1. Forensic Sediment Evaluation: Differentiating Basin
Derived Media vs. Anthropogenic Sources using
Multivariate Statistics
Eric M. Cherry, Principal Scientist
Gina Groom, MPH Health Scientist
Hexagon Environmental Solutions LLC
Environmental Chemistry | Forensics | Data Evaluation | Risk Analysis
2. Every Story has a Beginning
• A Little History
• Geochemical Prospecting
• Geophysics (statistics on a sphere)
• Multivariate Analysis since 1980 (punch cards)
• Learning to “keep it simple”
• Initiating Quotes
• “What do you mean these metals came from the
watershed? There is a source right here.”
Opposing counsel
• “What do you mean that most of these PAHs came
from upstream? That’s undeveloped land and there
are sources here in the harbor!” Senior technical
colleague
• “We use accepted protocols and high precision
analytical instruments, so that we can put data in
spreadsheets then run statistical models, and
ultimately derive a reasonable story of what is going
on. We are high-tech story tellers!” Eric Cherry
Hexagon Environmental Solutions
2
3. Sediment Assessment - Fundamental Questions
• Do the sediments in this river or harbor pose
a risk to the aquatic ecosystem or to human
health?
• If so, by what chemicals or elements?
• If so, where?
• If so, who is responsible and who will pay?
Hexagon Environmental Solutions
3
• What are these sediments composed of?
• Are there multiple chemical signatures in the
sediments?
• Are there locations that are clearly different
from others?
• How are they different?
• Can we identify a specific source?
• Do these sediments pose a risk?
• Why is the question being asked?
• Who is the audience?
• Who are the Stakeholders?
4. Approaches to Sediment Evaluation
Hexagon Environmental Solutions
4
• Traditional Approach
• Develop and Implement Sampling &
Analysis Plan
• Calculate chemical-specific distributions
• Compare to Sediment Quality Values
• Refine and Delineate Impacted Areas
• Develop and Implement Remedial Plan
• Obtain Funds from PRPs/RPs
• Alternate Forensic Approach
• Develop and Implement Tiered and Sequential
Sampling & Analysis Plan
• Evaluate multiple chemical relationships to
identify associated and unique sample groups
by multivariate methods
• Conduct supplemental sampling for
delineation, sequential extraction and toxicity
testing
• Refine and Delineate Impacted Areas based on
supplemental testing
• Develop and Implement Remedial Plan
• Obtain Funds from PRPs/RPs
5. The Traditional Approach to Sediment Evaluation
• Identify Contamination
based on Criteria or Limit
• Freshwater
Lowest Effects Level (LEL)
Probable Effects Level (PEL)
Severe Effects Level (SEL)
• Marine
Effects Range Low (ERL)
Effects Range Medium (ERM)
• State Values
• International Values
Hexagon Environmental Solutions
5
USEPA/Weston, 2012. Sediment Assessment Report – St. Louis Bay-St. Louis River
Area of Concern. DCN 1023-2A-ATMN
6. The Math of How the Traditional Approach Works
• Obtain sediment data for
arsenic (or other chemical)
• Sort by Concentration
• Compare to Consensus
Value
• Green Data Set
• 43.8% Exceed Tel
• 5.5% Exceed Background
• 1.8% Exceed PEL
• 0.0% Exceed SEL
Hexagon Environmental Solutions
6
Background Metals vs. Potentially Impacted Sediments
0
5
10
15
20
25
30
35
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161
S ample Number
Severe Effects Level 33 mg/kg
Probable Effects Level 17 mg/kg
Threshold Effects Level 5.9 mg/kg
Background = mean + 2 sd 13.9 mg/kg
Arsenic vs. Consensus Value
7. Evaluation of Traditional Approach
• Advantages of Traditional Approach
• Easy to perform evaluation
• Clear decision points
• Delineation sampling to refine extent
of impact
• Very conservative approach (i.e.
“protective”)
• Easy to communicate to Stakeholders
• Disadvantages
• Default classification of “contamination”
based on Consensus values (how do we
define contamination?)
• Non-holistic
• Is not capable of identifying natural
relationships
• Oversimplifies a complex system
• Probably overestimates extent of toxic
impacts
• More expensive to implement remedy
Hexagon Environmental Solutions
7
8. Overview of the Forensic Approach
• Defining “Forensics”
• It’s all about “making the argument” in a
science-based and logical manner
• Start with a “Single Blind” approach to
identify what the data is saying
chemically, then expand to spatial
relationships (minimize investigator bias)
• Does not require, but may include,
advanced analytical methods
• Does include more sophisticated data
evaluation techniques
• Objective is to translate complex
information into a story that is
understandable to multiple Stakeholders
• Forensic Toolbox
• Given . . . A big data set!
• Pair-wise regression (Fe:As, Pb:Zn)
• Cluster Analysis (Family Associations)
• Principal Component Analysis
• Concentration Distributions
• Spatial Distribution of Families
• Association of Family Composition Profiles to
Potential Source Profiles
• Toxicity Testing and Sequential Extraction
• Infographics!
Hexagon Environmental Solutions
8
10. Meet the Stakeholders!
• What are our goals?
