Heavy-Metal Analysis
Shinn and Reich (1999) have demonstrated use of Ion Coupled
Plasma spectrography (ICP) as a rapid, low-cost method for obtaining accurate data for 30 elements.
Mercury, Cd, Cu, V, and other trace elements are well-known toxicants in marine environments, and
P and Fe stimulate eutrophication.
Potential sources of heavy-metal pollution include leachates from copper bottom paint on boats in marinas and a coastal landfill at
Black Point, and from one or more of the 25 (3,000-ft-deep) disposal wells located at Black Point. Other potential sources include the highly polluted Miami River, the Turkey Point Nuclear Power Plant and sacrificial anodes on boats docked at marinas. Sacrificial anodes protect other metals on boats from breakdown by electrolysis.
Geochemical analyses indicated that concentrations of silver, copper, lead, and zinc were highest near marinas in the upper part of the bay. Water circulation at these sites is more restricted than at other sites in the pilot study, implying longer residence times for the contaminants.
A statistical cluster analysis showed that copper, lead, and zinc clustered strongly with aluminum and iron, which are often associated with
clays. Clays in the marine environment suggest a terrigenous source. Of the metals detected in the geochemical analysis, copper, lead, zinc, and mercury were the only ones significantly higher than in normal marine water.
Trends indicate a decrease in heavy-metal concentrations from north to south along the shoreline, away from the 'older' part of urbanized
Miami, and a general decrease from nearshore to the center of the bay. Strontium and calcium typically occur together in a biogenic environment (i.e., where sediments are derived from organisms) and were accordingly found in the samples.
continue to Grain-Size Analysis
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U. S. Department of the Interior | U.S. Geological Survey
