Sediment-Contaminant Database

Sampling Purpose: In 1992, the U.S. Fish and Wildlife Service conducted an investigation to determine the potential toxicity and contaminant concentrations of surficial sediments from near-shore zones of twenty regulated discharge points and at major stormwater outfalls between Pools 4 through 10 of the Upper Mississippi River National Wildlife and Fish Refuge. A total of 31 sediment grab samples were analyzed for organic carbon, water content, particle size, metals, organochlorines, fungicides, polynuclear aromatic hydrocarbons, and polychlorinated biphenyls. Microtox bioassays were conducted to evaluate the toxicity of the "biologically-active" chemicals in the sediment pore water, and the results from the bioassays were used to rank the relative toxicity of sediments at all discharge sites.
Cautionary note: As stated in the U.S. Fish and Wildlife Service report, the sediment samples collected for chemical analysis were collected in July 1992 and stored frozen until May and June of 1993. The sediment samples collected for Microtox testing where held at ~ 4°C prior to pore water extraction and subsequent testing. Because certain metals and metalloids (e.g., arsenic, selenium, mercury, lead, and tin) are more likely to be affected by changes in the sediment redox potential and microbial metabolism, which can occur during long periods of storage or the freezing process, subtle differences in the correlation between sediment metal concentrations (on stored samples) and the reported Microtox toxicity values may have occurred.