1. Partitioning and Bioavailability Assessment for Sediments from South Wilmington Wetlands
Huan Xia and Upal Ghosh
Department of Chemical, Biochemical, and Environmental Engineering
University of Maryland, Baltimore County

2. Location 27-acre degraded wetland Contaminants detected in marsh soil:
Metals (e.g. As, Pb, Cr)
PAHs (e.g. Benzo(a)pyrene, Benzo(k)fluoranthene)
PCBs such as Arochlor-1248
(Hendershot and Asreen Jr. 2005)

3. Introduction
Hydrophobic organic compounds (HOCs) like PCBs and PAHs strongly bound to sediment geochemical components
Some carbonaceous particles (e.g. soot and charcoal) exhibit greater sorption capacity than organic matter, resulting in reduced exposure
Traditional risk assessment uses default values from generic organic matter
Site specific values can be orders of magnitude different from default values
EPA recommends using site specific measurement of partition constants to refine the risk assessment

4. Study Objectives: Methods
Evaluate site specific bioavailability of PAHs and PCBs in South Wilmington Wetland sediment and refine risk assessment.
Methods
Sediment samples collected from 12 locations of wetland.
Measurement of PAH and PCB concentrations in sediment samples.
Laboratory partitioning study to measure PAH and PCB porewater concentrations using Polyethylene (PE) as passive sampler
5 PRCs used to correct for equilibrium porewater concentration
Laboratory bioaccumulation study for PCBs using Lumbriculus variegatus

5. Results: Total PAH and PCB concentrations in sediments
Total PAH range from mg/kg , mean value: 12 mg/kg
Total PCB range from mg/kg , mean value :0.7 mg/kg

6. Total Equilibrium porewater concentrations of PAHs & PCBs
The highest PAH porewater concentration was measured in Sed01.
Sed02 and Sed03 were amended with 5% activated carbon to evaluate the effect of the carbon treatment, named as Sed02T and Sed03T. “U” refers to “untreated”.
70% to 90% reduction in PAH porewater concentration observed in treated samples

7. Total Equilibrium porewater concentrations of PAHs & PCBs
The highest total PCB porewater concentration was measured in Sed02U, Sed03U and
80% to 90% reduction in PCB porewater concentration also observed in treated samples
Site specific organic partition constants : Koc= Cs/Cw/foc

8. Bioaccumulation of PCBs in Lumbriculus variegatus
Worm recovery ranges from %.
The highest bioaccumulations in worms were in samples 1330, Sed03 and Sed02, which also had the highest PCB levels in sediment.
Reduction in PCB bioaccumulation was 97-98% in treated samples

9. partition constants for PAHs and PCBs
Measured Koc values for both PAHs and PCBs were 1-2 orders of magnitude higher than the generic values used in preliminary risk assessments
Median value of BC/OC ratio : 9%, n=300 (Cornelissen et al. 2005)
Measured BC/OC ratio: 17-36%
Human Health Risk Assessment Protocol, 2012
Karickoff 1981, Werner et al 2010

10. PCB Bioaccumulation Factors (BCF) in worms
log BCF= log Kow
BCF calculated as: BCF= Clipid/Cporewater
Measured BCF (blue diamonds) are consistent with the generic values (green dash), but nearly 1 order of magnitude higher than those in initial PRG (red dash)
EPA. (1999). Screening Level Ecological Risk Assessment Protocol for Hazardous Waste Combustion Facilities

11. PRGsediment = Toxicity Value × foc × Koc
Calculation for Preliminary Remediation Goals (PRGs)
Benthic organism-based PRGs (Equilibrium Partitioning Approach):
PRGsediment = Toxicity Value × foc × Koc
PRG, concentration in sediment (mg/kg DW sediment)
Toxicity Value , Aquatic community-based toxicity value (μg/L)
foc, Organic carbon fraction (2 % default used in initial calculation, average of 4% TOC was detected in sediments )
Koc, Organic carbon partition constants (default value from HHRAP used in initial calculation, measured specific Koc used in revised version)
Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: PAH Mixtures (EPA, 2003e)

12. Revised Benthic Organism-based PRGs using site specific Koc
Human Health Risk Assessment Protocol, 2012

13. Calculation for Preliminary Remediation Goals (PRGs)
PRGs based on invertebrate –based food web modeling: (bioamagnification and trophic transfer through dietary exposure)
PRGsediment= 𝑇𝐻𝑄 ∗𝑇𝑅𝑉 𝐹𝑇 ∗(𝐹𝐼𝑅∗ 𝐵𝐶𝐹 𝑓 𝑜𝑐 𝐾 𝑜𝑐 +𝑆𝐼𝑅)
Local receptors: American robin, Raccoon, Spotted sandpiper, etc.
Spotted sandpiper was selected due to its most rigid sediment concentration criteria.
(Ecological Sediment Screening Level, EPA 2007a, 1999, 1993)

