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Polybrominated dibenzo-p-dioxins: Natural formation mechanisms and biota retention, maternal transfer, and effects
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Environmental analytical chemistry using hyphenated and bioanalytical techniques ; EcoChange)
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 [en]
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: urn:nbn:se:umu:diva-50887OAI: oai:DiVA.org:umu-50887DiVA: diva2:470963
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
List of papers
1. Retention and maternal transfer of environmentally relevant polybrominated dibenzo-p-dioxins and dibenzofurans, polychlorinated dibenzo-p-dioxins and dibenzofurans, and polychlorinated biphenyls in zebrafish (Danio rerio) after dietary exposure
Open this publication in new window or tab >>Retention and maternal transfer of environmentally relevant polybrominated dibenzo-p-dioxins and dibenzofurans, polychlorinated dibenzo-p-dioxins and dibenzofurans, and polychlorinated biphenyls in zebrafish (Danio rerio) after dietary exposure
2012 (English)In: Environmental Toxicology and Chemistry, ISSN 0730-7268, E-ISSN 1552-8618, Vol. 31, no 4, 804-812 p.Article in journal (Refereed) Published
Abstract [en]

High levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), mono- and non-ortho polychlorinated biphenyls (PCBs), and polybrominated dibenzo-p-dioxins (PBDDs) are found in fish from coastal areas in the Baltic Sea, which may cause ecotoxicological effects. To increase our understanding of the persistency of the emerging pollutants polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), fish feed was spiked with 21 PBDD/Fs, 17 PCDD/Fs, and 30 PCBs and fed to zebrafish. Concentrations in fish and eggs were examined during a six- or twelve-week uptake period, and a six-week elimination period. Steady-state was reached for 2, 3, 7, and/or 8-substituted tri- and tetra-BDD/Fs, with 2,3,7,8-tetra-BDD (2,3,7,8-TeBDD) being the most strongly retained. Steady-state was not reached for tetra- to hexa-CDDs. Non-2,3,7,8-congeners showed little of or no retention. Most PCBs had high retention and did not reach steady-state. Half-lives decreased in the order: PCBs > PCDD/Fs > PBDD/Fs. Concentrations of 2,3,7,8-penta- to octa-CDD/Fs decreased with their degree of chlorination suggesting that the rate-limiting factor for uptake is low bioavailability. Maternal transfer was observed for all retained compounds, with most transfer factors < 1, indicating that transfer rates are affected by the poor water solubility of the compounds. The limited retention of the major PBDD congeners found in Baltic Sea fish suggests that they are exposed to high or very high concentrations via either food or water.

Place, publisher, year, edition, pages
John Wiley & Sons, 2012
Keyword
polybrominated dibenzo-p-dioxins, dietary uptake, metabolism, maternal transfer, zebrafish
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-50900 (URN)10.1002/etc.1750 (DOI)000301575700016 ()22278820 (PubMedID)
Available from: 2011-12-30 Created: 2011-12-30 Last updated: 2017-08-31Bibliographically approved
2. Retention and maternal transfer of brominated dioxins in zebrafish (Danio rerio) and effects on reproduction, aryl hydrocarbon receptor-regulated genes, and ethoxyresorufin-O-deethylase (EROD) activity
Open this publication in new window or tab >>Retention and maternal transfer of brominated dioxins in zebrafish (Danio rerio) and effects on reproduction, aryl hydrocarbon receptor-regulated genes, and ethoxyresorufin-O-deethylase (EROD) activity
Show others...
2011 (English)In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 102, no 3-4, 150-161 p.Article in journal (Refereed) Published
Abstract [en]

