This study analyzed polycyclic aromatic hydrocarbons (PAHs) in sediments from the San Francisco Estuary from 1993-2001 to examine spatial distributions, temporal trends, and sources. PAH levels were highest in Central and South Bays compared to other areas and decreased significantly at only one station. Sources were identified using PAH isomer ratios as petroleum and fossil fuel combustion, biomass burning, and unburned petroleum. The study found PAH levels remained largely constant over the study period.

1. Polycyclic Aromatic Hydrocarbons in the
San Francisco Estuary
Distributions, Trends, and Sources
in Sediments (1993-2001)
Daniel R. Oros and John R.M. Ross
San Francisco Estuary Institute
7770 Pardee Lane, Oakland, CA 94621

2. 9-Year Synthesis 1993-2001: PAH Series
Oros and Ross. PAH in SF Estuary sediments.
Marine Chemistry 86:169-184, 2004.
Ross and Oros. PAH in the in SF Estuary water column.
Submitted to Chemosphere
Oros and Ross. PAH in SF Estuary bivalves.
Submitted to Marine Environmental Research

3. Why are PAH of concern?
• Genotoxic
• Mutagenic
• Carcinogenic
• Ubiquitous
• Constant input (limited or no control of non-point
sources)
• Regional Board’s Section 303(d) “Watch” List

4. How do PAH enter the estuary?
Trains
Ferries
Vehicular Traffic
Industrial Emissions
Fishing and Commercial Vessels
Combustion of Refined Petroleum Products

5. Natural and Intentional Burning of Biomass Fuels
Fireplaces
Natural Fires
Campfires

6. Uncontrolled and Accidental Input of Unburned
Petroleum and its Refined Products
Asphalt and Lube Oil
Creosote Treated Pier Pilings
Spills (e.g., crude oil)

7. 60,000 gallon diesel spill at Suisun Marsh April 27, 2004.
Concern: Toxicity depending on exposure and dosage
Diesel fate: dispersion, evaporation, and biodegradation.
Photo credit: Kurt Rogers, San Francisco Chronicle

8. Examine PAH in sediments to determine:
• Spatial distributions
• Temporal trends
• Sources
Objective

9. Figure 1. Map of sediment sampling stations (1993-2001)

10. Methods: Spatial Distributions
• 25 PAH were summed (PAH) for each station
• PAH concentrations were normalized to TOC
content (significant relationship)
• Stations were grouped into 5 segments: Delta, North
Estuary, Central Bay, South Bay, and Extreme South
Bay
• Comparisons between segments, seasons, and
stations were conducted using the non-parametric
Kruskal-Wallis test

11. Results: Spatial Distributions
• Central Bay and South Bay PAH were significantly
higher than North Estuary, Extreme South Bay, and
Delta
• South and Central Bays were not significantly different
• Delta was significantly lower than all other segments
230
217
96 87
31
0
50
100
150
200
250
CB SB NE ESB Delta
Estuary Segment
Mean
Total
PAH
(mg/kg
TOC)
Figure 2. Mean PAH distributions by segment

12. Methods: Temporal Trends
• PAH concentrations were first normalized to TOC
and % fines content by multiple linear regression
analysis
• Trends for PAH were examined for each station by
linear regression analysis using the ln(rescaled
residual) as the dependent variable and sampling
date as independent variable
• A significant positive slope (p<0.05) indicated an
increase, a significant negative slope a decrease, and
a lack of significance no detectable trend in PAH at a
station over time

13. Results: Temporal Trends (1993-2001)
Station Analysis
• A statistically significant (p<0.05) decreasing trend
in PAH was found only at San Pablo Bay (1 of 26
stations)
• No trends were detected at any other stations,
which suggests that PAH levels remained constant
over the 9 year period
Seasonal Analysis
• Sacramento River and Oyster Point showed
significantly higher PAH in the wet season than the
dry season. No significant seasonal differences
were found at other stations

14. Methods: Sources
• PAH isomer pair ratios were used as diagnostic
indicators to identify possible sources. Isomers
have similar partitioning behavior and solubility.
Anthracene / Anthracene + Phenanthrene
Benz[a]anthracene / Benz[a]anthracene + Chrysene
Fluoranthene / Fluoranthene + Pyrene
Indeno[1,2,3-c,d]pyrene / Indeno[1,2,3-c,d]pyrene +
Benzo[g,h,i]perylene

