A mass balance model for the fate of PAHs in the San Francisco Estuary Ben K. Greenfield Jay A. Davis San Francisco Estuary Institute Presented at the Calfed Science Conference, January, 2003

Source: U.S.G.S./Center For Land Use Interpretation

Population Growth, Bay Area to 2000 Data Source: MTC and ABAG, ,000,000 2,000,000 3,000,000 4,000,000 5,000,000 6,000,000 7,000, (Each Color is a Bay Area County)

Mass balance models Understand compound fate Identify research priorities (e.g. chemical properties) Synthesize available data Estimate loading rate

Simple mass balance model Mackay et al. (1994) Equilibrium partitioning based on chemical properties Single pool of interacting water and sediment Daily rate constants Spreadsheet format

Combined External Loads Volatilization Outflow Dissolved PCB Sorbed PAH Dissolved PAH Sorbed PAH Burial Water Active Sediment Layer Buried Sediment Dissolved PAH Particulate PAH Degradation Diffusion Deposition And Resuspension

2 ring – naphthalene 3 ring – phenanthrene 4 ring – fluoranthene and benz(a)anthracene 5 and 6 ring – e.g. benzo(b)fluoranthene Fluoranthene Benz[a]anthracene

Year PAH in Bay Percent Original Mass Naphthalene Phenanthrene Fluoranthene Benz(a)anthracene Benzo(b)fluoranthene 0 Turnover Rate

Year Percent Original Mass Phenanthrene Fluoranthene Benzo(b)fluoranthene PCB 118 PAHs

Loss Pathways of PAH Mass in Estuary Assuming No Load (One Year Simulation) Compound NFB(a)aB(b)f Proportion of Total Volatilization Outflow Degradation Mass Remaining

Compound NPFB(a)aB(b)fDaB(a)p Degradation Rate (d -1 )

Vary by PAH Compound Water Side MTC Air Side MTC Henry's Law Constant Kow Degradation Water Degradation Sediment Proportion of Total Uncertainty for Benzo(b)fluoranthene Sensitivity to Different Chemical Parameters Water Side MTC Air Side MTC Henry's Law Constant Kow Degradation Water Degradation Sediment

Losses Degradation Volatilization Outflow Burial Inputs? Loading Point Source Air Deposition Rivers Storm Drains Trend?

Inputs? Loading? Trend? Losses Degradation? Volatilization Outflow Burial

Total PAHs (µg/kg) Sediment Trends Year Total PAHs (  g/kg lipid) Bivalve Trends Year

From Pereira, W.E., et al Marine Chemistry Dated Sediment Core Chemistry

Inputs? Loading? Trend? Losses Degradation? Volatilization Outflow Burial

Loading rate (kg/yr) Degradation rate (d -1 ) 300< , , , Literature Estimates

Result summary Loss rates (half life) 2 ring PAH - 3 week 4 ring PAH - 1 year 5 ring PAH - 6 years Degradation rate uncertainty causes considerable model uncertainty Obtained upper bound on degradation rate and lower bound on loading rate

Significance of findings Much more rapid expected response to management changes than PCBs Future priorities:  Local degradation rates  Dr. Michael Montgomery (NRL) - experimental data on Bay sediments  Local sediment-water partitioning

Acknowledgments Don Yee Jon Leatherbarrow Sarah Lowe Cristina Grosso Patricia Chambers