Research Product

Metal concentrations have been examined in sediments collected from 497 sites within the estuaries of the Gulf of Mexico by the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP). To isolate natural factors from anthropogenic ones, data were normalized for extant concentrations of aluminum. The normalization was based on the hypothesis that metals are anthropogenic. 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 has been examined, and it was found that 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.