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Hydroxylated polybrominat­ed diphenyl ethers in Baltic Sea biota: Natural production, food web distribution and biotransformation
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are naturally produced in aquatic ecosystems e.g. by algae. Many OH-PBDEs have been observed to be highly bioactive and to cause adverse effects through several pathways, e.g. via disrupting oxidative phosphorylation (OXPHOS). The levels of some OH-PBDEs have increased in Baltic biota over the past decades. This may be associated with the nutrient enrichment of the Baltic Sea, which has favored growth of some of the OH-PBDE producers.

Ceramium tenuicorne has been suggested to be a producer of OH-PBDEs in the Baltic Sea, which is supported by the results presented in this thesis. The levels of OH-PBDEs were observed to fluctuate greatly in C. tenuicorne over the summer season, and to correlate with the levels of pigments in the algae. However, the observed congener pattern in C. tenuicorne questioned theories regarding the mechanism of their biosynthesis. The results indicate a much more selective pathway for biosynthesis than previously suggested for the production of OH-PBDEs.

One of the most abundant OH-PBDEs in C. tenuicorne, 6-OH-BDE137, has previously been observed to be toxic to bacteria, fungi, and crustaceans. Furthermore, Baltic gammarids seemed to change their feeding preferences towards less grazing on C. tenuicorne during the production peek of OH-PBDEs in the alga. This suggests that OH-PBDEs may serve as allelochemical defense agents for C. tenuicorne.

The transport and fate of OH-PBDEs through a Baltic food chain was also studied, including C. tenuicorne, Gammarus spp., three-spined stickleback (Gasterosteus aculeatus), and perch (Perca fluviatilis). A small portion of the OH-PBDEs were observed to be methylated in the alga, or by associated bacteria. The methylated OH-PBDEs biomagnified in the food chain up to perch, in which they were converted back to the OH-PBDEs via demethylation. The OH-PBDEs and their methylated counterparts were also partially debrominated in the food chain, which resulted in high concentration of 6-OH-BDE47 in the perch. This congener is the most toxic OH-PBDE with regards to OXPHOS disruption.

Another biotransformation of OH-PBDEs was identified in Baltic Sea blue mussels (Mytilus edulis). High concentrations of OH-PBDEs were conjugated with lipophilic moieties, e.g. fatty acids. This increases the residence time of the OH-PBDEs in the mussels. Mussels have been suggested to conjugate steroids with fatty acids as a means to regulate hormone levels. The conjugation of OH-PBDEs to fatty acids may occur due to intrusion into this pathway. Methods were developed to include quantification of conjugated OH-PBDEs in the analysis of mussels.

OH-PBDEs were also quantified in blood from Baltic Sea grey seals (Halichoerus grypus). Seals originating from the Baltic proper were observed to be more highly exposed to 6-OH-BDE47 than seals from the Gulf of Bothnia. However, the levels of OH-PBDEs were generally low. A major effort was invested into securing these results, including development of a new analytical method. Blood obtained from dead seals is a difficult matrix for quantification of OH-PBDEs, and previous attempts using an established method yielded unsatisfactory results.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University , 2016. , p. 78
Keywords [en]
OH-PBDEs, Baltic Sea, Biosynthesis, Environmental fate, Wildlife exposure, Metabolism, Analytical methods, Ceramium tenuicorne, Blue mussel, Gammarus spp., Stickleback, Perch, Grey Seal
National Category
Other Chemistry Topics
Research subject
Environmental Chemistry
Identifiers
URN: urn:nbn:se:su:diva-135789ISBN: 978-91-7649-585-8 (print)ISBN: 978-91-7649-586-5 (print)OAI: oai:DiVA.org:su-135789DiVA, id: diva2:1049110
Public defence
2017-01-17, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-12-22 Created: 2016-11-23 Last updated: 2016-12-08Bibliographically approved
List of papers
1. Biosynthesis of hydroxylated polybrominated diphenyl ethers and the correlation with photosynthetic pigments in the red alga Ceramium tenuicorne
Open this publication in new window or tab >>Biosynthesis of hydroxylated polybrominated diphenyl ethers and the correlation with photosynthetic pigments in the red alga Ceramium tenuicorne
2017 (English)In: Phytochemistry, ISSN 0031-9422, E-ISSN 1873-3700, Vol. 133, p. 51-58Article in journal (Refereed) Published
Abstract [en]

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been identified in a variety of marine organisms from different trophic levels indicating a large spread in the environment. There is much evidence pointing towards natural production as the major source of these compounds in nature. However, much is still not known about the natural production of these compounds. Seasonal trend studies have shown large fluctuations in the levels of OH-PBDEs in Ceramium tenuicorne from the Baltic Sea. Yet, even though indications of stimuli that can induce the production of these compounds have been observed, none, neither internal nor external, has been assigned to be responsible for the recorded fluctuations. In the present study the possible relationship between the concentration of pigments and that of OH-PBDEs in C. tenuicorne has been addressed. Significant correlations were revealed between the concentrations of all OH-PBDEs quantified and the concentrations of both chlorophyll a and Σxanthophylls + carotenoids. All of which displayed a concentration peak in mid-July. The levels of OH-PBDEs may be linked to photosynthetic activity, and hence indirectly to photosynthetic pigments, via bromoperoxidase working as a scavenger for hydrogen peroxide formed during photosynthesis. Yet the large apparent investment in producing specific OH-PBDE congeners point towards an targeted production, with a more specific function than being a waste product of photosynthesis. The OH-PBDE congener pattern observed in this study is not agreeable with some currently accepted models for the biosynthesis of these compounds, and indicates a more selective route than previously considered in C. tenuicorne.

