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| 2. |
- Anderson, Craig, 1976, et al.
(författare)
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Autoradiographic comparisons of radionuclide adsorption between subsurface anaerobic biofilms and granitic host rocks
- 2006
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 23:1, s. 15-29
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Tidskriftsartikel (refereegranskat)abstract
- In high level nuclear waste repositories, the host rock is considered to be an important barrier to radionuclide migration by adsorbing metals at fluid rock interfaces. In granitic rock environments the surfaces of hydraulically conductive fractures are covered with mixed community biofilms. Biofilms were grown in situ on glass and rock surfaces in high pressure flow cells using groundwater sourced from a borehole 450 meters below sea level in the Aspo hard rock laboratory, Sweden. Scanning electron microscopy (SEM), epifluorescence microscopy and energy dispersive X-Ray spectroscopy (EDS) revealed monolayer biofilms consisting of up to 2 x 10(4) bacteria/mm(2) surrounded by an extensive extracellular matrix and carbonate precipitates that covered
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| 3. |
- Anderson, Craig, 1976, et al.
(författare)
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In situ ecological development of a bacteriogenic iron oxide-producing microbial community from a subsurface granitic rock environment
- 2006
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 4:1, s. 29-42
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Tidskriftsartikel (refereegranskat)abstract
- The initial development and diversity of an in situ subsurface microbial community producing bacteriogenic iron oxides (BIOS) were investigated at the initiation of biofilm growth (2-month period) and after a 1-year period of undisturbed growth. Water chemistry data, samples of iron encrusted biofilm material and groundwater were collected from BRIC (BIOS reactor, in situ, continuous flow) apparatuses installed 297 m below sea level at the Äspö Hard Rock Laboratory (HRL) in south eastern Sweden. Comparisons between the BIOS BRIC system and an anaerobic control (AC) BRIC revealed that water mixing at the inflow leads to profuse development of BIOS related to a slightly elevated level of O2 (up to 0.3 mg L-1 at the transition zone between BIOS development and non-development) and elevated Eh (>120 mV) in the first 70 mm of water depth. Decreases in dissolved and particulate iron were connected to the visible appearance of BIOS biofilms. The basic phylogenetic diversity of this site was evaluated using amplified ribosomal DNA restriction enzyme analysis (ARDRA), denaturing gradient gel electrophoresis (DGGE) and partial sequencing of 16S rDNA. From 67 clones that were positive for 16S rDNA inserts, a total of 42 different ARDRA profiles were recognized, representing four bacterial phyla and 14 different metabolic lifestyles. DGGE profiles indicated that there are differences in the representative bacteria when considering either BIOS biofilms or groundwater. DGGE also indicated that the DNA extraction protocols and any polymerase chain reaction biases were consistent. Bacterial metabolic groups associated with indirect metal adsorption and reduction along with bacteria utilizing many alternative electron acceptors were strongly represented within the clones. This study indicates that the microbial diversity of BIOS is greater than previously thought.
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| 4. |
- Anderson, Craig, 1976, et al.
(författare)
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In situ growth of Gallionella biofilms and partitioning of lanthanides and actinides between biological material and ferric oxyhydroxides
- 2003
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 1:2, s. 169-178
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Tidskriftsartikel (refereegranskat)abstract
- Gallionella ferruginea is an iron-oxidizing chemolithotrophic micro-organism that lives in low-oxygen conditions (0.1–1.5 mg L-1 saturation). It produces a stalk structure from the concave side of the cell depending on population development, pH and redox conditions. After Gallionella oxidizes ferrous iron, bacteriogenic iron oxides (BIOS) precipitate on the stalk material and over time the stalks and/or the precipitated BIOS attenuate trace metals from surrounding groundwater. Gallionella ferruginea biofilms were cultured in situ in an artificial channel (2000 × 300 × 250 mm) using groundwater sourced from a borehole 297 m below sea level in the Äspö Hard Rock Laboratory in southern Sweden. The pH of the groundwater in the channels was always between 7.4 and 7.7 with oxygen saturation below 1.5 mg L-1 and Eh between 100 and 200 mV. Oxygen eventually declined to <0.3 mg L-1, terminating prolific biofilm growth. Biofilms formed within 2 weeks and were sampled every 2 weeks over 3 months. Cell number, stalk length and ferric iron concentration were measured for each sample and trace metal concentration was measured by inductively coupled plasma mass spectrometry. Results from well-developed in situ biofilms suggest that Gallionella could concentrate metals at levels up to 1 × 103-fold higher than found within the host rock and more than 1 × 106 times the levels found in the groundwater. These new experiments were used to support the results from the well-developed biofilms and to relate biofilm development and population characteristics to metal attenuation. After 3 months, rare earth element (REE) plots indicated that BIOS can accumulate metals at levels up to 1 × 104-fold higher than found in the groundwater and fractionate heavy rare earth elements over light rare earth elements. Generally the presence of the organic phase promotes the adsorption of all lanthanides and actinides that are not adsorbed by the inorganic phase. The iron oxides are directly correlated with stalk length (R = 0.96), indicating that rapid REE and actinide adsorption requires both iron oxides and a nucleating biological structure for the iron oxides.
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| 5. |
- Anderson, Craig, 1976, et al.
(författare)
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Influence of in situ biofilm coverage on the radionuclide adsorption capacity of subsurface granite
- 2007
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:3, s. 830-836
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Tidskriftsartikel (refereegranskat)abstract
- Any migration of radionuclides from nuclear waste repositories is expected to be mitigated by adsorption to the host rocks surrounding hydraulically conductive fractures. Fluid rock interfaces are considered to be important barriers for nuclear waste disposal schemes but their adsorptive capacity can be affected by the growth of microbial biofilms. This study indicates that biofilms growing on fracture surfaces decrease the rocks adsorption capacity for migrating radionuclides except for trivalent species. Potential suppression of adsorption by biofilms should, therefore, be accounted for in performance safety assessment models. In this study, the adsorptive capacity of in situ anaerobic biofilms grown 450 m underground on either glass or granite slides was compared to the capacity of the same surfaces without biofilms. Surfaces were exposed to the radiotracers Co-60(II), Pm-147(III), Am-241(III), Th-234(IV), and Np-237(V) for a period of 660 h in a pH neutral anaerobic synthetic groundwater. Adsorption was investigated at multiple time points over the 660 h using liquid scintillation and ICP-MS. Results indicate that these surfaces adsorb between 0 and 85% of the added tracers under the conditions of the specific experiments. After 660 h, the distribution coefficients, R (ratio between what is sorbed and what is left in the aqueous phase), approached 3 x 10(4) m for Co-60, 3 x 10(5) m for Pm-147 and 24 'Am, I x 106 m for 234Th, and 1 x 103 m for 237Np. The highest rate of adsorption was during the first 200 h of the adsorption experiments and started to approach equilibrium after 500 h. Adsorption to colloids and precipitates contributed to decreases of up to 20% in the available Co-60, Pm-147, Am-241, and Np-237 in the adsorption systems. In the 234Th system 95% of the aqueous 234Th was removed by adsorbing to colloids. Although the range of R values for each surface tested generally overlapped, the biofilms consistently demonstrated lower R values except for the trivalant Pm-147 and Am-241 adsorption systems.
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| 8. |
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| 9. |
- Crozier, R.H, et al.
(författare)
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Phylogenetic assessment of total biodiversity
- 1999
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Ingår i: Ponder, W. and Lunney, D. (eds). The other 99%. The conservation and biodiversity of invertebrates. - Mosman 2088 : Royal Zoological society of New south Wales. ; , s. 30-33
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 10. |
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