Publication Summary

The Washington State Department of Ecology has been developing criteria and testing procedures for several freshwater sediment contaminants. Copper, a metal highly toxic to aquatic life, is the focus of this study. Sediment copper levels exceed 1,000 mg/kg, dry weight in Steilacoom Lake, a shallow, eutrophic lake in Pierce County. The primary source of the metal in the sediments is many years of application of the algicide, copper sulfate. Three separate approaches were tested to determine the effects of copper on Steilacoom Lake: triad, acid volatile sulfide, and "battery of tests."

The Washington State Department of Ecology has been developing criteria and testing procedures for several freshwater sediment contaminants. Copper, a metal highly toxic to aquatic life, is the focus of this study. Sediment copper levels exceed 1,000 mg/kg, dry weight in Steilacoom Lake, a shallow, eutrophic lake in Pierce County. The primary source of the metal in the sediments is many years of application of the algicide, copper sulfate. Three separate approaches were tested to determine the effects of copper on Steilacoom Lake: triad, acid volatile sulfide, and "battery of tests."

Sediment samples were collected in Steilacoom Lake for metals analyses, bioassays, and benthic macroinvertebrate identification and enumeration. Bioassays included Daphnia magna, Hyalella azteca, Hexagenia limbata, Chironomus tentans, Microtox®, microbial enzymes, Ceriodaphnia dubia and ostracods. Benthic samples were identified to the genus and, if possible, species level. Black Lake, with little history of copper treatment, provided reference sediment.

Sediment copper levels in Steilacoom Lake ranged from 180 to 1100 mg/kg, dry weight. Hyalella (acute) and Hexagenia (acute) bioassays showed significant response. Microbial enzyme tests showed reduced activity with increasing contaminant concentrations. Interpretation of benthic invertebrate data was inconclusive due to variation among replicate samples. The benthic organisms in Steilacoom Lake are all pollution-tolerant. Acid volatile sulfide, a possible normalizing factor for metal toxicity, was not a controlling factor for copper. Black Lake was a poor reference because of dearth of benthic diversity and the presence of unidentified toxic compounds in the sediment.