incorporation of weathering in pah source apportionment
TRANSCRIPT
Incorporation of Weathering in PAH Source Apportionment
Caroline Tuit and Jeffrey Rominger
National Environmental Measurement Conference
August 11, 2017Washington DC
2Copyright Gradient 2017
PAH Urban Sediment Sites = High Stakes Allocations
ROD Estimated Clean-up Costs
ā¢ Ottawa River ($49 Million)
ā¢ Thea Foss Waterway ($105 Million)
ā¢ Lower Duwamish Waterway ($342 Million)
ā¢ Gowanus Canal ($506 Million)
ā¢ Portland Harbor ($1.05 Billion)
ā¢ Extremely expensive clean-ups
ā¢ Multiple Contaminants of Concern
ā¢ Multiple Sources
ā¢ Complex Histories
ā¢ Dynamic Environment
ā¢ Complex and Weathered Fingerprints
Forensics tools are typically needed to allocate PAH sources
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Key Findings
ā¢ PAHs are subject to extensive weathering in sediment sites
ā¢ Water-washing models can approximate weathering effects on PAH fingerprints
ā¢ PAH source apportionment models rely on well-defined end-members
ā¢ Evaluation of weathering trends in PAH source apportionment models can
āŖ Link upland sources to sediment end-members
āŖ Identify where weathering trends may obscure mixing trends
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Polycyclic Aromatic Hydrocarbons (PAHs)
ā¢ PAHs can be divided into parent (8270) or alkylated (8270 SIM)
ā¢ Typical anthropogenic sources:
āŖ Pyrogenic (burning of coal, petroleum, wood etc.; coal tar; creosote)
āŖ Petrogenic (oil; gasoline; diesel; asphalt)
āŖ Urban background (weathered mix of petrogenic and pyrogenic sources)
ā¢ The pattern of alkylated PAHs can distinguish the PAH source as petrogenic or pyrogenic
ā¢ Typical source concentrations
āŖ Crude oil: 0.2 to 7 wt %
āŖ Coal tar: up to 70 wt %
0
0.2
Petrogenic
0
0.1
0.2
0.3Pyrogenic
LMW (2-3 ring) HMW (4-6 ring)
0
0.1
0.2
N0
N1
N2
N3
N4
AC
YA
CE F0 F1 F2 F3 A0
P0
P1
P2
P3
P4
D0
D1
D2
D3 FL PY
FL1
BA
A C0
C1
C2
C3
C4
BB
FB
KF
BA
P IN DA
GH
I
Urban Runoff
2-Methylnaphthalene
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PAH Weatheringā¢ Evaporationāmost PAHs are
non-volatile
ā¢ BiodegradationāSlow, mechanisms are poorly understood
āŖ Rate and extent correlated with the number of aromatic rings and the presence/absence of side chains
ā¢ Water-washingāControlled by the aqueous solubility of the individual PAH
āŖ Solubility of PAHs decreases with number of rings and increasing alkylation
Sources: Haritash, AK; Kaushik, CP. 2009. "Biodegradation aspects of polycyclic aromatic hydrocarbons (PAHs): A review." J. Hazard. Mater. 169(1-3):1-15; Neff, JM; Burns, WA. 1996. "Estimation of polycyclic aromatic hydrocarbon concentrations in the water column based on tissue residues in mussels and salmon: An equilibrium partitioning approach." Environ. Toxicol. Chem. 15(12):2240-2253.
