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The Long Term Fate of PCBs in San Francisco Bay Jay A. Davis San Francisco Estuary Institute

The Long Term Fate of PCBs in San Francisco Bay Jay A. Davis San Francisco Estuary Institute. Regional Monitoring Program. Regional Monitoring Program for Trace Substances in the San Francisco Estuary Innovative partnership between government, dischargers, and scientists

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The Long Term Fate of PCBs in San Francisco Bay Jay A. Davis San Francisco Estuary Institute

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  1. The Long Term Fate of PCBs in San Francisco Bay Jay A. Davis San Francisco Estuary Institute

  2. Regional Monitoring Program • Regional Monitoring Program for Trace Substances in the San Francisco Estuary • Innovative partnership between government, dischargers, and scientists • $ 3 million/year of stable funding • Began in 1993 • World class monitoring • www.sfei.org

  3. PCB Concentrations in San Francisco Bay Fish Fillets, 2000

  4. PCBs in mussels 1981-2000 ng/g lipid ~ 50% decline

  5. Questions • Why is the Bay responding so slowly? • How long will it take for fish to be safe to eat? • What would the response be with reduced inputs? • How large are the inputs? • What studies are needed to better understand PCB fate in the Bay?

  6. A PCB Mass Budget • A first step toward a PCB mass budget for the Bay • Followed approach described by: • Gobas et al. 1995 (EST 29: 2038-2046) • Mackay et al. 1994 (JGLR 20: 625-642) • One-box model for the whole Bay • A water and sediment model • Individual congeners • PCB 118 used as “typical” PCB • Report benefited from extensive peer review

  7. Input Data • Approximately 30 input parameters • Physical data for the Bay • Flow • Sediment budget • RMP concentration data • Chemical properties • Sensitivity analysis conducted on all parameters

  8. PCB Fate in Bay Water and Sediment

  9. Predicted Long Term Trends in PCB Mass with Varying Loads

  10. Predicted Trends in PCB Mass for Different PCB Congeners

  11. Predicted Long Term Trends in PCB Mass with Varying Depth of the Active Sediment Layer

  12. Conclusions • At this stage, the value of the model is in showing the response to ranges of input values, not in the precision of estimates • The most influential parameters included degradation half-life in sediment, Kow, outflow, average PCB concentration in sediment, and depth of the active sediment layer • Sediment dynamics are very important, including mixing and erosion/burial

  13. Conclusions (continued) • The model suggests that annual loads from 1982 to 2000 were in the 0 to 20 kg range • Annual inputs of 10 to 20 kg could significantly delay declines in PCBs • Different PCB congeners are predicted to have very different response times • For more information or a copy of the report: jay@sfei.org

  14. Next Steps for PCB Fate Modeling in San Francisco Bay • Food web model coming soon (Frank Gobas and John Wilcockson)

  15. Modeling PCB Trophic Transfer

  16. Mass Budget for a White Croaker Growth Dilution Gill Elimination Metabolism Gill Uptake Dietary Uptake Fecal Egestion

  17. Next Steps for PCB Fate Modeling in San Francisco Bay • Quantify uncertainty of estimates • Go multibox

  18. The Multibox Model • Collaboration with Dave Schoellhamer (USGS, Sacramento) • Builds on existing model calibrated for salinity • RMP really interested in 5 boxes

  19. Next Steps for PCB Modeling in San Francisco Bay • Better characterization of sediment dynamics • Also need better estimates of: • Degradation rates • Outflow • Average concentrations • Historic long term trends

  20. Next Steps for Management • Look for manageable PCB loads • Watch out for “PCBs” of the future (e.g., PBDEs)

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