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Uranium, in its pure form is a silvery-white, weakly radioactive metal. It is the heaviest of the naturally occurring elements and is present in the earth’s crust at an average concentration of 0.0003% (i.e., 3 parts per million or 3 mg/kg). Uranium is found in a variety of chemical forms in all soils, oceans, food, and drinking water (Bleise 2003). Uranium deposits have been reported across Canada, with several large mineral deposits containing uranium at concentrations greater than crustal abundance. The richest uranium deposit in the world is in northern Saskatchewan (Painter et al. 1994). Uranium occurs in 5 oxidation states (+2, +3, +4, +5, +6); however, only two oxidation states (+4, +6) are considered stable enough to be of practical importance (ATSDR 1999). The physical and chemical properties of uranium metal are summarized in Table 1. In the earth’s crust, uranium is generally found as oxides, such as uranium dioxide (UO2) or triuranium octaoxide (U3O8). The mineral pitchblende, the main uranium ore, consists primarily of uranium oxides. In soil, uranium is primarily (80-90%) present in the +6 oxidation state as the uranyl cation (UO2 2+) (Ebbs et al. 1998). Speciation of uranium in soil and aqueous systems is pH-dependent. Therefore, under acidic reducing conditions, UO2 2+ is the predominant uranium species in the soil; under neutral conditions, hydroxide complexes such as UO2OH+ , (UO2)2(OH)2 2+,(UO2)3(OH)5+ and (UO2)3(OH)7 – and phosphate complexes such as UO2HPO4 0 and UO2(HPO4)2 2- form; under alkaline conditions, carbonate complexes such as UO2CO3 0 , UO2(CO3)2 2- and UO2(CO3)3 4- predominate (Ebbs et al. 1998).