NOAA Study Highlights Extent Of Contamination, Toxicity In Chesapeake Bay Sediments

The major portion of the Chesapeake Bay, called the "mainstem," has minimal sediment contamination. However, there are localized areas of the bay showing elevated contaminant levels, according to the National Oceanic & Atmospheric Administration (NOAA).

Researchers from the NOAA National Centers for Coastal Ocean Science collected sediment samples from the Chesapeake Bay between 1998 and 2001 to determine where and how severely the sediments are contaminated by toxic chemicals. The comprehensive contaminant report, "Magnitude and Extent of Contaminated Sediment and Toxicity in Chesapeake Bay," covers the entire mainstem of the Chesapeake Bay, along with its major western tributaries -- the Patuxent, Potomac, Rappahannock, York and James rivers.

Toxic contaminants enter the bay from these and other tributaries, as well as from a variety of other sources, including windblown dust, storm water runoff, spills and direct discharge.

"NOAA shares in the widespread public concern that the ecological functions of the bay are becoming impaired and that has the potential to impact human health," said John H. Dunnigan, director of the NOAA Ocean Service. "Understanding the impacts and sources of contaminants to the nation's largest estuary is part of a long-term commitment to understanding the bay's ecosystem. We are committed to working with our federal, state and local partners in restoring its integrity as a sustainable coastal resource."

NOAA's study examined a variety of toxic contaminants found in Chesapeake Bay, including metals, polychlorinated biphenyls (PCBs), persistent chlorinated pesticides and polycyclic aromatic hydrocarbons (PAHs). NOAA scientists also studied the organisms living in the sediments (also called the benthos) within the research area, to determine which animals live where. Scientists then conducted laboratory studies to assess how the contaminants affect estuarine organisms. The report summarizes where contamination exists and the correlation between benthic community impacts, observed toxicity and contaminant levels.

While the study found most of the Chesapeake mainstem is relatively uncontaminated, most sample locations in the major western tributaries were determined to have higher contaminant concentrations than the mainstem. In addition to contaminant hot spots in Baltimore and Norfolk harbors, contaminants accumulate in the Susquehanna Flats and the deep trough areas west of Kent Island and south of the Chesapeake Bay Bridge. The Hart Miller Island area, where dredge spoil from Baltimore harbor and its approach channels are deposited in a containment facility, shows metals are at higher concentrations there than at other location in the mainstem.

The study also found benthic (the lowest level of a body of water) species richness, abundance and diversity went down as contamination levels and toxicity increased. Toxicity elevated as contamination levels increased. Though the types of fine sediments where contaminants accumulate also are where many aquatic animals tend not settle and live due to poorer habitat conditions, when sediment type was taken into account, researchers found toxicity still affected benthic communities.

"The benthic environment is a part of the food chain which supports many estuarine fish and wildlife species," said Ian Hartwell, an ecologist with the NOAA National Status and Trends Program's Bioeffects Project. "Sediment contaminants often pose ecological and human health risks through degraded habitats, loss of fauna, contaminants accumulating in the coastal food chain, and human consumption of contaminated fish and wildlife. Characterizing coastal sediment contamination is critical for understanding where contamination exists, how bad it is and for creating management plans."

The report can be accessed in PDF format at

This article originally appeared in the 01/01/2007 issue of Environmental Protection.

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