Assessment of elemental contamination in estuarine and coastal environments based on geochemical and statistical modeling of sediments

Sediment of variable mineralogical, textural and metal contaminant composition was collected from 38 estuaries along the Atlantic and Gulf of Mexico coasts of the United States and analyzed for total Al, Ag, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Si, Sn, Tl and Zn concentrations. Based on observed covariation of elements at 15 estuaries remote from contaminant inputs, linear regressions of metals on Al were used to model the metal content in baseline sediments. A geochemical model for the covariation was developed, verified and used to guide the statistical modelling approach. Comparison of metal concentrations predicted by the models with those occurring in uncontaminated geological materials suggests that baseline relationships are valid for the entire region sampled. Using these baseline relationships, sediment metal concentrations can be partitioned into natural and anthropogenic fractions. Models improve the comparability of metal levels in sediments by correcting for variable background concentrations that, if left uncorrected, only serve to increase total data variability and reduce detection of spatial and temporal differences. Examples of the application of baseline models to pollution studies are provided. A continuing decline in Pb concentrations in Mississippi River delta sediments is observed consistent with the declining use of Pb additives in gasoline since 1970. Major spatial trends in contaminant metals in sediments along the Atlantic and Gulf of Mexico coasts are noted.