Fish and fish-eating wildlife are exposed to a number of contaminants in their diets that affect endocrine system function and their survival, growth and reproduction. Some contaminants concentrate (or biomagnify) up through food webs to levels that threaten the health of top predators. Predicting the types of contaminants that will biomagnify through food webs and the concentrations in at-risk predators remains a challenge because results from lab studies do not always reflect processes occurring in the environment. A newer approach is being used to understand and contrast the fate of contaminants across diverse ecosystems. Trophic magnification factors (TMFs) represent the average biomagnification of contaminants through entire food webs, rather than the individual species metrics that are highly variable from one predator-prey combination to another. TMFs are calculated from the slope of logarithmically transformed concentrations of contaminants in organisms versus their trophic level in the food web; the latter is often calculated from stable nitrogen isotope ratios. This approach is being used increasingly to understand whether persistent chemicals like mercury, PCBs, and flame retardants biomagnify at a comparable rate across diverse systems (i.e. lakes, rivers, oceans). Despite the potential for TMFs to be used for broader comparisons, there are some assumptions and limitations of this approach, as well as several considerations when designing the study and analyzing the data. Interspecies and intrinsic ecological and organismal properties, such as thermoregulation, reproductive status, migration, and age - particularly among species at higher trophic levels with high contaminant concentrations - can influence the calculation of TMFs (i.e. regression slopes). Sensitivity analyses indicate that these relationships are also affected by unbalanced study designs. This presentation will review the current understanding and applications of TMFs in aquatic systems and identify areas for further research.

Keywords: Persistent contaminants; Food webs; Trophic magnification; Aquatic ecosystems

Biography: Karen Kidd is a Canada Research Chair and Professor of Biology at the University of New Brunswick in Saint John, New Brunswick, Canada. Her research is on understanding the effects of municipal and industrial effluents, aquaculture and agricultural runoff on fish and invertebrate populations and food web structure of lakes, wetlands and rivers, and on the factors affecting accumulation of persistent contaminants such as chlorinated pesticides and mercury through freshwater communities in tropical through arctic systems.