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PROPOSED
MEASURES: CHEMICAL CONTAMINANTS
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Contaminants
in mussels and oysters, as a measure of the degree to which contaminants
are accumulating in living tissues in coastal areas. (Fig. 1)
Contaminants
in sediments, as a measure of the degree to which these chemicals
are distributed throughout the coastal environment. (Fig. 2)
Humans introduce
heavy metals such as lead and zinc, and organic chemicals such as polychlorinated
biphenyls (PCBs) and pesticides, into coastal areas through many activities.
These materials may affect water quality, settle to the bottom and contaminate
the mud or sand in which important food web organisms live, or be degraded
or diluted below levels of concern. Measurements of contamination in
both shellfish and sediments (i.e., mud, sand) can indicate whether
the risks posed by these chemicals are increasing or decreasing.
Between 1985 and
1996, there was little change in the levels of most chemical contaminants
found in mussels and oysters. This trend was observed in all areas surveyed.
In all areas but one, chemicals that decreased in concentration were
more prevalent than were those that increased.
Pesticides
and other contaminants were detected in most coastal sediments surveyed
between 1990 and 1996, but rarely in concentrations that exceeded advisory
guidelines designed to identify potential biological impacts.
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| Contaminants
in Coastal Sediments (1) Technical
Note |
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These
graphs show the percentage of estuary sediments, in several coastal
regions, that contain measurable amounts of pesticides, polychlorinated
biphenyls (PCBs), and metals; and the percentage of sediments that
exceed sediment quality guidelines developed by NOAA’s National
Status and Trends Program. |
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| Source:
U.S. Environmental Protection Agency |
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| Contaminants
in Living Organisms (2) Technical
Note |
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Shellfish
such as oysters and mussels are sensitive indicators of long-term
average water contamination because they filter large quantities
of water as they feed and tend to accumulate the contaminants in
their tissues. |
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| Source:
NOAA, National Status and Trends Program |
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| STATUS
OF DATA & OTHER NOTES |
Data on mussel
and oyster contamination are from a continuing monitoring program,
NOAA’s National Status and Trends Program, or Mussel Watch. These
data are believed to be representative of overall conditions in
U.S. coastal waters, but they do not represent either the most
contaminated or the most pristine waters. In addition, these data
do not describe the specific levels of contamination, merely whether
they are increasing, decreasing, or stable. Values for each city
represent averages; values for individual sampling sites may exceed
or fall short of the average.
Sediment
contamination data are from an ongoing monitoring program, the
U.S. Environmental Protection Agency’s Environmental Monitoring
and Assessment Program (EMAP). These data provide comparative
levels for major regions of the country but do not represent conditions
in every location within a region. Sufficient data on sediment
contamination in the Northwest and Northeast are not available.
The NOAA sediment quality guidelines used as reference points
here are intended to identify areas contaminated with chemicals
that are persistent and that accumulate in living tissue, where
levels are high enough that effects on living organisms are likely.
Please see
the Technical
Notes for additional information.
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