TOXICITY OF SEDIMENT COLLECTED UPRIVER AND DOWNRIVER OF MAJOR CITIES ALONG THE LOWER MISSISSIPPI RIVER

The Lower Mississippi River contributes significantly to the biodivers ity and ecological stability of the alluvial valley, but agricultural, industrial, and municipal developments have historically impacted env ironmental quality of the river. Toxicity of sediment and sediment por e water was used to assess the current effects of major cities on sedi ment quality along the Lower Mississippi River. Composite sediment sam ples were collected from four sites upriver and four sites downriver o f five major cities: Cairo, IL; Memphis, TN; Vicksburg, MS; Baton Roug e, LA; and New Orleans, LA. Acute toxicity was determined by exposing Hyalella azteca to solid-phase sediment for 10 days with two water ren ewals per day and to sediment pore water under static conditions for 9 6 h. After the initial tests, animals were exposed to ultraviolet ligh t for 16 h. Sediments were analyzed for organics (organochlorine pesti cides, PCBs, organophosphate insecticides, and PAHs) and metals (Cr, C u, Pb, Mn, Ni, Zn). With the exception of upriver from Memphis, solid- phase sediments were not toxic to H. azteca. Pore water from sediments collected upriver of Memphis also showed slight toxicity. Exposure of H. azteca to ultraviolet light did not increase the toxicity of the s ediment or pore-water samples, indicating a lack of toxicity from PAHs that are photoactivated by ultraviolet light. Chemical analyses did n ot reveal any contaminant levels of concern in the sediments. Based on toxicity testing and chemical analyses, quality of sediments collecte d from the Lower Mississippi was good, with the exception of sites sam pled upriver of Memphis.