Distribution of uranium isotopes in surface water of the Llobregat river basin (Northeast Spain)

A study is presented on the distribution of ²³⁴U, ²³⁸U, ²³⁵U isotopes in surface water of the Llobregat river basin (Northeast Spain), from 2001 to 2006. Sixty-six superficial water samples were collected at 16 points distributed throughout the Llobregat river basin. Uranium isotopes were measured by alpha spectrometry (PIPS detectors). The test procedure was validated according to the quality requirements of the ISO17025 standard. The activity concentration for the total dissolved uranium ranges from 20 to 261 mBq L⁻¹. The highest concentrations of uranium were detected in an area with formations of sedimentary rock, limestone and lignite. A high degree of radioactive disequilibrium was noted among the uranium isotopes. The ²³⁴U/²³⁸U activity ratio varied between 1.1 and 1.9 and the waters with the lowest uranium activity registered the highest level of ²³⁴U/²³⁸U activity ratio. Correlations between uranium activity in the tested water and chemical and physical characteristics of the aquifer were found.     

A study of radionuclides, metals and stable lead isotope ratios in sediments and soils in the vicinity of natural U-mineralisation areas in the Northern Territory

Australian guidelines recommend that tailings materials from uranium (U) mining and milling be contained without any detrimental impact on the environment for at least 1000 years. Natural analogue sites are being investigated to determine if they can provide data on the rates of natural erosion processes which occur over these timescales, for input into predictive geomorphic computer models. This paper presents radionuclide, metal and stable lead (Pb) isotope data from sediment cores and surface soils in the vicinity of two mineralised areas in the Alligator Rivers Region.Surface scrapes from the natural Anomaly #2, south of the Ranger mineral lease, exhibit radiogenic ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios, and elevated U and metal concentrations typical for a near surface U anomaly. In contrast, samples taken from the Koongarra mineral lease (KML) show radionuclide activity and metal concentrations similar to natural areas elsewhere in the Alligator Rivers Region and Pb isotope ratios are closer to present day average crustal ratios (PDAC), as the orebodies at KML are covered by surficial sand. A sediment core collected from Anbangbang Billabong, downstream of KML, exhibits small variations in Pb isotope ratios that indicate that approximately 1% of the upper sediments in the sediment core may be derived from material originating from the U anomaly at Koongarra.     

Spatial distribution of arsenic in the intertidal sediments of River Scheldt, Belgium

A study was carried out to assess the spatial distribution of arsenic in the intertidal sediments of the River Scheldt in Belgium. Sediment samples were collected from different locations along the River Scheldt up to 100 cm depth and analysed for the major physicochemical properties. The study reveals that the arsenic contents in the sediment samples vary in a wide range, from 2.3 to 140.2 mg kg(-1) dry weight. Moreover, the arsenic concentrations are generally below the background concentrations and remediation thresholds of arsenic in Flanders, Belgium. The occurrence of arsenic is found closely related to some physicochemical properties of the sediments. Arsenic has a strong positive correlation with organic matter and clay contents. On the contrary, a negative correlation exists between arsenic, sand and pH. It is recommended to develop and use organic matter control practices for lowering further accumulation of arsenic within the sediments.     

Spatial distribution of natural radioactivity levels in topsoil around the high-uranium mineralization zone of Kylleng-Pyndensohiong (Mawthabah) areas, West Khasi Hills District, Meghalaya, India

A study of background radiation and the distribution of radionuclides in the environment of the proposed uranium mining sites of Kylleng-Pyndensohiong (Mawthabah) areas, West Khasi Hills District, Meghalaya, India, has been carried out with the objective of establishing a baseline radiation level of the region. Topsoil samples collected from the region are analysed for radioactivity measurements of primordial radionuclides by gamma-spectrometry technique. Direct dose measurement using a survey meter was also carried out simultaneously. Measurement carried out in the region shows that the activity concentration of (238)U and (232)Th in soil samples is found to be highest in Kylleng with respective median values of 335.3Bqkg(-1) and 283.9Bqkg(-1) followed by Syngkai with activity concentration of 285.3Bqkg(-1) and 257.4Bqkg(-1) for (238)U and (232)Th, respectively. The distribution of (40)K concentration in the study area is found to be in the range of 173.1-359.0Bqkg(-1) which is below the global and Indian average values of 420Bqkg(-1) and 394Bqkg(-1), respectively. The contribution of the primordial radionuclides to the total dose of the study area is found to be very high with a range of 136.8-334.5nGyh(-1) in comparison to the global as well as Indian average values.     

