Equilibrium sampling for a thermodynamic assessment of contaminated sediments

Abstract

Hydrophobic organic contaminants (HOCs) reaching the aquatic environment are largely stored in sediments. The risk of contaminated sediments is challenging to assess since traditional exhaustive extraction methods yield total HOC concentrations, whereas freely dissolved concentrations (C_free) govern diffusive uptake and partitioning. Equilibrium sampling of sediment was introduced 15 years ago to measure C_free, and it has since developed into a straightforward, precise and sensitive approach for determining C_free and other exposure parameters that allow for thermodynamic assessment of polluted sediments. Glass jars with µm-thin silicone coatings on the inner walls can be used for ex situ equilibration [1] while a device housing several silicone-coated fibers can be used for in situ equilibration [2]. In both cases, parallel sampling with varying silicone thicknesses can be applied to confirm valid equilibrium sampling (method incorporated QA/QC). The measured equilibrium concentrations in silicone (Csil) can then be divided by silicone/water partition ratios to yield C_free. CSil can also be compared to CSil from silicone equilibrated with biota in order to determine the equilibrium status of the biota relative to the sediment [3]. Furthermore, concentrations in lipid at thermodynamic equilibrium with sediment (C_(Lip⇌Sed)) can be calculated via lipid/silicone partition ratios (C_Sil×K_(Lip:Sil)), which has been done in studies with limnic, river and marine sediments [1,3-5]. The C_(Lip⇌Sed) data can then be compared to lipid-normalized concentrations in aquatic organisms or to regulatory thresholds. Finally, CSil can also be converted into chemical activities (a), which express the energetic level of the chemicals, drive several spontaneous processes and are well linked to the potential for baseline (mixture) toxicity [6]. This overview lecture will focus at the latest developments in equilibrium sampling concepts and methods. Further, we will explain how these approaches can provide a new basis for a thermodynamic assessment of polluted sediments.

References. [1] Jahnke et al., Environ. Sci. Technol., 2012, 46: 10114; [2] Witt et al., Environ. Sci. Technol., 2013, 47: 7830; [3] Jahnke et al., Environ. Sci.: Processes Impacts, 2014, 16: 464; [4] Mäenpää et al., Environ. Toxicol. Chem, 2015, 34, 2463–2474, ; [5] Jahnke et al., Environ. Sci. Technol., 2014, 48: 11352; [6] Mayer et al., Integr. Environ. Assess. Manag., 2014, 10: 197.

Full text

Equilibrium sampling for a
thermodynamic assessment of
contaminated sediments
Philipp Mayer1, Stine N. Schmidt1, Kimmo Mäenpää 2,
Gesine Witt 3, Sabine Schäfer4, Phil Gidley5 & Annika Jahnke6
1Technical University of Denmark, 2University of Eastern Finland, 3Hamburg
University of Applied Sciences, Germany, 4German Federal Institute of Hydrology,
5 USACE-ERDC, USA & 6Stockholm University, Sweden (now UFZ, Germany)

F. Reichenberg & P. Mayer, Environ. Toxicol. Chem. 2006, 25, 1239-1245.
Classical extraction Equilibrium sampling device (ESD)

1) Matrix-SPME with disposable fibers (2000)
1. Equilibrate thin polymer with sample
Mayer et al, ES&T, 2000, V 34: 5177-5183
Mayer et al., ES&T, 2003, V37: 184A-191A
kCounts
2.0
1.5
1.0
0.5
kCounts
5
4
3
2
1
Hexachlorobenzene
0
25
50
75
100
0.0
0.5
1.0
1.5
2.0
kCounts
kCounts
Flu Fl u
32.5
31.0
minutes
0.0
2.5
5.0
7.5
10.0
12.5
15.0
PCB-52
PCB-65
PCB-52
PCB-65
kCounts
0.00
0.25
0.50
0.75
1.00
1.25
1.50
kCounts
Hexachlorobenzene
28.0
2. Measure CPDMS
3. Cfree=CPDMS/KPDMS,water

