An ecological risk assessment of the effects of polychlorinated biphenyl, dibenzo-p-dioxin, and dibenzofuran congeners on the survival of the early life stages of lake trout (Salvelinus namaycush) in Lake Ontario

The objective of this study was to conduct an ecological risk assessment to determine if concentrations of 11 congeners of polychlorinated biphenyl, dibenzo-p-dioxin, and dibenzofuran present in Lake Ontario have been or are a risk to the survival of the early life stages of lake trout from 1930 to 1999. Concentrations of the 11 congeners in the eggs of lake trout were determined using chemical fate and bioaccumulation modelling. Model results were partially validated against observed concentrations in lake trout from 1977 to 1993. Toxic equivalent concentrations (TEQs) of 2,3,7,8-tetrachlorodibenzo-p-dioxin were determined for the concentrations of the 11 congeners in the eggs. These toxic equivalent concentrations were then used to determine mortality in the early life stages of lake trout resulting from contamination of the eggs by the 11 congeners. Risk was determined as the probability that the eggs of lake trout would experience concentrations that resulted in 95 percent mortality. This risk was determined by taking into account discrepancies between observed and predicted concentrations of the congeners in adult lake trout. Based on an endpoint of mortality, the results indicate that the 11 congeners were a very high risk to the early life stages of lake trout in the past but since 1981 have played little to no role in inhibiting the survival of the early life stages of lake trout. Of the 11 congeners, the congeners that contributed the most to risk over time were 3,3...