Association of radionuclides with colloids in soil solutions

Association of Pu and Am with variously sized particles in soil extracts is studied by ultrafiltration. In aqueous extracts, the Pu and Am concentrations depend on the soil type and aqueous solution composition. In the aqueous extracts, from 60 to 100% of the radionuclides and organic carbon are associated with fine colloidal particles (<0.05 μm). The presence of humic acid increases the recovery of radionuclides by a factor of 4–8 depending on the soil type. The Pu and Am distribution among the groups and fractions of humus acids is studied. In the group of humic acids of chernozem, from 65 to 75% of the radionuclides are associated with the fraction with MW > 100 kDa; about 25%, with the fraction with MW 50–10 kDa; and 2–4%, with the low-molecular-weight fraction with MW < 3 kDa. In the group of fulvic acids, 44–49% of the radionuclides is found in the fraction with MW > 100 kDa, and 42–51%, in the fraction with MW < 3 kDa.     

Extraction of radionuclides from aqueous HNO3 by adducts of complex inorganic acids with monosubstituted polyethylene glycols

The adducts of complex inorganic acids (CIAs) with monosubstituted derivatives of polyethylene glycols (PEGs) were prepared in aqueous acids. These adducts are poorly soluble in water (below 1 g/l) and readily soluble in polar organic solvents (up to 400 g/l). The adduct stoichiometry is a function of acidity, and the physicochemical and extraction characteristics of adducts depend on particular PEG and CIA. With increasing PEG content in the adducts, their extractive power decreases, the solubility in polar organic solvents increases, and the solubility in water passes through a minimum. All these adducts are highly resistant to hydrolysis and radiation. The extraction of Cs, Sr, Ba, Eu, and Am from aqueous HNO₃ with solutions of phosphomolybdic and hexachloroantimonic acid adducts with oxyethylated n-nonylphenol in organic solvents was studied.     

Effect of fulvic acids on Th(IV) sorption on montmorillonite

The effect of fulvic acids on Th(IV) sorption on montmorillonite is studied. Over the pH range 3.0–7.0, the sorption decreases as a result of formation of fulvate and hydroxofulvate complexes. The composition and formation constants of mixed Th(IV) hydroxofulvates are estimated using mathematical simulation. In acidic solutions, Th fulvates are partially sorbed on montmorillonite.     

Limitations of electrospray ionization of fulvic and humic acids as visible from size exclusion chromatography with organic carbon and mass spectrometric detection

A method was developed to link size exclusion chromatography electrospray ionization mass spectrometry (SEC-ESI-MS) analyses of fulvic and humic acids with SEC and organic carbon detection (SEC-OCD), the latter providing an absolute measure of the amount of organic matter eluting from the SEC column. This approach allows us to determine which molecular weight fraction of the complex polydisperse mixtures is detectable by ESI-MS. It could be shown that the cone voltage setting for the ESI interface has strong impact on ESI-MS detection. Using conventional settings for low molecular weight compounds, the high molecular weight (HMW) compounds are hardly amenable to ESI-MS. With increasing cone voltage, an increasing signal intensity is obtained for the HMW fraction that elutes at shorter retention times. However, mostly fragment ions are obtained under these conditions. Thus, the range of compounds amenable to ESI-MS analysis is restricted by the limited stability of the fulvic and humic acid molecules of higher molecular weight in the electrospray process rather than by the mass spectrometer used. Compounds above 1000 amu are hardly visible as intact ions. However, insight into structural characteristics of these compounds can be gained by investigating their fragment ions by SEC-ESI-MS. The use of SEC-OCD parallel to SEC-MS helps to assess and optimize the detection potential of ESI-MS for polydisperse mixtures.     

Distribution of naturally occurring radionuclides in soils of the southern districts of Bangladesh

The activity concentrations of naturally occurring radioactive materials in soil samples of an elevated radiation background area of nine southern districts of Bangladesh were determined using gamma-ray spectrometry with an aim of evaluating the environmental radioactivity. The outdoor and indoor external effective dose rates and the radiation hazard indices from the soil activity were evaluated with an aim of minimising the harmful effects of ionising radiation to the population of the area concerned. The activity of (137)Cs was measured and observed in some of the locations.     

