2.4. Toxicity Assays for Year 2 



2.4. 1 . Ceriodaphnia dubia Survival / Reproduction Assays 



Procedures for the C. dubia survival/reproduction assays were the same as above using 

 porewaters from the sediments collected the second year of the study. 



2.4.2. Mussel Filtering Assay (MFA) 



A mussel filtering assay was used to assess chronic toxicity of the collected porewaters 

 in the second year of the study. The mussel filtering assay is based on the premise that the 

 ability of bivalves to filter particles from water is impaired by the presence of pollutants 

 (Anderson et al. 1978; Sparks etal. 1981; Aldridge et al 1987; Sparks and Sandusky 1983; 

 Sparks etal. 1992;). 



Filtering rates were determined by measuring the ability of native deertoe mussels 

 (Truncillo (runcata) to filter yeast from a suspension of known concentration. In this study, one 

 mussel was placed in each of five replicate 1000-ml beakers containing 500 ml test solution (i.e.. 

 porewaters or control solutions). Because of the limited amount of porewater collected from 

 Campbell's Slough, only three replicates were used. Mussels were exposed to porewaters and 

 control solution using a static-renewal procedure where porewaters and control solutions were 

 exchanged at 24 hours of exposure. The static-renewal procedure was used to prevent the build 

 up of metabolic wastes and the depletion of dissolved oxygen in replicate beakers. After 

 exposure, we tested individual mussels for filtering ability by placing them in a yeast suspension 

 (10 mg/L yeast in distilled water) and allowing them to filter for 4 h. The mussels were removed 

 from the beakers and rinsed with deionized water to remove any particulate matter. A "\ east 

 control" beaker consisting of 10 mg/L yeast suspension with no mussels was used to determine 



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