Geochemical pathways and biological uptake of radium in small Canadian Shield lakes

The sediment-water interactions and biological uptake of 226Ra are described for four small Canadian Shield lakes at the Experimental Lakes Area, Kenora, Ontario. A single addition of 226Ra was made to each lake between 1970 and 1976. Approximately 90 percent of the added 226Ra initially sorbed to the sediments. Outflow from the lakes showed losses of only 5-11 percent 226Ra per year. Models are proposed for adsorption and outflow of 226Ra from lakes. Biological uptake and long-term 226Ra concentrations were measured in three species of macrophytes, crayfish, and five species of fish. Bioaccumulation ranged from 1100 to 5000 in macrophytes, 705 in crayfish, from 30 to 80 in large trout (Salvelinus namaycush), white sucker (Catostomus commersoni), and lake whitefish (Coregonus clupeaformis), and from 230 to 1200 in fathead minnows (Pimephales promelas), pearl dace (Semotilus margarita), and northern redbelly dace (Chrosomus eos). The concept of Ra/Ca ratio in organisms versus water and food is used to explain the differences in bioaccumulation. 226Ra is discriminated against versus calcium by fish but favoured by macrophytes and crayfish