NORMALIZATION OF METAL CONCENTRATIONS IN ESTUARINE SEDIMENTS FROM THEGULF-OF-MEXICO

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 i solate natural factors from anthropogenic ones, The normalization was based on the hypothesis that metal concentrations vary consistently wi th the concentration of aluminum, unless metals are of anthropogenic o rigin. Strong linear correlations (>75% variation explained) were obse rved between Al and Cr, Cu, Pb, Ni, and Zn, Moderate correlations (50- 75% variation explained) were observed between Al and As or Ag. Weak b ut significant correlations (30-40% variation explained) were observed between Al and Hg or Cd. Based on these results, the spatial extent o f contamination was examined. About 39% of sites with contamination by at least one metal occurred near population centers, industrial disch arge sites, or military bases. The remainder of the observed contamina tion represented a dispersed pattern, including the lower Mississippi River (7%) and numerous agricultural watersheds (54%), suggesting that the contamination might be from nonpoint sources.