Biomagnification and bioaccumulation of mercury in an arctic marine food web: insights from stable nitrogen isotope analysis

Abstract

Several recent studies have shown that the use of delta 15 N analysis to characterize trophic relationships can be useful for tracing biocontaminants in food webs. In this study, concentration of total mercury was measured in tissues from 112 individuals representing 27 species from the arctic marine food web of Lancaster Sound, Northwest Territories. Samples ranged from particulate organic matter through polar bears (Ursus maritimus). Using delta 15 N values to identify trophic position, we found that total mercury in muscle tissue biomagnified in this food web. Polar bears were a notable exception, having a lower mean mercury concentration than their main prey, ringed seals (Phoca hispida). Most vertebrates showed greater variance in mercury concentration than invertebrates, and there was a trend in seabirds toward increased variability in mercury concentration with trophic position. Within species, we found no evidence of bioaccumulation of mercury with age in the muscle tissue of clams (Mya truncata) or ringed seals. Because stable nitrogen isotopes illustrated the relationship in this biome between trophic position and mercury level on a continuous, quantitative scale, we were able to determine that log 10 [Hg] ( µg/g dry weight) = 0.2( delta 15 N) - 3.3. The measurement of delta 15 N values and mercury concentration allowed us to quantitatively assess mercury biomagnification within this extensive arctic marine food web.