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.     

Effect of Humic Substances on Plutonium and Americium Speciation in Soils and Soil Solutions

The molecular-weight distribution of humic substances (HSs) of the organic and mineral soils and corresponding soil solutions was studied by gel chromatography, and their distribution over fractions of humus acids was evaluated by the Ponomareva-Plotnikova chemical fractionation technique. Distribution of ^239,240Pu and ²⁴¹Am over HS fractions of different dispersity was studied. In these fractions, HSs are associated with different mineral components and have different solubility and mobility. Plutonium and americium are more strongly associated with humic substances of organic soils as compared to those of mineral soils. Therefore, in passing from mineral to organic soils, the migration ability of radionuclides decreases. These effects are caused by qualitative difference in the HS chemical composition of the HSs of organic and mineral soils. As compared to plutonium, americium enters the composition of poorly soluble organomineral complexes to a smaller extent, forming to a greater extent mobile anionic complexes in the soil solutions. This difference can be responsible for enhanced americium mobility and its easier availability to plants.     

Association of radionuclides with components of fulvic acids isolated from soils

The distribution of Pu and Am between specific and nonspecific components of various groups of the organic matter of soil was studied. For chernozem and soddy podzolic soil, 63 and 53% of Pu and only 1 and 8% of Am, respectively, are bound with fulvic acid purified to remove low-molecular-weight compounds by fractionation on BAU activated charcoal. Larger relative amount of Am, compared to Pu, in the form of low-molecular-weight nonspecific compounds is responsible for higher migration mobility of Am, compared to Pu, in the environment. The sorption of organic complexes of Pu and Am on carbon nanotubes was studied. The degree of Pu sorption only slightly depends on the nature of the organic substance, except solutions of humic acids from which the Pu sorption is appreciably higher. The degree of Am sorption regularly increases with a decrease in the molecular weight of the organic substances.     

Pu and Am Distribution in the System Soil-Water-Carboxylic Resin

Dynamics of Pu and Am distribution between components of the system soil-water-carboxylic resin is studied for soils with various absorbing (clay-humus) complexes. The fractional composition of organic components of the aqueous phase of the system and TUE content in the fractions were examined to elucidate the Pu and Am speciation in the solution. The Pu and Am concentrations in the aqueous phase strongly depend on the content and composition of the soil humus matter. Transuranic elements are associated essentially with the humic acid fractions, this trend being more pronounced for Pu. In the system with increased humus content, TUE occur in the solution as complexes with humus substances, and in the system with lower humus content, as hydrolyzed species. The features of sorption processes occurring on the clayhumus complex of the soil were judged from the sorption isotherms of the radionuclides on a resin. Sorption on the resin is controlled by the Pu and Am speciation in the solution.     

Speciation and Migration Behavior of Pu and Am in Floodplain Soils and Bottom Sediments of the Yenisei River

Am and Pu speciation in floodplain soils and bottom sediments of the Yenisei River is studied. Pu is more tightly associated with amorphous hydroxides as compared to Am. Am associated with organic matter is potentially more mobile than Pu. Model experiments showed that fulvic acids decelerate Am sorption from water to floodplain soil.     

Distribution of <Superscript>137</Superscript>Cs, <Superscript>90</Superscript>Sr, <Superscript>239 + 240</Superscript>Pu, <Superscript>241</Superscript>Am,and <Superscript>244</Superscript>Cm among Components of Organic Matter of Soils in Near Exclusion Zone of the Chernobyl NPP

Distribution of Chernobyl-derived ¹³⁷Cs, ⁹⁰Sr, ^{239 + 240}Pu, ²⁴¹Am, and ²⁴⁴Cm among organic fractions of soddy-podzolic, sandy, soddy-meadow, and peat soils collected from the Chernobyl Exclusion Zone along the North-Western radioactive fallout track was determined. Regardless of the soil type, 80–85% of ¹³⁷Cs is tightly fixed on the mineral fraction of the soil. Depending on the soil type, 50–70% of ⁹⁰Sr and 15– 45% of ²⁴¹Am are associated with fulvic acid fractions. ²⁴¹Am and ²⁴⁴Cu are similarly distributed among the organic acid fractions. In all the soil types studied, ^{239 + 240}Pu is associated essentially with humic acid fractions. Natural ^{230, 232}Th and technogenic ^{239 + 240}Pu are similarly distributed among the organic fractions.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 91–96.Original Russian Text Copyright © 2005 by Odintsov, Pazukhin, Sazhenyuk.     

