The Arctic is considered an important area for mercury accumulation, because of long-range atmospheric transport and deposition. Following transformation to organic mercury (e.g. methylmercury, MeHg) the toxicity and bioaccumulative potential in Arctic biota is high. In the International Polar Year project "Contaminants in Polar Regions" (COPOL), the aim was inter alia to study how prospective climate changes may affect the dynamics of environmental contaminants in Arctic marine food chains.This aim was addressed by scrutinising bioaccumulation of contaminants across years, seasons and locations (i.e. locations affected by Arctic or Atlantic water masses). In the COPOL project we have shown that trophic magnification of lipid soluble organohalogen contaminants may vary across species, seasons and locations in an Arctic food web. The enrichment in organic contaminant concentrations from plankton to higher trophic organisms did, for instance, increase throughout the year, and the time for concentration peak differed between plankton, fish and birds, with a delay up through the food chain. In the present work, the food web biomagnification of mercury and methylmercury, and its comparability to organic halogens, was analysed.