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Ah receptor agonists in UV-exposed toluene solutions of decabromodiphenyl ether (decaBDE) and in soils contaminated with polybrominated diphenyl ethers (PBDEs)
Örebro University, Department of Natural Sciences. (Bioanalytisk miljötoxikologi)
Örebro University, Department of Natural Sciences.ORCID iD: 0000-0003-4128-8226
Örebro University, Department of Natural Sciences. (Molekylär biokemi)
Örebro University, Department of Natural Sciences. (MTM)
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2006 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 13, no 3, p. 161-169Article in journal (Refereed) Published
Abstract [en]

GOAL, SCOPE AND BACKGROUND: The use of polybrominated diphenyl ethers (PBDEs) as flame retardants increases the risk for emissions of other brominated compounds, such as polybrominated dibenzodioxins (PBDDs) and dibenzofurans (PBDFs). The large homology in structure of PBDD/Fs and mechanism of toxic action, i.e. the capacity to activate the Ah receptor (AhR) pathway, compared to their well-studied chlorinated analogues, justifies a raised concern to study the environmental levels and fate of these compounds. Decabromodiphenyl ether (decaBDE) is the most widely used PBDE today. Studies on photolytic debromination of decaBDE in organic solvents have shown debromination of decaBDE, as well as formation of PBDFs. However, little is known about the transformation mechanisms and there are only scarce data on photoproducts and PBDE transformation in environmentally relevant matrices. In this study, mechanism-specific dioxin bioassays were used to study photolytic formation of AhR agonists in toluene solutions of decaBDE. In addition, the influence of irradiation time and UV-light wavelength on the formation was studied. PBDE congener patterns and presence of PBDD/Fs were analysed. Further, AhR agonists were analysed in agricultural soils contaminated with PBDEs. Soils were also exposed to UV-light to study changes in AhR agonist levels. METHODS: Toluene solutions of decaBDE were irradiated using three different spectra of UV-light, simulating UV-A (320-400 nm), UV-AB (280-400 nm), and UV-ABC (250-400 nm). Additionally, decaBDE solutions were exposed to narrow wavelength intervals (10 nm bandwidth) with the central wavelengths 280, 290, 300, 310, 320, 330, 340, 350, 360 nm. AhR agonists in decaBDE solutions were analysed with two different bioassays, the chick embryo liver-cell assay for dioxins (Celcad) and the dioxin responsive, chemically activated luciferase expression assay (DR-Calux). Also, the decaBDE solutions were analysed with LRGC-LRMS to obtain PBDE congener patterns for breakdown of decaBDE, and with HRGC-HRMS, for presence of PBDD/Fs. Four soils were exposed to UV-AB light, under both dry and moist conditions. Levels of AhR agonists in soil extract fractions, before and after UV-exposure, were analysed with the DR-Calux. RESULTS AND DISCUSSION: Significant levels of photoproducts able to activate the AhR pathway, up to 31 ng bio-TEQ/ml, were formed in UV-exposed decaBDE solutions. The transformation yield of decaBDE into AhR agonists was estimated to be at the 0.1%-level, on a molar basis. The net formation was highly dependent on wavelength, with the sample irradiated at 330 nm showing the highest level of dioxin-like activity. No activity was detected in controls. PBDE analysis confirmed decaBDE degradation and a clear time-dependent pattern for debromination of PBDE congeners. AhR agonist effect in the recalcitrant fractions of the soils corresponded to the levels of chemically derived TEQs, based only on chlorinated dioxin-like compounds in an earlier study. It was concluded that no significant levels of other AhR agonists, e.g. PBDFs, were accumulated in the soil. UV-light caused changes in AhR-mediated activity in the more polar and less persistent fractions of the soils, but it is not known which compounds are responsible for this. RECOMMENDATIONS AND PERSPECTIVES: The laboratory experiments in this study show that high levels of AhR agonists can be formed as photoproducts of decaBDE and it is important to elucidate if and under which conditions this might occur in nature. However, soil analysis indicates that photoproducts of PBDE do not contribute to the accumulated levels of persistent dioxin-like compounds in agricultural soil. Still, more data is needed to fully estimate the environmental importance of PBDE photolysis and occurrence of its photoproducts in other environmental compartments. Analysis with dioxin bioassays enabled us to gather information about photoproducts formed from decaBDE even though the exact identities of these compounds were not known. CONCLUSION: Bioassays are valuable for studying environmental transformation processes like this, where chemical analysis and subsequent toxicological evaluation requires available standard compounds and information on toxicological potency. The use of bioassays allows a rapid evaluation of toxicological relevance.

