Source: U.S.G.S./Center For Land Use Interpretation
description
Transcript of Source: U.S.G.S./Center For Land Use Interpretation
A mass balance model for the fate of PAHs in the San Francisco Estuary
Ben K. GreenfieldJay 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 - 1860 to 2000Data Source: MTC and ABAG, 2002
0
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
6,000,000
7,000,000
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
(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
DissolvedPCB
Sorbed PAH
Dissolved PAH
Sorbed PAH
Burial
Water
Active
Sediment
Layer
Buried
Sediment
Dissolved PAH
Particulate PAH
DegradationDegradation
Degradation DiffusionDeposition
AndResuspension
• 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
0 1 2 3 4 5
PA
H in
Bay
Pe
rce
nt
Ori
gin
al M
ass
50
100
Naphthalene Phenanthrene Fluoranthene Benz(a)anthraceneBenzo(b)fluoranthene
0
Turnover Rate
Year
0 5 10 15 20
Per
cent
Orig
inal
Mas
s
0
25
50
75
100Phenanthrene
Fluoranthene
Benzo(b)fluoranthene
PCB 118
PCB 118
PAHs
Loss Pathways of PAH Mass in EstuaryAssuming No Load (One Year Simulation)
Compound
N F B(a)a B(b)f
Pro
port
ion
of T
otal
0.0
0.2
0.4
0.6
0.8
1.0
Volatilization Outflow Degradation Mass Remaining
Compound
N P F B(a)a B(b)f Da B(a)p
Deg
rada
tion
Rat
e (d
-1)
0.0001
0.001
0.01
0.1
1
10
Vary by PAH Compound
Wat
er S
ide
MT
C
Air
Sid
e M
TC
Hen
ry's
Law
Co
nst
ant
Ko
w
Deg
rad
atio
n W
ater
Deg
rad
atio
n S
edim
ent
Pro
port
ion
of T
otal
0
20
40
60
80
100
Uncertainty for Benzo(b)fluoranthene
0
20
40
60
80
100
Sensitivity to Different Chemical Parameters
Wat
er S
ide
MT
C
Air
Sid
e M
TC
Hen
ry's
Law
Co
nst
ant
Ko
w
Deg
rad
atio
n W
ater
Deg
rad
atio
n S
edim
ent
Losses
DegradationVolatilizationOutflowBurial
Inputs?
Loading Point Source Air Deposition Rivers Storm Drains
Trend?
Inputs?
Loading?
Trend?
Losses
Degradation?VolatilizationOutflowBurial
To
tal P
AH
s (µ
g/k
g)
Sediment Trends
Year
1990 1992 1994 1996 1998 2000 20020
200
400
600
800
1000
1200
1400
1600
1800
2000
To
tal P
AH
s (
g/k
g li
pid
)
Bivalve Trends
Year
1993 1994 1995 1996 1997 1998 1999 2000 20010
1000
2000
3000
4000
5000
6000
1990
1980
From Pereira, W.E., et al. 1999 Marine Chemistry
Dated Sediment Core Chemistry
Inputs?
Loading?
Trend?
Losses
Degradation?VolatilizationOutflowBurial
Loading rate (kg/yr)
Degradation rate (d-1)
300 < 0
2000 0
10,000 0.0002
20,000 0.00035
460,000 0.01
Lit
era
ture
Est
imat
es
Result summaryLoss 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