Distribution of Natural Radionuclides and 137Cs in Urban Soil Samples from the City of Novi Sad, Serbia-Radiological Risk Assessment.

This work presents the natural radioactivity distribution of 21 surface soil samples taken in the city of Novi Sad, Serbia. The analysis for radioactivity was performed using a gas low-level proportional counter for gross alpha and gross beta activity, while the specific activities of radionuclides were determined using HPGe detectors. The gross alpha activity of 20 samples was below the minimum detectable concentration (MDC), while in 1 sample it was 243 Bq kg-1; the gross beta activity ranged from the MDC (11 samples) to 566 Bq kg-1. The gamma spectrometry measurements showed naturally occurring radionuclides 226Ra, 232Th, 40K, and 238U in all investigated samples, with average values (Bq kg-1) of 33.9, 36.7, 513.8, and 34.7, respectively. Natural radionuclide 235U was detected in 18 samples with activity concentrations in the range of 1.3-4.1 Bq kg-1, while in the other 3 samples, the values were below the MDC. The artificial 137Cs radionuclide was detected in 90 percent of the samples, with a maximum value of 21 Bq kg-1, while the other artificial radionuclides were not detected. Based on the obtained concentrations of natural radionuclides, hazard indexes were estimated, and radiological health risk was assessed. The results present the absorbed gamma dose rate in the air, annual effective dose, radium equivalent activity, external hazard index, and lifetime cancer risk.

Novel approach for strontium preconcentration from seawater and rapid determination of 89,90Sr in emergency situations.

A novel approach for rapid 89,90Sr determination in seawater samples is developed. For the first time in the radioanalytical application, the features of the synthetic zeolite Z4A and a highly selective material for Sr separation were synergically employed. Seawater composition significantly reduces Sr yield on highly selective solid-phase extraction materials, making the preconcentration step essentially important but laborious and time-consuming. To address this issue, the ability of zeolite 4A to concentrate the Sr from the seawater matrix was employed. With the proposed method, two important goals were achieved: (i) simple preconcentration of Sr that can be conducted directly at the sampling site, enabling a rapid procedure for 89,90Sr determination in emergencies, and (ii) high and stable Sr recoveries (89 ± 4%) necessary for lowering detection limits. Strontium is effectively separated from 1 L of seawater in less than 1.5 h, which is especially important in emergency situations, such as the Fukushima Daiichi Nuclear Power Plant accident. Minimum detectable activities achieved for 89Sr:90Sr activity ratio ∼10:1 were 0.74 Bq/L for 89Sr, and 1.47 Bq/L for 90Sr, detected by Cherenkov counting, 36-38 h after separation, and 30 min counting time.

Efficient separation of strontium radionuclides from high-salinity wastewater by zeolite 4A synthesized from Bayer process liquids.

The efficient, selective, and economical sorbents for the removal of Sr radionuclides are largely needed for the decontamination of effluents with high salinity. In this study, the removal of Sr was investigated using the zeolite produced from the Bayer process liquids. Based on the XRD, SEM/EDS analysis, the product was pure and highly crystalline zeolite 4A (Z4A). Removal of Sr was fast (5 min for 100% removal at 8.80 mg/L), with high maximum sorption capacity (252.5 mg/L), and independent on the initial pH in the range 3.5-9.0. Specific sorption of Sr by protonated groups on the Z4A surface was operating in addition to ion-exchange with Na ions. The selectivity of Z4A decreased in the order Sr > Ca > K > Mg > Na. 84% of Sr was separated from seawater within 5 min, at the Z4A dose of 5 g/L, while efficiency increased to 99% using the dose of 20 g/L. Desorption of radioisotope 89Sr from seawater/Z4A solid residue was very low in deionized water (0.1-0.2%) and groundwater (0.7%) during 60 days of leaching. Z4A is a cost-effective, selective, and high-capacity medium for Sr removal, which provides high stability of retained radionuclides.