Keywords
Ceramium tenuicorne, Ceramiaceae, Biosynthesis, OH-PBDE, Bromophenols, Pigments, Chlorophyll
National Category
Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-135593 (URN)10.1016/j.phytochem.2016.10.009 (DOI)000390513000006 ()
Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2017-11-29Bibliographically approved
2. Lipid-soluble conjugates of hydroxylated polybrominated diphenyl ethers in blue mussels from the Baltic Sea
Open this publication in new window or tab >>Lipid-soluble conjugates of hydroxylated polybrominated diphenyl ethers in blue mussels from the Baltic Sea
2014 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 21, no 2, p. 954-961Article in journal (Refereed) Published
Abstract [en]

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) of proposed natural origin have been detected throughout the food web of the Baltic Sea. Some OH-PBDEs have been shown to disrupt oxidative phosphorylation and the thyroid hormone system in exposed organisms. This paper describes an investigation into the fate of OH-PBDEs in the Baltic Sea's predominant specie, the blue mussel. The main focus was on the conjugation of OH-PBDEs with lipophilic moieties (e.g., fatty acids) and the potential role this transformation mechanism may have in heavily exposed mussels in nature. Analytical methods were developed to accurately determine the concentrations of these conjugates in blue mussels collected on different occasions during the summer in a coastal area of the Baltic proper. The measured concentrations of conjugated OH-PBDEs were compared to those of the unconjugated parent compounds, and it was found that in some cases, the levels of the conjugated derivatives can be equal or even higher than the levels of the unconjugated OH-PBDEs. This is, to our knowledge, the first study on lipid-soluble OH-PBDE conjugates, and the first study to investigate the occurrence of such conjugates of halogenated phenolic compounds in environmentally exposed mussels. The mussels were also found to contain hydrolysable water-soluble derivatives of OH-PBDEs (such as e.g., glucuronic acid and/or sulfate conjugates etc.). These were tentatively determined to be of lower concentration (by up to an order of magnitude) than that of the OH-PBDEs which were conjugated with lipophilic moieties.

Keywords
Analysis, Conjugates, Detoxification, Fatty acid esters, Halogenated phenols, OH-PBDE, Transesterification
National Category
Earth and Related Environmental Sciences Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-100380 (URN)10.1007/s11356-013-1962-9 (DOI)000329243700014 ()
Note

AuthorCount:3;

Available from: 2014-02-04 Created: 2014-02-03 Last updated: 2017-12-06Bibliographically approved
3. Trophic transfer of naturally produced brominated aromatic compounds in a Baltic Sea food chain
Open this publication in new window or tab >>Trophic transfer of naturally produced brominated aromatic compounds in a Baltic Sea food chain
Show others...
2016 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 144, p. 1597-1604Article in journal (Refereed) Published
Abstract [en]

Brominated aromatic compounds (BACs) are widely distributed in the marine environment. Some of these compounds are highly toxic, such as certain hydroxylated polybrominated diphenyl ethers (OH-PBDEs). In addition to anthropogenic emissions through use of BACs as e.g. flame retardants, BACs are natural products formed by marine organisms such as algae, sponges, and cyanobacteria. Little is known of the transfer of BACs from natural producers and further up in the trophic food chain. In this study it was observed that total sum of methoxylated polybrominated diphenyl ethers (MeO-PBDEs) and OH-PBDEs increased in concentration from the filamentous red alga Ceramium tenuicorne, via Gammarus sp. and three-spined stickleback (Gasterosteus aculeatus) to perch (Perca fluviatilis). The MeO-PBDEs, which were expected to bioaccumulate, increased in concentration accordingly up to perch, where the levels suddenly dropped dramatically. The opposite pattern was observed for OH-PBDEs, where the concentration exhibited a general trend of decline up the food web, but increased in perch, indicating metabolic demethylation of MeO-PBDEs. Debromination was also indicated to occur when progressing through the food chain resulting in high levels of tetra-brominated MeO-PBDE and OH-PBDE congeners in fish, while some penta- and hexa-brominated congeners were observed to be the dominant products in the alga. As it has been shown that OH-PBDEs are potent disruptors of oxidative phosphorylation and that mixtures of different congener may act synergistically in terms of this toxic mode of action, the high levels of OH-PBDEs detected in perch in this study warrants further investigation into potential effects of these compounds on Baltic wildlife, and monitoring of their levels.

Keywords
Natural production, Chemical pollutant, Bromophenols, Trophic transfer, Bioaccumulation, Baltic Sea
National Category
Earth and Related Environmental Sciences Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-126880 (URN)10.1016/j.chemosphere.2015.10.024 (DOI)000367774400202 ()26517387 (PubMedID)
Available from: 2016-02-22 Created: 2016-02-16 Last updated: 2017-11-30Bibliographically approved
4. Determination of hydroxylated polybrominated diphenyl ethers in blood from Baltic grey seals
Open this publication in new window or tab >>Determination of hydroxylated polybrominated diphenyl ethers in blood from Baltic grey seals
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-135594 (URN)
Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2016-11-24Bibliographically approved

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