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Formation of environmentally relevant brominated dioxins from 2,4,6-tribromophenol via bromoperoxidase-catalyzed dimerisation
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Environmental analytical chemistry using hyphenated and bioanalytical techniques)
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Environmental analytical chemistry using hyphenated and bioanalytical techniques)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Polybrominated dibenzo-p-dioxins (PBDD) are emerging environmental pollutants with structural similarities to the highly characterized toxicants polychlorinated dibenzo-p-dioxins. The geographical and temporal variations of PBDD in biota samples from the Baltic Sea do not display features that are normally related to anthropogenic sources, and therefore the natural formation of PBDDs has been suggested. This study of the bromoperoxidase mediated oxidative coupling of 2,4,6-tribromophenol (an abundant substance that is naturally formed in marine systems) identified the formation of ppb-level yields of 1,3,6,8-tetrabromodibenzo-p-dioxin (1,3,6,8-TeBDD) through direct condensation. Additional TeBDDs (1,3,7,9-TeBDD, 1,2,4,7-TeBDD and/or 1,2,4,8-TeBDD) and tri-BDDs (1,3,7-TrBDD and 1,3,8-TrBDD) were frequently formed, but at lower yields. The formation of these TeBDDs probably proceeds via bromine shifts or Smiles rearrangements, while the TrBDDs may result from subsequent debromination processes. Since all of the congeners formed by oxidative coupling and subsequent reactions are also found in Baltic Sea biota, the results support the theory that PBDDs are formed from natural precursors.

Keyword [en]
bromoperoxidase, enzymatic coupling, 2, 4, 6-tribromophenol, polybrominated dibenzo-p-dioxins, oxidative coupling, Baltic Sea
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-50901OAI: oai:DiVA.org:umu-50901DiVA: diva2:470833
Available from: 2011-12-30 Created: 2011-12-30 Last updated: 2012-01-09Bibliographically approved
In thesis
1. Polybrominated dibenzo-p-dioxins: Natural formation mechanisms and biota retention, maternal transfer, and effects
Open this publication in new window or tab >>Polybrominated dibenzo-p-dioxins: Natural formation mechanisms and biota retention, maternal transfer, and effects
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polybrominated dibenzo-p-dioxins (PBDD) and dibenzofurans (PBDF) are a group of compounds of emerging interest as potential environmental stressors. Their structures as well as toxic responses are similar to the highly characterized toxicants polychlorinated dibenzo-p-dioxins. High levels of PBDDs have been found in algae, shellfish, and fish, also from remote areas in theBaltic Sea. This thesis presents studies on PBDD behavior in fish and offspring, and natural formation of PBDDs from naturally abundant phenolic precursors.

The uptake, elimination, and maternal transfer of mono- to tetraBDD/Fs were investigated in an exposure study reported in Paper I. The effects of PBDDs in fish were examined in a dose-response study (Paper II). It was shown that fish can assimilate PBDD/Fs from their feed, although non-laterally substituted congeners were rapidly eliminated. Laterally substituted congeners were retained as was congeners without vicinal hydrogens to some extent. PBDD/Fs were transferred to eggs, and congeners that were rapidly eliminated in fish showed a higher transfer ratio to eggs. Exposure to the laterally substituted 2,3,7,8-TeBDD had significant effects on the health, gene expression and several reproduction end-points of zebrafish, even at the lowest dose applied.

The geographical and temporal variations of PBDD in biota samples from the Baltic Seasuggest biogenic rather than anthropogenic origin. In Paper III, bromoperoxidase-mediated coupling of 2,4,6-tribromophenol yielded several PBDD congeners, some formed after rearrangement. The overall yield was low, but significantly higher at low temperature, and the product profile obtained was similar to congener profiles found in biota from the Swedish West Coast. In Paper IV, photo­chemi­cally induced cyclization of hydroxylated polybrominated diphenyl ethers under natural conditions produced PBDDs at percentage yield. Rearranged products were not detected, and some abundant congeners do not seem to be formed this way. However, the product profile obtained was similar to congener profiles found in biota from the Baltic Proper.

Since the PBDD congeners found in biota have a high turn-over in fish, the exposure must be high and continuous to yield the PBDD levels measured in wild fish. Thus, PBDDs must presumably be formed by common precursors in general processes, such as via enzymatic oxidations, UV-initiated reactions or a combination of both. The presented pathways for formation of PBDDs are both likely sensitive to changes in climatic conditions.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2012. 65 p.
Keyword
polybrominated dibenzo-p-dioxins, PBDDs, Baltic Sea, uptake, retention, maternal transfer, metabolism, bioavailability, natural formation, precursor, bromoperoxidase, bromophenol, photochemical transformation, oxidative coupling, hydroxylated polybrominated diphenyl ethers
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-50887 (URN)
Public defence
2012-02-03, KBC-huset, Hörsal KB3B1, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2012-01-13 Created: 2011-12-29 Last updated: 2017-09-01Bibliographically approved

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