Clemens Walther

Role of phosphate fertilizers in heavy metal uptake and detoxification of toxic metals.

As a nonrenewable resource, phosphorus (P) is the second most important macronutrient for plant growth and nutrition. Demand of phosphorus application in the agricultural production is increasing fast throughout the globe. The bioavailability of phosphorus is distinctively low due to its slow diffusion and high fixation in soils which make phosphorus a key limiting factor for crop production. Applications of phosphorus-based fertilizers improve the soil fertility and agriculture yield but at the same time concerns over a number of factors that lead to environmental damage need to be addressed properly. Phosphate rock mining leads to reallocation and exposure of several heavy metals and radionuclides in crop fields and water bodies throughout the world. Proper management of phosphorus along with its fertilizers is required that may help the maximum utilization by plants and minimum run-off and wastage. Phosphorus solubilizing bacteria along with the root rhizosphere of plant integrated with root morphological and physiological adaptive strategies need to be explored further for utilization of this extremely valuable nonrenewable resource judiciously. The main objective of this review is to assess the role of phosphorus in fertilizers, their uptake along with other elements and signaling during P starvation.

Plutonium release from Fukushima Daiichi fosters the need for more detailed investigations

The contamination of Japan after the Fukushima accident has been investigated mainly for volatile fission products, but only sparsely for actinides such as plutonium. Only small releases of actinides were estimated in Fukushima. Plutonium is still omnipresent in the environment from previous atmospheric nuclear weapons tests. We investigated soil and plants sampled at different hot spots in Japan, searching for reactor-borne plutonium using its isotopic ratio 240Pu/239Pu. By using accelerator mass spectrometry, we clearly demonstrated the release of Pu from the Fukushima Daiichi power plant: While most samples contained only the radionuclide signature of fallout plutonium, there is at least one vegetation sample whose isotope ratio (0.381 ± 0.046) evidences that the Pu originates from a nuclear reactor (239+240Pu activity concentration 0.49 Bq/kg). Plutonium content and isotope ratios differ considerably even for very close sampling locations, e.g. the soil and the plants growing on it. This strong localization indicates a particulate Pu release, which is of high radiological risk if incorporated.

Laser induced breakdown detection for the assessment of colloid mediated radionuclide migration

Abstract Colloids play an important role in the transport of pollutants in the environment. Harmful substances can undergo transport over large distances if bound to colloids in aqueous surrounding. One important example is the migration of Pu(IV) at unexpectedly high rates over several miles at a Nevada nuclear detonation test site. For long term safety assessments of radioactive waste repositories, it is hence crucial to know about the amount, size distribution and chemical composition of colloids in the ground water. Standard methods (e.g. light scattering) can be applied for high concentrations and large sizes of particles. Colloids smaller than 50 nm, however, are detected with very low efficiency. Laser induced breakdown detection (LIBD) can fill this gap. A new instrumentation is presented, which as compared to previous instruments, opens up a much wider operational dynamic range, now covering three orders of magnitude in size (5–1000 nm) and seven orders of magnitude in particle concentration (1 ppt – several ppm). The technique is based on plasma formation on colloidal particles inside the focus of a pulsed laser. The plasma plume is detected by three-dimensional optical observations and by means of its shock wave with a piezo-detector. For mathematical modelling, detailed knowledge on the photon fluence distribution in the focal region is indispensable. For the first time a true Gaussian TEM00 mode has been achieved in the focus of a LIBD apparatus and great care has been taken to guarantee long-term stability of the optical parameters. Automated control of the laser pulse energy and beam shape is introduced to allow routine reproducible measurement. The apparatus combines acoustic detection with three-dimensional optical monitoring of the focal region with two CCD cameras placed perpendicular to each other in order to gain additional size information. The breakdown events are systematically characterized with respect to the number density and size of aquatic colloids as a function of the laser pulse energy. Whereas the threshold energy (irradiance) only depends on the colloid size, the breakdown probability at higher pulse energies is a direct function of the number density of colloids. A correlation of the two facts allows the speciation of the colloidal size distribution.

