Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation

Colombini, Maria Perla; Francesco, Fabio Di; Fuoco, Roger

doi:10.1006/mchj.1996.0108

Cited by 8 publications

(7 citation statements)

References 11 publications

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“…As mentioned previously, the dechlorination pathway may contribute more than the presence of observable products indicates, possibly up to 30% conversion. The lack of observable dechlorinated PCDDs is consistent with previous studies in aqueous and organic solvents (<20% mass balance) ( , ). Quantum yields for dechlorinated PCDDs resulting from 2,3,7,8-TeCDD are ∼4 times larger than the starting material.…”

Section: Resultssupporting

confidence: 91%

“…The lack of observable dechlorinated PCDDs is consistent with previous studies in aqueous and organic solvents (<20% mass balance) (27,28). Quantum yields for dechlorinated PCDDs resulting from 2,3,7,8-TeCDD are ∼4 times larger than the starting material.…”

Section: Resultssupporting

confidence: 87%

“…This congener has been assigned a toxic equivalence factor of 1.0 relative to other polychlorinated diaryl systems such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) (22). While numerous studies have sought to achieve a quantitative photochemical mass balance of 2,3,7,8-TeCDD on photolysis in either organic (23)(24)(25)(26)(27) or aqueous solvents (17,26,28), identifying all of the photochemically converted starting material has remained elusive. Early studies suggested reductive dechlorination was only a minor photolytic pathway for 2,3,7,8-TeCDD, even in organic solvents (29).…”

Section: Introductionmentioning

confidence: 99%

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Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Rayne

Wan

Ikonomou

et al. 2002

Environ. Sci. Technol.

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Polychlorinated dibenzo-p-dioxins (PCDDs) are a class of halogenated diaryl compounds that are environmentally important because of their high toxicity and bioaccumulatory properties. There is an incomplete understanding of their photochemistry because the majority of photoproducts, as indicated by incomplete mass balances, have not been identified. We studied the photochemical transformation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) in aqueous solution using 302 nm light. Our results allow for the first photochemical mass balance (92-99%) for this compound and confirm the operation of a novel photochemical pathway, which gives rise to 2,2'-dihydroxy-4,4',5,5'-tetrachlorobiphenyl (4,4',5,5'-TeCDHBP) at >50% conversion from the starting material. Rearrangement from 2,3,7,8-TeCDD to 4,4',5,5'-TeCDHBP takes place following preferential homolytic C-O bond cleavage via a proposed mechanism analogous to the parent dibenzo-p-dioxin system. Photochemical conversion from the starting material to dechlorinated PCDDs or chlorinated phenoxyphenols are minor pathways, although the exact contribution of the strictly dechlorination pathways remains uncertain because of the complexity of the system. The results suggest that the photochemical conversion of PCDDs to chlorinated dihydroxybiphenyls, which are also polychlorinated biphenyl (PCB) metabolites, may be an important part of their environmental fate.

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Section: Resultssupporting

confidence: 91%

Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Rayne

Wan

Ikonomou

et al. 2002

Environ. Sci. Technol.

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“…Since dioxins are resistant to thermal, chemical, and biological degradation, they accumulate in natural environ ment (). There has been growing interest in developing efficient and economically feasible methods that destroy these recalcitrant compounds, which include incineration and thermal treatment ( , ), catalytic destruction ( , ), photolysis ( − ), photocatalysis ( − ), ozonolysis (), radiolysis (), and biodegradation ( , ). Among them, photocatalytic process is highly promising because it operates at ambient temperature and pressure with low energy photons (λ < 388 nm for anatase TiO 2 ), requires no chemical reagents except O 2 in the ambient air and no expensive catalysts, and utilizes natural sunlight.…”

Section: Introductionmentioning

confidence: 99%

Photocatalytic Degradation of Polychlorinated Dibenzo-p-dioxins on TiO₂ Film under UV or Solar Light Irradiation

Choi

Hong

Chang

et al. 2000

Environ. Sci. Technol.