Determination of U, Pu and Am isotopes in Irish Sea sediment by a combination of AMS and radiometric methods

Samples from a marine sediment core from the Irish Sea (54.416 N, 3.563 W) were analyzed for the isotopic composition of uranium, plutonium and americium by a combination of radiometric methods and AMS. The radiochemical procedure consisted of a Pu separation step by anion exchange, subsequent U separation by extraction chromatography using UTEVA^® and finally Am separation with TRU^® Resin.Additionally to radiometric determination of these isotopes by alpha spectrometry, the separated samples were also used for the determination of ²³⁶U/²³⁸U and plutonium isotope ratios by Accelerator Mass Spectrometry (AMS) at the VERA facility.     

The distribution of plutonium,Americium and curium isotopes in pond and stream sediments of the Savannah river plant,South Carolina,USA

The concentrations of ²³⁸Pu, ^239,240Pu, ²⁴¹Am and ²⁴⁴Cm were determined in sediment samples from five streams and two ponds on the Savannah River Plant (SRP) and in four sediment samples from the Savannah River above and below the plant site. The following concentration ranges were determined: ²³⁸Pu, 0·07–386 fCi g⁻¹; ^239,240Pu, 0·37–1410 fCi g⁻¹; ²⁴¹Am, 0·1–4360 fCi g⁻¹; ²⁴⁴Cm, <0·01–392 fCi g⁻¹. Comparisons of the elemental and isotopic ratios of the sediments show that the majority of the sediments studied have been impacted upon by plant operations and that sediments outside the plant boundary in the Savannah River have only been influenced by aerial releases. Atom ratios of ²⁴⁰Pu/²³⁹Pu indicate that up to 86% of the Pu in these sediments is derived from plant operations. However, comparisons of the concentration data with values for other impacted sediments near nuclear facilities indicate that the levels are relatively small. Finally, <13% of the Pu, Am or Cm in pond sediments is associated with humic or fulvic acids, indicating that little of the material should be remobilized in oxic environments through organic complexation.     

The distribution and inventory of fallout plutonium in sediments of the Ligurian Sea near La Spezia,Italy

Pu concentrations in surface sediments of the Ligurian Sea are about ten times higher than in adjacent river sediments and are highly correlated with sediment porosities. The integrated inventory of ^239,240Pu in a sediment core is calculated to be 3·5 mCi km^?2, nearly twice the average input from fallout at these latitudes, apparently because Pu is removed from seawater by particle scavenging.The sedimentation rate is calculated from the depth of the ^239,240Pu maximum to be 0·52 ± 0·06 cmy^?1.     

Characterization of plutonium in deep-sea sediments of the Sulu and South China Seas

Anthropogenic Pu isotopes are important geochemical tracers for sediment studies. Their distributions and sources in the water columns as well as the sediments of the North Pacific have been intensively studied; however, information about Pu in the Southeast Asian seas is limited. To study the isotopic composition of Pu, and thus to identify its sources, we collected sediment core samples in the South China Sea and the Sulu Sea during the KH-96-5 Cruise of the R/V Hakuho Maru. We analysed the activities of ^239+240Pu and the atom ratios of ²⁴⁰Pu/²³⁹Pu using isotope dilution sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS). The ²⁴⁰Pu/²³⁹Pu atom ratios in the sediments of both areas (inventory weighted mean: 0.251 for the South China Sea and 0.280 for the Sulu Sea) were higher than the global fallout value (0.178 ± 0.019), suggesting the existence of Pu from the Pacific Proving Grounds in the North Pacific. Low inventories of ^239+240Pu in sediments were observed in the South China Sea (3.75 Bq/m²) and the Sulu Sea (1.38 Bq/m²). Most of the Pu input is still present in the water column. Scavenging and benthic mixing processes were considered to be the main processes controlling the distribution of Pu in the deep-sea sediments of both study areas.     

