Radionuclides (lead-210, polonium-210, thorium-230, and -232) and thorium and uranium in water, sediments, and fish from lakes near the city of Elliot Lake, Ontario, Canada

Abstract

Radionuclides ( 210Pb, 210Po, 230Th, and 232Th) and chemical Th and U were measured in water, sediments, and fish tissues (bone, muscle, and gut contents of laketrout, Salvelinus namaycush, whitefish, Coregonus clupeaformis and Prosopium cylindraceum) from four lakes in a watershed affected by U mining and milling operations at Elliot Lake, Ontario, and from control lakes in an adjacent, non-industrialized, watershed. Radionuclide concentration ratios between tissue levels and sediment and water levels were calculated. Annual radionuclide intakes and resulting doses were estimated for humans consuming fish from the watershed. Bone 210Pb levels were higher (186 mBq g −1 dry wt in laketrout and 230 mBq g −1 dry wt in one lake whitefish) than in muscle (< 50 mBq g −1 dry wt in all cases), and generally higher in fish from study lakes than from controls, but no consistent differences were observed among fish species. Similarly, 210Po levels were higher in bone (208 ± 33 mBq g −1, in laketrout) than muscle (maximum 26 ± 4 mBq g −1, in laketrout), and in study lake populations compared to controls. Laketrout 210Po bone concentrations were higher than previously reported in Canada. Levels of 230Th, 232Th, and Th were below detection limits (20 mBq g −1, 0.05 μg g −1) in body tissues in all fish species. Bone levels of U (14.6 ± 3.0 μg g −1, in lake whitefish) were higher than in muscle (most < 0.05 μg g −1, except 0.12 ± 0.04 and 0.08 ± 0.03 μg g −1 in lake whitefish) in fish from waters affected by industrial activity. In control lakes, bone and muscle levels were lower and not significantly different from each other. Muscle levels did not vary consistently with location. Concentration of 210Pb and U was seen from water and ‘gut’ material (taken as a surrogate for diet) to bone in laketrout and whitefish, and of U from water to muscle in whitefish, but in no case from sediments to tissues. Human intakes of 210Pb, 210Po, 230Th, 232Th, and U from consuming one meal of fish (375 g) per week could, in aggregate, represent an annual effective dose < 15% of the public dose limit (5 mSv). Monitoring biota living near the decommissioned Elliot Lake U operations, especially of 210Pb levels in fish muscle, with further assessment of human doses attributable to local fish and other animals in the diet, should continue. Because radionuclide effects on fish health (and on other non-human organisms) are of increasing concern, neoplasms, malformations, and reproductive anomalies in local fish deserve examination.