Formation and hydrolysis of polynuclear Th(IV) complexes – a nano-electrospray mass-spectrometry study

Polynuclear hydroxide complexes play an important role for the hydrolysis of tetravalent thorium ions in aqueous solution, in particular for Th(IV) concentrations exceeding some [Th(IV)]=10−4 M. Consequently, these polymers must be considered when describing hydrolysis of Th(IV) or dissolution processes of Th(IV) solids. In the past, considerable efforts were made to obtain equilibrium formation constants of these polymers and different stoichiometries for dimers, tetramers and hexamers have been suggested. However, most information was obtained from indirect methods, in particular, from potentiometric titrations. In the present work, we present an approach of directly quantifying polymeric metal hydroxide complexes in solution. By nano-electrospray mass-spectrometry the degrees of polymerization, i.e. the numbers of Th4+ ions and the numbers of hydroxide ligands, and as a consequence, also the charges of the complexes are measured. All mono- and polynuclear species which are present in solution are quantified simultaneously down to species contributing less than 0.1% of the total [Th(IV)] concentration. Solutions of [Th(IV)]=6×10−6–10−1 M are investigated in HCl at [H+]=10−4–0.1 M. More than 30 different polymeric complexes are observed with the general trend of increasing number of hydroxide ligands with decreasing acidity. A surprising finding is the presence of the pentamer Th5(OH)yz +, which was not described in the literature before. With decreasing Th(IV) concentration the stability field of polymers narrows continuously until polymers can no longer be detected below [Th(IV)]=10−5 M.

Site-selective time-resolved laser fluorescence spectroscopy of Eu3+ in calcite.

Three samples of calcite homogeneously doped with Eu(3+) were synthesized in a mixed-flow reactor. By means of selective excitation of the 5D0-->7F0 transition at low temperatures (T<20 K), three different Eu(3+) species (species A, B, and C, respectively) could be discriminated. For each one, the emission spectrum and lifetime were obtained after selective excitation of the single species. On the basis of these data, species C could be identified as Eu(3+) incorporated into the calcite lattice on the (nearly) octahedral Ca(2+) site. Species B was also identified as Eu(3+) incorporated into the calcite lattice, but the ligand field shows a much weaker symmetry. Species A, however, is not incorporated into the crystals bulk, having 1-2 H(2)O ligands left in its first coordination sphere and showing very little symmetry, and is considered as Eu(3+) adsorbed onto the calcite surface. The emission spectra of species C for Eu:calcite grown in the presence of Na(+) were found to differ from those of Eu:calcite synthesized in the presence of K(+). The latter revealed a strong distortion in site symmetry, which was not observed in the samples grown in Na(+) solutions. This finding provides spectroscopic evidence in favor of an incorporation mechanism based on the charge-balanced coupled substitution of Na(+)+Eu(3+)<-->2Ca(2+).

Post-Accident Sporadic Releases of Airborne Radionuclides from the Fukushima Daiichi Nuclear Power Plant Site

The Fukushima nuclear accident (March 11, 2011) caused the widespread contamination of Japan by direct deposition of airborne radionuclides. Analysis of weekly air filters has revealed sporadic releases of radionuclides long after the Fukushima Daiichi reactors were stabilized. One major discharge was observed in August 2013 in monitoring stations north of the Fukushima Daiichi nuclear power plant (FDNPP). During this event, an air monitoring station in this previously scarcely contaminated area suddenly reported (137)Cs activity levels that were 30-fold above the background. Together with atmospheric dispersion and deposition simulation, radionuclide analysis in soil indicated that debris removal operations conducted on the FDNPP site on August 19, 2013 are likely to be responsible for this late release of radionuclides. One soil sample in the center of the simulated plume exhibited a high (90)Sr contamination (78 ± 8 Bq kg(-1)) as well as a high (90)Sr/(137)Cs ratio (0.04); both phenomena have usually been observed only in very close vicinity around the FDNPP. We estimate that through the resuspension of highly contaminated particles in the course of these earthmoving operations, gross (137)Cs activity of ca. 2.8 × 10(11) Bq has been released.

