Martin Mkandawire

Capacity of Lemna gibba L. (Duckweed) for Uranium and Arsenic Phytoremediation in Mine Tailing Waters

ABSTRACT The potential of Lemna gibba L. to clean uranium and arsenic contamination from mine surface waters was investigated in wetlands of two former uranium mines in eastern Germany and in laboratory hydroponic culture. Water and plants were sampled and L. gibba growth and yield were monitored in tailing ponds from the field study sites. Contaminant accumulation, growth and yield experiments were conducted in the laboratory using synthetic tailing water. Mean background concentrations of the surface waters were 186.0 ± 81.2 μg l−1 uranium and 47.0 ± 21.3 μg l−1 arsenic in Site one and 293.7 ± 121.3 μg l−1 uranium and 41.37 ± 24.7 μg l−1 arsenic in Site two. The initial concentration of both uranium and arsenic in the culture solutions was 100 μg l−1. The plant samples were either not leached, leached with deionized H2O or ethylenediaminetetracetic (EDTA). The results revealed high bioaccumulation coefficients for both uranium and arsenic. Uranium and arsenic content of L. gibba dry biomass of the field samples were as follows: nonleached samples > deionized H2O leached (insignificant ANOVA p = 0.05) > EDTA leached. The difference in both arsenic and uranium enrichment were significantly high between the nonleached and the other two lead samples tested at ANOVA p > 0.001. Estimated mean L. gibba density in surface water was 85,344.8 ± 1843.4 fronds m−2 (∼1319.7 g m−2). The maximum specific growth rate was 0.47 ± 0.2 d−1, which exceeded reported specific growth rates for L. gibba in the literature. Average yield was estimated at 20.2 ± 6.7 g m−2 d−1, giving approximately 73.6 ± 21.4 t ha−1 y−1 as the annual yield. The highest accumulations observed were 896.9 ± 203.8 mg kg−1 uranium and 1021.7 ± 250.8 mg kg−1 arsenic dry biomass for a 21-d test period in the laboratory steady-state experiments. The potential extractions from surface waters with L. gibba L. were estimated to be 662.7 kg uranium ha−1 yr−1 and 751.9 kg arsenic ha−1 yr−1 under the above conditions.

Metal/metalloid accumulation/remobilization during aquatic litter decomposition in freshwater: A review

The focus of this article is to combine two main areas of research activities in freshwater ecosystems: the effect of inorganic pollutants on freshwater ecosystems and litter decomposition as a fundamental ecological process in streams. The decomposition of plant litter in aquatic systems as a main energy source in running water ecosystems proceeds in three distinct temporal stages of leaching, conditioning and fragmentation. During these stages metals and metalloids may be fixed by litter, its decay products and the associated organisms. The global-scale problem of contaminated freshwater ecosystems by metals and metalloids has led to many investigations on the acute and chronic toxicity of these elements to plants and animals as well as the impact on animal activity under laboratory conditions. Where sorption properties and accumulation/remobilization potential of metals in sediments and attached microorganisms are quite well understood, the combination of both research areas concerning the impact of higher trophic levels on the modification of sediment sorption conditions and the influence of metal/metalloid pollution on decomposition of plant litter mediated by decomposer community, as well as the effect of high metal load during litter decay on organism health under field conditions, has still to be elucidated. So far it was found that microbes and invertebrate shredder (species of the genera Gammarus and Asellus) have a significant influence on metal fixation on litter. Not many studies focus on the impact of other functional groups affecting litter decay (e.g. grazer and collectors) or other main processes in freshwater ecosystems like bioturbation (e.g. Tubifex, Chironomus) on metal fixation/release.

Invertebrates control metals and arsenic sequestration as ecosystem engineers

Organic sediments are known to be a significant sink of inorganic elements in polluted freshwater ecosystems. Hence, we investigated the role of invertebrate shredders (the freshwater shrimp Gammarus pulex L.) in metal and arsenic enrichment into organic partitions of sediments in a wetland stream at former uranium mining site. Metal and metalloid content in leaf litter increased significantly during decomposition, while at the same time the carbon content decreased. During decomposition, G. pulex as a ecosystem engineer facilitated significantly the enrichment of magnesium (250%), manganese (560%), cobalt (310%), copper (200%), zinc (43%), arsenic (670%), cadmium (100%) and lead (1340%) into small particle sizes. The enrichments occur under very high concentrations of dissolved organic carbon. Small particles have high surface area that results in high biofilm development. Further, the highest amounts of elements were observed in biofilms. Therefore, invertebrate shredder like G. pulex can enhance retention of large amounts of metal and arsenic in wetlands.

Uranium attenuation from tailing waters by floating macrophyte Lemna gibba L.

Biosorption of uranium from mine tailing waters by floating macrophyte Lemna gibba L. was investigated in nutrition solutions. Changes in pH (from average 7.0 to 5.5), speciation and removal of U from the solutions and accumulation in the plant directly corresponded to specific growth rate, Fe and PO4 speciation. Macrophytes (e.g. Lemna sp.) are reported to produce a range of 5-l000µg kg-1 day-1 dry biomass of organic compounds particularly oxalic acids and proteins which are triggered by Fe, or PO4 deficiency. Modelling predicts specation change of Fe and PO4, and U-oxalic comlexation which influence U speciation and its bioavailability.

