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.
Using transplanted mussels as an in-situ bioassay to assess marine environmental quality has provided important information on bioavailability of contaminants and associated bioeffects that would not have been available with traditional chemical monitoring, biomonitoring, or laboratory bioassays. It is one of the most promising field bioassay systems because of the relative ease in making synoptic measurements of bioaccumulation and growth to estimate chemical exposure and bioeffects, respectively. In-situ field studies that utilize transplanted animals combine the advantages of environmental realism associated with field monitoring and experimental control associated with laboratory testing. Because they are sedentary and concentrate contaminants, resident mussels have been used extensively to estimate exposure by measuring contaminants in their tissues. The use of resident mussels as a response indicator has been very limited because of the difficulties associated with measuring biological processes and defining the exposure period in natural populations. Transplanting caged mussels facilitates measurements of bioeffects and clearly defines the exposure period. Data from a series of mussel (Mytilus galloprovincialis) transplants in San Diego Bay, California, demonstrate how this methodology can be used to assess the extent of contamination and associated biological effects. Although more than 18 sites were studied in nine separate transplants between 1987 and 1990, emphasis-will be placed on two sites in the Shelter Island Yacht Basin separated by only 3 meters vertical distance. The mussel field bioassay was used to identify the following: (1) site-specific differences, (2) temporal and spatial variability, (3) short-term and long-term trends, (4) potential sources of contamination, and (5) dose-response relationships.
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