Jens Kruse

Phosphorus L2,3‐edge XANES: overview of reference compounds

Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy is becoming an increasingly used tool for the element speciation in complex samples. For phosphorus (P) almost all XANES measurements have been carried out at the K-edge. The small number of distinctive features at the P K-edge makes in some cases the identification of different P forms difficult or impossible. As indicated by a few previous studies, the P L(2,3)-edge spectra were richer in spectral features than those of the P K-edge. However, experimentally consistent spectra of a wide range of reference compounds have not been published so far. In this study a library of spectral features is presented for a number of mineral P, organic P and P-bearing minerals for fingerprinting identification. Furthermore, the effect of radiation damage is shown for three compounds and measures are proposed to reduce it. The spectra library provided lays a basis for the identification of individual P forms in samples of unknown composition for a variety of scientific areas.

Phosphorus Speciation in Agro-Industrial Byproducts: Sequential Fractionation, Solution 31P NMR, and P K- and L2,3-Edge XANES Spectroscopy

Little is known about P species in agro-industrial byproducts from developing countries, which may be either pollutants or valuable soil amendments. The present study speciated P in dry (COD) and wet (COW) coffee, sisal (SIS), barley malt (BEB) and sugar cane processing (FIC) byproducts, and filter cakes of linseed (LIC) and niger seed (NIC)with sequential fractionation, solution (31)P nuclear magnetic resonance (NMR) spectroscopy, and P K- and L(2,3)-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sequential P fractionation recovered 59% to almost 100% of total P (P(t)), and more than 50% of P(t) was extracted by H(2)O and NaHCO(3) in five out of seven samples. Similarly, the NaOH + EDTA extraction for solution (31)P NMR recovered 48-94% of P(t). The (31)P NMR spectra revealed orthophosphate (6-81%), pyrophosphate (0-10%), and orthophosphate monoesters (6-94%). Orthophosphate predominated in COD, COW, SIS, and FIC, whereas BEB, UC, and NIC were rich in orthophosphate monoesters. The concentrations of P(i), and P(o) determined in the sequential and NaOH + EDTA extractions and (31)P NMR spectra were strongly and positively correlated (r = 0.88-1.00). Furthermore, the P K- and L(2,3)-edge XANES confirmed the H(2)SO(4)--P(i) detected in the sequential fractionation by unequivocal identification of Ca--P phases in a few samples. The results indicate that the combined use of all four analytical methods is crucial for comprehensive P speciation in environmental samples and the application of these byproducts to soil.

Spatial distribution of arsenic and heavy metals in willow roots from a contaminated floodplain soil measured by X-ray fluorescence spectroscopy

Under changing redox conditions some plants create plaques at their root surface, which may affect the mobility and uptake of As and heavy metals but it is unknown to what extent this also holds true for willows in contaminated floodplain soils. Therefore, willow roots were sampled from a phytoremediation trial in the contaminated floodplain of the river Elbe (Germany), cryofixed, freeze-dried, and cross sections were mapped for the distribution of As, Ca, Cu, Fe, K, Mn, Ni, S and Zn by synchrotron based X-ray fluorescence spectroscopy. The elements Ca, Cu, Ni, S and Zn were concentrated in the aerenchymatic tissue, and not associated with Fe and Mn. Mixed Fe-Mn plaques covered the surface of the willow roots and As was accumulated in these plaques. The observed association pattern between As and Fe was explained by the different sorption/desorption properties of As(III) and As(V). The Cu and Zn intensities were not associated with the intensity of Fe in the plaque, which seems to be a willow-specific difference compared to other wetland plants. These results suggested that willows are especially suited to stabilize low-phytoextractable elements like Cu and As in their roots and rhizosphere. Thus, short rotation coppicing of willows may be a practical approach to mitigate the adverse effects of floodplain soil contamination.