Brominated dioxins have recently been detected in Baltic Sea biota. Due to their similarities to the highly toxic chlorinated dioxins, concern has been raised about their potential biological effects. The present study investigated retention and effects of brominated dioxins in adult zebrafish, as well as maternal transfer and effects on offspring. We exposed adult zebrafish for nine weeks via feed to 2,3,7,8-tetrabromodibenzo-p-dioxin (TBDD) or to a mixture of brominated dioxins (Baltic Sea mixture), which was designed to reflect relative concentrations found in Baltic Sea biota. We studied spawning success, gonad morphology, hepatic vitellogenin gene expression, and offspring early life-stage development to investigate effects on zebrafish reproduction. Hepatic ethoxyresorufin-O-deethylase (EROD) activity and hepatic expression of a number of aryl hydrocarbon receptor (AHR)-regulated genes were studied to investigate if the brominated dioxins can activate gene transcription through the AHR pathway in zebrafish. In addition, glutathione reductase activity and expression of genes involved in adaptive responses to intracellular stress were studied to investigate potential stress effects of brominated dioxins. After nine weeks of exposure, all brominated dioxins spiked to the feed were detected in female fish and transferred to eggs. Exposure to the Baltic Sea mixture and TBDD clearly induced AHR-regulated genes and EROD activity. Exposure to TBDD reduced spawning success, altered ovarian morphology and reduced hepatic vitellogenin gene expression, which implies that TBDD has a similar effect pattern as the chlorinated analogue. Overall, our results show that dietary exposure to sublethal concentrations of brominated dioxins may impair reproductive physiology in fish and induce AHR-regulated genes. (C) 2011 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2011
Keyword
zebrafish, polybrominated dibenzo-p-dioxins, dietary exposure, maternal transfer, CYP1A1 induction, reproduction
National Category
Other Veterinary Science
Research subject
Ecotoxicology
Identifiers
urn:nbn:se:umu:diva-50885 (URN)10.1016/j.aquatox.2011.01.008 (DOI)000289399400004 ()
Available from: 2011-12-29 Created: 2011-12-29 Last updated: 2017-12-08Bibliographically approved
3. Formation of environmentally relevant brominated dioxins from 2,4,6-tribromophenol via bromoperoxidase-catalyzed dimerisation
Open this publication in new window or tab >>Formation of environmentally relevant brominated dioxins from 2,4,6-tribromophenol via bromoperoxidase-catalyzed dimerisation
(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
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:nbn:se:umu:diva-50901 (URN)
Available from: 2011-12-30 Created: 2011-12-30 Last updated: 2012-01-09Bibliographically approved
4. Photochemical formation of polybrominated dibenzo-p-dioxins from environmentally abundant hydroxylated polybrominated diphenyl ethers
Open this publication in new window or tab >>Photochemical formation of polybrominated dibenzo-p-dioxins from environmentally abundant hydroxylated polybrominated diphenyl ethers
2012 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 14, 7567-7574 p.Article in journal (Refereed) Published
Abstract [en]

High levels of polybrominated dibenzo-p-dioxins (PBDDs) have been found in Baltic Sea biota, where the toxic load owing to, for example, polychlorinated dibenzo-p-dioxins and other organic pollutants is already high. The levels and geographic pattern of PBDDs suggest biogenic rather than anthropogenic origin, and both biotic and abiotic formation pathways have been proposed. Photochemical formation from hydroxylated polybrominated diphenyl ethers (OH-PBDE) is a proposed pathway. for PBDDs in marine environments. Ultraviolet radiation-initiated transformations of OH-BDEs 47, 68, 85, 90, 99, and 123, which all are abundant in the environment, were investigated. It was shown that the most abundant PBDDs in the environment (1,3,7-triBDD and 1,3,8-triBDD) can be formed from the most abundant OH-BDEs (OH-BDE 47 and OH-BDE 68) at high rates and with percentage yields. In fact, most of the PBDDs that have been identified in the Baltic Sea environment were formed with high yield from the six studied OH-PBDE, through initial cyclization and subsequent debromination reactions. The high formation yields point to this route as an important source of PBDDs in biota. However, congeners showing relatively high retention in fish, specifically 1,3,6,8- and 1,3,7,9-tetraBDD, were not formed. These are likely formed by enzymatic coupling of brominated phenols.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-59535 (URN)10.1021/es301256x (DOI)000306441000019 ()
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2017-12-07Bibliographically approved

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