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Acid-mine discharges from the Spring Creek drainage contribute large quantities of toxic copper, zinc, and cadmium to anadromous chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Salmo gairdneri) fisheries below Keswick Dam after regulated release with the Sacramento River, California. Release criteria and water quality objectives for the protection of salmonids from the metals in the waste have been developed using laboratory toxicity tests and field monitoring studies. These metal criteria and objectives were evaluated by on-site toxicity tests and additional monitoring studies.
Chinook salmon and steelhead trout fry were exposed to Spring Creek acid-mine waste in on-site toxicity tests. Acutely lethal concentrations of copper, zinc, and cadmium from the waste were similar to those from laboratory tests on metal sulfate mixtures, indicating that these metals are the major toxic components of the waste. Monitoring the waste in the Sacramento River after controlled dilution using criteria for copper and zinc indicated the following: (1) mean concentrations of the metals approached or exceeded incipient lethal levels (96-h LC10 values); (2) short-term (<5 out of 24 h) peak concentrations of copper, zinc, and cadmium in the Sacramento River exceeded median lethal levels (96-h LC50 values) under normal operating conditions; and (3) no measurable loss of copper from adsorption onto particulate matter and subsequent precipitation and deposition occurred when the waste was diluted to levels tolerable to fish. New criteria for zinc and new release schedules for the copper criteria that will protect against acutely lethal levels should be developed.
toxicity, salmonids, copper, zinc, cadmium, water quality objectives, field tests, acid-mine waste, aquatic toxicology
Environmental services supervisor, Aquatic Toxicology Laboratory, Elk Grove, CA
Environmental specialist, California Regional Water Quality Control Board, Central Valley Region, Redding, CA