Effect of basic chemical characteristics of soils on mobility of radionuclides in them

Interplay between the basic chemical characteristics of soils of the Belarussian Polessie and the tightness of fixation of Chernobyl-derived ¹³⁷Cs and ⁹⁰Sr in them is studied. The mobility of radionuclides in the soil proved to be controlled essentially by the soil type and organic matter content. In the investigated soils, nonexchange sorption of ¹³⁷Cs and exchange sorption of ⁹⁰Sr dominate.     

Association of radionuclides with the colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Associations of radionuclides with colloidal particles of various sizes, isolated from underground waters of the Lake Karachai contamination area, were studied. Analysis by photon correlation spectroscopy showed that the total content of colloidal matter in deeper horizons is higher by an order of magnitude than in near-surface horizons. The mean particle radius also increases with the depth. The major fraction of Pu, Am, and Cm is associated with colloids (40–90%). U and Np are associated with colloidal particles to a lesser extent (2–20%), which determines their higher migration mobility in underground waters. The amount of actinides associated with coarse colloidal particles of size from 450 to 200 nm is insignificant. A considerable fraction of actinides is in the deep-lying water (depth ≥40 m) is associated with colloidal particles of size from 200 to 50 nm. No more than 30% of Pu and Am in water of these horizons is associated with finer colloids (from 10 kDa to 50 nm). With approaching the surface, the amount of actinides in the fraction of nanometer-sized particles (50 nm-10 kDa) increases (to 50%).     

Carbon isotope composition of dissolved humic and fulvic acids in the Tokachi River system

This study reports carbon isotopic ratios (Δ(14)C and δ(13)C) of dissolved humic and fulvic acids in the Tokachi River system, northern Japan. These acids have a refractory feature and they represent the largest fraction of dissolved organic matter in aquatic environments. The acids were isolated using the XAD extraction method from river water samples collected at three sites (on the upper and lower Tokachi River, and from one of its tributaries) in June 2004 and 2005. δ(13)C values were -27.8 to -26.9 ‰ for humic and fulvic acids. On the other hand, the Δ(14)C values ranged from -247 to +26 ‰ and the average values were -170 ± 79 ‰ for humic acid and -44 ± 73 ‰ for fulvic acid. The difference was attributed to the residence time of fulvic acid in the watershed being shorter than that of humic acid. The large variation suggested that humic substances have a different pathway in each watershed environment.     

Isolation of radionuclides from thorium targets irradiated with 300-MeV protons

Procedures were developed for isolation and separation of radionuclides from a thorium target irradiated with 300-MeV protons. A large set of radionuclides, including those of heavy elements (^225,226Ac, ^223,224,225Ra, ²³⁰U, ²³⁰Pa), were obtained. A perspective scheme was suggested for separation of radionuclides from irradiated thorium.     

Complexation of furosemide with fulvic acid extracted from shilajit: a novel approach

The aim of the present work was to complex furosemide (FSM) with fulvic acid (FA) extracted from shilajit with the hope of having a better understanding of the complexation behavior. The effect of FA on the aqueous solubility, dissolution rate, and permeability of FSM was investigated. Different techniques, such as grinding, freeze drying, solvent evaporation, and so forth, were used for the preparation of the complex. The complexes were prepared in molar ratios of 1:1 and 1:2 FSM:FA and were evaluated for drug inclusion, solubility, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, dissolution study, and permeation study. These methods confirm the formation of an amorphous inclusion complex of FSM with FA.     

Removal of radionuclides from spent technical oils

The possibility of decontamination of spent technical oils (STOs) from radionuclides using calcium oxide, Portland cement, and sulfuric and phosphoric acids was examined. The optimal values of the reagent dosage and contact time of oil with the reagents were determined. With CaO and Portland cement of grade 400, the decontamination factors are low (<10). Treatment with sulfuric or phosphoric acid allows efficient decontamination of STOs, with reducing the activity by a factor of 300–15 000. One- or two-step scheme can be used depending on the required level of purification. Two-step STO treatment with sulfuric acid allows the residual activity of intermediate-level wastes to be decreased to a level below 100 Bq kg^?1, at which unlimited use of the product is permissible.     

