[Estuarine and coastal marine environments are affected by a wide range of pollutants owing to increased anthropogenic activity from a burgeoning population in the coastal zone. Estuaries in particular have served as major repositories for the disposal of industrial and municipal wastes, sewage sludge, and dredged material. Contaminants associated with these wastes (e.g., heavy metals, chlorinated hydrocarbons, polynuclear aromatic hydrocarbons, petroleum hydrocarbons, and radioactivity) have impacted biotic communities and sensitive habitat areas. Pollutants primarily enter estuaries and nearshore oceanic waters via pipeline discharges, disposal from vessels, riverine input, atmospheric deposition, and nonpoint source runoff from land. Ocean dumping of anthropogenic wastes, employed increasingly in the U.S. until 1972, has been gradually reduced since that time because of the enactment of federal regulations designed to minimize environmental impacts in aquatic ecosystems. In addition to the planned disposal of wastes at sea, accidental spills are responsible for occasional, yet substantial, quantities of pollutants in estuarine and shallow marine waters. For example, large oil spills at times have eradicated entire communities and destroyed many hectares of adjoining wetlands area. More insidious pollution problems (e.g., organic loading), while commonly perceived to be less damaging to the environment, often have a greater long-term impact on these coastal systems. Concomitant with the growing societal concern of marine pollution has been the development of various ocean monitoring programs. Most important among them is NOAA's National Status and Trends (NS&T) Program which has measured toxic contamination at almost 300 estuarine and coastal locations throughout the U.S. since 1984 to determine trends of environmental quality in space and time and to discern biological responses to the chemical contamination. On a national scale, the highest and most biologically significant concentrations of contaminants in the NS&T Program occur predominantly in urbanized estuaries.]