IN-SITU MONITORING OF DREDGED MATERIAL SPOIL SITES USING THE OYSTER CRASSOSTREA-VIRGINICA

In situ and laboratory bioassays using the eastern oyster, Crassostrea virginica, were undertaken in the Wright River Estuary, South Carolin a, to determine the toxic potential of effluent and sediment from rece ntly dredged sediments. Current standards (ASTM, USEPA, and USAGE) rel y solely on laboratory-based bioassays to assess toxicity of dredge sp oils prior to disposal. These bioassays do not necessarily replicate t he natural physicochemical estuarine processes, limiting the environme ntal realism of this approach. In this study, oysters were collected f rom a site on Leadenwah Creek (SC) and deployed in plastic cages ancho red above the sediment and within the intertidal zone for 90 days at f our dredge spoil disposal areas (18 sites total, one bushel/site). Oys ters were also deployed at a reference site (New River Estuary, SC) an d the original collection site. Trace metals and polycyclic aromatic h ydrocarbons (PAHs) in tissue, sediment, and effluent samples as well a s the assessment of oyster health in adults (% mortality and % reducti on in potential yield) and larvae; (larval development) were measured. Results indicated high arsenic concentrations in surface water sample s (<10 to 147 mu g/L), some of which exceeded the USEPA chronic marine water quality criteria and sediment concentrations (<1.0-82.2 mg/kg), which also exceeded the ERM (70 mg/kg) and the ERL (8.2 mg/kg) for ar senic, and which may have contributed to the toxic response seen in de ployed oysters. A positive relationship was also seen between the in s itu percent reduction in potential yield and laboratory-derived data f rom larval oyster development bioassays. The advantage of the combined in situ/laboratory approach used in this study is the ability to reso lve probable factors influencing the toxicity of these effluents to oy sters.