Place, publisher, year, edition, pages
2006. Vol. 13, no 3, p. 161-169
Keyword [en]
Animals, Biological Assay, Cell Line; Tumor, Chick Embryo, Flame Retardants/radiation effects/toxicity, Phenyl Ethers/*chemistry/radiation effects/toxicity, Photolysis, Polybrominated Biphenyls/*chemistry/radiation effects/toxicity, Rats, Receptors; Aryl Hydrocarbon/*agonists, Soil Pollutants/radiation effects/toxicity, Solutions, Spectrometry; Mass; Electrospray Ionization, Toluene/chemistry, Ultraviolet Rays
National Category
Biological Sciences Chemical Sciences
Research subject
Biology; Chemistry
Identifiers
URN: urn:nbn:se:oru:diva-4132DOI: 10.1065/espr2005.08.280PubMedID: 16758706OAI: oai:DiVA.org:oru-4132DiVA, id: diva2:138431
Available from: 2008-11-12 Created: 2008-11-12 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Bioassay analysis of dioxin-like compounds: response interactions and environmental transformation of Ah receptor agonists
Open this publication in new window or tab >>Bioassay analysis of dioxin-like compounds: response interactions and environmental transformation of Ah receptor agonists
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dioxin-like compounds mediate their toxicity by binding to the aryl hydrocarbon receptor (AhR) and through this receptor a cascade of biochemical and toxic events are triggered. Mechanism-specific dioxin bioassays utilise the AhR coupled induction of endogenous CYP1A proteins or reporter gene systems for detection of dioxin-like compounds and other AhR ligands. The use of mechanism-specific in vitro bioassays as a complement or alternative to conventional GC-MS analysis of dioxin-like compounds has gained acceptance over the last years and is also in part a search for a tool for rapid and facilitated dioxin risk assessment.

This thesis includes several applications for bioassay analysis using the two bioassays Dioxin Responsive Chemically Activated Luciferase eXpression assay (DR-CALUX) and Chick Embryo Liver Culture Assay for Dioxins (CELCAD). The two dioxin bioassays were used to study the AhR mediated induction for single compounds, as well as for mixtures of AhR active compounds in different sample matrices, also including studies of the influence of clean-up methods and fractionation on bioassay response.

Bioanalysis gave valuable information on the toxicological relevance of decaBDE UV photoproducts. The bioassay methodology was able to reflect the actual variation in PBDF formation, and enabled a good estimation of toxicity of the congeners formed, regardless of chemical identification and congener specific potency data. The congeners formed had low potencies compared to the most toxic 2,3,7,8-substituted congeners, but the high concentrations resulted in considerable levels of TEQs.

For complex samples like organic household waste digestates it is advisable to use both bio- and chemical analysis, for confirmation of results, as far as possible. The bioassay-directed fractionation approach requires several fractionation steps (i.e. different methods) in order to obtain well-defined fractions, from which detailed conclusions can be drawn.

Also, proper analysis of human adipose tissue, although by far less complex than organic household waste, requires fractionation. Bioanalysis of these samples showed large deviations from the additivity assumption applied in the TEF calculation from chemical analysis. Thus, it is not clear how to interpret the bioassay results in relation to chemical results, although both methods gave the same information on relative levels of AhR agonists and showed good reproducibility.

Both DR-CALUX and CELCAD proved to be useful for AhR agonist analysis in mixtures and for single compounds. The DR-CALUX enables more rapid analysis of large number of samples and is therefore, a more suitable tool for AhR agonist detection, whereas CELCAD has more limitations and is more suitable for the study of AhR mediated toxicity with special emphasis on avian species. In vitro bioassays have many implications for the analysis of AhR agonists, yielding reliable and reproducible results, provided that proper clean-up and fractionation of samples is applied. Bioassays enable fast determinations of total or integrated effects of AhR ligands in samples, as well as specific potency studies. Thus, bioassays are in all a valuable and necessary complement to chemical analysis.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek, 2005. p. 58
Series
Örebro Studies in Biology, ISSN 1650-8793 ; 3
Keyword
bioassay, dioxin-like, Ah receptor
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:oru:diva-192 (URN)91-7668-456-3 (ISBN)
Public defence
2005-11-25, Hörsal P2, Prismahuset, Fakultetsgatan 1, Örebro, 10:00
Opponent
Supervisors
Available from: 2005-11-04 Created: 2005-11-04 Last updated: 2017-10-18Bibliographically approved

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Olsman, HelenaHagberg, JessikaKalbin, GeorgiJulander, Annelivan Bavel, BertStrid, ÅkeEngwall, Magnus

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