Radium-226 in cattails, Typha latifolia, and bone of muskrat, Ondatra zibethica (L.), from a watershed with uranium tailings near the city of Elliot Lake, Canada

Abstract

Radium-226 concentrations were measured in the main food plants (cattails, Typha latifolia) and bone of adult muskrats ( Ondatra zibethica (L.)), taken from a study area near Quirke Lake in the Serpent River drainage basin. This watershed receives drainage containing radionuclides from the U tailings near the City of Elliot Lake, Ontario, Canada. Two control sites (one local, one 130 km distant) were also sampled. Radium-226 levels in cattails varied by plant part and place of collection. Roots sampled in the study area had the highest mean 226Ra level (1135.0 mBq g −1), stems and leaves had 284.2 and 275.9 mBq g −1, respectively (dry-weight basis, n = 6 in all cases). Local and distant control cattails carried much lower 226Ra levels (20.2 and 15.2 mBq g −1 dry weight, respectively, using pooled equal portions of all plant parts, n = 3 in both cases). Muskrats from waters with mean total 226Ra levels in the period, 1984–1987 greater than 75.0 mBq litre −1 (‘study-high’ sites), near U tailings within 10 km of Quirke Lake, had a mean (geometric) bone level of 226Ra of 344.9 mBq g −1 (dry-weight basis, n = 36); those from nearby waters, containing < 75.0 mBq litre −1 of 226Ra (‘study-low’ sites), had a mean bone level (80.3 mBq g −1, n = 9) similar to animals taken in unaffected local control areas 20 km from the tailings (79.1 mBq g −1, n = 12); animals from the distant control area, near Sudbury, Ontario, had the lowest mean burden (11.5 mBq g −1, n = 24). Levels were unrelated to age or sex of the animals. Dry-weight based 226Ra concentration ratios (bone concentration/plant tissue concentration) were calculated to range from 0.3–1.4 in the study-high area to 2.4–6.3 in the local control area. Wet-weight based concentration ratios were about 4.3 times higher. Concentration ratios were similar to values calculated for other species and in general agreement with values calculated for humans. The muskrat is judged to be a useful indicator (biomonitor) of environmental 226Ra levels as there is a highly significant positive correlation coefficient ( r = 0.74) between bone and ambient (water) concentrations of the radionuclide ( F 79 = 95.04, P < 0.0001) Estimated yearly 226Ra intake by people eating muskrats was calculated to be below the current allowable level set by Canadian regulatory authorities.