195

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The photocatalytic degradation of polychlorinated dibenzo-p-dioxins (PCDDs), which include mono-, tetra-, hepta-, and octachlorinated congeners (MCDD, TCDD, HpCDD and OCDD), was carried out on TiO2 films under UV (λ > 300 nm) or solar light irradiation in the air. All the dioxin congeners tested were successfully degraded on TiO2 while the direct photolysis of them in the absence of TiO2 was negligible. The photocatalytic degradation rates of PCDDs decreased with the number of chlorines and were described by the first-order reaction kinetics with half-lives of 5.8, 3.9, 0.71, and 0.38 h for OCDD, HpCDD, TCDD, and MCDD, respectively. The degradation rates increased with light intensity and TiO2 coating weights up to 2 mW/cm2 (300 < λ < 400 nm) and 200 μg of TiO2/cm2, respectively. Further increases in either the light intensity or the TiO2 coating mass did not much affect the degradation rate. The natural solar light under clear sky conditions was as effective as a 200-W mercury lamp irradiation (filtered through a Pyrex filter) in degrading OCDD on TiO2. The photocatalytic degradation of PCDDs seems to be initiated by OH radical attack and not by conduction band electron transfer. From a diffuse reflectance FTIR study, the degradation of OCDD was found to involve the cleavage of the aromatic ring. Neither stable intermediates nor dechlorinated PCDDs were detected during the photocatalytic degradation.

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“…The most important mechanism for dioxin degradation in the environment is believed to be degradation by the UV component of sunlight (). Many studies report photolytic decomposition of dioxins in water ( , ), in organic solutions ( , ), in gases (), and also in soils and sediments ( , ). Here we report that UVB light can be used to selectively remove dioxin from fishmeal.…”

Section: Discussionmentioning

confidence: 99%

UV Treatment of Fishmeal: A Method To Remove Dioxins?

Baron

Børresen

Jacobsen

2005

J. Agric. Food Chem.

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This study evaluates the use of UV on contaminated fishmeal and photodegradation of dioxins. Fishmeal samples were placed under UVA or UVB light for 2, 5, and 10 days. Subsequently, analysis of amino acid content, lipid oxidation marker, ethoxyquin content, dioxin, and polychlorinated biphenyl (PCB) profiling was carried out. Exposure of fishmeal for 5 days to UVB light resulted in the degradation of approximately 70% of the dioxin content, while UVA had little effect, only resulting in the degradation of 10% of the dioxin content. UVB did not affect the protein and amino acid content of fishmeal; however, lipid oxidation was triggered. Addition of ethoxyquin prevented oxidation but simultaneously slowed dioxin breakdown. Increasing UVB intensity resulted in a more efficient dioxin degradation of 90%. Exposure of fishmeal to UVB also resulted in an increase in PCBs. UVB light is shown to photodegrade dioxin in fishmeal, indicating the needs to further investigation of methods for application at industrial scale.

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Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation

Cited by 8 publications

References 11 publications

Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Photocatalytic Degradation of Polychlorinated Dibenzo-p-dioxins on TiO₂ Film under UV or Solar Light Irradiation

UV Treatment of Fishmeal: A Method To Remove Dioxins?

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Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation

Cited by 8 publications

References 11 publications

Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Photochemical Mass Balance of 2,3,7,8-TeCDD in Aqueous Solution under UV Light Shows Formation of Chlorinated Dihydroxybiphenyls, Phenoxyphenols, and Dechlorination Products

Photocatalytic Degradation of Polychlorinated Dibenzo-p-dioxins on TiO2 Film under UV or Solar Light Irradiation

UV Treatment of Fishmeal: A Method To Remove Dioxins?

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Photocatalytic Degradation of Polychlorinated Dibenzo-p-dioxins on TiO₂ Film under UV or Solar Light Irradiation