Degradation of Polychlorinated Biphenyls by UV-Catalyzed Photolysis
Titel:
Degradation of Polychlorinated Biphenyls by UV-Catalyzed Photolysis
Auteur:
Wong, K. H. Wong, P. K.
Verschenen in:
Human and ecological risk assessment
Paginering:
Jaargang 12 (2006) nr. 2 pagina's 259-269
Jaar:
2006-04-01
Inhoud:
Photolysis of five polychlorinated biphenyl (PCB) congeners [2,4,4'-trichlorobiphenyl (PCB 28), 2,2',5,'5-tetrachlorobiphenyl (PCB 52), 2,2',4,5,5'-pentachlorobiphenyl (PCB 101), 2,2',4,4',5,'5-hexachlorobiphenyl (PCB 153) and 2,2',3,4,4',5,'5-heptachlorobiphenyl (PCB 180)] individually and in combination were carried out in the solvents methanol, ethanol, and 2-propanol. The disappearance of parent congener generally increased with UV intensity. The solvents had significant or limited effect on the removal of PCBs depending on the congener used. Because 2-propanol was highly toxic and methoxylated products were formed when methanol was used, ethanol was selected as the optimum solvent. The results of photolysis of the PCB mixture showed that PCB 52 was formed and accumulated after 4 h of photolysis. The addition of sodium hydroxide increased the rate of photolysis of the PCB mixture. One hundred percent removal can be obtained of the PCB in mixture in 90 min under optimized conditions. Gas chromatography-mass spectrometry was used to determine the intermediates of the photolysis of PCBs under optimized conditions. For the PCB congeners and mixture studied, the major photolytic intermediates were less chlorinated congeners, and biphenyl was the major product with minor amounts of hydroxylated PCBs, ethylated, dimethylated, and methylated biphenyls. Biphenyl could be further degraded by a prolonged photolysis. Toxicity of the PCB mixture during photolysis was monitored by the Microtox® test. It was found that the toxicity increased at the early stage of photolysis, and gradually decreased as the reaction proceeded. After 90 min, the EC50 of the reaction mixture was similar to that of the untreated sample.
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