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Locating Contaminated Sediments
Water pollution is a significant problem in the United States.
In the 1970s, a host of measures were taken to improve water
quality, including bans on the use of DDT and PCBs. Major
water quality legislation in the 1970s included the Federal
Water Quality Pollution Control Act Amendments of 1972 and
the Clean Water Act (CWA) of 1977. Water quality began to
improve, but by the early 1980s scientists realized that many
toxic contaminants remained in sediments and that they could
be resuspended by storms, ships, or even passing aquatic animals.
In 1985 and 1987, the EPA Office of Water began to document
the extent and severity of sediment contamination. Surveys
showed that the types and levels of contamination varied greatly
at sites throughout the country.
More recently, under the Water Resources Development
Act of 1992 (WRDA), Congress directed EPA--in consultation
with the National Oceanic and Atmospheric Administration (NOAA)
and the Secretary of the Army--to conduct a comprehensive
national survey of data on sediment quality. In response,
EPA undertook the National Sediment Quality Survey
(NSQS), a compilation of data on sediment quality.
EPA submitted to Congress its first survey report on sediment
contamination in 1998. The survey found that there is
contaminated sediment in all regions and every state.
The affected water bodies include streams, lakes, harbors,
near-shore areas, and oceans. Some of the most contaminated
sediments are found in the Great Lakes and in the harbors
of Boston, Los Angeles, Chicago, Detroit, and Puget Sound.
All of these water bodies have been impacted throughout the
years by heavy shipping traffic, contamination from upstream
sources, and local municipal and industrial discharges.
Although the NSQS is an important step in the identification
and analysis of contaminated sediments, the study does have
its limits. For example, many of the data in the inventory
were collected before experts had identified all of the important
factors that affect sediment contamination.
Today, scientists realize that the size of a sediment grain,
the amount of organic carbon in the sediment, and other characteristics
determine the bioavailability of contaminants. Unfortunately,
this important information is not always available in historical
sediment data. EPA believes that better data on sediment quality
and direct measurements of chemical concentrations in edible
fish tissue are needed. Efforts to gather this information
are underway.
EPA's Environmental Monitoring and Assessment Program (EMAP),
NOAA's National Status and Trends Program, and EPA's Great
Lakes National Program Office are among the programs monitoring
sediments more comprehensively. They are collecting data on
the physical and chemical characteristics of sediments, the
bioavailability of contaminants, levels of contaminant residues
in the tissues of aquatic organisms, and the health of benthic
communities.
Even if toxic chemicals and metals are present in sediments,
they may not be harmful. Bioavailablity is a measure of how
likely it is that the contaminants will actually affect living
organisms. Many factors affect the bioavailability of contaminants.
These factors include the acidity/alkalinity of the water
and the presence or absence of sulfur in the sediment.
To assess the ecological and human health risks posed by
contaminated sediments at a site, it is not enough to
measure the types and amounts of pollutants present.
Scientists may conduct field surveys to assess the health
of benthic communities and the levels of contaminants found
in the resident fish species. They may run chemical tests
to assess the factors that affect bioavailability, and often
times conduct biological tests by actually exposing benthic
organisms to the contaminated sediment and observing the results.
contaminated sediment home |
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locating contaminated sediments
species affected |
protecting sediments from contamination
management options |
preventing contaminated sediment
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