14. Revised PRGs based on exposure to Spotted Sandpiper

15. Conclusions
Observed site specific Koc values were higher than generic values derived from organic matter, mainly due to elevated black carbon in sediment
BCF measures in good agreement with literature values
PCB bioaccumulation is explained well by porewater data
Site specific measurements provided realistic parameters to refine the remediation goals

16. Acknowledgements City of Wilmington, Delaware Brightfields Inc
Acknowledgements City of Wilmington, Delaware Brightfields Inc. Labmates for worm retrieval

17. Methods
Correction based on different properties: diffusivity, partitioning coefficient, molar volume
Molar volume adjustment
Calculate residual PRC in PE: 𝐶 𝑝𝑟𝑐,𝑓 𝐶 𝑝𝑟𝑐,𝑖
Exchange rate (for PRC) : 𝐾 𝑒,𝑝𝑟𝑐 =− ln⁡( 𝐶 𝑝𝑟𝑐,𝑓 𝐶 𝑝𝑟𝑐,𝑖 ) 𝑡
Sampling rate (for PRC) : 𝑅 𝑠,𝑝𝑟𝑐 = 𝐾 𝑒,𝑝𝑟𝑐 𝐾 𝑝𝑒𝑤,𝑝𝑟𝑐 𝑀 𝑝𝑒
𝑅 𝑠,𝑡𝑎𝑟𝑔𝑒𝑡 = 𝑅 𝑠,𝑝𝑟𝑐 ( 𝑉 𝑚,𝑝𝑟𝑐 𝑉 𝑚,𝑡𝑎𝑟𝑔𝑒𝑡 ) 0.39
𝐾 𝑒,𝑡𝑎𝑟𝑔𝑒𝑡 = 𝑅 𝑠,𝑡𝑎𝑟𝑔𝑒𝑡 𝐾 𝑝𝑒𝑤,𝑡𝑎𝑟𝑔𝑒𝑡 𝑀 𝑝𝑒
𝐶 𝑤,𝑡𝑎𝑟𝑔𝑒𝑡 = 𝐶 𝑝𝑒,𝑡𝑎𝑟𝑔𝑒𝑡 𝐾 𝑝𝑒𝑤,𝑡𝑎𝑟𝑔𝑒𝑡 [1− exp − 𝐾 𝑒,𝑡𝑎𝑟𝑔𝑒𝑡 𝑡 ]
𝐾 𝑝𝑒𝑤 , PE sampler partition coefficient; 𝑀 𝑝𝑒 , mass of PE sampler; 𝑉 𝑚 , molar volume; t, exposure time (28days)
(Huckins et al 2006)

18. partition constants for PAHs and PCBs
Elevated Koc (3-4 orders of magnitude range) for PAHs previously observed from industrially impacted sites (n=117)
Hawthorne et al. 2006

19. Methods Impregnate PE sampler with PRCs
Measured CW may not be at equilibrium
CW corrected using Performance Reference Compounds (PRCs)
Assume absorption = desorption
Assume PRCs have similar properties as HOCs
PRCs: PCB 29 (mono, di, tri), 69 (tetra, penta), 155 (hexa), (hepta, octa, nona and deca groups) for PCB correction and d-10 pyrene for PAH.
Preload PE sampler with PRCs for two week and measure initial concentration in sampler (CPRC,i)
Add PE sampler into sediment

20. Methods Laboratory worm bioaccumulation study for PCBs
Species: Lumbriculus variegatus
Daily water exchange and water quality monitoring
28 days bioaccumulation
Worm collection
Analyzed worm tissue for PCBs

21. Revised Benthic Organism-based PRGs using site specific Koc

22. Revised PRGs based on exposure to Spotted Sandpiper
SVOCs
2,4-Dinitrophenol NA
PAHs
2-Methylnaphthalene
6280
356
Acenaphthene
6010
167
Acenaphthylene
1570
346
Anthracene
7270
256
Benzo(a)anthracene
5050
360
Benzo(a)pyrene
4850
477
Carbazole 37
Chrysene
3500
367
Dibenz(a,h)anthracene
4120
255
Fluoranthene
8110
209
Indeno(1,2,3-cd)pyrene
3820
521
Phenanthrene
5860
288
Pyrene
7570
347
Pesticides
4,4'-DDE
0.017
4,4'-DDT
0.0036
Dieldrin
0.005
0.0014
Endrin
0.013
0.0097
Endrin aldehyde
0.0047
Endrin ketone
0.014
0.0045
gamma-Chlordane
1.61
Heptachlor epoxide
0.030
0.0087
PCBs
PCBs,total
0.40
0.09
Dioxins/Furans
2,3,7,8-TCDD
PRG C
sed
(mg COPEC/kg DW sediment)
NOAEL Based using site BCF
NOAEL Based from initial report
COPEC

23. Revised PRGs : Bentho-based Vs. Exposure to Spotted Sandpiper

24. Revised PRGs : Bentho-based Vs. Exposure to Spotted Sandpiper