Advances in Understanding Organic Nitrogen Chemistry in Soils Using State-of-the-art Analytical Techniques

Abstract During the past decade, soil and geochemists have adopted a variety of novel chemical–analytical methods to explore the chemistry of soil organic N (N org ). This chapter summarizes some of the more recent developments in the use of wet-chemical and instrumental methods to determine total N org concentrations as well as to speciate the N org in soils. A critical evaluation of 15 N nuclear magnetic resonance (NMR) spectroscopy found the technique to be wanting, in terms of its sensitivity and ability to identify classes of N org compounds in soils. Complementary mass spectrometric techniques are described briefly, and improved data evaluations based on broad applications of high-resolution pyrolysis-field ionization mass spectrometry are presented and discussed. A reassessment of older data sets using the new spectral evaluation algorithms provides strong evidence of fire- and management-induced changes in N org speciation. Isotope-ratio mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry, and nanoscale secondary ion mass spectrometry (Nano-SIMS) also are discussed, with the latter two techniques having potential to (1) identify N org compounds and (2) provide spatially resolved information on the molecular, elemental and isotopic composition of soil N org . The use of 15 N labeling techniques is discussed both from a methodological standpoint and in terms of tracking the fate of plant-derived (residue or rhizodeposit) N in the soil. Indeed, coupling 15 N labeling with analytical techniques such as 15 N NMR, Nano-SIMS and high- or ultrahigh-resolution mass spectrometry can provide information on how N is incorporated into soil organic matter. Analytical and instrumental innovations have resulted in new insights into the chemistry of N org —together with a revised summary of the relative amounts of the different N org compound classes present in soils (e.g. aliphatic amine and amide N, aromatic heterocyclic N), as well as their ecophysiological functions. Particular emphasis is given to the use of multitechnique analyses and the outstanding molecular–chemical diversity of biogenic heterocyclic N org compounds. Examples are given of the new insights obtained using multi-analytical research approaches to explore microbial utilization of heterocyclic N and organic–mineral interactions, as well as the ability of human and environmental intervention to alter the composition of soil N org . Finally, we examine future challenges and propose analytical approaches to tackle open questions regarding the basic chemistry and cycling of N org in soils, as well as the agronomic and environmental consequences associated with N transformations in agro-ecosystems.

A modified method for measuring saturated hydraulic conductivity and anisotropy of fen peat samples

The determination of the anisotropic and heterogeneous character of the saturated hydraulic conductivity (Ks) of wetland soils is technically challenging, but is crucial for the accurate quantification of flow and transport processes. We modified a laboratory method to determine Ks both in the vertical (Ks,v) and horizontal directions (Ks,h), and tested it on the same undisturbed peat samples using a constant head upward flow permeameter. The first results showed that Ks,v was greater than Ks,h in the majority of samples from two profiles of a degraded fen peat, indicating that Ks was anisotropic. In conclusion, the described method was suitable to determine Ks,v and Ks,h and can be recommended to estimate the anisotropy of Ks in wetland soils.

Nitrogen speciation in fine and coarse clay fractions of a Cryoboroll - new evidence from pyrolysis-mass spectrometry and nitrogen K-edge XANES

Soil clay fractions are usually enriched in nitrogen (N), but the chemical identity of this N is largely unknown. Therefore, we investigated organic N in fine and coarse clay of a clay-rich Cryoboroll by Curie-point pyrolysis-gas chromatography/mass spectrometry (Cp Py-GC/MS), Pyrolysis-field ionization mass spectroscopy (Py-FIMS) and synchrotron-based nitrogen K-edge X-ray absorption near edge structure (N-XANES) spectroscopy. The Cp Py-GC-MS revealed 30 structurally different N-containing compounds, such as substituted pyridines, pyrroles; pyrazines, pyrazoles, imidazoles, quinolines, side-chain N-containing benzenes, and single compounds of substituted benzotriazole, purine and indole. These accounted for about 10% of peak area in the Py-GC chromatograms. The Py-FIMS and N-XANES spectra indicated interlayer-NH4+ and revealed pyridinic and nitrilic N compounds, but disagreed in the proportions of pyrroles. All three complementary methods confirmed to different extents previous wet-chemical data on N-fra...

Chapter 9 – Nitrogen Compounds in Dissolved and Solid Environmental Samples

The chapter describes the state of the art in Nitrogen K-edge X-ray absorption near-edge structure (N-XANES) spectroscopy applied to environmental problems. Technical details of beamline optimization are given as well as advice for sample preparation and spectral evaluation. The thorough overview of reference compounds includes mineral N-compounds, amino acids, amides, nitriles, and a wide range of heterocyclic compounds. We show new evidence of radiation damage on N-XANES spectra of proteinaceous N-reference compounds and soil-related materials, and propose approaches to minimize it. Calculated N-XANES spectra using density functional theory showed excellent agreement with measurements that resolved pyridinic and pyrrolic N in the same molecule. Using environmental samples, we demonstrate that measurements of soil solutions indicate a large contribution of mineral N (NO3−, NH4+). In particle-size fractions and bulk soil samples, differences in the proportions of various N functions may originate from clay-organic matter interactions, rhizosphere processes, and soil management practices. In conclusion, N-XANES is a valuable component in the multimethod approach toward the study of inorganic and organic N in environmental samples.

