FROM GLASS TO SILVER EEL – BROMINATED FLAME RETARDANTS AND DECHLORANES IN EUROPEAN AND AMERICAN EELS Roxana Sühring 1 *, Jonathan Byer 2, 4 , Marko Freese 3 , Jan-Dag Pohlmann 3 , Hendrik Wolschke 1 , Axel Möller 1 , Renate Sturm 1 , Peter Hodson 2 , Mehran Alaee 4 , Reinhold Hanel 3 , Ralf Ebinghaus 1 1 Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Max-Planck-Strasse 1, 21502 Geesthacht, Germany 2 Queen's University, Kingston, Ontario, K7L3N6 Canada 3 Johann Heinrich von Thünen-Institut (vTI), Institute of Fisheries Ecology, Palmaille 9, 22767 Hamburg 4 Water Science and Technology Directorate, Environment Canada, Burlington, Ontario, L7R4A6 Introduction European eel (Anguilla anguilla) and American eel (Anguilla rostrata) are facultatively catadromous, carnivorous and during their continental phase benthic species with unique life cycles. They spawn in the Sargasso Sea, hatch and are transported as larvae by oceanic currents to the North African/European and American coasts, where they metamorphose into glass eels until they further develop to elvers and yellow eels. During their continental growth phase, eels build up large energy resources (body fat of ~30%). Prior to maturation and migration back to their spawning grounds, eels undergo a silvering process accompanied by drastic changes in the physiology including the degeneration of the alimentary tract. Stored fat is used to develop gonads and used as energy to make their way back to the Sargasso Sea to reproduce once and die 1 . European eels are of high economic value. However, the population has been declining rapidly since the 1980s 2,3 leading to its listing under Appendix II of CITES as well as on the Red List of species (IUCN), rating it as "critically endangered". A similar downward trend in American eel lead to the closure of commercial yellow eel fishery in Lake Ontario in 2004 and the rating “threatened” in Canada by COSEWIC in 2012. Chemical contaminants are postulated as one of the possible causes for the decline of freshwater eel populations since due to their high lipid contents 4,5 eels are predestined to take up large quantities of lipophilic organic pollutants. Halogenated flame retardants (HFRs) are a group of possibly harmful and accumulating organic contaminants. They are used in a variety of consumer products such as textiles, electronic equipment, plastics and furniture 6–8 . The largest group among the current use HFRs are brominated flame retardants (BFRs). For several decades polybrominated diphenyl ethers (PBDEs) were the most widely used BFRs 6 . However, due to their adverse effects to the environment and human health, PBDEs have been banned from production and usage in the European Union (EU) 9 , and are being voluntarily withdrawn or phased out in North America 10 . Congeners used in the technical Penta- and OctaBDE mixtures have been classified as Persistent Organic Pollutants (POPs) under the Stockholm Convention 11 . Government regulations require consumer products to meet certain demands for flame retardancy, which has led to the usage of substitutes such as alternate (non-PBDE) BFRs and chlorinated Dechloranes (Decs). There is little knowledge concerning production, usage or the POP potential of these substitutes for PBDEs yet many are suspected to at least partially fulfil the criteria 7 . The aim of this study was the comparison of concentrations and contamination patterns of PBDEs, alternate BFRs and Decs throughout the life cycle of European and American eels in order to identify the decisive factors for spatial and life cycle dependent distribution of halogenated flame retardants. Materials and methods One hundred European glass eels were purchased from a glass eel distributer, originally caught on the French Atlantic coast, and were combined into 10 samples. Data for adult European eels were presented in Sühring et al. 2012 12 . Gonads were sampled from silver eels and yellow eels from that study. Thirty-seven American glass eels from Baie des Sables, Matane, Quebec, Canada were pooled into three samples. Ten American yellow eel samples were taken each from Beauharnois Dam, Quebec, Canada and Moses-Saunders Dam, Cornwall,