Åge Oterhals a Marianne Solvang a Ragnar Nortvedt b Marc H. G. Berntssen c a Norwegian Institute of Fisheries and Aquaculture Research Dept Bergen, Fyllingsdalen, Norway b Applied & Industrial Biology, Department of Biology, University of Bergen, Bergen, Norway c NIFES, Bergen, Norway Optimization of activated carbon-based decontamination of fish oil by response surface methodology The effect of activated carbon (AC) adsorption on the reduction of persistent organic pollutants (POP) in fish oil was studied based on response surface meth- odology at a 5-g/kg AC inclusion level. Pretreatment of the oil by alkali refining and bleaching increased the POP levels. The tested process variables (contact time and temperature) affected the AC adsorption rate and significant first- and sec- ond-order response models could be established. Polychlorinated dibenzo-p- dioxins and dibenzofurans (PCDD/F) showed a very rapid adsorption behavior and the concentration and toxic equivalent (TEQ) level could be reduced by 99%. Adsorption of dioxin-like polychlorinated biphenyls (DL-PCB) was less effective and depended on ortho substitution, i.e. non-ortho PCB were adsorbed more effectively than mono-ortho PCB with a maximum of 87 and 21% reduction, respectively, corresponding to a DL-PCB-TEQ reduction of 73%. A common opti- mum for both PCDD/F and DL-PCB adsorption could not be identified. AC treat- ment had no effect on the level of polybrominated diphenyl ether flame retardants. The differences in adsorption patterns may be explained based on molecular conformation. No change in oil quality could be observed based on oxidation pa- rameters. Compliance with present PCDD/F and DL-PCB legislation levels in fish oil can be achieved based on AC adsorption. Keywords: Adsorption, dioxins, PCB, brominated flame retardants, persistent organic pollutants. Eur. J. Lipid Sci. Technol. 109 (2007) 691–705 DOI 10.1002/ejlt.200700083 691 1 Introduction Persistent organic pollutants (POP) are a complex group of toxic substances comprising a wide variety of industrial compounds and by-products such as flame retardants, dioxins, and polychlorinated biphenyls (PCB) [1]. POP are highly persistent and fat-soluble environmental pollutants that are ubiquitous in the marine ecosystem and are readily biomagnified in the food chain. POP relevant for human health include dioxins, dioxin-like PCB (DL-PCB) and brominated flame retardants [2–4]. The feed is the main source of POP in farmed animals and the European Commission implemented in July/August 2002 new leg- islation on dioxin and pesticide contents in feed ingre- dients and formulated feed [5, 6]. The feed, and corre- sponding foodstuff, legislation was amended in Novem- ber 2005 to also include maximum levels for the sum of dioxins and DL-PCB in addition to the present maximum levels for dioxins only [7, 8]. Among products intended for animal feed, the highest levels of undesirable organic pollutants are found in fish oil extracted from pelagic fish species [9]. In general, Eu- ropean fish stocks, and hence fish oil and meal derived from these fish species, are more contaminated than those from the South Pacific. The fish stocks of concern for the North European industry is sprat (Sprattus sprat- tus) and herring (Clupea harengus) in the Baltic Sea and herring, sprat, sand eel (Ammodytes tobianus and A. marinus) and blue whiting (Micromesistius poutassou) in the North Sea [10, 11]. The observed contamination levels are reflecting the general pollution level in the re- spective fishing areas and this will disfavor the North Eu- ropean fishmeal and fish oil producers on the world mar- ket. POP levels on fat basis will fluctuate with the seasonal variation in fat content [11]. The highest levels found in produced fish oil will coincide with the lowest fat content observed in the respective fish stocks, i.e. after the spawning period. The need for decontamination of commercially produced fish oil to comply with the present legislation will therefore depend on fishing area, fish stock and to which degree the fishing season coincides with the period of low fat content. Correspondence: Åge Oterhals, Norwegian Institute of Fisheries and Aquaculture Research Dept Bergen, Kjerreidviken 16, N- 5141 Fyllingsdalen, Norway. Phone: 147 55501274, Fax: 147 55501299, e-mail: aage.oterhals@fiskeriforskning.no  2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com Research Paper