Heavy metals and arsenic fixation into freshwater organic matter under Gammarus pulex L. influence

Organic sediments are a main sink for metal pollutants in aquatic systems. However, factors that make sediments a sink of metals and metalloids are still not clear. Consequently, we investigate the role of invertebrate shredders (Gammarus pulex L.) on quality of metal and arsenic fixation into organic partitions of sediment in the course of litter decay with laboratory microcosm experiments. During the decomposition of leaf litter, G. pulex significantly facilitated the development of small particles of organic matter. The capacity of metal fixation was significantly higher in smaller particles than leaf litter and litter residuals. Thus, G. pulex enhanced metal fixation into the organic partition of sediments by virtue of increasing the amount smaller particles in the aquatic system. Furthermore, invertebrates have a significant effect on formation of dissolved organic matter and remobilization of cobalt, molybdenum and cesium, but no significant effect on remobilization of all other measured elements.

Spectrophotometric verification of biodegradation of phenol in a flow dynamic biocers-based bioreactor system.

A quick fingerprint spectrophotometric procedure based on the absorbance in the ultraviolet spectrum region was developed to verify biodegradation of phenol in flowing contaminated water. The procedure was employed to test the functional feasibility of a biocers-packed bioreactor to filter phenol on a bench-scale fluidic dynamic system, which should simulate a macroscopic microorganism-based remediation system. The biocers contained Rhodococcus sp. P1, a phenol degrading bacteria. An influent with initial phenol concentration of 500 mg L−1 was fed into the bioreactor at different flow rates, and the effluent was continuously monitored for residual phenol concentration by coupling the fluid dynamic system to a UV-vis spectrophotometer. Within 3 days, the effluent from bioreactor reached a minimum residual concentration of phenol of <40 mg L−1. Therefore, the aim of the current paper is to report results of the procedure for on-line spectrophotometric detection of phenol, and the feasibility of a biocers-packed bioreactor for degradation of phenol.

Homeostatic regulation of elemental stoichiometry by Lemna gibba L. G3 when nutrient interact with toxic metals

We investigated responses of Lemna gibba L. to exposure to UO22+ and AsO43− under variable PO43− concentration. Total plant phosphorus (Ptot) in L. gibba and accumulation of dissolved organic carbon (DOC) in the media were quantified and tested for correlation with plant yield and initial concentrations of PO43−, UO22+ and AsO43−. The accumulation of DOC in medium was high under low PO43− supply and increased loading of either UO22+ or AsO43−. The Ptot was low in high initial concentration of UO22+ and AsO43− as well under acute low PO43− supply. The DOC accumulation correlated negatively to the Ptot. This reveals interaction between PO43− and UO22+ or AsO43− in the medium interferes with the uptake process of PO43−. Hence, the DOC accumulation is exudation of low molecular weight organic substance by L. gibba in response to the reduced Ptot: biomass ratio (carbon in the yield) due to delimited acquisition of phosphorus from the medium. It is a homeostatic regulation of the stoichiometry, which is disturbed during the interaction between PO43− and UO22+ or AsO43−. Further investigations are necessary to relate these interactions to traditional resource stoichiometry elements of C, N, and P.

Possible biomineralisation of uranium in Lemna gibba G3

We investigate biomineralisation of U(VI) accumulated in Lemna gibba G3 under laboratory conditions. Almost 50.3±11.2 % of uranium was eluted from biomass resulting into 243.5±111.7 mg Kg−1, and 308.9±189.3 μg L-1 in eluates in a 30 minutes deportation experiment. No further uranium losses or concentration increase in aliquot were observed in weekly analysis of soaked biomass for 5 weeks. Phase Contrast and Scanning Electron Microscope shows crystal formation in and on the fronds. Energy dispersion X-ray showed that the crystals contain uranium and elements that support the phenomenon of metal oxalate formation in Lemna sp. Uranium was likely fixed culture as uranyl oxalates species in Lemna gibba. Hence, further studies are required to determination uranyl oxalates species structures and ascertain the biomineralisation.

Natural occurring uranium nanoparticles and the implication in bioremediation of surface mine waters

We investigated the fractionation of mobile uranium in surface water from an abandoned uranium-mining site in eastern Germany. The water samples were sequentially ultra-filtrated to fractionate uranium into different sizes and delineate the colloidal and nanoparticle from dissolve U phases. The results revealed that only 20% of total dissolved uranium filtrates were lower than five kDa (i.e. ca. 1-3 nm). Between 30-40% of the total mobile U were either associated with colloids or exist as nanoparticles. Among others, biotic activities contribute significantly to the formation of colloidal or nanoparticle U. Thus, we discuss the implication of natural occurring colloidal and nanoparticle U on bioremediation technology.

Optischer Biosensor auf Basis abhängiger Expression fluoreszierender Proteine

Zusammenfassung Eine Vielzahl von Prozessen in der Medizin, Biotechnologie, Verfahrenstechnik und Analytik erfordern die spezifische Detektion und Quantifizierung bestimmter Stoffe, wie zum Bespiel Schwermetalle, Antibiotika oder Stoffwechselintermediate. Zahlreiche Studien der letzten Jahre haben bewiesen, dass biologische Wandler grundsätzlich in der Lage sind, solche vielfältigen Messaufgaben zu bewältigen. In dieser Arbeit wird eine Entwicklung vorgestellt, bei der ein solcher Wandler als Chip-basierter Ganzzellsensor aufgebaut wurde, bei dem die abhängige Fluoreszenz optisch ausgelesen wird. Dabei wird das Potential robuster, optischer Biosensoren untersucht. Abstract A wide range of processes in the fields of medicine, biotechnology, process engineering, as well as chemical analyses require a specific detection and quantification of certain substances like heavy metals, antibiotics, or metabolic intermediates. Numerous recent studies have clearly demonstrated the ability of biological transducers to cope with such measurement tasks. This paper presents the development of an integrated Whole-Cell sensor, which is based on the detection of a dependent fluorescence. Thereby we investigate the potential of a compact and robust optical biosensor.