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Spatial Trends in Sediment Contamination
The national distribution of chemical concentrations in sediments was based on data from 287 sites, including Mussel Watch sites sampled in 1986 through 1989 and Benthic Surveillance sites sampled in 1984 through 1986. Sediment with at least 20% silt or clay was collected at 232 of these sites. Each time sediments were sampled three separate samples of surface sediment were collected.
In general, there are a great many low concentrations and relatively few high ones. On a national scale, the high levels of contamination of organics [e.g., polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs)] and trace elements are clearly in the urbanized areas of the Northeast states; near San Diego, Los Angeles, and Seattle on the West Coast; and, except at a few sites, relatively rare in the Southeast and along the Gulf of Mexico Coast.
There are also areas where higher levels of certain trace elements may be natural. For example, concentrations of chromium and nickel are elevated along the Northwest Coast from Point Conception, CA, to Hood Canal, WA. In this area, levels of human population and industrialization are low, so the elevated levels of these elements probably result from bedrock of that region being enriched in these elements.
High concentrations in sediments elsewhere in the nation can be attributed to human activity and considered to be contamination.
References
Daskalakis, K.D. and T.P. O'Connor. 1994. Inventory of chemical concentrations in coastal and estuarine sediments. NOAA Technical
Memorandum 76. NOS/ORCA. Silver Spring , MD 47pp + appendices.
Daskalakis, K.D. and T.P. O’Connor. 1995. Distribution of chemical concentrations in U.S. coastal and estuarine sediment. Marine Environmental Research 40(4):381-398.