (1-4). Until relatively recently (5), however, simple chloroarornatic compounds have not received much attention. The limited interest of photochemists in compounds of this type can perhaps be explained by the commonly held view that there is generally little cleavage of the C-Cl bond in chloroaromatic compounds (6). We have previously shown (7) that 2,2',4,4', 6,6'-hexachlorobiphenyl, when irradiated at 3100 i in hexane, photolyzes rather readily to give products which are formed by loss of chlorine, rearrangement and condensation. We now wish to present a first report of our studies on the photochemical stability of a number of chlorobiphenyl isomers in hexane as well as on the breakdown of chlorobiphenyls under natural and simulated "natural conditions", with particular emphasis on polar products. Considerable experience in laboratory irradiations of pesticides has accumulated (1, 3, 8) and an elaborate "weathering chamber", which also allows controlled irradiation, has been described