Cadmium retention and distribution in contaminated soil: effects and interactions of soil properties, contamination level, aging time and in situ immobilization agents.

As soil cadmium (Cd) contamination becomes a serious concern and one of the significant environmental pollution issues all over the world, knowledge of the basic chemistry, origin, inputs, sources, quantity, chemical forms, reactions, as well as the fate and transport of Cd in different types of soil is crucial for better understanding Cd bioavailability, health risks and remedial options. This study aimed to increase the current knowledge on the complex interdependence between the factors affecting behavior, transport and fate of Cd in the soil and to test and compare the performance of the stabilization agents in different soil types. Soils demonstrated various sorption affinity and capacity for Cd accumulation, which proved to be positively correlated with soil pH and the cation exchange capacity (CEC). With increasing levels of contamination, sequential extraction analysis showed the highest increase of relative Cd amounts in the exchangeable fraction regardless of the soil properties, suggesting that added Cd is principally associated with the easily accessible and mobile fraction. For different initial Cd concentrations and soil types, Cd sorption reached the quasi-equilibrium within 24 h of contact. Prolonged aging (two months) influenced the natural stabilization of Cd in all types of soil, but only at low contamination level. The application of both, conventional (slaked lime Ca(OH)2) and alternative phosphate-rich (annealed bovine bones B400) amendments, resulted in Cd relocation and reduction of exchangeable Cd content. Although the effect was smaller when apatite amendment was utilized, observed re-distribution of Cd to more stable soil fractions is preferable for achieving long-term stabilization. Cd concentrations extracted in exchangeable and acid soluble fractions after the treatments of contaminated soil samples suggest that the practical applicability of in situ immobilization depends on the soil properties and the level of contamination, as well as that effect, should be monitored for the possible re-mobilization of Cd.

Estimation of Cadmium uptake by tobacco plants from laboratory leaching tests.

The objective of the present study was to determine the impact of cadmium (Cd) concentration in the soil on its uptake by tobacco plants, and to compare the ability of diverse extraction procedures for determining Cd bioavailability and predicting soil-to-plant transfer and Cd plant concentrations. The pseudo-total digestion procedure, modified Tessier sequential extraction and six standard single-extraction tests for estimation of metal mobility and bioavailability were used for the leaching of Cd from a native soil, as well as samples artificially contaminated over a wide range of Cd concentrations. The results of various leaching tests were compared between each other, as well as with the amounts of Cd taken up by tobacco plants in pot experiments. In the native soil sample, most of the Cd was found in fractions not readily available under natural conditions, but with increasing pollution level, Cd amounts in readily available forms increased. With increasing concentrations of Cd in the soil, the quantity of pollutant taken up in tobacco also increased, while the transfer factor (TF) decreased. Linear and non-linear empirical models were developed for predicting the uptake of Cd by tobacco plants based on the results of selected leaching tests. The non-linear equations for ISO 14870 (diethylenetriaminepentaacetic acid extraction - DTPA), ISO/TS 21268-2 (CaCl2 leaching procedure), US EPA 1311 (toxicity characteristic leaching procedure - TCLP) single step extractions, and the sum of the first two fractions of the sequential extraction, exhibited the best correlation with the experimentally determined concentrations of Cd in plants over the entire range of pollutant concentrations. This approach can improve and facilitate the assessment of human exposure to Cd by tobacco smoking, but may also have wider applicability in predicting soil-to-plant transfer.

Effect of experimental variables onto Co(2+) and Sr(2+) sorption behavior in red mud-water suspensions.

