In-Situ Bioassays Using Transplanted Mussels: II. Assessing Contaminated Sediment at a Superfund Site in Puget Sound

Abstract

In a pilot study for the U.S. EPA, bioaccumulation and growth in mussels (Mytilus trossulus) were used to assess the bioavailability of contaminants and potentially adverse bioeffects in water overlying contaminated sediments. Caged juvenile and adult mussels were transplanted to 12 locations around a Super fund Site (Harbor Island), and a reference site (Carr Inlet) in Puget Sound, Washington. The exposure period was 82 days and animals were held 1 meter from the bottom. Accumulation of contaminants in adult mussel tissues was used to help identify the extent and magnitude of contamination in the overlying water. Reduced growth in juvenile mussels was used as an indicator of adverse bioeffects. Sites were ranked for these potentially adverse biological impacts. Juvenile mussel growth rates combined with toxicity-normalized sediment chemistry and toxicity-normalized tissue chemistry, provided a first-order approximation of potential biological effects associated with chemicals of concern in sediment and mussel tissues. Mussels from Harbor Island accumulated higher concentrations of contaminants and had significantly lower growth rates than the reference site mussels. Some differences were detected among the Harbor Island sites. Mussels from one site were much more contaminated than the others and, based on extremely low growth rates, exhibited the greatest potential for adverse biological effects. TBT and copper were the contaminants of greatest concern in both tissues and sediments; lead and zinc were an additional concern in sediments. A statistically significant inverse relationship was found between growth rate, toxicity-normalized tissue accumulation, and toxicity-normalized sediment contamination. Based on our results, we recommend the following integrated approach for evaluating contaminated sediments: (1) conduct in-situ bioassays, (2) estimate bioaccumulation in addition to bioeffects, and (3) evaluate water overlying the sediments.