Degradation pathways of PCB upon gamma irradiation

Abstract

In order to understand the modifications of the chromatographic profile of Aroclor 1260 upon gamma irradiation, a total of 14 pure polychlorinated biphenyl (PCB) congeners were separately irradiated in solution. Dechlorination was observed, and the generated products were investigated by gas chromatography and mass spectrometry. Degradation proceeds more rapidly in methanol/water mixture than in petroleum ether, but the relative amount of ortho-dechlorinated congeners formed upon irradiation was smaller in the former solvent. Ortho chlorines are preferentially lost in petroleum ether except when they are involved in a 2.5 (or 3.6) substitution pattern, in which case para dechlorination becomes predominant. The precursors of some toxicologically important congeners such as congeners 77, 118, 167, and 189 have been identified. These data are useful to rationalize the modifications of the chromatographic profile of PCB complex mixture upon gamma irradiation.

Degradation of Polychlorinated Biphenyls Induced by Ionizing Radiation in Aqueous Micellar Solutions

“…Cleavage of the aromatic rings, hydrogenation, and reactions with the surfactant are likely to have contributed to this behavior. Similar observations have been made by other researchers (18,42).…”

“…Previous work has noted rates of radiation-induced PCB dechlorination to increase in more polar solvents (12,17,18,24), as a result of higher yields and longer lifetimes of solvated electrons (18). However, significant deviations from this trend have been reported.…”

“…The radiation-induced decomposition of PCBs has been investigated in a variety of organic solvents (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27), including mineral oils (22)(23)(24)(25)27), and in a 2-propanol soil slurry (14). Detailed scavenger studies by Mincher et al (25) and Arbon et al (22) implicated the solvated electron as the major reactive species in the γ-radiation-induced destruction of PCBs in neutral solutions of both 2-propanol (25) and isooctane (22).…”

“…Detailed scavenger studies by Mincher et al (25) and Arbon et al (22) implicated the solvated electron as the major reactive species in the γ-radiation-induced destruction of PCBs in neutral solutions of both 2-propanol (25) and isooctane (22). The reaction efficiency has been observed to vary significantly in different solvents (12,13,17,18,24), and a chain dechlorination reaction has been reported to occur in alkaline solutions of 2-propanol (13). In addition, the yield for radiation-induced dechlorination of different PCB congeners has, in general, been demonstrated to increase with an increasing degree of chlorine substitution (12,21), consistent with the corresponding decrease in the energy level of the lowest unoccupied molecular orbital (21).…”

γ-Ray Destruction of PCBs in Isooctane and Transformer Oil

“…Webber (9) examined the radiolysis of air-equilibrated Aroclor 1260 in transformer oil and concluded that, even at an absorbed dose of 1540 kGy, there was no evidence of degradation having taken place. However, radiolytic degradation of PCBs has been observed to occur in cyclohexane and petroleum ether (10,11), but no effort was made to determine the reactive agent responsible for the degradation or the factors that influence individual PCB congener degradation susceptibility. Given the fundamental differences between polar and nonpolar solvents, the radiolytic chemistry of PCBs in these solvents may be quite different.…”