MECHANISMS OF IONIZING RADIATION-INDUCED DESTRUCTION OF 2,6-DICHLOROBIPHENYL IN AQUEOUS-SOLUTIONS

Polychlorinated biphenyls (PCBs) appear as environmental pollutants in Various phases. Aqueous media polluted with such compounds may potent ially be detoxified by electron beam irradiation. In the present study , we discuss the possible mechanisms of radiolytic detoxification unde r various conditions, and we study 2,6-dichlorobiphenyl (DCB) as a mod el compound for PCBs. Electron beam and gamma-irradiation of DCB in aq ueous methanol solutions lead to degradation of this compound and form ation of Cl- ions, but high doses are required. Solutions of 1 mmol L- 1 DCB require a dose of 30 kGy to produce 1 equiv of Cl- (G = 0.03 mu mol J(-1)) to form the less toxic monachlorobiphenyl (MCB), but 600 kG y is required to achieve full dechlorination. This low yield is due to the concomitant formation of acid, which competes with DCB for the so lvated electrons, the main reducing species in this system. The radiol ytic yields are improved dramatically by the addition of carbonate; on ly 20 kGy are required far practically quantitative dechlorination of DCB. For the oxidation process, the dechlorination of DCB by (OH)-O-. radicals was measured in N2O-saturated solutions and found to be much less effective than the reduction process.