Trace Metal Mineral Equilibria in Lake Erie Sediments
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Date
1900
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Abstract
Mineral equilibria were examined for the system Cd-Pb, Zn-Fe (II)-CO3- PO4 -H20 in the interstitial waters of the upper meter of Lake Erie sediments. To closely approximate anoxic sediment conditions, extrusion and squeezing were performed under a nitrogen atmosphere shortly after coring. Interstitial water concentrations of ferrous iron, zinc, cadmium, lead, and carbonate alkalinity were about a factor of 3-5 greater in the near-shore Ashtabula cores than in the central basin. Pore waters were supersaturated with respect to vivianite (Fe3 (PO4)2 8H20) and siderite (FeC03) which were generally in equilibrium with each other. Cadmium, lead and zinc, however, were under saturated with respect to carbonate and phosphate minerals phases. Metal concentrations were generally greatest in the 10 cm immediately below the sediment-water interface. Calculations showed 90-98 percent of the lead, 20-60 percent of the zinc, and 5 percent of the cadmium to be inorganically complexed. Organic complexation tied up additional metal and may account for the larger total dissolved metal levels in the upper 10 cm of the sediment pore waters.
This report was submitted in fulfillment of Contract No. R-803704 by Case Western Reserve University, Cleveland, Ohio under the sponsorship of the U.S. Environmental Protection Agency. This report covers the period June 15, 1976 to February 28, 1978, and was completed as of December, 1977.
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Lake Erie sediments, mineral equilibria