3
4
5
6
7
8
9
100 150 200 250 300
Log
K OW
Molecular WeightAfter Neff and Burns (1996)
PAHs
P0/A0 Series
N0 Series
C0/BaA Series
Water-washing may approximate other weathering
processes
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PAH Weathering
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
N C1-N C2-N C3-N C4-N
Petrogenic Weathering Trend
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
N C1-N C2-N C3-N C4-N
Pyrogenic Weathering Trends
Weathering (e.g., water-washing) can alter PAH distributions preferentially removing low molecular weight (LMW) and parent PAHs
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PAH Forensics ā Typical Allocation Techniques
Principal Component Analysis (PCA)
ā¢ A statistical tool widely used to determine the number of dominant chemical fingerprints present in the system and examination of relationships between samples and putative sources
ā¢ Can look at many variables (PAH analytes) at once
Important considerations
ā¢ Evaluate data for analytical artifacts such as non-detects and low concentrations
ā¢ Normalize data to eliminate bias due to concentration differences (total normalization) or analytes (variance scaling)
1
23
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PAH Forensics ā Typical Allocation TechniquesReceptor Modeling
ā¢ Many Techniques: EPA UMIX; EPA Positive Matrix Factorization; Polytopic Vector Analysis; Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS)
ā¢ An iterative linear algebra method in which the end-member fingerprints that contribute to the sample data are identified and optimized such that the unexplained variance in the data is minimized
ā¢ Receptor modeling further identifies the fraction that each end-member contributes to every sample
Important Considerations
ā¢ Well defined end-members
ā¢ Link end-members to site-specific sources
ā¢ Evaluate how weathering effects source signatures and end-members
EWP: 55% Tar: 44%
ModelMeas.
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Weathering Model
ā¢ Based on theoretical model of Short and Heinz (1997) used to identify Exxon Valdez oil in Prince William Sound
ā¢ Assumptions:
āŖ Water-washing dominates weathering
āŖ Equilibration of a small amount of PAH-containing material (NAPL) with a larger volume of clean water
āŖ PAH concentration calculated separately based on individual KOW
ā¢ Iterative Depletion: after equilibration, the volume of water is replenished with clean water, and the process repeats itself
ā¢ The ratio of clean water to NAPL is specified VWater/VNAPL ~10
ā¢ Higher volume ratios would result in faster weathering; Burns et al. (1997) used 600-700
Short and Heintz (1997); Kow available in Neff and Burns, (1996); Burns et al. (1997).
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Model Equations
š¶šš“ššæ,šššš“ššæ = š¶šš“ššæ,šššš“ššæ + š¶š¤šš”šš,ššššš”šš
Where:CNAPL,i = The initial PAH concentration in the NAPLVNAPL = The volume of NAPLCNAPL,f = The finishing PAH concentration in the NAPL volume after a
water-washing periodCwater,f = The finishing PAH concentration in the waterVwater = The volume of water in contact with the NAPL
š¶šš“ššæ,š = š¾šš¤š¶š¤šš”šš,š
š¶šš“ššæ,ššššš = š¶šš“ššæ,š 1 +šššš”šš
ššš“ššæš¾šš¤
āš
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Important Considerations
ā¢ NOT quantitativeāallows evaluation of fingerprint evolution, not age dating of spills
ā¢ Most useful in regions with sediment disturbance:
āŖ Tidal resuspension
āŖ Storm surge
āŖ Propeller wash
āŖ Dredging
ā¢ Requires well known starting compositions
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Literature Study: Creosote WeatheringAfter Stout et al. (2005); Stout et al. (2001); and Brenner et al. (2002)
ā¢ PAH weathering based on the Eagle Harbor Superfund Site
ā¢ Identified 3 source compositions
āŖ Creosote: pyrogenic; enriched in naphthalene and phenanthrene; high concentration
āŖ Natural Background: weathered pyrogenic; tPAH < 5 mg/kg
āŖ Urban Background: enriched in HMW PAHs; tPAH 10-20 mg/kg
0
0.1
