Frida Edberg

Microbial Mobilization of Uranium from Shale Mine Waste

The alum shale in the Billingen area in southern Sweden was mined in Ranstad for 5 years during the 1960s. The crushed tailings (processed and unprocessed) were left behind when the Ranstad mine was closed that has caused leaching of metals to the surroundings. The siderophore producing bacterium Pseudomonas fluorescens (Äspö, SE Sweden) was grown in batch cultures for 5 to 8 days with naturally weathered (unprocessed) uranium ore (0.0029% U by weight), kolm (0.52% U by weight) and acid-leached ore (0.0099% U by weight) in chemically defined media (unbuffered and buffered). Pseudomonas fluorescens grown with ore and unbuffered medium changed the pH from 4.7 to 9.3 and leached out 0.016 to 0.9% (normalized to surface area) of the total amount of U from the different ores. Incubation of the acid-leached ore with bacteria in buffered medium leached out 0.04% of the total U. Uranium was leached out selectively at all conditions, but this could be a pH effect, as pH increased at the same time as the U concentrations did. The observed release of Fe was most likely attributed to the production of microbial siderophores (Fe3+ specific chelators) since Fe3+ has a low solubility at pH > 4. As siderophores contain a number of chelating groups they may still function as complexators even in partly degraded form also for other metals than Fe. Thus, the production of microbial chelators could contribute to the elevated metal concentrations in the drainage water from the closed Ranstad mine, as abiotic processes cannot fully explain these high metal concentrations. In the extension: ligand promoted leaching of toxic elements could also be the key to bioremediation as there is a need for nontoxic cleanup methods for metal contaminated sites.

The influence of pH on aluminium toxicity in the phytoplankton species Monoraphidium dybowskii and M. griffithii

The toxicity of aluminum on the phytoplankton species Monoraphidium griffithii and M.dybowskii (Chlorophyceae) was investigated. At pH 6.8 and low humus concentration, the growth of both species was reduced at 100–200 μg Al/l, whereas at pH 4.8 only the growth of M.griffithii was affected. The toxicity on the two species showed different relations to the pH-value. The results, supported by analyses of Al-fractions — total acid soluble, total monomeric and none-labile monomeric Al — indicate that the Al-toxicity is species-dependent, and that aluminium, soluble at neutral pH-conditions, can be toxic to the phytoplankton.

Mobilization of metals from uranium mine waste: the role of pyoverdines produced by Pseudomonas fluorescens

Microorganisms produce chelating agents, such as siderophores and other ligands, which allow them to mobilize and scavenge essential elements from the environment when bioavailability is low. To better understand the effects of biologically mediated leaching of metals from mine waste, Pseudomonas fluorescens was cultivated in the presence of processed ore from the former uranium mine in Ranstad, southern Sweden. Light conditions, the concentration of the mineral source and oxygen availability were varied. The presence of ore in the culture flasks enhanced bacterial growth and raised the pH of the culture medium. Increasing the amount of ore or enhancing aeration of the medium further encouraged cell growth and pH rise. Bacteria mobilized Fe, Ni and Co from the ore. Fe-siderophore complexes were detected and estimated to be present at approximately 9 mum. In the presence of bacteria and light, dissolved Fe and U concentrations were higher compared to dark conditions. Increasing the amount of ore resulted in higher dissolved Ni concentrations but lower dissolved Fe, most likely due to precipitate formation. Data from this study support siderophore production by bacteria that allowed mobilization of essential nutrients from the processed ore. However, the availability of potentially toxic metals like Ni and U may also be enhanced. Microbial-promoted mobilization could contribute to leaching of toxic metals in current and historic mining areas. This process should be considered during design and implementation of remediation projects where trace metals are of environmental concern.

Long-term water chemical trends in two Swedish lakes after termination of liming

Lime treatment has been extensively used as a remedial measure against acidification of surface waters. In view of the decreasing acid deposition, the possible consequences of a termination of liming are discussed intensively in Sweden. This paper presents the results of the first study of long-term effects of termination of liming. The temporal trends in water chemistry were studied in two lakes after termination of liming, in a still-limed lake and in an unlimed reference lake. The lime treatment was intentionally stopped in order to evaluate the effects on water chemistry and biota. After the last liming, pH decreased steadily in both reacidifying lakes until annual mean values stabilised around 5.5-6.0 and 6.2-6.5 respectively. ANC and concentrations of non-marine Ca+Mg decreased after the termination of liming. The decreasing pH resulted in increasing trends of inorganic Al (Al(i)), which during recent years exceeded the lowest known effect level for fish on several occasions. This indicates that the lime treatment may have been terminated to early from an ecological perspective and with respect to the critical load of acidifying substances during the study period. However, during the same time, non-marine sulphate decreased in all lakes in the study and pH and ANC increased in the unlimed reference lake.

Episodic Events in Water Chemistry and Metals in Streams in Northern Sweden During Spring Flood

Thirteen streams in the province of Jamtland in northern Sweden were monitored during spring in 1995 (December 94 – July 95) to study changes in water chemistry and metal concentrations during snow melt. The brooks are not treated with lime, with one exception, and can be approximately divided into three groups according to watershed characteristics; A) > 65% above tree line, B) > 65 % wetland, C) > 55% forested. During peak flow, pH dropped 0.5–2.5 units and alkalinity generally to zero. The brooks above tree line were lowest in base cations and reached the lowest pH-values (4.4–4.6) during peak flow, while sulphate levels were about the same as in the forested watersheds. During peak flow, organic anions showed the highest increase in the wetland and forested catchments. Compared to base flow, Al, Zn, Pb and to some extent Mn was enriched during peak flow. The results also illustrate the difficulties in generalising the reasons for alkalinity losses during spring flood in this kind of streams. In some of the brooks, the use of either base cations or silica, when calculating dilution effects, gave deviating results concerning the relative contribution of strong acids in the snow pack.