Biological Testing of Solid Phase and Suspended Phase Dredged Material from Commencement Bay, Tacoma, Washington

Abstract : Sediments from nine sites in Blair and Sitcum Waterways, Commencement Bay, Tacoma, Washington, were tested for potential acute chemical toxicity using chinook salmon smolts, Pacific oyster larvae, and phoxocephalid amphipods. Survival of salmon smolts was not affected by 96 hr exposure to elutriates of up to one part per thousand by volume from 5 sites. Oyster larvae developed abnormal shells following 48 hr exposure using undiluted water drained from defrosted sediment from 4 sites, but were not affected by 1:5 dilutions of artificially prepared elutriates. Two hundred four hr exposure to sediments from each of the nine sites neither decreased survival of amphipods nor altered the time spent in the sediment or the amphipod's ability to rebury in sand. Ammonia- nitrogen concentrations in artificially prepared 1:5 elutriates at ambient pHs would be potentially toxic to salmonids and other fishes; therefore dredging methods that dilute the elutriate are recommended. An elutriate dilution of 1:1000 was shown to be safe; elutriate concentrations greater than 1:1000 could be toxic to salmonids and other fishes. Amphipod bioassays should not be used to assess potential chemical toxicity of dredged sediments until further research clarifies confounding factors such as anoxia and starvation. Additional keywords: Water quality.