Photodechlorination Pathways of Non-Ortho Substituted PCBs by Ultraviolet Irradiation in Alkaline 2-Propanol

Yao, Yuan; Kakimoto, Kohji; Ogawa, Hiroaki; Kato, Yasuhiko; Hanada, Yoshifumi; Shinohara, Ryota; Yoshino, Eiichi

doi:10.1007/s001289900470

Cited by 25 publications

(14 citation statements)

References 9 publications

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“…TBBPA undergoes photooxidation in the presence of humic acid to form a highly reactive benzoquinone radical intermediate (Han, et al, 2008; Han, et al, 2009) and photodegrades in a pH-dependent manner (Eriksson, et al, 2004), supporting the plausibility that TBBPA chemically converts carboxy-H 2 DCFDA to the DCF fluorescent moiety. Additionally, others have demonstrated that halogenated compounds with structural similarity to TBBPA are transformed photochemically in the natural environment and under certain experimental conditions (Ohko, et al, 2001; Yao, et al, 1997). Future experiments are needed to determine whether oxidation of TBBPA could explain increased fluorescence in cell-free and serum-free salt solutions containing carboxy-H 2 DCFDA.…”

Section: Discussionmentioning

confidence: 99%

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

Tetz

Kamau

Cheng

et al. 2013

Journal of Pharmacological and Toxicological Methods

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Introduction The dichlorofluorescein (DCF) assay is a popular method for measuring cellular reactive oxidant species (ROS). Although caveats have been reported with the DCF assay and other compounds, the potential for artifactual results due to cell-free interactions between the DCF compound and toxicants has hardly been explored. We evaluated the utility of the DCF assay for measuring ROS generation by the toxicants mono-(2-ethylhexyl) phthalate (MEHP), and tetrabromobisphenol A (TBBPA). Methods DCF fluorescence was measured spectrofluorometrically after a 1-h incubation of toxicants with 6-carboxy-2′,7′-dichlorodihydrofluorescein diacetate (carboxy-H2DCFDA). MEHP was incubated with carboxy-H2DCFDA in cell-free solutions of Hank’s buffered salt solution (HBSS), or in Royal Park Memorial Institute (RPMI) medium with or without fetal bovine serum. TBBPA was incubated with carboxy-H2DCFDA in cell-free HBSS and with human trophoblast cells (HTR8/SVneo cells). Results MEHP did not increase fluorescence in solutions of carboxy-H2DCFDA in HBSS or RPMI medium without serum. However, MEHP (90 and 180 μM) increased DCF fluorescence in cell-free RPMI medium containing serum. Furthermore, serum-free and cell-free HBSS solutions containing 25 μM TBBPA exhibited concentration-dependent increased fluorescence with 5–100 μM carboxy-H2DCFDA (p<0.05), but not 1 μM carboxy-H2DCFDA. In addition, we observed increased fluorescence in HTR8/SVneo cell cultures exposed to TBBPA (0.5–25 μM) (p<0.05), as we had observed in cell-free buffer. Discussion MEHP demonstrated an interaction with serum in cell-free generation of DCF fluorescence, whereas TBBPA facilitated conversion of carboxy-H2DCFDA to the fluorescent DCF moiety in the absence of serum. Because TBBPA increased fluorescence in the absence of cells, the increased DCF fluorescence observed with TBBPA in the presence of cells cannot be attributed to cellular ROS and may, instead, be the result of chemical activation of carboxy-H2DCFDA to the fluorescent DCF moiety. These data illustrate the importance of including cell-free controls when using the DCF assay to study toxicant-stimulated cellular production of ROS.

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Section: Discussionmentioning

confidence: 99%

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

Tetz

Kamau

Cheng

et al. 2013

Journal of Pharmacological and Toxicological Methods

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“…The photosensitized production of radicals and oxygen consumption were completely inhibited by the azide anion, an efficient physical 1 O 2 quencher. Because TBBPA is a stable compound that at neutral pH does not absorb much of the atmosphere-filtered solar radiation, its photosensitized oxidation by 1 O 2 may be the key reaction initiating/mediating TBBPA degradation in the natural environment.A large number of halogen-containing organic compounds have been reported to undergo photochemical transformations, under both experimental and natural conditions (15)(16)(17). Photolytic decomposition of TBBPA in the environment occurs in the atmosphere and in surface waters.…”

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confidence: 99%

Oxidation of Flame Retardant Tetrabromobisphenol A by Singlet Oxygen

Han

Bilski

Karriker

et al. 2007

Environ. Sci. Technol.