Application of multivariate statistical analyses in the interpretation of geochemical behaviour of uranium in phosphatic rocks in the Red Sea,Nile Valley and Western Desert,Egypt

Factor and cluster analyses as well as the Pearson correlation coefficient have been applied to geochemical data obtained from phosphorite and phosphatic rocks of Duwi Formation exposed at the Red Sea coast. Nile Valley and Western Desert. Sixty-six samples from a total of 71 collected samples were analysed for SiO2, TiO2, Al203, Fe2O3, CaO, MgO, Na2O, K2O, P2O5, Sr, U and Pb by XRF and their mineral constituents were determined by the use of XRD techniques. In addition, the natural radioactivity of the phosphatic samples due to their uranium, thorium and potassium contents was measured by gamma-spectrometry. The uranium content in the phosphate rocks with P2O5 > 15% (average of 106.6 ppm) is higher than in rocks with P2O5 < 15% (average of 35.5 ppm). Uranium distribution is essentially controlled by the variations of P2O5 and CaO, whereas it is not related to changes in SiO2, TiO2, Al2O3, Fe2O3, MgO, Na2O and K2O concentrations.-Factor analysis and the Pearson correlation coefficient revealed that uranium belaves geochemically in different ways in the phosphatic sediments and phosphorites in the Red Sea, Nile Valley and Western Desert. In the Red Sea and Western Desert phosphorites, uranium occurs mainly in oxidized U6+ state where it seems to be fixed by the phosphate ion, forming secondary uranium phosphate minerals such as phosphuranylite. In the Nile Valley phosphorites, ionic substitution of Ca2+ by U4 is the main controlling factor in the concentration of uranium in phosphate rocks. Moreover, fixation of U6- by phosphate ion and adsorption of uranium on phosphate minerals play subordinate roles.     

Origin and transport of U and Ra in riverine,estuarine and marine sediments of the Krka River,Croatia

Spatial distribution of ²³⁸U and ²²⁶Ra activities in sediment columns along the Krka River and estuary, were studied using gamma spectrometry. Markedly different ²³⁸U and ²²⁶Ra activities between riverine, estuarine and marine sediments were observed. Distribution of these radionuclides, as well as their anthropogenic and natural origin, was evaluated by activity measurements, taking into account sedimentation rates estimated by ¹³⁷Cs distribution in sediment columns.     

Temporal and spatial distribution of Cs in Eastern Mediterranean Sea. Horizontal and vertical dispersion in two regions

Caesium-137 activity concentration in the water columns of the Gulf of Patras (Central Greece) and the North-Eastern Aegean Sea (easterward to Lemnos Island) was investigated in selected sampling stations during the period September 2004–June 2006. The methodology followed was based on the sorption of caesium (Cs) on cotton wound cartridge filters impregnated by Cu₂[Fe(CN)₆] via in-situ pumping. In terms of the horizontal and vertical records, the activity concentrations of ¹³⁷Cs in the Gulf of Patras ranged between 1.2 and 6.7 Bq m⁻³, depending on the sampling period and the prevailing physicochemical regime at the sampling station. The general pattern of the decreased activity concentrations of ¹³⁷Cs with increasing depth was reversed in the Gulf of Patras during the cold period attributed to the prevailing advective processes of the area. The activity concentrations of ¹³⁷Cs in the North-Eastern Aegean Sea ranged from 2.6 to 12.8 Bq m⁻³, whereas significant stratified curves were observed during the warm period and also, in one station during the cold period. In terms of temporal variation, the discharges in the Gulf of Patras resulted in enhanced levels of ¹³⁷Cs, whereas in the North Aegean Sea the incoming water masses form the Black Sea had an apparent influence throughout the year by increasing the ¹³⁷Cs levels, hence presenting a weak seasonal variation. Comparing the two studied areas, one could say that the North Aegean Sea, as an open sea environment, presented higher concentrations due to the influence of the Black Sea water masses. The estimated inventories of ¹³⁷Cs in the Gulf of Patras ranged 0.25 ± 0.03–0.79 ± 0.03 kBq m⁻², whereas in the North-Eastern Aegean Sea they ranged 0.33 ± 0.02–0.92 ± 0.03 kBq m⁻².     

Distribution of (226)Ra-(210)Pb-(210)Po in marine biota and surface sediments of the Red Sea, Sudan

