ASSESSING SEDIMENT TOXICITY FROM NAVIGATIONAL POOLS OF THE UPPER MISSISSIPPI RIVER USING A 28-DAY HYALELLA-AZTECA TEST

To assess the extent of sediment contamination in the Upper Mississipp i River (UMR) system after the flood of 1993, sediment samples were co llected from 24 of the 26 navigational pools in the river and from one site in the Saint Croix River in the summer of 1994. Whole-sediment t ests were conducted with the amphipod Hyalella azteca for 28 days meas uring the effects on survival, growth, and sexual maturation. Amphipod survival was significantly reduced in only one sediment (13B) relativ e to the control and reference sediments. Body length of amphipods was significantly reduced relative to the control and reference sediments in only one sample (26C). Sexual maturation was not significantly red uced in any treatment when compared to the control and reference sedim ents. No significant correlations were observed between survival, grow th, and maturation to either the physical or chemical characteristics of the sediment samples from the river. When highly reliable effect ra nge medians (ERMs) were used to evaluate sediment chemistry, 47 of 49 (96%) of the samples were correctly classified as nontoxic. These resu lts indicate that sediment samples from the Upper Mississippi River ar e relatively uncontaminated compared to other areas of known contamina tion in the United States.