The prospects of rinsed red mud (alumina production residue) utilization for liquid radioactive waste treatment have been investigated, with Co(2+) and Sr(2+) as model cations of radioactive elements. To evaluate the sorption effectiveness and corresponding binding mechanisms, the process was analyzed in batch conditions, by varying experimental conditions (pH, Co(2+) and Sr(2+) concentrations in single solutions and binary mixtures, contact time, and the concentration of competing cations and ligands common in liquid radioactive waste). Comparison of the Co(2+) and Sr(2+) sorption pH edges with the red mud isoelectric point has revealed that Co(2+) removal took place at both positive and negative red mud surface, while Sr(2+) sorption abruptly increased when the surface became negatively charged. The increase of initial cation content and pH resulted in increased equilibrium times and sorption capacity and decreased rate constants. From single metal solutions and various binary mixtures, Co(2+) was sorbed more efficiently and selectively than Sr(2+). While Sr(2+) sorption was reduced by coexisting cations in the order Al(3+) ≥ Ca(2+) >Na(+) ≥Cs(+), removal of Co(2+) was affected by Al(3+) species and complexing agents (EDTA and citrate). Desorption of Co(2+) was negligible in Ca(2+) and Sr(2+) containing media and in solutions with initial pH 4-7. Sr(2+) desorption was generally more pronounced, especially at low pH and in the presence of Co(2+). Collected macroscopic data signify that Co(2+) sorption by red mud minerals occurred via strong chemical bonds, while Sr(2+) was retained mainly by weaker ion-exchange or electrostatic interactions. Results indicate that the rinsed red mud represent an efficient, low-cost sorbent for Co(2+) and Sr(2+) immobilization.

Evaluation of factors influencing Co²âº removal by calcinated bone sorbent using experimental design methodology.

Experimental design methodology was applied for evaluation of factors influencing Co(2+) sorption by thermally treated bovine bones. The major aim of this study was to determine factors which affect process the most, as well as their mutual interactions, in order to select conditions that provide maximum sorbent loading. Five process variables (sorbent mass, sorbate concentration, contact time, initial pH and agitation speed) were examined by full factorial design at two levels. The initial sorbate concentration and sorbent mass were found to be a principle factors influencing cation sorption. Furthermore, a considerable interaction effect between these two factors was detected. Optimal conditions for the maximum sorbent loading include the use of small sorbent doses and concentrated Co(2+) solution, without any previous pH adjustment, at least if the pH of actual waste water is within tested range (3 < pH < 6). The contact time and agitation speed, which within investigated ranges had no significant effect on sorption, may be set at their minimum levels (1 h; 10 rpm) to shorten the reaction time and reduce energy consumption. The influence of process factors on other system responses (amounts of Ca(2+) released from apatite phase of bones, and final pH values) were also determined and analyzed. Empirical mathematical models illustrated the dependences of responses on the process variables, whereas residual and statistical analysis confirmed model adequacy.

The effect of process parameters on kinetics and mechanisms of Co2+ removal by bone char.

Bone char powder, composed mainly of poorly crystalline hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2)), carbon and CaCO(3), has potential applicability in the removal of Co(2+) ions from contaminated effluents. In the present study, the influence of process parameters: particle size, agitation speed, initial pH and initial sorbate concentration, onto kinetics and mechanism of Co(2+)sorption was studied and discussed. In order to describe and compare time evolution of the process under different conditions, the experimental data were analyzed using pseudo-first, pseudo-second and Vermeulen's kinetic models. Generally, experimental results were best fitted with the pseudo-second-order model, which accurately predicted the equilibrium sorbed amounts. The pseudo-second-order rate constant was the most influenced by variations in initial metal concentration and pH, in the investigated ranges. The conclusions about sorption mechanism were derived based on Co(2+) amounts sorbed during time, as well as considering solution pH changes, changes of Ca(2+) amounts released into liquid phase and Ca(2+)/Co(2+) molar ratios. It was concluded that rapid sorption stage was governed by surface complexation reactions, whereas the contribution of the ion-exchange mechanism increased with time and became more significant in the second, slower phase. Experimentally determined maximum sorption capacity towards Co(2+), under optimal conditions, was found to be 0.38 mmol/g. The results show that bone char represents cost-effective alternative to synthetic hydroxyapatite sorbent.