Photolysis of polychlorinated biphenyls on octadecylsilylated silica particles

PCBs were decomposed in a quartz column packed with octadecylsilylated sili ca particles (ODS-silica) by external UV irradiation. The photolysis of PCB s having two to eight chlorines, including those which are the major consti tuents of Aroclors (PCB-180, PCB-153. PCB-118, and PCB-105) as well as copl anar PCBs, allowed the examination of the factors that affect the reactivit y acid product distribution. Steric congestion and molecular symmetry were found to be the major factors affecting the reactivity and the site of the reaction. Some general rules can explain the seemingly complicated decompos ition pathways of various congeners. The results indicate that the dechlori nation at the ortho-position which is predominant leads to products having not only higher toxic equivalency factors but also much longer life under p hotolysis conditions. Highly chlorinated PCBs showed tendency to lose chlor ines from meta- or para-positions. The reaction pathways were not much affe cted by the light source, a mercury lamp with or without a pyrex filter or sunlight, in spite of the reduction in decomposition rate with a weaker lig ht source. Continuous photolysis of highly chlorinated PCBs trapped on ODS- silica from aqueous solution was also possible. (C) 1999 Elsevier Science L td. All rights reserved.