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() An assessment of potential sediment-related risks using an acute in situ toxicity test.

Lavoie, D1, Weier, J2, Hurff, S3, Parker, N3, 1 CH2M HILL, Herndon, Virginia, USA2 CH2M HILL, Boston, Massachusetts, USA3 Engineering Field Activity Chesapeake, US Navy, Washington, DC, USA

ABSTRACT- Acute (96-hour), in situ sediment toxicity tests using midge fly larvae (Chironomus tentans) were performed to evaluate sediment of the Supply Pond at Naval Air Station Patuxent River (NASPR), St. Marys County, Maryland. The Supply Pond has been impacted by the release of jet fuel to the environment. In situ toxicity testing is performed by transporting organisms to the field where they are exposed to environmental media within enclosed, flow-through exposure chambers. Advantages of in situ tests over laboratory-based tests include: (1) improved organism exposure accuracy by allowing for the natural fluctuations and interactions of light, temperature, flow, and medium-specific constituents; and (2) reduced impact of artifacts and altered bioavailability resulting from sample collection, transport, storage and manipulation. A previous laboratory-based C. tentanssediment toxicity test at this site resulted in significant toxicity (IT, 1989). In situ toxicity tests with the same test organism and similar exposure period were performed in 2004 to evaluate the current toxicity of pond sediments and the extent of impact throughout the pond. Organisms were also exposed at two reference locations. Exposure chambers consisted of clear core tubing cut to approximately 15 cm in length, with polyethylene caps sealing each end. Each chamber contained windows covered with Nitex mesh to allow water/constituent exchange. In one treatment, chambers were suspended in the water column (WC). In a second treatment, chambers were placed, window down, against the sediment (AS). Chambers were deployed at each location in replicates of six and each chamber contained 10 organisms. This testing was used as part of the watershed-level screening ecological risk assessment to quickly assess whether further risk assessment work on the pond was warranted. A repeat of the 1989 results would move the Supply Pond into the feasibility study phase of the site management process.

Key words: in situ, sediment, chironomids

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