Toxic chemicals found in the water, sediment and fish of the Bay’s tidal tributaries can have adverse effects on the ecosystem and human health. Chemical contaminants such as polychlorinated biphenyls (PCBs) can accumulate in the tissues of fish; this can provide an indication of the overall presence of these substances in the ecosystem. These chemicals can build up in certain species of fish to levels that can potentially be harmful to humans who consume them.
The Bay Program’s goal is for 100 percent of tidal tributaries to be unimpaired by chemical contaminants such as metals, PCBs and tributyltin.
*Note: The historic data featured in this indicator changed from that reported in the 2007 assessment. The 2006 and 2007 data changed due to provision of corrected data in 2008.
Long-term trend
N/A -- can only compare the 2006 and 2008 303(d) assessments by Maryland, Virginia and the District of Columbia
Short-term trend (10-year trend)
N/A -- can only compare the 2006 and 2008 303(d) assessments by Maryland, Virginia and the District of Columbia
Change from previous year
Based on the 2006 303(d) assessments by Maryland, Virginia and the District of Columbia, 33.7 percent of the goal was achieved (30 out of 89 monitored tidal tributary segments contained no impairment for chemical contaminants). This is compared to 28.1 percent goal achieved based on the 2008 303(d) assessments (25 out of 89 monitored tidal tributary segments contain no impairment for chemical contaminants).
There may be little positive change seen in the short term since a majority of impaired waterways have persistent problems with PCBs in fish tissues.
The issue of chemical contamination within the Chesapeake Bay is often characterized as a localized problem pertaining to “hot spots” or the “Regions of Concern” (Baltimore Harber, Anacostia River and Elizabeth River). This indicator shows that chemical contaminants are a concern for segments beyond these emphasized areas.
- More than two-thirds of the Bay’s tidal segments contain partial or full impairments related to chemical contaminants.
- Metals, PCBs, tributyltin and priority organics are found exceeding the TMDL in part or the entirety of tributaries that deliver water to the mainstem of the Chesapeake Bay.
- PCB listings are present in 98% of impaired or partially impaired segment.
Due to the bioaccumulative nature of many of these substances, even if inputs to the tributaries decreases, fish tissue concentrations will not respond quickly.
Chemical Contaminants Indicator Data
The data used in this indicator are the same data used by Maryland, Virginia and the District of Columbia to determine impairments for the 2008 and 2006 impairment listing years. Some of the 2006 listings were first determined during previous listing cycles, which used data beginning in 1996. Therefore, a 10-year period is reflected in the data.
It is valuable to use state data to feed the indicator because the states use this data to develop 303(d) lists and eventually TMDLs.
Virginia and Maryland use different contaminant concentration thresholds and use different species of fish to determine whether a body of water passes the “fishable” designation of use. For this reason, there is some variation between adjacent waters such as the Middle Chesapeake Bay segment, which covers a portion of both Maryland and Virginia. Virginia has assigned an impairment due to PCBs but Maryland has not. However, the Middle Chesapeake Bay is counted as a single segment and therefore is considered partially impaired following the method used for all other waters under consideration. It is included in the overall count of PCB listings within major tidal waters.
Greg Allen at 800-968-7229 ext. 746
Chesapeake Bay Program Office