Primarily relying on five contaminants as "representatives" - copper, mercury, atrazine, PAHs (polycyclic aromatic hydrocarbons), and PCBs (polychlorinated biphenyls) - the scientists and managers meeting at the Belmont Center attempted to summarize what we now know about contaminants in the Chesapeake, and to give some priority to what we need to know in the areas of sources, transport and biological effects.

Sources of Contaminants

Research guided by the Chesapeake Bay Program, the Chesapeake Bay Environmental Effects Committee (CBEEC) and others, as well as related monitoring, has focused on identifying and quantifying sources of priority pollutants and on the processes that serve to transport these contaminants throughout the Chesapeake Bay. This research emphasis has led to a strong understanding and - in a number of instances - quantification of basic pathways by which contaminants reach the Bay. We now know that:

• Specific point sources of contaminants from industries and sewage treatment plants have been significantly reduced, largely in response to the Clean Water Act and the Clean Air Act.
  
  
• Increasing human population in the 64,000 square mile watershed and the even larger airshed - together with related developments such as deforestation, dredging, septic seepage and stormwater runoff - has meant that contaminants from diffuse sources account for increasingly greater inputs to the Bay ecosystem.
  
  
• Mechanisms of diffuse contaminant delivery vary widely throughout the Bay depending on the contaminant. Mercury, for example, arrives primarily from coal-fired power plants, atrazine via runoff from agricultural lands, PAHs from the burning of fuels (e.g., engine exhaust, power plan emissions), PCBs from recycling in Bay sediments.
  
  
• In the upper mainstem Bay - where river flow has more immediate influence than in the lower Bay - direct discharges, usually from urban and industrial areas, are major sources of contaminants entering the estuary. In the lower mainstem Bay, atmospheric deposition and other diffuse sources dominate.
  
  
• Contaminated Bay sediments have become potential reservoirs of toxic chemicals through recycling. Many of these buried contaminants are otherwise now heavily regulated (such as Kepone or DDT).
  
  
• How contaminants accumulate in the water and sediment depends both on the source (point or diffuse loadings) and on the areas in the Bay where contaminants arrive.
  
  
• Efforts to control diffuse inputs resulting from general patterns of land use and development, and air deposition, have been less successful than past management efforts to reduce point source loadings of contaminants such as PCBs, DDT and TBT.

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