Summary

Description

The purpose of these studies was to determine the potential for interactions between thiamine deficiency and polychlorinated biphenyl PCBinduced toxicity on the development of lake trout embryos and fry. The potential interaction between thiamine deficiency and PCBinduced toxicity is important to the Green BayFox River NRDA because, if it is true, lake trout in Lake Michigan may be more susceptible than hatcheryreared stocks. As a result, the injury to lake trout populations from the PCBs and other dioxinlike compounds released into the Fox River and subsequently into Green Bay, may have been greater than expected from laboratory studies. The experiments reported here were an extension of the studies conducted in 19961997. Technical difficulties during the course of those studies made interpretation of the results for the injury determination impossible. So, the studies in the current report were again designed to test the hypothesis of an interaction between low thiamine content and elevated PCB content in lake trout fry mortality. Eggs from lake trout containing high or low thiamine were injected with graded doses of a dioxinlike PCBs PCB 126, 2,3,7,8tetrachlorodibenzopdioxin TCDD, or a PCBcontaining extract of walleye from the Fox River. Thiamine and the contaminant concentrations were measured for the treatments. The survival and development of the lake trout were monitored through swimup. The symptoms of PCBinduced toxicity in the sac fry hemorrhage, yolksac edema, and craniofacial anomalies were monitored between hatch and swimup stages of the lake trout. Dose related increases in fry mortality were observed with PCB 126 3,3,4,4,5pentachlorobiphenyl and the median toxicity values obtained in our studies 20 and 27 ngg egg confirm the one study from the literature. The complex mixture of organic chemicals extracted from the Fox River walleye caused dioxinlike toxicity in early life stages of lake trout. The greatest dose tested 157 pg TEQsg caused deformities in all of the fry and nearly complete mortality. The next lower dose of the walleye extract 15 pg TEQsg caused increases in deformities and mortality in some groups, but the increases were not statistically significant. This dose appears to be just below the threshold for dioxinlike toxicity for lake trout fry survival, which is again consistent with the literature. The result of the injection studies with the walleye extract are also consistent with an additive model of toxicity, and support the continued use of the TEFTEQ approach for assessment of dioxinlike effects in developing lake trout. These studies confirmed that the lake trout is one of the most sensitive species toward the adverse effects of dioxinlike chemicals, including PCBs. However, these studies failed to support our original hypothesis that low thiamine status in lake trout eggs would further enhance the sensitivity of this species toward dioxinlike toxicity. The data did not support the contention that low thiamine content in lake trout embryos and fry might exacerbate the effects of PCBs or dioxins on fry survival. Various technical factors compromised the studies and a rigorous test of the hypothesis was not possible.