Recycled Products from Municipal Wastewater: Composition and Effects on Phosphorus Mobility in a Sandy Soil

Recycled products from wastewater may contain high concentrations of phosphorus (P) and are thus promising alternative fertilizers. However, to better predict their P fertilizer efficiency and potential for P leaching, investigations on P forms and P mobility in soil are essential. In this study, different recycled products-an untreated sewage sludge ash (SSA), an HSO-digested SSA, four thermochemically treated SSAs (two Mg-SSAs and two Ca-SSAs), and struvite-were investigated using a combination of wet chemical methods and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy concerning their composition and their effects on P sorption in a sandy soil in comparison to triple superphosphate. Most of the P in the SSAs was associated with Ca in stable P fractions. The lowest P values in labile fractions (HO-P, NaHCO-P) were found for the untreated SSA and struvite. However, the addition of struvite resulted in an immediate increase in the bioavailable P fractions and the degree of P saturation in soil after only 1 d of incubation. This suggests a high P fertilizer potential for struvite but also a risk of P losses. Among the SSAs, the two Mg-SSAs increased the bioavailable P fractions in soil the most, whereas the lowest values were measured after application of the untreated SSA. Our results demonstrate that chemical analyses of recycled P products may involve the risk of misjudging the fertilizer quality when performed alone, without considering the behavior of these products in soil.

Solid-phase cadmium speciation in soil using L3-edge XANES spectroscopy with partial least-squares regression

Cadmium (Cd) has a high toxicity and resolving its speciation in soil is challenging but essential for estimating the environmental risk. In this study partial least-square (PLS) regression was tested for its capability to deconvolute Cd L(3)-edge X-ray absorption near-edge structure (XANES) spectra of multi-compound mixtures. For this, a library of Cd reference compound spectra and a spectrum of a soil sample were acquired. A good coefficient of determination (R(2)) of Cd compounds in mixtures was obtained for the PLS model using binary and ternary mixtures of various Cd reference compounds proving the validity of this approach. In order to describe complex systems like soil, multi-compound mixtures of a variety of Cd compounds must be included in the PLS model. The obtained PLS regression model was then applied to a highly Cd-contaminated soil revealing Cd(3)(PO(4))(2) (36.1%), Cd(NO(3))(2)·4H(2)O (24.5%), Cd(OH)(2) (21.7%), CdCO(3) (17.1%) and CdCl(2) (0.4%). These preliminary results proved that PLS regression is a promising approach for a direct determination of Cd speciation in the solid phase of a soil sample.

Pyrolysis-field ionization mass spectrometry and nitrogen K-edge XANES spectroscopy applied to bulk soil leachates—a case study

Although dissolved organic matter (DOM) is an important component of C- and N-fluxes in the environment, its structural composition is still poorly understood due to methodological challenges. We explored the potential of combining pyrolysis-field ionization mass spectrometry (Py-FIMS) and N X-ray absorption near edge structure (N-XANES) spectroscopy to study the molecular-chemical composition of lyophilized bulk soil solution samples that were not subjected to pretreatment like dialysis. Soil leachates were collected at 90 cm and 220 cm depth from an arable and a fallow site. Py-FIMS spectra reflected differences in DOM composition related to land use and sampling depth. Land use effects were expressed in higher abundances of carbohydrates and peptides at the arable than at the fallow site. The relative proportions of carbohydrates decreased and the proportions of lignin-derived compounds increased with depth, indicating a relative enrichment to more stabilized DOM along the flow path. Nitrogen XANES spectra were dominated by the signal of NO(3)-salts but also indicated the presence of organic, non-amidic N as found in imidazoles, pyrazoles, purines and/or nitrile-N, whereas N-compounds like pyridines, pyrroles, quinoline and indole were detected by Py-FIMS. Thus, the combined application of Py-FIMS and N-XANES yielded complementary information regarding the molecular-chemical composition of DOM. Future applications of these techniques may benefit from selectively analyzing soil solution samples with lower nitrate concentrations collected in early spring.