• Understand the concerns
• Protect/Restore the environment
• Be true to the science
• Understand the physical system
• Be fiscal stewards with limited resources
• Communicate clearly and involve
stakeholders
Hexagon Environmental Solutions
10
I’m Roy
the
Regulator
I’m Black
Hat
Industries
I’m Freddy
Fisherman,
Nature
Lover
11. Quick Summary with Legos!
Hexagon Environmental Solutions
11
Sediments are “in the Basin”
Complex mixture, but we have a sampling and
analysis plan . . . And a sequential protocol for
data evaluation
Each sample (n=10) contains target and
non-target analytes
12. Quick Summary with Legos!
Hexagon Environmental Solutions
12
Target analyte concentrations vary within a
sample and total (sum) of analytes varies
Relative proportions of different analytes may
vary between samples, and some analytes
may be absent
13. Dealing with real data
• Given a real data set, what are the
questions?
• What are the baseline relationships
between chemical parameters?
• Where are the commonalities?
• Where are the differences?
• What is unique?
• What are the methods?
• Regression – line, lines, shotguns
• Cluster Analysis – family groups
• Principal Component – prom night
• Confounders - yea, that influences things
• Spatial Relationships – there but not here
• Supplemental evaluation – how bad is it,
really
• Infographics – every picture tells a story
• Conclusions – many legs make a stable
table
Hexagon Environmental Solutions
13
14. Regression and Cross-Plots
Hexagon Environmental Solutions
14
45000
30000
15000
0.20.10.0
1000
500
0 300
150
0 80400 420 0.010
0.005
0.000
1000
500
0
1000
500
0
300
150
0
100
50
0
80
40
0
10
5
0 4
2
0
50
25
0
0.010
0.005
0.000
45000
30000
15000
0.2
0.1
0.0
1000
5000
100500 1050 50250
Fe
Zn
Pb
Cu
Cr
Ni
As
Cd
Hg
2b-TIN
3b-TIN
Matrix Plot of Fe, Zn, Pb, Cu, Cr, Ni, As, Cd, Hg, 2b-TIN, 3b-TIN
Fe
Zn
Pb
Cu
Cr
Ni
As
Hg
Cd
2Sb
3Sb
Fe:Cd
Shotgun(?)
Hg
Outlier!
Zn:Pb
Multi-Linear
Fe:Ni
Linear
17. Clusters by Relative Proportion of Target Metals
Hexagon Environmental Solutions
17
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Mean ALL Group MCA D 1
n=151
Group MCA D 4
n=51
Group MCA D 3
n=5
Group MCA D 5
n=4
Group MCA D 2
n=2
Group MCA D 7
n=2
Group MCA D 6
n=1
Relative Metal Proportions in MCA Cluster Groups
Zn Pb Cu Cr Ni As
18. Clusters by Concentration
Hexagon Environmental Solutions
18
0
200
400
600
800
1000
1200
1400
1600
Mean ALL Group MCA D 1
n=151
Group MCA D 4
n=51
Group MCA D 3
n=5
Group MCA D 5
n=4
Group MCA D 2
n=2
Group MCA D 7
n=2
Group MCA D 6
n=1
CumulativeMetalsConcentration(mg/kg)
Cumulative Metal Concentrations in MCA Cluster Groups
Zn Pb Cu Cr Ni As
19. Principal Component Analysis – Let’s Dance
Hexagon Environmental Solutions
19
-8
-6
-4
-2
0
2
4
-4 -2 0 2 4 6 8 10
PrincipalComponent2(fromMCADGroupings)
Principal Component 1 (from MCA D Groupings)
Group 1 PCA 2 Group 4 PCA 2 Group 3 PCA 2 Group 5 PCA 2
Group 2 PCA 2 Group 7 PCA 2 Group 6 PCA 2
-8
-6
-4
-2
0
2
4
6
-4 -2 0 2 4 6 8 10
PrincipalComponent3(fromMCADGroupings)
Principal Component 1 (from MCA D Groupings)
Group 1 PCA 2 Group 4 PCA 2 Group 3 PCA 2 Group 5 PCA 2
Group 2 PCA 2 Group 7 PCA 2 Group 6 PCA 2
20. What about those Anthropogenic Metals!
Hexagon Environmental Solutions
20
y = 0.1202x - 0.3098
R² = 0.8416
y = 0.0003x + 0.0078
R² = 0.0005
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 2 4 6 8 10
TributylTin(mg/kg)
Arsenic (mg/kg)
Tributyltin vs. Arsenic
As As-lo Linear (As) Linear (As-lo)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 2 4 6 8 10
Tributyltin(mg/kg)
Arsenic (mg/kg)
Tributyltin vs. Arsenic
TBT Fraser Shipyard TBT Other Howard's Bay
Tributyltin is an anthropogenic organometallic compound
Its primary function is as an additive to marine paints to prevent
biofouling on ships. It is intentionally toxic.