Model Study of Migration Behavior in Floods of 241Am and 152Eu Associated with Humus Compounds in Floodplain Soils of the Yenisei River

It is demonstrated in model experiments that in the presence of Ca ions (typomorphous cations of water of the Yenisei River) fulvic acids of floodplain soils and associated radionuclides (Am, Eu) form poorly soluble mixed Ca, Fe, Al(Am, Eu) fulvates. As a result, under the flooding conditions the migration of Am and Eu in the form of solubilized organomineral complexes is practically totally suppressed. With decreasing pH in the model system from 8 to 6 the mobility of the radionuclides noticeably increases.     

Sorption of long-lived radionuclides onto main types of rocks of the Novaya Zemlya Archipelago

The ability of black carbonaceous siltstones and silt sandstones, lime sandstones, gray limestones, carbon–silicon carbonate schists with pyrite, and other rocks that most widely occur on the Novaya Zemlya Archipelago to sorb ¹³⁷Cs, ⁹⁰Sr, ^239+240Pu, and ²⁴¹Am was studied. The distribution coefficients K _d (cm³ g^–1) are as follows: for ^239+240Pu, 2.7 × 10³–7.7 × 10³; for 241Am, 2.5 × 10³–1.8 × 10⁴; and for ¹³⁷Cs, 1.1 × 10²–2.0 × 10³. Strontium-85(90) it not noticeably sorbed (within the measurement uncertainty) by any of the rocks studied. ^239+240Pu, ²⁴¹Am, and ¹³⁷Cs are strongly sorbed onto the rocks studied and are not noticeably desorbed from them with distilled water. The data obtained are required for predicting the migration of long-lived radionuclides generated by nuclear explosion with surface waters from test sites on the Novaya Zemlya Archipelago.     

Effects of dissolved low molecular weight organic acids on oxidation of ferrous iron by Acidithiobacillus ferrooxidans

A few researchers have reported on work concerning bioleaching of heavy-metal-contaminated soil using Acidithiobacillus ferrooxidans, since this acidophile is sensitive to dissolved low molecular weight (LMW) organic acids. Iron oxidation by A. ferrooxidans R2 as well as growth on ferrous iron was inhibited by a variety of dissolved LMW organic acids. Growth experiments with ferrous iron as an oxidant showed that the inhibition capability sequence was formic acid>acetic acid>propionic acid>oxalic acid>malic acid>citric acid. The concentrations that R2 might tolerate were formic acid 0.1mmolL(-1) (2mmolkg(-1)soil), acetic and propionic acids 0.4mmolL(-1) (8mmolkg(-1)soil), oxalic acid 2.0mmolL(-1) (40mmolkg(-1)soil), malic acid 20mmolL(-1) (400mmolkg(-1)soil), citric acid 40mmolL(-1) (800mmolkg(-1)soil), respectively. Although R2 was sensitive to organic acids, the concentrations of LMW organic acids in the contaminated soils were rather lower than the tolerable levels. Hence, it is feasible that R2 might be used for bioleaching of soils contaminated with metals or metals coupled with organic compounds because of the higher concentrations of LMW organic acids to which R2 is tolerant.     

Effect of Contact Time of Liquid Radioactive Waste with Bed Rock of Underground Repository on Migration Behavior of 90Sr, 137Cs, 239Pu,and 241Am

Behavior of radionuclides caused by interaction of acidic waste with sandy bedrock in deep underground repositories is studied, including sorption-desorption of ⁹⁰Sr, ¹³⁷Cs, ²³⁹Pu, and ²⁴¹Am. The amount of mobile forms of radionuclides decreases with increasing contact time with bedrock, thus decreasing the migration rate of the radionuclides in the collector bed.     

