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SUSTAINABILITY: A GLOBAL DILEMMA

For drinking water consumption, an urban exposure scenario is the most common situation expected to arise as 77% of Canadians live in cities (Statistics Canada 1993) and 82% of these urban dwellers receive treated water supplies, mostly from surface water sources A concentration of 0.2 µg/L was used as the typical uranium level in Canadian drinking water, based on a survey of uranium in drinking water (n=258) collected between 1998 to 2002 from 129 lake and river water treatment plants under the Ontario Drinking Water Surveillance Program (P. Cheung, Ontario MOE, pers. comm.). Slightly higher uranium concentrations were reported for drinking water from groundwater sources in Quebec (geometric means ranging from 0.35 to 0.97 µg/L), and the Yukon (up to 7.2 µg/L) (E. Bergsam, Yukon Department of Environmental Health, pers. comm.). However, the Quebec water samples are dated (sampled between 1974 and 1982) and the Yukon data set contained relatively few samples (n=18). In addition, both data sets were limited by high detection limits. A background soil concentration of uranium of 2 mg/kg was assumed, both for purpose of deriving estimated daily (background) intake from soil, and as the starting point for the derivation of the hypothetical soil quality guidelines derived herein. This concentration is reflective of the uranium concentration measured in background soils collected in Ontario and New Brunswick (Gordon, 1992; OMEE, 1993; Pilgrim and Schroeder, 1997;. As noted above, soil concentrations of uranium vary according to local geology. Although no single soil concentration can adequately represent the variance in background soil concentrations across Canada (Painter et al., 1994), it is also essential to define a reasonable value for purpose of generic, national guidelines development. Refer to Table 5 for more details on background uranium concentrations in Canadian soils. The total daily uranium intake via food was calculated using food intake rates for various age groups of Canadians (Table 15) and mean concentrations for 238-uranium determined in the 2001 UK Total Diet Study (Table 7). No Canadian food concentration data were located in the literature reviewed. However, given the similarities between the UK (238-U) and Ottawa (total U) adult dietary intakes, it was considered reasonable to assume that the UK data were applicable to Canada. Consumption of cereals-grains, sugar-sweets, and meat-poultry-eggs contributed the greatest to uranium exposure (in decreasing order) for all age groups