15. Table 1. PAH isomer pair ratios of specific sources
Source An/178 BaA/228 Fl/Fl+Py IP/IP+BghiP
Petroleum (unburned) <0.10 <0.20 <0.40 <0.20
Petroleum combustion 0.40-0.50 0.20-0.50
Petroleum and combustion (mixed) 0.20-0.35
Combustion >0.10 >0.35
Biomass and coal combustion >0.50 >0.50
PAH Isomer Pair Ratio

16. • Bar plots of PAH isomer pair ratios were generated
to show estimated frequency (%) of PAH from the
various sources in each segment
• PAH isomer pair ratios determined from estuary
were compared to PAH isomer pair ratios from
known environmental, petroleum, and single-source
combustion sources compiled from the scientific
literature by Yunker et al. (2002)
Methods (cont’d): Sources

17. An/178 (3 Rings)
2 1
100 98 99 100 100
0%
50%
100%
Delta NE CB SB ESB
Petroleum Combustion
BaA/228 (4 Rings)
24 5 4 1 9
76 95 96 99 91
0%
50%
100%
Delta NE CB SB ESB
Mixed Combustion
Figure 3. Bar plots showing frequency (%) of PAH
from various sources in each segment
Estuary Segment
Frequency
(%)

18. IP/IP+BghiP (6 Rings)
1
89 90 83 82 63
11 9 17 18 37
0%
50%
100%
Delta NE CB SB ESB
Petroleum Petroleum Combustion Biomass and Coal Combustion
Fl/Fl+Py (4 Rings)
10 12 4
81 78 92 91 91
10 10 8 5 9
0%
50%
100%
Delta NE CB SB ESB
Petroleum Petroleum Combustion Biomass and Coal Combustion
Figure 3 (cont’d). Bar plots showing frequency (%)
of PAH from various sources in each segment
Estuary Segment
Frequency
(%)

19. Summary and Conclusions
Mean PAH was significantly higher in the Central and
South Bays compared to the North Estuary, Extreme
South Bay and Delta. Delta was significantly lower
than all others
• Distribution could reflect the large amount of
urbanized area that surrounds Central and South
Bays and the less urbanized area in the Delta

20. A significant decreasing trend in PAH levels was
found at San Pablo Bay
• PAH decreasing trend is consistent with previous
observations that San Pablo Bay is eroding due to
diminished sediment supply and as currents and
waves transport sediment from the bay (Jaffe et al.,
1998, USGS)
No trends were found at any other stations
• Estuary PAH levels remained constant, which is
consistent with other national studies that reported
no increasing or decreasing trends for PAH
Summary and Conclusions (cont’d)

21. Sacramento River and Oyster Point showed
significantly higher PAH in the wet season than the
dry season. No significant seasonal differences at
other stations
• Location near freshwater discharges and estuary
margins is an important determinant of PAH
sediment concentration
Summary and Conclusions (cont’d)

22. PAH sources were identified by PAH isomer pair ratio
analyses using values compiled by Yunker et al.
(2002)
Petroleum and Fossil Fuel Combustion
• gasoline, diesel, crude oil, and coal
(e.g., coal from historical use)
Biomass Burning
• wood, wood soot, and grasses
Unburned Petroleum
• shale oil, lube oil, and creosote
(e.g., shale oil from refined Monterey oil)
Summary and Conclusions (cont’d)

23. This study was funded by the RMP as a contribution to the 9-Year
Synthesis
Laboratory Analyses, Field Work and Data Management
Dr. Robert Risebrough (Bodega Bay Institute)
Dr. Jose Sericano (GERG, Texas A&M)
Dr. Francois Rodigari (EBMUD & BACWA)
Genine Scelfo (UCSC)
Capt. Gordon Smith (RV David Johnston)
Applied Marine Sciences
Sarah Lowe (SFEI)
Cristina Grosso (SFEI)
Scientific Peer-Review
SFEI Staff
Three “Unknown” Reviewers
Acknowledgements