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Wide use of flame retardants can pose an environmental hazard, and it is of interest to investigate how they may degrade. We report here that 3,3',5,5'-tetrabromobisphenol A (TBBPA) is subject to photosensitized oxidation involving singlet molecular oxygen ((1)O2). By using visible light and rose bengal or methylene blue as 102 photosensitizers, we have found that TBBPA is a 102 quencher. The quenching rate constant, k(q), depends on TBBPA ionization (pK = 7.4). In acetonitrile, where TBBPA is undissociated, the kq value is 6.1 x 10(5) M(-1) s(-1) for a TBBPA monomer and decreases to 2.9 x 10(4) M(-1) s(-1) for TBBPA dimers and/or aggregates. TBBPA dissociates in aqueous solutions, and its kq value is 1.44 x 10(9) M(-1) s(-1) in alkaline solution, decreasing to 3.9 x 10(8) M(-1) s(-1) at pH 7.2. The strong 102 quenching by TBBPA anion initiates an efficient oxidation of TBBPA, which results in oxygen consumption in aqueous micellar (e.g., Triton X-100) solutions containing photosensitizer. This oxygen consumption is mediated by transient radical species, which we detected by using EPR spectroscopy. We observed two major radicals and one minor radical generated from TBBPA by reaction with 102 at pH 10. One was identified as the 2,6-dibromo-p-benzosemiquinone radical (a2H = 2.36 G, g = 2.0056). A second radical (aH = 2.10 G, g = 2.0055) could not be identified butwas probably a 2,6-dibromo-p-benzosemiquinone radical containing an EPR-silent substituent at the 3-position. Spin trapping with 5,5-dimethyl-1-pyrroline N-oxide (DPMO) showed that other minor radicals (hydroxyl, carbon-centered) are also generated during the reaction of TBBPA with (1)O2. The photosensitized production of radicals and oxygen consumption were completely inhibited by the azide anion, an efficient physical (1)O2 quencher. Because TBBPA is a stable compound that at neutral pH does not absorb much of the atmosphere-filtered solar radiation, its photosensitized oxidation by (1)O2 may be the key reaction initiating or mediating TBBPA degradation in the natural environment.

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“…Also, a similar network for T 4 CB in 2-propanol is proposed for a photodechlorination process which implies a similar free-radical reaction mechanism (Yao et al, 1997). To characterize in a simpler way the dechlorination step of T 4 CB/MeOH, a threelevel lumpingstrategy is alsoproposed (Fig.2B-D).…”

Section: Global Kinetics Of T 4 Cb Disappearancementioning

confidence: 84%

Supercritical Water Oxidation

2003

Physicochemical Treatment of Hazardous Wastes

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Supercritical water oxidation (SCWO) reaction is effective in destruction of polychlorinated biphenyls (PCBs) to mineral products of CO 2 , HCl, and H 2 O such that 99.95% conversion of Aroclor 1248 is possible in 54.5 seconds residence time at 823 K and 25.3 MPa. Yet to design and operate SCWO reactors to avoid harmful products formation such as polychlorinated dibenzofurans and dioxins, it is necessary to understand the PCB reaction pathway leading to final products. This study shows the dechlorination reaction pathway of 3344-Tetrach lorobiphenyl (a surro gate for Aroclo r 1248) in methanol solutions. It is suggested that hydrogen species from methanol act as reaction rate enhancers and lead to a series reaction pathway of dechlorination to biphenyl followed by ring-opening oxidation to mineral products. Also, reaction kinetics for this system are presented. These results are of value for reactor design to ensure oxidation of these recalcitrant pollutants in an environmentally safe manner.

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Photodechlorination Pathways of Non-Ortho Substituted PCBs by Ultraviolet Irradiation in Alkaline 2-Propanol

Cited by 25 publications

References 9 publications

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

Oxidation of Flame Retardant Tetrabromobisphenol A by Singlet Oxygen

Supercritical Water Oxidation

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