Geochemical Study ofToxic Heavy Metals Suite in Sediment.
Becerra, Caryl Ann
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Experiments are being done at Point Mugu Naval Air Station to determine the feasibility of using contaminated sewage sludge from sewage oxidation ponds to restore a saltwater marsh. A geochemical study of 134 samples of sewage sludge and saltwater marsh sediment using an inductively coupled plasma atomic emission spectroscopy and matrix-matched standards was done to investigate the concentration of a suite of heavy metals (As, Ag, Al, Cd, Cr, Cu, Mo, Ni, Pb, Se, Zn) by a) comparing total concentration to environmental regulatory standards and b) sequentially extracting and analyzing fractions using increasingly chemically aggressive conditions. The sample population displays 3 general patterns of metals fractionation. The first pattern shows that the highest concentrations of metals are found in the crystalline framework of the sediment which are not easily bioavailable. Ag and Al tend to dominate this fraction.The second pattern shows that anomalously high concentrations of metals are released in strongly oxidizing conditions since many of the sediment samples are high in organic carbon, which strongly adsorbs metals.In this sample population, As, Cr, Cu, Pb, and Se are mostly released in oxidizing conditions and are bioavailable.The third pattern show that the largest concentrations of metals are released in conditions associated with ionic strength change or when the sediment is in a strongly reducing environment such as the digestive systems of animals. Cd, Mo, Ni, and Zn in this sample population are released under these conditions and are most bioavailable.