Natural Attenuation Processes in Contaminated Sediments

1
Natural Attenuation Processes in Contaminated
Sediments
Danny Reible Chevron Professor of Chemical
Engineering Director, Hazardous Substance
Research Center/SSW Louisiana State
University Baton Rouge, LA 70810
2
Outline
What do we know about contaminated sediment
processes? - Dynamic sediment environments -
Stable sediment environments Assessing Exposure
and Risk - Contaminant Accessibility -
Contaminant Availability - Organism Assimilative
Capacity
3
Contaminant Processes at the Sediment-Water
Interface
4
Dynamic Sediment Environments

• Contaminants typically strongly associated with
  solids
• Especially fine particulate fraction
• Erosive characteristics difficult to define due
  to cohesiveness, spatial variability
• Contaminant dynamics often defined by sediment
  dynamics
• Historical sediment contamination often
  associated with stable deposits
• Sediments may still be subject to erosional
  events
• Due to changes in hydraulics
• Due to sediment changes affecting equilibrium
  surface
• Due to storm events

5
Stable Sediment Environments

• Associated with low flow environments
• Contaminant dynamics controlled by
• Water side mass transfer resistances
• Sorption retarded diffusion/advection in pore
  water
• Bioturbation - normal life cycle activities of
  benthic organisms
• Bioavailability
• Bioavailability
• Accessibility - Within biologically active zone?
• Availability - Sequestered or available to
  porewater?
• Assimilative Capacity - Can uptake occur?

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Bioturbation

• Dominated by deposit feeders that ingest sediment
  
• Increases sediment cycling to the surface
• Increases porewater irrigation of sediments
• Increases oxygen transport into the sediments-
  enhancing biodegradation
• Organism uptake contributes to transmission up
  food chain
• 90 of measurements worldwide show biologically
  mixed zone lt15 cm
• Defines region of accessibility
• EXCEPT - if depth of sediment layer dynamic

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Effective Transport Coefficients
Bioturbation by Tubificid Oligochaetes
Bioturbation

M-
T
Coeff
.
Sediment
Age
W
Pyrene
days
mg/kg
Limnodrilus
Lumbriculus
2
26,700 /cm
26,700 /cm
2
2
0.48 mg/cm
1.27 mg/cm
2
0.42
Bayou
30
749
0.46
Manchac
65
60
6
0.290.13
0.350.06
University
30
683
0.41
0.39
Lake
60
596
0.370.12
0.260.06
8
1.2
1
0.8
0.6
0.4
Log(Flux)
0.2
0
-1
-0.5
0
0.5
1
1.5
2
2.5
-0.2
log(flux)
square root prediction
-0.4
linear growth
Poly. (log(flux))
-0.6
Log(Fauna Density/ /cm2)
9
100
80
60
Worm
Control
Moisture Content ()
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Depth (mm)
10
70
60
50
40
Worm
Control
Pyrene (mg/kg dry)
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Depth (mm)
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Contaminant Availability

• Metals availability
• Some success with AVS/SEM ratio
• gt 1 indicates several important metals fixed in
  sulfide form and unavailable
• lt 1 not a clear indicator
• Full description requires sophisticated metal
  speciation dynamics
• Hydrophobic organic availability
• Significant limitations shown for PAHs in soils
  (e.g. Martin Alexander)
• Significant sequestration in sediments containing
  soots
• Biphasic desorption rates and equilibrium
  commonly observed
• Linear, reversible compartment
• Nonlinear, desorption resistant compartment
  (Langmuir in shape)
• Biological Availability?

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UNWEATHERED
WEATHERED
Sediment
Sediment
max
60
6
0
5
0
50
(Fg/g)
(Fg/g)
4
0
40
max
3
0
30
20
2
0
10
1
0
.
Water

Water

max
30
30
(Fg/ml)
(Fg/ml)
20
20
10
10

max
0.02
0.02
0.01
0.01
.
.
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Implications for Sediment Quality Criteria (Ex.
Utica Harbor)
Present SQC for
Phenanthrene
is 150
g/g-OC
m
Observed 1149 g/kg-OC
Phenanthrene
in Utica Harbor Sediment
100000
Irr
.
g/g-OC)
10000
Observed
Rev.
m
1000
. (
SQC
100
Conc
Source Tomson and Kan
10
No
FCV
Risk
1
Soil Phase
0.0001
0.001
0.01
0.1
1
Water Phase
Conc
. (
m
g/ml)
14
Organism Assimilative Capacity

• Accessible region typically limited to upper
  10-15 cm in stable sediment deposit
• Availability potentially limited by sequestration
  
• Assessment of organism assimilative capacity?
• Microorganisms?
• Macrobenthos??

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Comparison of Desorption to
Biodegradation Rates
40
Phe-low biomass
Phe-high biomass
30
Phe - abiotic
20
10
0
0
100
200
300
400
500
600
Time, Hours
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Table 1 - Comparison of observed contaminant
accumulation in various benthic worms and
predicted by effective partitioning between
sediment and water
Contaminant - dominant state
Concentration
K

BSAF
Predicted
sw
eff
mg/kg
BSAF
2

1
Pyrene
- reversibly sorbed
lt50
750
1.010.45
1
127
980
0.70.1
0.77
Pyrene -
Supersaturated sediments
1
240
1850
0.47
Pyrene -
Supersaturated sediments
0.40.05
1
Fluoranthene -
with adsorbent resin
97
38,250
0.01390.01
0.019
3
85 mg/kg
260
1.200.44
1
- reversibly sorbed
Phenanthrene
4
32 mg/kg
350
0.75
1.190.23
Phenanthrene
mostly reversibly sorbed
4
8 mg/kg
- mostly sequesztered
760
0.600.16
0.34
Phenanthrene
rapid isopropanol washes
4
Phenanthrene
- mostly sequestered
14 mg/kg
-
0.2450.004
-
with XAD in sediment
4
1
Note
Pyrene experiments conducted with
Limnodrilus hoffmeisteri

2
Predicted BSAF is defined by effective partition
coefficient
3
Kasian et al. (1999) with
Lumbriculus variegatus
4
Phenanthrene experiments conducted with
Illodrillus templetoni
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Effective Partition Coefficient as a Predictor of
BSAF
2
1 - flouranthene with sorbent
2 - pyrene
Balance phenanthrene
2
1
BSAF Predicted
2
2
2
r
0.75
1
0
0
1
2
BSAF Observed
18
1
Organism Assimilation Processes
2
4
1
2
Lipid
3
Digestive canal
Sediment particle
Lipid
19
Conclusions

• Exposure dependent upon
• Accessibility
• Availability
• Organism Assimilative Capacity
• Accessibility limited to upper 10-15 cm in stable
  sediments
• Availability may be limited by sequestration
• Assimilation defined largely by sediment-water
  partitioning
• Porewater fate processes allow continued release
  of sequestered contaminants (Controlled by
  release dynamics)
• Accumulation consistent with two stage model of
  uptake in benthic macroorganisms (Controlled by
  release equilibrium)