Laboratory toxicity test with Hyalella azteca exposed to whole-sediments from the upper Mississippi River

To assess the extent of bottom sediment contamination in the upper Mississippi river system after the flood of 1993, sediment samples were collected from 23 of the navigational pools in the river and from one station in the Saint Croix River. Whole sediment tests were conducted with Hyalella azteca for 28-d measuring effects on survival, growth, and sexual maturations. Survival was reduced from the control sediments in about 10% of the pools. Sub-lethal effects (i.e., reduction in growth or sexual maturation) were not reduced in any of the samples compared to the control sediment. No relationship was evident between toxicity and sediment physical characteristics (e.g., grain size, total organic carbon) or sediment chemical concentrations (metals or organics). The authors suspect the low survival in some of the samples may have resulted from the use of reconstituted water as the overlying water in these tests. Data from these exposures will be analyzed to provide information regarding the degree of degradation in the upper Mississippi River system due to contamination.