Elin Dahlgren, Department of Environmental Science and Analytical Chemistry, Stockholm University
Elin Dahlgren, Department of Environmental Science and Analytical Chemistry, Stockholm University

How would you describe your project in a few sentences?

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. Little is known of the causes for this production or the transfer from natural producers and further up in the food chain. In my project, I study production of BACs by the filamentous red alga Ceramium tenuicorne. Through field studies and laboratory experiments, underlying causes of BAC production, seasonal variations and trophic transfer has been investigated.

What are your most important results, and for whom are they particularly useful?

Through my studies, I have been able to demonstrate natural production of methoxylated polybrominated diphenyl ethers (MeOPBDEs), hydroxylated polybrominated diphenyl ethers (OHPBDEs) and brominated phenols (BPs) in C. tenuicorne, grown in a controlled laboratory setting as well in field collected algal material. The identified substances displayed large seasonal variations in the alga, with a concentration peak in July. Based on three replicates, herbivory, as well as elevated levels of light and salinity in the culture medium, significantly increased the production of 2,4,6-tribromophenol (2,4,6-TBP).

Study on trophic transfer of BACs in the Stockholm archipelago, provided evidence for bioaccumulation of naturally produced ΣMeO/OH-PBDEs, in particular the toxic 6-OH-BDE47, from C. 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 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.

How can it assist an ecosystem-based management of the marine environment?

The intensive outbursts of toxic brominated aromatic compounds by filamentous algae during the summer season, add to already high loads of anthropogenic outputs in the Baltic Sea and may have severe consequences on the marine environment. As demonstrated by my research, production by the algae can be induced by external factors, and in order to predict future emissions, it is important to understand the cause of this production. The ongoing eutrophication of the Baltic Sea may in several ways promote the emissions of naturally produced BACs. Firstly, the amounts of fast-growing filamentous, opportunistic species, such as C. tenuicorne, increase in response to enrichment with nitrogen and phosphorus. Secondly, the effects of eutrophication provide a stressful environment for many marine organisms, due to factors such as nutrient availability or competition for resources such as light and/or space.

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 high up in the trophic food chain, warrants further investigation into potential effects of these compounds on Baltic wildlife, and monitoring of their levels.

Project collaborators:

Henrik Dahlgren (Naturhistoriska riksmuseet), Lillemor Asplund (Stockholms universitet), Dennis Lindqvist (Stockholms universitet), Kari Lehtilä (Södertörns högskola).