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Sometimes the Question Is "Who Isn't Living There?"
Predicting Species Traits and Function Can Help Decisionmakers with Remediation of PCB-Laden Sediment

Scientists collecting biological samples from mud flats near Hunters Point, California.
Scientists collecting biological samples from mud flats near Hunters Point, a Superfund site in San Francisco Bay, California. The samples provided data for a tool that can help assess the effectiveness of the remediation of contaminated sediments. Photo credit: Richard Luthy, Stanford University.
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A photo collage of Hunters Point, a Superfund site in San Francisco Bay, Calif.

Study Site - Hunters Point Naval Shipyard Superfund Site
Hunters Point, a Superfund site in San Francisco Bay, California, that's heavily contaminated with PCBs, was used as a study area to develop tools and methods to assess contaminated sediments. The standard method to assess an ecological hazard made analyses very difficult and inconclusive. Therefore, the goal of USGS scientists and their colleagues was to characterize the relationship between bioavailable PCB (controlled in situ by amendments of activated carbon) and the functional ecology of the benthic community.

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Lake and river bottom sediments contaminated with polychlorinated biphenyls (PCBs) have been documented in industrial areas (past and current) throughout the United States. These contaminated sediments raise concerns because they have known and suspected ecological impacts. Although various remediation approaches ranging from complete removal of the contaminated sediment offsite to in situ sequestering of contaminated sediments have been in place for decades, remediation decisions are often encumbered by a lack of understanding of the long-term effectiveness and potential ecological consequences of various techniques. Through ecological modeling of benthic communities (bottom dwelling) and by collecting data on what aquatic organisms are or are not present, U.S. Geological Survey (USGS) and Stanford University, California, scientists have developed a tool to aid in those decisions.

In a paper recently published in Environmental Toxicology and Chemistry (Janssen and others, 2011) the scientists defined the role (or function) of different organisms in a community that lives in or on the sediments (the benthic community) at the Hunters Point Naval Shipyard Superfund Site, California (see text box). The scientists compared the total function of PCB-contaminated and uncontaminated benthic communities. The functions they studied included feeding method (food sources that are sediment borne or water borne, organisms that are carnivores, parasites, ...), reproductive method (egg laying, broadcast spawner, ...), and position in the sediment (a surface dweller protected from the sediment vs a burrower that is exposed to the sediment and its contaminants). Because it's important to know what organisms are and are not living in an area, the scientists assessed the population of benthic organisms in both the contaminated and uncontaminated sediments. By relating functional composition of the benthic community and its members to PCB bioavailability that is potentially induced by in situ remediation, the model provides a measure of the ecosystem recovery expected if the in situ treatment is effective. This is the first time the challenge of defining the effectiveness of the in situ sequestering of PCB's has been addressed in terms of the function of the local community of organisms.

This study was funded by the USGS Toxic Substances Hydrology, Hydrologic Research and Development, and Priority Ecosystem Science Programs, and by the Strategic Environmental Research and Development Program (SERDP - ER-1552).

References

Janssen, E.M.L., Thompson, J.K., Luoma, S.N., and Luthy, R.G., 2011, PCB-induced changes of a benthic community and expected ecosystem recovery following in situ sorbent amendment: Environmental Toxicology and Chemistry, v. 30, no. 8, p. 1819-1826, doi:10.1002/etc.574.

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Created on March 16, 2012