Fallout plutonium in two oxic‐anoxic environments1

Abstract

The profiles of soluble fallout plutonium in two partially anoxic waters revealed minimum concentrations at the O2‐H2S interface, indicating Pu removal onto particulate phases of Fe and other oxidized species that form during the redox cycle. In Saanich Inlet, an intermittently anoxic fjord in Vancouver Island, Canada, the concentration of soluble Pu in the anoxic zone was slightly less than in the oxygenated surface layer. In Soap Lake, a saline meromictic lake in eastern Washington State, Pu concentrations in the permanently anoxic zone were at least an order of magnitude higher than at the surface. Differences in the chemical characteristics of these two waters suggest important chemical species that influenced the observed Pu distribution. In the permanently anoxic zone of Soap Lake, high values of total alkalinity ranging from 940 to 1,500 meq liter−1, sulfide species from 38 to 128 µM, dissolved organic carbon from 163 to 237 mg liter−1, and total dissolved solids from 80 to 140 ppt, all correlated with the observed high concentration of Pu. In Saanich Inlet, where total alkalinity ranged from 2.1 to 2.4 meq liter−1 and salinity from 25 to 32‰ and H2S concentration in May 1981 showed a maximum of 8 µM, the observed Pu concentrations were significantly lower than for the Soap Lake monimolimnion.