Degradation pathways of PCBs upon UV irradiation in hexane

The photodegradations of eight individual PCB congeners (5, 31, 52, 77, 87, 126, 138, 169 ) in hexane have been investigated employing a mercury lamp. All degradation reactions of the above mentioned PCS congeners are of the pseudo first order. The principal products of PCB decomposition are the les s chlorinated biphenyls, and no PCB-solvent adducts are found. Symmetrical and coplanar PCB congeners show lower photoreactivities. The reactivities o f the chlorine atoms at various positions of PCB rings are generally in the order: ortho > meta > para. Photodechlorinations occur mainly on the more substituted rings, when the numbers of chlorine atoms on the two phenyl rin gs are unequal, During photodegradation, some coplanar PCB congeners are fo rmed, which make the TEQ of solutions to decrease slowly or even to increas e. (C) 1999 Elsevier Science Ltd. All rights reserved.