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Chemical Contaminants

Based on the 2012 303(d) assessments of 92 tidal segments analyzed 74 percent had partial or full impairments due to chemical contaminants.

Chemical Contaminants

Chemical Contaminants (2012)

Map: Chemical Contaminants (2012)

Date created: Oct 18 2013 / Download

Tidal waters that are impaired for part or all of the indicated Bay segment by toxic chemicals based on each state's implementation of the Clean Water Act.


Chemical contaminants such as metals and polychlorinated biphenyls (PCBs) can be found in the Chesapeake Bay’s fish and bottom sediments. Toxic chemicals can harm the Bay ecosystem and human health. Toxins tend to accumulate in predatory species at the top of the food web. These contaminants have the potential to affect humans who eat contaminated fish.

By analyzing the tissues of specific types of fish, scientists can estimate the overall presence of contaminants in the Bay ecosystem.


The Bay Program’s goal is for 100 percent of analyzed segments in the Bay and its tidal tributaries to contain no impairments due to toxic chemicals.

Long-term trend

N/A – can only compare the 2006, 2008, 2010 and 2012 303(d) assessments by Maryland, Virginia and the District of Columbia.

Short-term trend (10-year trend)

We can only compare the 2006, 2008, 2010 and 2012 303(d) assessments by Maryland, Virginia and the District of Columbia.

  • In 2008, 71.9% of analyzed tidal segments were partially or fully impaired, up from 66.3% in 2006.  In 2010, we see a continued increase to 72.2% partially or fully impaired. In 2012, there is an additional increase to 73.9 percent.

It is important to note the number of segments increased to 92 in 2012 to make the segmentation consistent with the 2010 Chesapeake Bay TMDL for nitrogen, phosphorous, and sediment.  Previous years were based on 89 tidal segments.

  • These additional segments were not listed as impaired and may deflate the percentage slightly, relative to previous years.
  • The additional segments add more detail and may more accurately capture the extent of tidal impairments. The total number of impaired segments increased from 65 to 68 between 2010 and 2012. However, these new impairments are the result of revisions in listing geography, not on new data.

303(d) lists are updated every other year. The next update will be in 2014.

Change from previous year

In 2012, 73.9 percent of tidal segments analyzed were partially or fully impaired, up from 72.2 percent in 2010.

There may be little positive change in the short term because a majority of impaired waterways have persistent problems with PCBs in fish tissues.

Additional Information

Under Executive Order 13508, EPA released a technical report titled Toxic Contaminants in the Chesapeake Bay and its Watershed: Extent and Severity of Occurrence and Potential Biological Effects.

303(d) lists are updated every other year when the states submit their Integrated Reports to EPA.

Chemical contamination in the Chesapeake Bay is often characterized as a localized problem in “hot spots” or the “Regions of Concern” (Baltimore Harbor, Anacostia River and Elizabeth River). This indicator shows that chemical contaminants are a concern in segments beyond these localized areas.

  • Nearly three-quarters of segments analyzed in the Bay and its tidal tributaries contain partial or full impairments related to chemical contaminants..
  • Metals, PCBs, and priority organics exceed the impairment threshold in parts or entire tributaries that deliver water to the mainstem of the Chesapeake Bay.
  • PCB listings are present in 100 percent of impaired or partially impaired segments.

Because many of these substances bioaccumulate, contaminant concentrations in fish tissues will not decrease quickly, even if fewer toxic chemicals are delivered to waterways.

Chemical Contaminants Indicator Data

The data used in this indicator are the same data used by Delaware, Maryland, Virginia and the District of Columbia to determine impairments for the 2012 listing year. Some of the 2012 listings were first determined during previous listing cycles, which used data beginning in 1996.

It is valuable to use state data to feed the indicator because the states use the data to develop 303(d) lists and eventually TMDLs.

Virginia and Maryland use different contaminant concentration thresholds and different fish species to determine whether a body of water passes the “fishable” designation of use. For this reason, there is some variation between adjacent waters. For example, the Middle Chesapeake Bay segment covers portions of both Maryland and Virginia, but it is counted as a single segment. Virginia has assigned this segment impaired due to PCBs, but Maryland has not. Therefore, the segment is considered partially impaired following the method used for all other waters under consideration. The segment is included in the overall count of PCB listings within major tidal waters.

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