Comparison of Methods for Assessing Plutonium Speciation in Environmental Objects

Several methods for Pu speciation study are compared using the same sample of bottom sediment. Data on Pu distribution among different soil fractions (water-soluble, exchangeable and readily soluble, mobile, associated with organic matter, including humic and fulvic acids, and also with amorphous hydroxides, primarily of iron and manganese) are reported. The major fraction of plutonium is associated with the organic matter. The experimental results on the Pu speciation, obtained by different methods, show satisfactory agreement.     

Speciation of artificial radionuclides 60Co, 137Cs, 152Eu, and 241Am in bottom sediments of the Yenisei river

The speciation of artificial radionuclides ⁶⁰Co, ¹³⁷Cs, ¹⁵²Eu, and ²⁴¹Am in surface layers of bottom sediments of the Yenisei river, collected within the near zone of impact of the Mining and Chemical Combine (Rosatom), was studied. In these samples the radionuclides ⁶⁰Co, ¹⁵²Eu, and ²⁴¹Am are mainly associated with fractions of humic and fulvic acids. The fraction of ¹⁵²Eu associated with nonsilicate iron is approximately 92%. The migration capability of radionuclides collected near the Atamanovo settlement decreases in the order ¹⁵²Eu > ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. For samples collected near Bol’shoi Balchug settlement, this order is as follows: ¹⁵²Eu ≈ ²⁴¹Am > ⁶⁰Co > ¹³⁷Cs. The presence of radionuclide-bearing micro-particles in bottom sediments considerably complicates the distribution of radionuclides, in particular, of ²⁴¹Am and ¹³⁷Cs, among migration forms.     

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.     

Role of Suspended Matter and Dissolved Organic Substances in Behavior and Migration of Anthropogenic Radionuclides in River-Sea Aquatic Systems

Distribution of Cs, Sr, and Pu nuclides between suspended matter and the aqueous phase and the features of interaction of these radionuclides with dissolved organic matter are studied, to gain a better insight into the radionuclide behavior in the Ob and Yenisei estuaries and adjacent Kara Sea. For radionuclide speciation, the experimental study included determination of the radionuclide activities in aqueous solutions after filtration and ultrafiltration of large-volume water samples and membrane fractionation of small-volume water samples by passing the solution through a cartridge with filters of regularly decreasing pore size followed by mass-spectrometric determination of elements. In the water-soluble fraction, the ¹³⁷Cs activity increases with increasing salinity, whereas that of ⁹⁰Sr decreases, which can be attributed to the differences in the physicochemical behavior of the radionuclides in solutions and also to the effect of contamination sources. In seawater, suspended material can retain 1-10% of ¹³⁷Cs and ⁹⁰Sr. In the estuarine zones, these values can be 20-40%. More than 50% of ⁹⁰Sr and ^239,240Pu are associated with dissolved organic matter. In saline water this effect is less pronounced.     

Effects of organic complexing ligands and soil organic matter on the metal adsorption/migration in soil

Abstract

The adsorption of heavy metals on soil from the Neihu Landfill Site in Taipei City was investigated in order to assess the ground water pollution problems. The effects of soil organic matter and the behaviors of organic complexing ligands like EDTA and humic acid to the overall adsorption process were studied and discussed. In explaining the results, the pH of soil system and the properties of the soil/aqueous interface were chosen as two significant and interacting factors for discussion. The concept of the specific adsorption mechanism was also demonstrated and discussed. The results showed that the complexing ligands existing in soil liquid phase have more influences than natural organic matter does. The competitive sequences of different organic matter contents indicated that organic functional sites preferentially bind with Cu and Cd. The presence of EDTA and humic acid which formed ligandlike complexes will reduce Cd adsorption efficiency. These effects will induce mobility and the fate of heavy metals in soils, such as bioavailability.     

