ABSTRACT 

 The goal of this project was to determine whether Reach 15 of the Upper Mississippi 

 River contained any toxic sediments that would threaten the native mussel refuges within the 

 reach. Toxicity assays were conducted on porewaters collected from sediments of three sites of 

 Reach 15 during 1994 and 1995: near ALCOA, Sylvan Slough, and Campbell's Slough. 

 Ceriodaphnia dubia acute toxicity and survival/reproduction 7-day assays were performed on 

 porewaters of collected sediments in the first year. Results from the first year indicated 

 sediments collected from the ALCOA site were toxic. Work in the second year consisted of C. 

 dubia survival/reproduction 7-day assays and a mussel filtering assay (MFA) that measured 

 filtering rates of a native mussel, the deertoe (Truncilla truncata). In Year 2, chronic toxicity 

 was detected in sediments from Sylvan Slough and Campbell's Slough, but not in sediments 

 collected from the ALCOA site. The differences in the location of toxic sediments within 

 Reach 15 from Year 1 to Year 2 indicates that the sources and deposition sites for toxicants may 

 vary from year to year. We concluded that toxic sediments did occur within Reach 15 of the 

 Upper Mississippi River, especially within Sylvan Slough, home to the federally-endangered 

 Higgin's-eye pearly mussel, Lampsilis higginsi. The mussel filtering assay used in this project 

 proved to be an inexpensive tool for the assessment of sediment toxicity to native mussels. 