Determining activities of radionuclides from coincidence signatures

The spectral analysis of simultaneously observed photons in separate detectors may provide an invaluable tool for radioisotope identification applications. A general recursive method to determine the activity of an isotope from the observed coincidence signature rate is discussed. The method coherently accounts for effects of true coincidence summing within a single detector and detection efficiencies. A verification of the approach with computer simulations is also discussed.     

On-line coupling of size exclusion chromatography with electrospray ionization-tandem mass spectrometry for the analysis of aquatic fulvic and humic acids

A method was developed for the analysis of humic and fulvic acids by size-exclusion chromatography-electrospray ionization-tandem mass spectrometry using a completely volatile eluent. Humic and fulvic acids were separated into three peaks. These fractions occupied different mass ranges and showed differences in the fine structure of their mass spectra. The low-molecular-weight (LMW) fraction of fulvic acids is most sensitively determined by ESI-MS, and it appears that previous results obtained by infusion-ESI-MS were primarily determined by this fulvic acid fraction. The average molecular weight of this fractions turned out to be lower than that reported from infusion-ESI-MS measurements. Its scan spectra and the product ion spectra of some of its molecular anions perfectly match those previously obtained from whole fulvic acid mixtures. Obviously, a class of well-defined polycarboxylated molecules exist that occurs in all fulvic acid fractions thus far investigated. With decreasing elution time and increasing molecular weight, detection by ESI-MS loses sensitivity as compared to the parallel UV recording, and the fine structure of the scan spectra becomes increasingly uniform for both fulvic and humic acids. The average molecular weight of the HMW fraction exceeds those values calculated from infusion experiments. Scan spectra and product ion spectra of the high-molecular-weight (HMW) fraction of both the humic and the fulvic acids suggest that the HMW fraction consists of several subunits that originate from the LMW fraction.     

Analysis of diffusion coefficient distributions in humic and fulvic acids by means of diffusion ordered NMR spectroscopy

The use of the computer program CONTIN to analyze pulsed-field gradient NMR (PFG-NMR) data for several standard humic and fulvic acids is described. An advantage of PFG-NMR analysis is that integration of different spectral regions provides a picture of how the diffusion coefficients vary with functional group composition for a given sample. Using prior knowledge of the sample and the principle of parsimony, CONTIN approximates a solution to the inverse Laplace transform applied to the decay of peak intensity with gradient area in the PFG-NMR experiment. Thus, a continuous distribution of diffusion coefficients is resolved for the polydisperse humic and fulvic acids. The results of the CONTIN analyses are in the form of a distribution function and a two-dimensional DOSY plot. The 2D DOSY spectrum displays chemical shifts along one axis and diffusion coefficients along the other, while a number-average diffusion coefficient, D(N), a weight-average diffusion coefficient, D(W), and a most probable diffusion coefficient, D(P), are realized from the diffusion coefficient distribution. For all spectral regions of each humic sample, D(W) was greater than D(N), which in turn was greater than or equal to the D(P), suggesting that the diffusion coefficient distribution is weighted toward smaller, more rapidly diffusing molecules. Polydispersities, estimated from the ratio D(W)/D(N), were less than the reported M(W)/M(N) values for similar humic substances. Thus, the D(W)/D(N) ratio obtained by CONTIN analysis of PFG-NMR data can be at least a qualitative, and at best a semiquantitative, indication of the polydispersity of the humic sample, but should not be used as a quantitative measure of polydispersity.     

Multivariate curve resolution of synchronous fluorescence spectra matrices of fulvic acids obtained as a function of pH

Synchronous fluorescence spectra (excitation wavelength range between 280 and 510 nm and wavelength interval of 25 nm) of three samples of fulvic acids (FA) were obtained as a function of the pH, in the range from 2.0 to 10.5, and as a function of the FA concentration, in the range from 20 to 180 mg/L. FA were obtained from composted livestock materials (lsFA), composted sewage sludge (csFA), and Laurentian soil (laFA). Three-dimensional spectral matrices were obtained (wavelength, pH, and FA concentration) and multivariate curve resolution (MCR) was used to calculate spectra and fluorescence intensity profiles for the detected components. Cluster analysis of the calculated spectra showed the existence of similar and unique fluorescent properties in the three FA samples. Some of the calculated fluorescence intensity profiles have a shape compatible with acid-base species distribution diagrams, which allowed pKa values to be estimated, namely, a well-defined acid-base equilibrium with pKa 5.7 +/- 0.2 (lsFA), 6.9 +/- 0.4 (csFA), and 5.5 +/- 0.2 (laFA); and other acid-base systems not well defined with pKa at about 3.0 and 8.6. Other spectral variations revealed the existence of inner-filter effects or self-quenching as the concentration of FA increases.     

