FATES OF METAL RADIOTRACERS ADDED TO A WHOLE LAKE - ACCUMULATION IN FATHEAD MINNOW (PIMEPHALES-PROMELAS) AND LAKE TROUT (SALVELINUS-NAMAYCUSH)

Six gamma-emitting isotopes, Se-75, Hg-203, Cs-134, Fe-59, Zn-65 and Co-60, were introduced simultaneously in a single epilimnetic addition to an oligotrophic lake on the Precambrian Shield of northwestern Ontario, Canada. Accumulation of each isotope was monitored in fathead minnow (Pimephales promelas) for 274 days. Isotope accumulation in blood, gill, gut, liver, kidney, spleen, gonad, brain, muscle and gut contents of lake trout (Salvelinus namaycush) was monitored for 352 days. Fish accumulated only traces of Fe-59. Isotopes which occurred in water primarily in the charcoal-extracted fraction (Se-75 and Zn-65) were most readily accumulated by fish. Fathead minnow accumulated higher concentrations of all isotopes than lake trout. In lake trout, the highest concentrations of isotopes were found in the following tissues: Se-75, liver; Hg-203 and Co-60, kidney; Cs-134, muscle; Zn-65, gut. Food seemed to be the primary source of all isotopes to fish. Ratios of isotope concentrations in fish to those in water were higher for both fathead minnow and lake trout than ratios reported from laboratory studies using aqueous exposures. Concentration ratios for Cs-134 in both fathead minnow and lake trout from oligotrophic Lake 224 were over an order of magnitude greater than published data for fish from eutrophic lakes.