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Capping efficiency of various carbonaceous and mineral materials for in situ remediation of marine sediments contaminated with PCDD/Fs, OCS and HCB
Umeå University, Faculty of Science and Technology, Department of Chemistry.
NIVA, Norway.
Systemekologiska institutionen, Stockholms universitet.
Systemekologiska institutionen, Stockholms universitet.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The efficiency of various thin-layer capping materials in reducing the sediment-to-water flux and benthic organism bioaccumulation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), hexachlorobenzene (HCB) and octachlorostyrene (OCS) was investigated in a boxcosm experiment. The influence of cap layer thickness (0.5-5 cm) and different cap materials were tested using a three-factor experimental design. The capping materials consisted of a passive carrier (coarse or fine limestone material, or a marine clay sediment), and an active material (activated carbon (AC) or kraft lignin) to sequester the contaminants and decrease their bioavailability. Macrofauna was added to the boxes to get a semi-natural bioturbation. The sediment-to-water flux was measured using passive (SPMD) samplers, and the bioaccumulation by the surface-dwelling gastropod Hinia reticulata and the deep-burrowing polychaetes Nereis spp. was determined. Results showed substantial decreases in both flux and bioaccumulation as a result of thin-layer capping. The thickness of the capping layer and the choice of active material were important factors, while the use of different types of passive materials was not statistically significant for any of the observed endpoints. Flux and bioaccumulation decreased with increased cap thickness, and could be further decreased with addition of active material. Activated carbon was more efficient than lignin, and a ~90% reduction of the flux and bioaccumulation, compared to uncapped control sediment, could be achieved with 3 cm caps with 3.3% AC (g C/g ww clay). The reduction was generally larger in the surface-dwelling H. reticulata than in Nereis spp., and the magnitude of the reduction was frequently similar between Nereis spp. and sediment-to-water fluxes. The latter was interpreted to indicate a link between Nereis spp. bioirrigation and sediment-to-water fluxes. Furthermore, the reduction in sediment-to-water flux was dependent on the hydrophobicity of the congeners, with less hydrophobic congeners achieving a larger reduction than more hydrophobic congeners.      

Keyword [en]
sediment-to-water fluxes, benthic bioaccumulation, thin-layer capping, cap thickness
National Category
Environmental Sciences Environmental Sciences Other Environmental Engineering
Research subject
biology, Environmental Science
URN: urn:nbn:se:umu:diva-42104OAI: diva2:408597
Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-04-15Bibliographically approved
In thesis
1. Fate and transport of POPs in the aquatic environment: with focus on contaminated sediments
Open this publication in new window or tab >>Fate and transport of POPs in the aquatic environment: with focus on contaminated sediments
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Persistent organic pollutants (POPs) are hydrophobic substances that readily sorb to organic matter in particles and colloids instead of being freely dissolved in the water phase. This sorption affects the bio­availability and environmental transport of the POPs. The major part of this thesis concerns the role of sediments as secondary sources of POPs. As the primary emissions decrease, contaminated sediments where POPs have accumulated can become the main source of contamination. If the contaminated sediment by time becomes covered with cleaner layers, the POPs are buried and no longer in contact with the aquatic environment. Experiments in this thesis showed, however, that new invading species can alter the sediment-water dynamics as a result of their bioturbation, i.e. mixing of sediment particles and pore-water. Marenzelleria spp., invading species in the Baltic Sea that burrow deeper than native species, were found to increase the remobilization of buried contaminants. The sediment-to-water flux was inversely related to the burial depth (2-10 cm) of the POP congeners (polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers) and also inversely related to the hydrophobicity of the congener. The flux was therefore most pronounced for less hydrophobic contaminants, which was linked to the bioirrigating behaviour of these species. Marenzelleria spp. also accumulated the buried POPs and increased concentrations in surface sedi­ment. Contaminants previously considered buried at a ’safe’ depth can thus be remobilized as a result of the invasion of Marenzelleria spp. in the Baltic Sea.

One method to decrease the remobilization of contaminants from sediments is ’capping’, i.e. a layer of clean material is placed as a cap on the sediment. By amending the cap with active materials, which sequester the POPs and decrease their availability, thinner layers can be used (’active capping’ or ’thin-layer capping’). Results from an experiment with thin-layer capping using different active materials (activated carbon (AC) and kraft lignin) showed that both the sediment-to-water flux and the bioaccumulation by benthic species of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), hexachlorobenzene (HCB) and octachlorostyrene (OCS) decreased with increased thick­ness of the cap layer (0.5-5 cm). Amendments with active materials further increased the cap efficiency. AC was more efficient than kraft lignin, and a 3 cm cap with 3.3% AC reduced the flux and bioaccumulation with ~90%. The reduction of the sediment-to-water flux was inversely related to the hydrophobicity of the POP, and reductions in the flux had similar magnitudes as reductions in the concentration in deep-burrowing polychaetes, demonstrating the importance of bioturbation for sediment-to-water transport.

In a one-year study on the levels of PCDD/Fs, PCBs, and HCB in a coastal area of the Baltic Sea, the correlations between the POP levels and the levels of particles and organic carbon in the water were found to differ for POPs of different structure and hydrophobicity. The levels of PCDD/Fs decreased to one third in May, which could be related to the increased sedimentation, i.e. water-to-sediment transport, during spring bloom.

Place, publisher, year, edition, pages
Umeå: Kemiska institutionen, 2011. 65 p.
bioturbation, bioirrigation, bioaccumulation, secondary sources, buried contaminants, sediment remediation, active capping, thin-layer capping, Marenzelleria spp., Baltic Sea, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated biphenyls, hexachlorobenzene, octachloro¬styrene, polybrominated diphenyl ethers, PCDD/Fs, PCBs, HCB, OCS, PBDEs, water sampling, passive sampling, particulate fraction, freely dissolved, apparently dissolved, colloid, organic carbon, activated carbon, lignin, sediment-to-water flux, spring bloom
National Category
Chemical Sciences
Research subject
biology, Environmental Science
urn:nbn:se:umu:diva-42107 (URN)978-91-7459-179-8 (ISBN)
Public defence
2011-05-06, KB3B1, KBC-huset, Linnaeus väg 6, Umeå, 10:00 (English)
Available from: 2011-04-15 Created: 2011-04-05 Last updated: 2011-09-30Bibliographically approved

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