0.2
0.3
0.4
Creosote
0
0.05
0.1
0.15
Natural Background
0
0.02
0.04
0.06
0.08
0.1
0.12
N0
N1
N2
N3
N4
Acl
Ace F0 F1 F2 F3 AN P0
P1
P2
P3
P4
D0
D1
D2
D3 FL PY
FP1
BaA C
0C
1C
2C
3C
4B
bF
BkF
BaP ID DA
BgP
Urban Background
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Literature Study: Creosote Weathering
ā¢ Creosote Weathering
āŖ Loss of the LMW PAHs
āŖ Loss of parent PAHs
āŖ Pyrogenic ratios are still apparent in HMW PAHs
0
0.1
0.2
0.3
0.4
Creosote
0
0.1
0.2Slightly Weathered
0
0.05
0.1
0.15
0.2
Moderately Weathered
0
0.1
0.2
0.3
N0
N1
N2
N3
N4
Acl
Ace F0 F1 F2 F3 AN P0
P1
P2
P3
P4
D0
D1
D2
D3 FL PY
FP1
BaA C
0C
1C
2C
3C
4B
bF
BkF
BaP ID DA
BgP
Severely Weathered
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Principal Component Analysis: Creosote Weathering
ā¢ Modeled water washing trend follows literature weathering trend
ā¢ Non-detect effect seen in final water-washing steps
Upland Source
Fresh
Slightly
Moderately
Severely
Urban Background
Natural Background
Fresh
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
PC
2 (
18
.4%
)
PC1(60.1%)
Upland Source
Fresh
Slightly
Moderately
Severely
Urban Background
Natural Background
Fresh
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
PC
3(1
6.1
%)
PC1(60.1%)
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Literature Study: Creosote Weathering
0
0.1
0.2
0.3
0.4
Creosote
0
0.1
0.2
Slightly Weathered
0
0.05
0.1
0.15
0.2
Moderately Weathered
0
0.1
0.2
0.3
N0
N1
N2
N3
N4
Acl
Ace F0 F1 F2 F3 AN P0
P1
P2
P3
P4
D0
D1
D2
D3 FL PY
FP1
BaA C
0C
1C
2C
3C
4B
bF
BkF
BaP ID DA
BgP
Severely Weathered
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0.05
0.1
0.15
0.2
N0
N1
N2
N3
N4
Acl
Ace F0 F1 F2 F3 AN P0
P1
P2
P3
P4
D0
D1
D2
D3 FL PY
FP1
BaA C
0C
1C
2C
3C
4B
bF
BkF
BaP ID DA
BgP
0
0.05
0.1
0.15
0.2
0.25
Modeled Fingerprint
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Case Study 2: MGP Impacted
ā¢ Urban Sediment Superfund Site
ā¢ History of Combined Sewer Overflows and Manufactured Gas Plant (MGP) Operations
ā¢ Remedial Investigation with publicly available tPAH17
analyses
ā¢ Total normalized; Excludes samples with > 30% non-detected (ND) analytes and concentrations < 1 mg/kg
Question: How does weathering of MGP tar change the parent PAH fingerprint?
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Principal Component Analysis of Parent PAH Fingerprints
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3
PC
2(1
2.7
%)
PC1 (68.7%)
Native Sediment
Sediment
1
3
2
3 PotentialSources
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Principal Component Analysis of Parent PAH Fingerprints
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3
PC
2(1
2.7
%)
PC1 (68.7%)
Native Sediment
Sediment
0.0
0.1
0.2
0.3
0.4
0.0
0.1
0.2
0.3
0.4
0.0
0.1
0.2
0.3
0.4
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Principal Component Analysis of Parent PAH Fingerprints
Crude oilDiesel
#4 Fuel
#6 Fuel
Hi S gas oil
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3
PC
2(1
2.7
%)
PC1 (68.7%)
Native Sediment
Sediment
MGP Tar (EPRI 2000)
Petroleum Sources (EPRI 2000)
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Principal Component Analysis of Parent PAH Fingerprints
Crude oilDiesel
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3
PC
2(1
2.7
%)
PC1 (68.7%)
Native Sediment
Sediment
MGP Tar (EPRI 2000)
Petroleum Sources (EPRI 2000)
Most of the Sediment impacts can be explained by weathering of the MGP tar sources
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Conclusions
ā¢ It is critically important to evaluate weathering trends in Principal Component and Receptor Modeling
āŖ No fingerprint will survive contact with the environment intact
ā¢ Weathering can shift pyrogenic fingerprints into petrogenic patterns for LMW PAHs
ā¢ Weathering trends can obscure mixing trends
āŖ Where this occurs it may be important to incorporate tPAHconcentration or other source tracers into the PAH analysis
ā¢ Weathering can help identify more appropriate source compositions for use in receptor modeling