PARENT SESSION

1J - Bioaccumulation
Hall 9
10:45 AM - 12:30 PM, Wednesday, 30 April 2003
Chair: Tarazona, J.¹, ¹
Co-chair: Gobas, F.², ²

(WE9/6) Predictable Trophic Transfer of POPs and Mercury in Lake Trout Food Webs.

Muir, Derek¹, Evans, Marlene², Kidd, Karen³, Drouillard, Ken⁴, Guildford, Stephanie⁵, Fairchild, Wayne⁶, Whittle, Mike⁷, Wang, Xiaowa¹, ¹ National Water Research Institute, Burlington, ON² National Water Research Institute, Saskatoon, SK³ Freshwater Institute, Winnipeg, MB⁴ University of Windsor, Windsor, ON⁵ University of Waterloo, Waterloo, ON⁶ Dept of Fisheries and Oceans, Moncton, NB⁷ Dept of Fisheries and Oceans, Burlington, ON

ABSTRACT- Variability among lakes in the concentrations of persistent organic pollutants (POPs) and mercury in fish has been attributed to food chain and trophic status of the lake as well as to age, lipid content, size, of the fish. In this study whole fish samples of lake trout and brook trout their prey collected in 1999-2001 from lakes in New Brunswick, southern Ontario and northern New York state, northwestern Ontario, Saskatchewan, and Alberta, were analysed for PCBs, and other POPs as well as stable isotope ratios of C and N (to determine trophic positioning). Muscle samples from the same fish were analysed for Hg while invertebrates were analysed for methyl Hg. The main objective was to examine, on a large spatial scale, the physical, chemical and biological factors that predict concentrations of POPs and Hg in top predator fish. Concentrations of PCBs and Hg in food webs of each lake were strongly correlated with ¹⁵N in each sample. Food web biomagnification factors (FWMF) based on lake trout, forage fish and invertebrate were calculated for 18 lakes by regressing log transformed concentrations against ¹⁵N. FWMFs for PCBs and Hg varied over a relatively narrow range from 1.1-2.0 and from 1.5-2.0, respectively. These FWMFs were similar to other values reported for the Great Lakes and subarctic lakes indicating the rates of bioaccumulation are similar over a wide range of lake sizes, temperature and other factors. Concentrations of PCB in lake trout, as well as FWMFs for PCB, were positively correlated with proportions of the algae Peridineae and negatively related to phytoplankton biomass. Length adjusted Hg concentrations in lake trout were negatively related to particulate carbon and nitrogen and while Hg FWMFs were weakly correlated with % chryptophycea but not significantly with biomass or with particulate carbon or phorphorus. These results suggest that rates of Hg biomagnification in the food web are relatively unaffected by nutrient conditions and phytoplankton composition, unlike the results for POPs.

Key words: mercury, POPs, biomagnification, lakes