WP1 Sediment Quality Assessment
256 Portland Ballroom
1:20 PM - 4:40 PM, Tuesday

() Evaluation of risk from exposures to tributyltin in the Puget Sound sediments.

Gries, T.1, Meador, J.2, Michelson, T.3, 1 Department of Ecology, Olympia, Washington, USA2 NOAA Fisheries, Seattle, Washington, USA3 Avocet Consulting, Kenmore, Washington, USA

ABSTRACT- Tributyltin (TBT) is a chemical of concern in sediment throughout much of Puget Sound, especially urban harbors and commercial waterways, but risk-based evaluations of sediment TBT vary by regulatory program and individual site. The regional navigation dredging program uses a value of 0.15 g TBT/L porewater to trigger standard laboratory bioaccumulation tests. Sediments are unacceptable for in-water disposal if these bioaccumulation tests result in tissue residues significantly elevated relative to both a reference sample and a predetermined level of concern. Risk-based contaminated sediment site investigations, feasibility studies and remedy selections are led by either federal or state cleanup programs. Assessments of TBT-associated risk at sediment cleanup sites usually focus on the marine benthic community. A conceptual no effects level of 0.05 g TBT/L porewater is considered protective of almost all acute effects and most chronic effects in 95% of all species, and may be used on that basis as a cleanup goal. However, using existing whole-sediment TBT data and equilibrium partitioning theory may not accurately predict porewater TBT concentrations. Site-specific Koc values differ from literature values and vary between sites. Within a site, correlating whole sediment TBT with measured porewater TBT can be useful to interpret existing data and set cleanup levels. Results from laboratory bioaccumulation studies of TBT alone can result in controversial cleanup decisions. A more direct residue-based approach is being used for more recently-identified cleanup sites to assess potential toxicity for in situ benthic communities. In this presentation, we will summarize the approaches used throughout Puget Sound region for assessing TBT toxicity and will highlight the strengths and weakness of each.

Key words: sediment, tributyltin, bioaccumulation, cleanup

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