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 potentially be detoxified by electron beam irradiation. In the present study, we discuss the possible mechanisms of radiolytic detoxification under various conditions, and we study 2,6-dichlorobiphenyl (DCB) as a model compound for PCBs. Electron beam and gamma-irradiation of DCB in aqueous methanol solutions lead to degradation of this compound and formation 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 kGy is required to achieve full dechlorination. This low yield is due to the concomitant formation of acid, which competes with DCB for the solvated electrons, the main reducing species in this system. The radiolytic yields are improved dramatically by the addition of carbonate; only 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.