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(246) A mass balance model for the fate of PAHs in the San Francisco Estuary.
Greenfield, Ben*,1, Davis, Jay1, 1 San Francisco Estuary Institute, Oakland, California, USA
ABSTRACT- In the San Francisco Estuary (California, USA), polycyclic aromatic hydrocarbons (PAHs) have been identified by local regulatory agencies as potential threats to water quality. Increasing urbanization in this densely populated region may increase PAH loading in the future, making it important to estimate loading and the long term fate of PAHs. We present findings from a mass balance model that simulates the cycling of PAHs in the San Francisco Estuary. The model treats the Estuary as a single box with interacting water and sediment compartments and explicitly incorporates loading, volatilization, outflow to the ocean, degradation, and burial in deep sediment. Model results vary widely depending on the PAH compound modeled; this variation predominantly results from differences in degradation rates and octanol-water partition coefficients. The estimated time required for loss of one-half of the mass in the Estuary ranges from 21 days for naphthalene to five years for benzo[b]fluoranthene. Best available parameter estimates indicate that an external loading rate of approximately 20,000 kg/year has maintained the stable concentration observed in Estuary sediments over the past decade. Sensitivity analysis indicates a high degree of influence and uncertainty for degradation rates, suggesting that locally derived estimates of degradation would significantly improve predictive ability of the model.
Key words: PAH, urban, mass balance model, degradation
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