PCBs의 광화학적 연구: NaOH 및 휴믹산 (humic acid, HA)에 의한 분해특성
Effects of NaOH and Humic Acid on the UV Photolysis of PCBs
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Objectives: This study was carried out to examine whether the apparent photolysis with or without sensitizers[NaOH and humic acid (HA)] was prompted photodegradation of polychlorinated biphenyl (PCB) in aqueoussolution. Methods: PCBs photodegradation occurred using fluorescence black lamps at λmax = 300 nm. PCB congenerswere exposed in 10 ppm HA or 0.05N NaOH solutions, to investigate the decreasing profile of PCBconcentration with time. The PCBs were then analyzed by gas chromatography/mass spectrometry (GC-MS). Reductive degradation profile of PCB congeners in the presence of both sensitizers under oxygen-saturatedprotic conditions was described using the wind-rose diagrams. Results: Use of HA or NaOH decreased PCB concentration with time in the dark and on irradiation, indicating thatphotolysis underwent through reductive dechlorination through energy transfer and possibly with reactive oxygens. The dechlorination was marked by a chromatographic shift, observed in the GC-MS plots. Therefore it is logicalto assume that increasing the dose of sensitizers would increase the photodegradation rates of PCBs. The half-livesof pentachloro-PCB (penta-3) in 0.05N NaOH and 10 ppm HA were estimated at about 47 hours and 39 hours,respectively, under the same experimental conditions of photolysis. It was found that the rate of photolysis ofpentachloro-PCB in aqueous solution followed apparent first-order kinetics compared to other congeners. Conclusion: Photochemical degradation (using 328 nm UV light) of penta- and hexa-PCBs in HA or alkalinesolution is a viable method for pretreatment method. The results are helpful for the further comprehension of thereaction mechanism for photolytic dechlorination of PCBs in aquatic system.
Abstract
Objectives: This study was carried out to examine whether the apparent photolysis with or without sensitizers[NaOH and humic acid (HA)] was prompted photodegradation of polychlorinated biphenyl (PCB) in aqueoussolution. Methods: PCBs photodegradation occurred using fluorescence black lamps at λmax = 300 nm. PCB congenerswere exposed in 10 ppm HA or 0.05N NaOH solutions, to investigate the decreasing profile of PCBconcentration with time. The PCBs were then analyzed by gas chromatography/mass spectrometry (GC-MS). Reductive degradation profile of PCB congeners in the presence of both sensitizers under oxygen-saturatedprotic conditions was described using the wind-rose diagrams. Results: Use of HA or NaOH decreased PCB concentration with time in the dark and on irradiation, indicating thatphotolysis underwent through reductive dechlorination through energy transfer and possibly with reactive oxygens. The dechlorination was marked by a chromatographic shift, observed in the GC-MS plots. Therefore it is logicalto assume that increasing the dose of sensitizers would increase the photodegradation rates of PCBs. The half-livesof pentachloro-PCB (penta-3) in 0.05N NaOH and 10 ppm HA were estimated at about 47 hours and 39 hours,respectively, under the same experimental conditions of photolysis. It was found that the rate of photolysis ofpentachloro-PCB in aqueous solution followed apparent first-order kinetics compared to other congeners. Conclusion: Photochemical degradation (using 328 nm UV light) of penta- and hexa-PCBs in HA or alkalinesolution is a viable method for pretreatment method. The results are helpful for the further comprehension of thereaction mechanism for photolytic dechlorination of PCBs in aquatic system.
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