Stable C and N isotope abundances in water-extractable organic matter from air-dried soils as potential indices of microbially utilized organic matter

Stable carbon (C) and nitrogen (N) isotopes (13C and 15N) in water-extractable organic matter (WEOM) derived from air-dried soils may be applicable to elucidate the microbial decomposition of soil organic matter (SOM), which is crucial in terrestrial C cycles. A total of 40 soil samples were collected from a depth of 0–6 cm from a temperate broadleaved forest in Japan with vegetation succession from grassland approximately 150 years ago. Those soil samples were air-dried before the water extraction process and organic matter analysis. The C and N concentrations of WEOM were <3.6% of those of the bulk soil and were positively correlated with those of the bulk soil at a p-value of < 0.01. A positive correlation between the two fractions (i.e., WEOM and bulk soils) was also found for natural 13C and 15N abundances (δ13C and δ15N; p < 0.01). However, the C/N ratio of WEOM was slightly correlated with that of bulk soils, exhibiting a narrow range of values of ~10. Thus, those features of the WEOM were similar to the well-known features of microbial biomass. The δ13C and δ15N enrichments in WEOM relative to bulk soil, the difference in stable isotope abundances between bulk SOM and WEOM were negatively and positively correlated, respectively, with the concentrations of organo-mineral complexes and short-range order minerals (non-crystalline oxyhydroxides of aluminum and iron, allophane, imogolite, and allophane-like constituents), which play significant roles in SOM stabilization in soils. These relationships suggest that the stable isotopic enrichments in WEOM can be a good indicator of the microbial utilization of soil C and N under different substrate availabilities, which are crucial to SOM decomposition and decomposability substantially varying from local to global scales

Application of augmentation method to MCR-ALS analysis for XAFS and Raman data matrices in structural change of isopolymolybdates

We measured X-ray absorption fine structure (XAFS) and Raman spectra of isopolymolybdates(VI) in highly concentrated HNO3 solution (0.15–4.0 M), which change their geometries depending on acid concentration, and performed simultaneous resolution of the XAFS and Raman data using a multivariate curve resolution by alternating least-squares (MCR-ALS) analysis. In iterative ALS optimization, initial data matrices were prepared by two different methods. For low sensitivity of the XAFS spectra to geometrical change of the isopolymolybdates, the MCR-ALS result of single XAFS data matrix shows large dependence on the preparation method of the initial data matrices. This problem is improved by the simultaneous resolution of the XAFS and Raman data: the MCR-ALS result of an augmented matrix of these data has little dependence on the initial data matrices. It indicates that the augmentation method effectively improves the rotation ambiguities in the MCR-ALS analysis of the XAFS data

Selective Pd separation from a simulated radioactive liquid waste by precipitation using a xenon lamp irradiation for simplified procedure

In this study, we developed a simple and one-step Pd separation technique based on photoreduction with Xe lamp irradiation for the determination of 107Pd in highly radioactive samples. A simulated high-level radioactive liquid wastes (HLLW) solution, which consists of 14 major elements in a 3 mol L-1 HNO3 solution, was used to evaluate the separation performance. The Pd precipitate was formed by Xe lamp irradiation and recovered by centrifugation. The Pd recovery from the simulated HLLW solution reached up to 50 %, while 99.5 % of the other 13 elements were separated. These results indicate that the applicability of the proposed separation technique to HLLW samples

Dispersive XAFS Study on the Laser-Induced Reduction of a Rh3+ Ion Complex: Presence of a Rh+ Intermediate in Direct Photoreduction

The reaction mechanism of the direct photoreduction of a Rh3+ ion complex to a Rh0 species induced by pulsed ultraviolet laser irradiation was studied using dispersive X-ray absorption fine structure (DXAFS) spectroscopy. The time-resolved X-ray absorption near edge structure (XANES) showed the absence of isosbestic points and suggested that more than two Rhn+ species contribute toward the direct photoreduction of Rh3+. Analysis of the time-resolved XANES data by singular value deposition showed that the direct photoreduction involves three Rhn+ species. Multivariate curve resolution by alternating least-squares analysis (MCR-ALS) of the time-resolved XANES data gave pure spectra and concentration profiles of the three Rhn+ species. The Rhn+ species were assigned to Rh3+, Rh+, and Rh0 species based on the features of the pure XANES spectra. The concentration profiles suggested that the direct photoreduction proceeds in the order of Rh3+ → Rh+ → Rh0. A reaction mechanism, which was proposed involving photoreductions of Rh3+ and Rh+, photoinduced autocatalytic reductions of Rh3+ and Rh+, and photooxidation of Rh+, well reproduced the concentration profiles of three Rhn+ species

In Situ Time-Resolved XAFS Study on Laser-Induced Particle Formation of Pd(II) Ion in a Solution

Previously, we showed that the irradiation of a nanosecond pulsed UV laser with high pulse energy into the Pd(II) solution forms the Pd particle with submicron size (100–500 nm), which has not been generated in the photo-induced particle formation using a UV lamp. It indicates that the laser irradiation with high pulse energy promotes the Pd particle growth, the mechanism of which is unclear. In this work, we studied the particle formation in the Pd(II) solution in the laser irradiation with high pulse energy using time-resolved X-ray absorption fine structure (XAFS) spectroscopy.6th International Conference on Advanced Nanoparticle Generation & Excitation by Lasers in Liquid

Determination of ¹⁰⁷Pd in Pd Recovered by Laser-Induced Photoreduction with Inductively Coupled Plasma Mass Spectrometry

Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, ¹⁰⁷Pd, which can be found in radioactive wastes, is one of the difficult-to-measure nuclides and results in a deficit in experimentally determined contents. In this study, a precipitation-based separation method has been developed for the determination of ¹⁰⁷Pd with inductively coupled plasma mass spectrometry. The photoreduction induced by pulsed laser irradiation at 355 nm provides short-time and one-step recovery of Pd. The proposed method was verified by applying it to a spent nuclear fuel sample. To recover Pd efficiently, a natural Pd standard was employed as the Pd carrier. Taking advantage of the absence of ¹⁰²Pd in spent nuclear fuel, ¹⁰²Pd in the Pd carrier was utilized as the internal standard. The chemical yield of Pd was about 90% with virtually no impurities, allowing accurate quantification of ¹⁰⁷Pd. The amount of ¹⁰⁷Pd in the Pd precipitate was 17.3 ± 0.7 ng, equivalent to 239 ± 9 ng per mg of ²³⁸U in the sample