Evaluation of temporal and age-related trends of chemically and biologically generated 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents in lake Ontario lake trout, 1977 to 1993

Levels of selected non‐, mono‐, and di‐ortho‐substituted polychlorinated biphenyl (PCB) congeners, polychlorinated dibenzo‐p‐dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) were determined in 4‐year‐old lake trout from the eastern basin of Lake Ontario, collected from 1977 to 1993. Results confirm that overall levels of contaminants have decreased steadily in lake trout since 1977, and that coplanar PCB levels do not appear to be increasing over time in relation to levels of other PCBs. Contaminant levels in lake trout from 3 to 9 years old, collected in 1988 from the western end of Lake Ontario, show the body burden of contaminants increases with age. Relative levels of coplanar PCBs to other PCBs for the age study samples showed no change, except for PCB 77, which exhibited a slight decrease in relation to total PCB levels. Toxic equivalents (TEQs) were calculated from fish contaminant concentrations measured for the time study using toxic equivalence factors (TEFs) from both mammalian and teleost studies. The relative contributions of PCBs, PCDDs, and PCDFs to total TEQs were examined. When TEFs used for risk assessment are applied to temporal trend data, 15 to 20% of the total TEQs were due to mono‐ortho‐substituted PCBs; 40 to 50% to non‐ortho coplanar PCBs; and 20 to 30% to 2,3,7,8‐substituted PCDD and PCDFs. The TEQs determined from lake trout extracts by an H4IIE cell bioassay technique are compared to those determined by chemical analyses, using a variety of TEFs.