Formation of mixed halogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs)

Saeed, Ayesha; Altarawneh, Mohammednoor; Dlugogorski, Bogdan Z.

doi:10.1016/j.chemosphere.2015.06.054

Cited by 6 publications

(5 citation statements)

References 54 publications

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“…The congener profile of lignin digested with aqua regia was similar to that resulting from chlorine bleaching processes, with lowly chlorinated PCDFs and highly chlorinated PCDDs being the main congeners, − suggesting that the aqua regia digestion process may be similar to the chlorine bleaching process. During chlorination, the macromolecular aromatic ring in lignin could be decomposed to smaller components with similar structures to DBD and DBF via oxidative coupling reactions, further forming PCDD/Fs by chlorine electrophilic substitution. − Although there are no aromatic ring structures in high-purity cellulose, some phenolic residues inevitably remain after the cellulose extraction process, which are more likely to form DBD and DBF precursors and further form PCDD/Fs. The congener profile of digested HA was dominated by 2,3,7,8-TCDF, which was similar to that in digested soil samples.…”

Section: Resultsmentioning

confidence: 99%

“…In terms of the pulp and paper industry, previous studies have suggested that direct chlorination of dibenzo- p -dioxins (DBDs), dibenzofurans (DBFs), and non-extractable precursors was mainly responsible for the observed PCDD/Fs in wood or non-wood pulp bleached with chlorine. − The non-extractable precursors were speculated to be insoluble organic fragments containing oxygenated aromatic rings, such as DBD/F-like structures, phenols, hydroxylated benzenes, and diphenyl ethers . Among them, the most likely source of DBD/F-like structures is lignin since it already contains oxygenated aromatic rings. − …”

Section: Introductionmentioning

confidence: 99%

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Unexpected Dioxin Formation During Digestion of Soil with Oxidizing Acids

Xie,

Li,

Wang

et al. 2023

Environ. Sci. Technol.

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Dioxins, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), are among the most toxic unintentionally produced persistent organic pollutants, and their emission is of great concern. Herein, we discovered abundant dioxin formation in soil and various organic carbon-containing matrices after digestion with aqua regia. Σ17PCDD/Fs concentrations were in the range of 66.6–142,834 pg/g dw (5.6–17,021 pg WHO2005-TEQ/g dw) in 19 soil samples after digestion with aqua regia for 6 h. Σ17PCDD/Fs concentration was significantly and positively correlated with soil organic carbon content (R 2 = 0.89; p < 0.01). Compared with cellulose and lignin, humic acid served as an important organic matter component that was converted to PCDD/Fs during soil digestion. Strong oxidation and production of reactive chlorine by aqua regia may be the key factors in the formation of PCDD/Fs. The yearly emission of PCDD/Fs due to digestion with strong acids by the inspection and testing industry was estimated to be 83.8 g TEQ in China in 2021 based on the highest level, which was ∼0.9% of the total dioxin inventory in China. Great attention should be paid to unexpected dioxin formation during digestion processes considering the potential risk of release from laboratories and enterprises.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unexpected Dioxin Formation During Digestion of Soil with Oxidizing Acids

Xie,

Li,

Wang

et al. 2023

Environ. Sci. Technol.

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“…The exothermicities for chlorophenoxy radicals increase in the order 2-chlorophenoxyl < 2,4,6-trichlorophenoxyl < 2,4-dichlorophenoxyl < 2,4,5-trichlorophenoxyl. ,, The exothermicities for bromophenoxy radicals decrease in the order 2-bromophenoxyl > 2,4-dibromophenoxyl > 2,4,6-tribromophenoxyl . Cross-coupling of bromophenoxy and chlorophenoxy radicals and self-coupling of bromophenoxy radicals are much more exothermic than self-coupling of chlorophenoxy radicals. ,− Therefore, it can be inferred that, when both chlorinated and brominated phenoxy radicals are present, PBDD/Fs and PBCDD/Fs will form more readily than PCDD/Fs…”

Section: Framework For Identifying Pxdd/fs Formation Mechanisms Durin...mentioning

confidence: 99%

Framework of the Integrated Approach to Formation Mechanisms of Typical Combustion Byproducts─Polyhalogenated Dibenzo-p-dioxins/Dibenzofurans (PXDD/Fs)

Wang

Liu

Yang

et al. 2023

Environ. Sci. Technol.

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Understanding the mechanisms through which persistent organic pollutants (POPs) form during combustion processes is critical for controlling emissions of POPs, but the mechanisms through which most POPs form are poorly understood. Polyhalogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs) are typical toxic POPs, and the formation mechanisms of PXDD/Fs are better understood than the mechanisms through which other POPs form. In this study, a framework for identifying detailed PXDD/Fs formation mechanisms was developed and reviewed. The latest laboratory studies in which organic free radical intermediates of PXDD/Fs have been detected in situ and isotope labeling methods have been used to trace transformation pathways were reviewed. These studies provided direct evidence for PXDD/Fs formation pathways. Quantum chemical calculations were performed to determine the rationality of proposed PXDD/Fs formation pathways involving different elementary reactions. Many field studies have been performed, and the PXDD/Fs congener patterns found were compared with PXDD/Fs congener patterns obtained in laboratory simulation studies and theoretical studies to mutually verify the dominant PXDD/Fs formation mechanisms. The integrated method involving laboratory simulation studies, theoretical calculations, and field studies described and reviewed here can be used to clarify the mechanisms involved in PXDD/Fs formation. This review brings together information about PXDD/Fs formation mechanisms and provides a methodological framework for investigating PXDD/Fs and other POPs formation mechanisms during combustion processes, which will help in the development of strategies for controlling POPs emissions.

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“…[40][41][42][43][44][45] Halogenated phenoxy radicals have been considered crucial intermediates in the formation of halogenated dioxins and furans. [42][43][44][45][46] Under combustion or pyrolysis conditions, halogenated phenoxy radicals can be formed from BPs or CPs through the loss of the phenoxyl-hydrogen via unimolecular, bimolecular, or possibly other low-energy pathways (including heterogenous reactions). The unimolecular reaction includes the decomposition of bromophenoxy radicals (BPRs) and chlorophenoxy radicals (CPRs) with the cleavage of the O-H bond.…”

Section: Introductionmentioning

confidence: 99%

“…The gas-phase formation of PBCDD/Fs is likely to have similar mechanisms to those responsible for PBDD/F and PCDD/F productions. On the one hand, PBCDD/Fs can be formed from the combustion or high-temperature pyrolysis of the BP and CP mixture; [45][46][47][48][49] on the other hand, BCPs are also structurally similar to PBCDD/Fs and have been demonstrated to be the predominant precursors for or key intermediates in the formation of PBCDD/Fs. The dimerization of bromochlorophenoxy radicals (BCPRs) is the major pathway for the gas-phase formation of PBCDD/Fs from BCP precursors.…”

Section: Introductionmentioning

confidence: 99%