Food Web Magnification of Persistent Organic Pollutants in Poikilotherms and Homeotherms from the Barents Sea

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Abstract
Food web magnification of persistent organic pollutants (POPs) was determined for the Barents Sea food web using δ15N as a continuous variable for assessing trophic levels (TL). The food web investigated comprised zooplankton, ice fauna and fish (poikilotherms, TL 1.7−3.3), and seabirds and seals (homeotherms, TL 3.3−4.2), with zooplankton representing the lowest and glaucous gull the highest trophic level. Concentrations of lipophilic and persistent organochlorines were orders of magnitude higher in homeotherms than in poikilotherms. These compounds had significantly higher rates of increase per trophic level in homeotherms relative to poikilotherms, with the highest food web magnification factors (FWMFs) for cis-chlordane and p,p‘-DDE. Some compounds, such as trans-nonachlor and HCB, had similar rates of increase throughout the food web, whereas compounds that are more readily eliminated (γ-HCH) showed no relationship with trophic level. It is preferable to calculate FWMFs with regard to thermal groups, because the different energy requirements and biotransformation abilities between poikilotherms and homeotherms may give different rates of contaminant increase with trophic level. When biomagnification is compared between ecosystems, FWMFs are preferable to single predator−prey biomagnification factors. FWMFs represent a trophic level increase of contaminants that is average for the food chain rather than an increase for a specific predator−prey relationship. The Barents Sea FWMFs were generally comparable to those determined for marine food webs with similar food chain lengths in the Canadian Arctic.