Spectroscopic Identification of Ternary Cm−Carbonate Surface Complexes

The influence of dissolved CO(2) on the sorption of trivalent curium (Cm) on alumina (gamma-Al(2)O(3)) and kaolinite was investigated by time resolved laser fluorescence spectroscopy (TRLFS) using the optical properties of Cm as a local luminescent probe. Measurements were performed at T < 20 K on Cm loaded gamma-Al(2)O(3) and kaolinite wet pastes prepared in the absence and presence of carbonate in order to pictorially illustrate any changes through a direct comparison of spectra from both systems. The red-shift of excitation and emission spectra, as well as the increase of fluorescence lifetimes observed in the samples with carbonate, clearly showed the influence of carbonate and was fully consistent with the formation of Cm(III) surface species involving carbonate complexes. In addition, the biexponential decay behavior of the fluorescence lifetime indicated that at least two different Cm(III)-carbonate species exist at the mineral-water interface. These results provide the first spectroscopic evidence for the formation of ternary Cm(III)-carbonate surface complexes.

Sorption of Cm(III) onto different Feldspar surfaces: a TRLFS study

Summary The pH dependent sorption of Cm(III) onto alkali Feldspars (albite and orthoclase) is investigated by time resolved laser fluorescence spectroscopy (TRLFS) in the pH range from 3.4 to 9.4. Three single components are calculated from the raw spectra for both feldspar systems. The first component which corresponds to the Cm(III) aquo ion has a peak maximum at 593.8 nm and a fluorescence emission lifetime of 68±4 μs. This lifetime corresponds to a Cm(III) coordination of nine water molecules in the first coordination sphere of the actinide ion. The second component with a peak maximum at 601.4 nm corresponds to an adsorbed species. Its lifetime of 107±3 μs indicates a reduction of coordinating H2O/OH− ligands from nine to five caused by inner-sphere complex formation. The third component (603.6 nm) can be attributed to another sorption species. The corresponding lifetime is again 107±3 μs. Hence the number of coordinating ligands remains constant while the ligand field changes caused by the hydrolysis of the sorbed Cm(III). In a further set of experiments the Cm(III) sorption onto albite which is altered at pH 6.0 and pH 9.0 is also investigated by TRLFS. Independent of the dissolution and different surface morphologies caused by the alteration process the same Cm(III) species are formed as found for the sorption onto the untreated albite surface. With regard to the clarification of a feldspar dissolution mechanism the TRLFS results of the Cm(III) sorption onto altered feldspar surfaces give no evidence for a dissolution-reprecipitation based alteration mechanism.

Radionuclide Contamination and Remediation Through Plants

Phytoremediation of Radionuclides: A Report on the State of the Art.- Natural Plant Selection for Radioactive Waste Remediation.- Radionuclide Uptake From Soil to Plants: Influence of Soil Classification.- Contributions to the State of the Art in Radionuclides-Plants Interaction Field.- Transfer of Radionuclides to Plants: Influence on the Speciation of Radionuclides in Soil.- Radionuclide Uptake by Plants: Soil to Plant Transfer Factors, Kinetics of Absorption and Internal Radionuclide Distribution of 137Cs And 40K in South American Species.- Impact on Plant Growth in Waste Contaminated Areas.- Remediation of Radionuclide Contaminated Sites Using Plant Litter Decomposition.- Bioaccumulation of Radionuclide Metals in Plants: A Case Study of Cesium.- Speciation of Actinides After Plant Uptake.- Kinetic Models for Representing the Uptake of Radionuclides in Plants.- Metal-Microbe Interaction and Bioremediation.- Metabolism of 14C-Containing Contaminants in Plants and Microorganisms.- 90Sr and 137Cs Accumulation in Plants in the Area of Radiation Accidents.- Migration of 90Sr and 137Cs in the Soil After Radiation Accidents.

Fluorescence spectroscopy on protactinium(IV) in aqueous solution

Summary This work focuses on time-resolved laser fluorescence spectroscopy (TRLFS) of Pa(IV) in aqueous solution. Excitation at 308 nm causes a fluorescence emission with a peak maximum at about 460 nm. Thereby, the position of the band´s maximum depends on the concentration, the type of the acid, and the pH value. Increasing complexation of the Pa(IV) ion leads to an increasing hypsochromic shift of the emission band up to 46 nm. In contrast to the band position the half-width (61.6±1.4 nm) and the lifetime (16±2 ns) of the fluorescence emission do not change significantly with changes in the chemical environment of the Pa(IV). The results of this work show that speciation of Pa(IV) can be performed even in aqueous solution by using TRLFS.