2) Silicone coated vials (2008)

Coated vials with multiple coating thickness
Benzo(a)pyrene
0
50
100
010 20 30 40
VPDMS (mL)
n (pmole)
Confirms:
1. equilibrium
2. negligible depletion
3. no surface artefacts/abrasion

Hamburg University of Applied Sciences (HAW)
• in-situ deployment of sampler
•rinse with water and wipe dry
•store fiber in GC injection liner
•insert fiber with automated
injection liner exchange (ALEX)
•thermal desorption
•MS identification/ quantification
Sampling
Sample
preparation
Analysis
3)

PCB concentrations in polymer  can be converted into:
1) The effective concentration driving diffusion

  

(since 2000)
2) The chemical activity (energetic state) driving equilibrium partitioning
  

(since 2006)
3) The thermodynamic potential for bioaccumulation
     (since 2011)
Measurement endpoints of
Equilibrium Sampling

Case Studies focusing on
PCBs & 

1)

2)

3)

Prossen
0500 1000 1500 2000 2500 3000
Cbio,lip (µg kg-1 lipid)
0
500
1000
1500
2000
2500
3000
Barby
Clip sed (µg kg-1 lipid)
0500 1000 1500 2000 2500 3000
0
500
1000
1500
2000
2500
3000
Cumlosen
0500 1000 1500 2000 2500 3000
0
500
1000
1500
2000
2500
3000
PCB 28
PCB 52
PCB 101
PCB 118
PCB 138
PCB 153
PCB 180
y = 0.297x
R2 = 0.921 y = 0.390x
R2 = 0.997 y = 0.327x
R2 = 0.927
1. ex situ equilibrium sampling of sediment from 10 locations in River Elbe (Germany)
2. Clipid-normalized in common bream from independent monitoring program
4)
1. Cross validation of two monitoring programs
2. Bioaccumulation in common bream tightly linked to 
–R2 > 0.9 (linear scale!) & very similar slopes between sites

ET&C, 2015, V 34: 2463–2474 (DOI: 10.1002/etc.3099)
Fate of polychlorinated biphenyls in a contaminated lake ecosystem:
Combining equilibrium passive sampling of sediment and water with total
concentration measurements of biota
Kimmo Mäenpää, Matti Leppänen, Kaisa Figueiredo, Philipp Mayer, Dorothea Gilbert, Sirpa
Herve, Annika Jahnke, Carmen Gil-Allué, Jarkko Akkanen, Inna Nybom, Auli Kostamo
5)

ER-2431
Quantitative Thermodynamic Exposure
Assessment (Q-TEA) Supporting Resilient
Contaminated Sediment Site Restoration
USACE-ERDC (Lead): Todd S. Bridges, Philip T. Gidley,
Guilherme Lotufo, Carlos Ruiz, Alan J. Kennedy,
DTU: Philipp Mayer, Stine Nørgaard Schmidt
Sediment Solutions: Upal Ghosh
USA-EPA: Robert M. Burgess
Northeastern University: Loretta Fernandez,

Cross validation of equilibrium sampling
1. Coated jars produced at DTU & BfG
2. Equilibrium sampling of New Bedford sediment at BfG & ERDC
3. Instrumental analysis at BfG & ERDC

Conclusions and take home messages
Equilibrium sampling of sediments
–equilibrium sampling feasible even for PCBs
–can yield Cfree, chemical activity & 

–in all studies so far ≥ Clipid,normalized
–thermodynamic potential for bioaccumulation
Sediments have high PCB levels, not only in
concentration but also thermodynamically!

Acknowledgements
This research was financially supported by
•EU Commission (OSIRIS, NOMIRACLE & MODELPROBE)
•Danish Council for Independent Research in Technology and Production
Sciences (FTP)
•Swedish Research Council FORMAS
•German Federal Ministry for the Environment, Nature
Conservation, Building and Nuclear Safety
•German Research Council (DFG)
•Academy of Finland
•US Strategic Environmental Research and Development Program
(SERDP) (14 ER03-035/ER-2431).