Effect of humic substances on Cu(II) solubility in kaolin-sand soil

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (FAs) (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range typical of industrially contaminated soils. This study investigated the influence of three humic substances (HSs: humates, fulvates and humins) on the solubility of copper(II) ions in kaolinitic soil spiked with Cu at levels representative of industrially contaminated soil. Humates, fulvates and humin were extracted from Irish moss peat, and controlled pH batch leaching tests were conducted on an artificial kaolin-sand soil that was spiked with each. Further leaching tests were conducted on soil spiked with each HS and copper nitrate. Dissolved organic contents were determined by titration and total and free aqueous copper concentrations in the leachate were measured using AAS and ion selective electrode (ISE) potentiometry respectively (dissolved complexed copper levels were determined by difference). It was found that humates and fulvates are partially sorbed by the soil, probably by chemisorption on positively charged gibbsite (Al-hydroxide) sites in the kaolinite. The addition of 340 mg/kg Cu(II) ions did not significantly affect the amount of humate or fulvate sorbed. Dissolved humates and fulvates form soluble complexes with copper over the pH range 3-11. However, in the presence of kaolinite, soluble copper humates and fulvates are unable to compete with the kaolinite for Cu ions at pH 6-7. Above pH 8, humate and fulvate complexes are the only forms of dissolved Cu. Humin is largely insoluble and has little effect on Cu mobility between pH 2 and 12. The implication of this study is that measurement of total soil organic content and water leaching tests should be a standard part of contaminated site investigation.     

The influence of different soil constituents on the reaction kinetics of wet oxidation of the creosote compound quinoline

Creosote contaminated sites have become a widespread problem in industrialized countries. Recently, wet oxidation using high temperature, pressure, water and oxygen followed by activated sludge treatment proved to be an efficient method for removing a wide selection of creosote compounds in contaminated soils. Wet oxidation of the creosote compound quinoline was carried out in the presence of montmorillionite, quartz and humic acid. The products derived from wet oxidation were identified and treated biologically by activated sludge testing their biodegradability. The influence on the oxidation kinetics of quinoline during wet oxidation was pH dependent. Humic acid supported the oxidation of quinoline, whereas the addition of montmorillionite and quartz had either an inhibiting effect or led only to a slight increase in oxidation. In mixtures of soil constituents, especially at low contents of humic acid, the adsorption of quinoline on montmorillionite prevented oxidation at neutral pH. Thus, alkaline extraction of both quinoline and humic acid was needed for an efficient oxidation. A proposed reaction mechanism suggests that quinoline was oxidized by hydroxyl radicals formed during the oxidation of the humic acid. A wide selection of reaction products (mainly carboxylic acids, benzene and pyridine derivatives) derived from the wet oxidation of humic acid and quinoline. The reaction products from humic acid degradation had a rate limiting effect on the wet oxidation of quinoline leaving small residues of quinoline after the treatment. On the contrary, these reaction products also improved the biodegradation of products from the quinoline oxidation due to co-digestion of carboxylic acids. Therefore, the presence of soil components (mainly humic acid) improved the combined wet oxidation and biological activated sludge treatment of quinoline.     

Effect of humic acids and iron hydroxides deposited on the surface of clay minerals on the 137Cs immobilization

The effect exerted on the relationships of ¹³⁷Cs sorption by humic acids and iron hydroxides deposited on the surface of clay minerals, montmorillonite and kaolinite, differing in the exchange capacity, was studied. The presence of humic acids and Fe(OH)₃ deposited on the mineral surface leads to an increase in the ¹³⁷Cs sorption in a wide pH range (pH 4–9), suggesting the participation of functional groups of humic acids and ferrinol groups of iron(III) hydroxide in binding of the metal ions. The Na⁺, K⁺, and Ca²⁺ ions, on the contrary, with an increase in their concentration in aqueous solution decrease the immobilization of cesium radionuclides and favor their migration in the environment.     

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.     

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%).