Exact masses and chemical formulas of individual Suwannee River fulvic acids from ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectra

Molecular formulas have been assigned for 4626 individual Suwannee River fulvic acids based on accurate mass measurements from ions generated by electrospray ionization and observed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). Formula assignments were possible because of the mass accuracy of FTICR MS at high field (9.4 T) and the regular mass spacing patterns found in fulvic acid mixtures. Sorting the 4626 individually observed ions according to Kendrick mass defect and nominal mass series (z* score) revealed that all could be assigned to 1 of 266 distinct homologous series that differ in oxygen content and double bond equivalence. Tandem mass spectrometry based on infrared multiphoton dissociation identified labile fragments of fulvic acid molecules, whose chemical formulas led to plausible structures consistent with degraded lignin as a source of Suwannee River fulvic acids.     

Sorption of radionuclides from solutions with composite materials based on Mikoton natural biopolymer

Composite sorbents based on Mikoton natural biopolymer, selective to ⁹⁰Sr, were prepared, and features of ⁹⁰Sr sorption with these sorbents were discussed. The inorganic compound used as modifier is deposited on the surface of fibers of Mikoton biopolymer in the form of single crystals and polycrystals. Certain physicochemical parameters of the sorption were determined: static exchange capacity, constants of sorption equilibrium, etc. Deposition of BaSO₄ on the surface of biopolymer fibers increases the sorption capacity toward ⁹⁰Sr in solutions containing sulfate ions, and deposition of MnO₂ enhances the sorption of ⁹⁰Sr from solutions with high concentrations of salts. The influence of the chemical composition and pH of solution was studied in detail. The calculated low value of ΔG ⁰ of radionuclide sorption is attributed to the simultaneous occurrence of several parallel processes in the system, some of which are energy-consuming. The Mikoton-Cs sorbent {composite of Mikoton biopolymer with K₂Cu[Fe(CN)₆]} appeared to be only weakly sensitive to variation of the chemical composition of the solution in a wide range of salt concentrations.     

Uncertainties in doses from intakes of radionuclides assessed from monitoring measurements

The evaluation of uncertainties in doses from intakes of radionuclides is one of the most difficult problems in internal dosimetry. In this paper, the process of assessing internal doses from monitoring measurements is reviewed and the major sources of uncertainty are discussed. Methods developed independently at HPA and at IRSN for the determination of uncertainties in internal doses assessed from monitoring measurements are described. Both use a Monte Carlo simulation approach. Results are described for three illustrative examples. An alternative method developed at the Los Alamos National Laboratory that uses Bayesian statistical methods is also described briefly.     

High-resolution Fourier transform ion cyclotron resonance mass spectrometry of humic and fulvic acids: improvements and comparisons.

Full structural characterization of complex mixtures such as humic acid extracts has been elusive because of insufficient compound resolution with conventional techniques. Using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry, we were able to resolve individual compounds within humic and fulvic acid mixtures (mass resolving power approximately 80000 at 300 m/z). We examined two samples in detail: (1) dissolved organic matter (primarily fulvic acids) from Suwannee River, GA, and (2) a humic acid extract from a degraded wood collected on Mt. Rainier, WA. Sample conditions (such as solvent, pH, and concentration) and instrument parameters (such as source voltages, trapping potentials, and excitation parameters) were optimized to yield the highest mass resolving power with the least mass discrimination in positive ion mode. High resolving power was achieved with low ion densities combined with coadding numerous scans. The increased resolution allowed molecular-level comparisons of the two samples which in turn could be used to estimate the relative similarity of individual compound distribution as well as an indication of the dominant diagenetic processes in the two source environments.