AN ENVIRONMENTAL HAZARD EVALUATION OF URANIUM IN A ROCKY MOUNTAIN STREAM

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Abstract
Ur mining is an important industry in the Rocky Mountain region; little is known about the environmental hazards of Ur to fish and other aquatic organisms. Indian Creek, a hard-water stream (200 mg/l as CaCO3) near Gunnison, Colorado, receives periodic discharges of runoff from a Ur mine. Natural springs contribute Ur to the creek. As a result, Ur concentrations in the creek ranged up to 4 mg/l, concentrations potentially toxic to trout based on published toxicity data. A series of studies were conducted to analyze the potential toxicity and bioaccumulation of Ur in Indian Creek and downstream waters. A 60 day post-hatch, early life stage toxicity test was conducted with brook trout in water of hardness and alkalinity similar to Indian Creek. Additional tests were performed in soft and hard water (96 h acute toxicity tests) and in water of Indian Creek''s quality (48 h acute toxicity tests). Trout from the 60 day test were also analyzed for Ur bioaccumulation. To confirm the results of the laboratory studies, these data were compared with on-site field study data, including surveys of fish and benthic invertebrates, and analyses of U levels in trout. The laboratory results indicated that the high hardness and alkalinity of the test water greatly reduced the potential toxicity of Ur to trout. Concentrations etimated to be chronically toxic from the early life stage test were > 9 mg/l; 48 h LC50 was 59 mg/l. Bioconcentration factors for Ur were low, ranging from 1.9-4.3. Benthic invertebrate and fish studies conducted in Indian Creek confirmed that current Ur concentrations were not significantly toxic to resident aquatic biota. In-stream bioaccumulation of Ur was also low and was comparable to the laboratory-derived values. Laboratory toxicity and bioaccumulation tests accurately evaluated potential in-stream hazards of Ur. To accurately estimate in-stream toxicity and bioaccumulation of metals, it was important that laboratory tests simulated in-stream water quality.

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