Chemical Contaminants in the
Chesapeake Bay: an Introduction

The shallow Chesapeake, historically the nation's richest estuary, drains a 64,000 square mile watershed, with an extremely high ratio of land and population to volume of water, making it especially susceptible to impacts from human activities. According to one estimate, for every cubic kilometer of water in the Bay the watershed supports some 200,000 people, as contrasted with 4,000 people in the Baltic Sea watershed and only 85 in the Mediterranean Sea (Costanza 1995). Even beyond the Bay's sprawling watershed, an even larger airshed delivers nutrients and chemical contaminants from regions outside the borders of the Bay states.

A range of contaminants regularly enters the Chesapeake Bay, from land runoff, from the air, from both surface water and ground water. Even contaminants buried in sediments years ago can be resuspended both by human activities such as dredging or by natural events such as storms or the burrowing of bottom-dwelling animals. Once resuspended, these contaminants can be transported by physical processes (e.g., water circulation, tides, winds) to new locations throughout the Bay. While these contaminants would intuitively appear to be a threat, questions arise as to the extent of that threat. For example:

• What are the primary sources of contaminants in the Chesapeake Bay, and how does their importance vary in different regions of the Bay?
  
  
• How do toxic compounds move, and where do they end up?
  
  
• Can we construct the basic pathways of contaminants, including both recent and historical inputs?
  
  
• Have chemical contaminant loadings and transport processes changed as a result of management actions?
  
  
• How do chemical contaminants come in contact with the Bay's living organisms, and what effects do they have?
  
  
• What evidence is there for effects at low concentrations of chemical contaminants?

The Chesapeake Bay Program's Executive Council, recognizing the potential threat of contaminants to the current effort to restore the Bay, adopted in 1989 the Basinwide Toxics Reduction Strategy, which was re-evaluated in 1992. In 1993, the Executive Council called for the revised strategy to focus on four areas: pollution prevention, regulatory program implementation, regional focus, and directed assessments of toxic chemicals. Specifically, the assessments were to gauge "the potential impacts on the Bay's living resources from the observed widespread low level concentrations of toxics in Bay habitats."

In 1994 the Executive Council signed the revised Toxics Reduction Strategy and set as a goal a "toxics-free Bay." Although laudable, this strategy raised a number of significant questions. How much do we know about what chemicals or compounds are truly toxic, and at what concentrations? How much do we understand about the behavior of contaminants in an estuary like the Chesapeake Bay, where salinity and other factors vary widely, and where chemical compounds may exist in changing combinations, and may be converted to numerous forms, with uncertain biological effects?

To deal with such questions, the Sea Grant programs of Maryland and Virginia, the National Oceanic and Atmospheric Administration (NOAA) Chesapeake Bay Office, and the U.S. Environmental Protection Agency launched a Toxics Research Program in 1990. It is this program that sponsored a Toxics Synthesis Workshop in December, 1995, to bring together scientists engaged in these wide-ranging toxic research studies. The workshop, which included resource managers and science program administrators, aimed at synthesizing the current state of scientific information on the impact of contaminants in Chesapeake Bay.

A Focused Research Effort

The Toxics Research Program has been guided by the Chesapeake Bay Environmental Effects Committee (CBEEC), composed of representative researchers and managers from the Bay states, from EPA and from NOAA. Initial CBEEC work, beginning in 1985, focused on dissolved oxygen dynamics in the Chesapeake, in particular those factors that led to a severe reduction of oxygen (hypoxia) or a complete depletion of oxygen (anoxia). As a result of that research, our understanding of the complex network of processes that regulate oxygen concentrations in the Bay increased dramatically.

To capture that understanding, a workshop convened in late 1991 brought together researchers active in the CBEEC oxygen research program to produce a synthesis of their findings. The resulting document, "Dissolved Oxygen in the Chesapeake Bay: A Scientific Consensus," joined a book published by Sea Grant in 1992, Oxygen Dynamics in the Chesapeake Bay. Together, these documents described current scientific understanding of processes driving oxygen depletion in the Chesapeake.

A year earlier, in 1990, funds from NOAA were augmented by the EPA's Chesapeake Bay Program, with the recommendation that funds be redirected to study the effects of contaminants in the estuary. In response, researchers mounted a regional multi-disciplinary program aimed at increasing our understanding of how toxic contaminants affect the health and productivity of the Chesapeake Bay. The initial focus of this effort has been on the behavior and transport of contaminants in the estuary, an approach that built on the original five-year study of hypoxia and oxygen dynamics in the Bay - which also focused on Baywide physical and biological processes - and related work.

Questions surrounding the dynamics of chemical contamination in the ecosystem have proven to be considerably more complicated than the issue of oxygen dynamics. Where researchers formerly focused primarily on two nutrient compounds, nitrogen and phosphorus, the scientific analysis of chemical contaminants presents the prospect of hundreds of potentially harmful compounds, with different chemical properties and mechanisms of toxicity, some of which may join in synergies we do not yet understand.

With the EPA and others beginning to monitor the Bay for the presence of chemical contaminants beyond known areas of acute contamination such as Baltimore Harbor or the Elizabeth and Anacostia rivers, researchers concluded that an analysis of sublethal, ecological effects would prove especially valuable in revealing how even relatively low levels of chemical contaminants could affect biological communities in the Bay.

Specifically, we need to address three basic areas, around which the workshop discussions are based:

This synthesis presents the major points of consensus from the workshop. For those interested in additional information, the Appendix lists other, related publications.

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