Bioconcentration may be favoured over biomagnification for fish PCB contamination in high altitude lakes

Abstract

Cold aquatic ecosystems such as high altitude alpine lakes are expected to act as long-term sinks of polychlorinated biphenyls (PCBs), the burden of which might even be intensified by global warming. Because the physical, chemical, and biological structures of high altitude lakes are highly responsive to climate change, both PCB exposure and bioaccumulation are likely to be strongly altered in the near future. Yet, in the absence of mechanistic knowledge of the processes regulating fish contamination with PCB in such ecosystems, their fate cannot be predicted. The aim of this study was to investigate the relative roles of biomagnification and bioconcentration on the individual, seasonal, and between-site variability of fish PCB contamination in 2 alpine, high altitude lakes. The intra- and within-lake variability of fish PCBs was not related to differences in fish physiology (size, age, or lipid content) and only marginally tied to fish feeding habitats (assessed from fatty acid composition and δ13C) or trophic position (δ15N). These results suggested that the trophic pathway and biomagnification contributed little to the observed differences in fish PCB concentrations between lakes, seasons, and individuals. Moreover, the fish PCB levels did not depend on the total PCB concentration in the water, but the fish contamination dynamics during the spring thaw pointed to a significant role of dissolved PCBs during this season in both lakes. In high altitude lakes, low temperatures might contribute to kinetically limit equilibrium with dietary PCBs, thereafter favouring bioconcentration over biomagnification pathways by which fish become contaminated with PCBs.