SEWAGE CONTAMINATION IN THE UPPER MISSISSIPPI RIVER AS MEASURED BY THE FECAL STEROL, COPROSTANOL

The molecular sewage indicator, coprostanol, was measured in bed sedim ents of the Mississippi River for the purpose of determining sewage co ntamination. Coprostanol is a non-ionic, non-polar, organic molecule t hat associates with sediments in surface waters, and concentrations of coprostanol in bed sediments provide an indication of long-term sewag e loads. Because coprostanol concentrations are dependent on particle size and percent organic carbon, a ratio between coprostanol (sewage s ources) and cholestanol + cholesterol (sewage and non-sewage sources) was used to remove the biases related to particle size and percent org anic carbon. The dynamics of contaminant transport in the Upper Missis sippi River are influenced by both hydrologic and geochemical paramete rs. A mass balance model incorporating environmental parameters such a s river and tributary discharge, suspended sediment concentration, fra ction of organic carbon, sedimentation rates, municipal discharges and coprostanol decay rates was developed that describes coprostanol conc entrations and therefore, expected patterns of municipal sewage effect s on the Upper Mississippi River. Comparison of the computed and the m easured coprostanol concentrations provides insight into the complex h ydrologic and geochemical processes of contaminant transport and the a bility to link measured chemical concentrations with hydroiogic charac teristics of the Mississippi River.