Radium-226 in water, sediments, and fish from lakes near the city of Elliot Lake, Ontario, Canada

Abstract

Ra-226 was measured by α-emission spectroscopy in water, sediments, and fish (tissues and gut contents), from five lakes in a watershed containing U mining and milling operations at Elliot Lake, Ontario, and from control lakes in an adjacent non-industrialized watershed. Ra-226 transfer parameters from lake water and sediments to fish tissues, and annual intakes by humans consuming fish, were estimated. Mean dissolved 226Ra levels ranged from ∼76 mBq litre −1 in water of the most affected lake, to < 10 mBq litre −1 in control lakes. Levels in summer were consistently higher than in fall or winter; no consistent variation with depth was noted. Sediment levels ranged from ∼3000 mBq g −1 dry wt in one study lake to < 100 mBq g −1 dry wt of sediment in control lakes. Bone 226Ra concentrations were higher than in muscle. The lake trout ( Salvelinus namaycush), a predatory secondary consumer, had bone 226Ra levels (< 20 mBq g −1 dry wt) that did not show significant site variation. In contrast, bottom feeding whitefish had significantly more 226Ra in bone tissue (to 38 mBq g −1 dry wt in the lake whitefish, Coregonus clupeaformis, and 76 mBq g −1 in round whitefish, Prosopium cylindraceum) in study lakes than in controls (< 20 mBq g −1 dry wt). Ra-226 levels in lake trout muscle were low and showed erratic variation among lakes whereas levels in whitefish muscle did not vary significantly among study and control sites. Lake herring (= cisco, Coregonus artedii), a planktivorous fish taken only from Quirke Lake, had mean 226Ra levels of 18 and 1.4 mBq g −1 dry wt in bone and muscle, respectively. Gut 226Ra levels, highest in lake trout from McCabe and Quirke Lakes (126 ± 53, 64 ± 44 mBq g −1 dry wt, respectively), and just detectable in McCabe and Elliot Lake whitefish (24 ± 2, 36 ± 14 mBq g −1 dry wt, respectively), were below detection in lake trout and whitefish from other lakes. Concentration ratios (CRs) of 226Ra from water to muscle ranged from 8 to 14 in lake trout, 7 to 14 in whitefish, and 4 to 6 in lake herring. The water to bone CRs varied from 81 to 142, 314 to 548, and 126 to 272 in the same species. CRs were always < 1 between sediments and fish tissues. Annual intake of 226Ra by human consumers of these fish was estimated to provide an effective dose of 0.003 mSv year −1. This represents a small fraction of both natural background (> 2 mSv year −1) and the public dose limit (5 mSv year −1).