Normalization of metal concentrations in estuarine sediments from the Gulf of Mexico |
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Authors: | J. Kevin Summers Terry L. Wade Virginia D. Engle Ziad A. Malaeb |
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Affiliation: | 1. Gulf Ecology Division, United States Environmental Protection Agency, 1 Sabine Island Drive, 32561-5299, Gulf Breeze, Florida 2. Geochemical and Environmental Research Group, Texas A&M University, 833 Graham Road, 77845, College Station, Texas 3. National Biological Service, Southern Science Center, Gulf Breeze Project Office, 1 Sabine Island Drive, 32561-5299, Gulf Breeze, Florida
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Abstract: | Metal concentrations were examined in sediments from 497 sites within the estuaries of the Gulf of Mexico by the United States Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP). Data were normalized for extant concentrations of aluminum to isolate natural factors from anthropogenic ones. The normalization was based on the hypothesis that metal concentrations vary consistently with the concentration of aluminum, unless metals are of anthropogenic origin. Strong linear correlations (>75% variation explained) were observed between Al and Cr, Cu, Pb, Ni, and Zn. Moderate correlations (50–75% variation explained) were observed between Al and As or Ag. Weak but significant correlations (30–40% variation explained) were observed between Al and Hg or Cd. Based on these results, the spatial extent of contamination was examined. About 39% of sites with contamination by at least one metal occurred near population centers, industrial discharge sites, or military bases. The remainder of the observed contamination represented a dispersed pattern, including the lower Mississippi River (7%) and numerous agricultural watersheds (54%), suggesting that the contamination might be from nonpoint sources. |
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