21. Tributyltin and other Metals: Paint formulations?
Hexagon Environmental Solutions
21
In regression analysis, one must consider both statistical relevance and physical plausibility.
y = 1.1072x - 0.0618
R² = 0.6488
y = 0.0191x + 0.0017
R² = 0.1018
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.00 0.50 1.00 1.50
TributylTin(mg/kg)
Mercury (mg/kg)
Tributyltin vs. Mercury
Hg Hg-lo
Linear (Hg) Linear (Hg-lo)
y = 0.4659x - 0.128
R² = 0.779
y = 0.0238x - 0.0096
R² = 0.2448
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 0.5 1 1.5 2
TributylTin(mg/kg)
Cadmium (mg/kg)
Tributyltin vs. Cadmium
Cd Cd-lo
Linear (Cd) Linear (Cd-lo)
y = 0.0053x - 0.0046
R² = 0.6287
y = -1E-05x + 0.0099
R² = 0.002
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 100 200 300 400
TributylTin(mg/kg)
Lead(mg/kg)
Tributyltin vs. Lead
Pb Pb-lo
Linear (Pb) Linear (Pb-lo)
22. Confounding Variables
• A confounding variable is
something that may affect the
correlates with the dependent
and independent variable
• It is a factor that may need to be
adjusted for in interpreting a data
set
• Potential confounders for metals
in sediments include grainsize and
organic carbon
• Important general questions
• Where do sediments actually
come from?
• How is the sediment source area
characterized?
• What changes have happened in
the source area and when?
• What changes have happened in
the receiving are (sediment basin)
and when?
Hexagon Environmental Solutions
22
24. That Next? Supplemental Analyses
• Sequential Extraction
• Surrogate for bioavailability
• More expensive than standard
analyses
• Easily soluble
• Carbonate bound
• Organic bound
• Iron Oxide bound
• Residual
• Sediment toxicity testing
• Surrogate for actual toxicity based
on specified organisms
• More expensive than chemical
analysis or sequential extraction
• Probably best estimate of actual
ecological toxicity measure
Hexagon Environmental Solutions
24
25. Spatial Distribution – “Taking the blinders off”
• How does “what the data says”
from compositional profiles
compare with “location of
samples”?
• How does the “location of
samples” compare with
reasonable “potential source
areas”?
• Example from large sediment
study
• Active marine harbor
• Urban setting
• Drainage basin characterized by
mixed industry, agriculture and
large forest tracts
Hexagon Environmental Solutions
25
26. PAH Profiles and PCA Diagram
Hexagon Environmental Solutions
26
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
-15.0 -10.0 -5.0 0.0 5.0 10.0
Title
Title
Sediment PAH - PCA Results
PC 1 vs PC 2
Sed PAH Group A Sed PAH Group B Sed PAH Group C
Sed PAH Group D Sed PAH Group E Sed PAH Group F
Sed PAH Group G Sed PAH Group H Sed PAH Group I
0.00
0.05
0.10
0.15
0.20
NAP
1mNAP
2mNAP
ANY
ACE
FLU
ANT
PHE
FLA
PYR
BaA
CHR
BbF
BkF
BaP
BeP
DBA
PER
IP
BPE
PAH 1462 Group A n=677 (46.31%)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
NAP
1mNAP
2mNAP
ANY
ACE
FLU
ANT
PHE
FLA
PYR
BaA
CHR
BbF
BkF
BaP
BeP
DBA
PER
IP
BPE
PAH 1462 Group D n=40 (2.74%)
0.00
0.05
0.10
0.15
0.20
NAP
1mNAP
2mNAP
ANY
ACE
FLU
ANT
PHE
FLA
PYR
BaA
CHR
BbF
BkF
BaP
BeP
DBA
PER
IP
BPE
PAH 1462 Group F n=13 (0.89%)
27. Spatial Distribution after Cluster Analysis
Hexagon Environmental Solutions
27
620,000
640,000
660,000
680,000
700,000
720,000
7,600,0007,610,0007,620,0007,630,0007,640,0007,650,0007,660,000
Northing
Easting
Sediment PAH Group A
Distributions
Sed Samples Group A
620,000
640,000
660,000
680,000
700,000
720,000
7,600,0007,610,0007,620,0007,630,0007,640,0007,650,0007,660,000
Northing
Easting
Sediment PAH Group D
Distributions
Sed Samples Group D
620,000
640,000
660,000
680,000
700,000
720,000
7,600,0007,610,0007,620,0007,630,0007,640,0007,650,0007,660,000
Northing
Easting
Sediment PAH Group F
Distributions
Sed Samples Group F
Urban Background Petroleum Combustion
and Asphalt/Creosote
Coal and Natural Diagenetic PAHs
28. Conclusions
• Clearly identify the goals and objectives of a sediment project
prior to establishing all methods of evaluation
• Application of multivariate statistical methods in a forensic
approach can identify relationships within the basin
• Professional judgement combined with proper application of
methods is essential for resolving the story in complex data sets
• Multiple lines of evidence can help to determine whether high
concentration samples are associated with natural materials or
anthropogenic sources of contamination
• Forensic methods of data evaluation may be slightly more
expensive during investigation, but are negligible in comparison
to undertaking remediation of natural sediments without
significant contribution from anthropogenic sources.
Hexagon Environmental Solutions
28
Questions?