Activity concentration levels and ratios of (226)Ra, (210)Pb and (210)Po are presented in multicellular marine algae, molluscs, coral as well as in surface marine sediments collected from the shallower waters of the fringing reefs area extending towards north and south (Flamingo bay) of PortSudan harbour, Sudan. The analyses were performed adopting alpha-spectrometry, liquid scintillation and Cerenkov counting techniques. Surface sediments from this coastal region are poor in their radioactivity content in contrast to similar data reported from different coastal areas around the globe. There is surface enrichment of (210)Pb and (210)Po with respect to their progenitor (226)Ra as it is evident from the activity ratios of (210)Pb/(226)Ra (3.03+/-1.79) and (210)Po/(226)Ra (2.23+/-1.56). Among marine plants and animals investigated, the green algae species, Halimeda, and coral species, Favites, show substantial concentration of radium at 8.2Bq/kg and 21.9Bq/kg dry weight, respectively. Similarly, the highest concentration of (210)Po was met in Favites at 38.7Bq/kg followed by brown algae, Cystoseria sp., at 32.6Bq/kg. There is no variation seen among algal species for (210)Pb uptake, however, converse to radium and polonium, Favites (coral) was found to contain the minimum concentration of lead (3.88Bq/kg). In most species there is preferential accumulation of polonium over its parent radium as indicated by (210)Po:(226)Ra activity ratio with Cystoseria (brown algae) showing the highest value at 8.81. On the other hand, (210)Po:(210)Pb activity concentration ratio revealed that coral species Favites (9.97) and the brown algae Sargassum (1.85) have a greater tendency to accumulate (210)Po over (210)Pb, while in the rest of species; this ratio is less than unity.     

Distribution of radionuclides in the guano sediments of Xisha Islands, South China Sea and its implication

Several natural and anthropogenic radionuclides (²¹⁰Pb, ²²⁶Ra and ¹³⁷Cs) in guano-phosphatic coral sediments and pure guano particles collected from Ganquan, Guangjin, Jinqing and Jinyin Islands of the Xisha archipelago, South China Sea, were analyzed. The Constant Initial Concentration (CIC) model and the Constant Rate of Supply (CRS) model were applied for age calculation. The average supply rate of ²¹⁰Pb was 126 Bq m⁻² a⁻¹, very close to the flux of northern hemisphere average (125 Bq m⁻² a⁻¹). The activities of anthropogenic radionuclides in the sediments were very low, indicating that human nuclear tests did not notably impact this region. The main source of radionuclides in the sediments was from atmospheric precipitation, and the organic matter derived from plant and produced by nutrient-rich guano could further enhance them.     

Spatial distribution of uranium and thorium in the surface soil around proposed uranium mining site at Lambapur and its vertical profile in the Nagarjuna Sagar Dam

The understanding and evaluation of the possible interactions of various naturally occurring radionuclides in the world's third largest man-made dam, Nagarjuna Sagar located in Andhra Pradesh, India and built on river Krishna assumed significance with the finding of uranium deposits in locations near the dam. For the present work, surface soil samples from the mineralized area of Lambapur, Mallapuram, Peddagattu and sediment core samples from the Nagarjuna Sagar dam were analyzed for naturally occurring radionuclides namely uranium and thorium using gamma spectrometric technique. Also toxic elements lead and chromium were analysed by the Energy Dispersive X-ray Fluorescence Spectrometer (EDXRF) technique. Surface soil samples show a variation from 25 to 291 Bq/kg (2.02–23.5 mg/kg) for ²³⁸U and 32–311 Bq/kg (7.9–76.9 mg/kg) for ²³²Th. U/Th concentration ratio in surface soil samples ranged from 0.19 to 0.31 and was found comparable with the nation wise average of 0.26. The study of sediment core samples reflected higher U/Th concentration ratio of 0.30–0.33 in the bottom section of the core as compared to 0.22–0.25 in the upper section. The concentration ratio in the upper section of the core was similar to the ratio 0.23 found in the western Deccan Basalt region through which the river originates. A higher concentration of lead and chromium was observed in the upper section of the core compared to bottom section indicating the impact of river input on the geochemical character of dam sediment.     

Modelling the reworking effects of bioturbation on the incorporation of radionuclides into the sediment column: implications for the fate of particle-reactive radionuclides in Irish Sea sediments

A microcosm laboratory experiment was conducted to determine the impact of biological reworking by the ragworm Nereis diversicolor on the redistribution of particle-bound radionuclides deposited at the sediment-water interface. Over the course of the 40-day experiment, as much as 35% of a ¹³⁷Cs-labelled particulate tracer deposited on the sediment surface was redistributed to depths of up to 11 cm by the polychaete. Three different reworking models were employed to model the profiles and quantify the biodiffusion and biotransport coefficients: a gallery-diffuser model, a continuous sub-surface egestion model and a biodiffusion model. Although the biodiffusion coefficients obtained for each model were quite similar, the continuous sub-surface egestion model provided the best fit to the data. The average biodiffusion coefficient, at 1.8 ± 0.9 cm² y⁻¹, is in good agreement with the values quoted by other workers on the bioturbation effects of this polychaete species. The corresponding value for the biotransport coefficient was found to be 0.9 ± 0.4 cm y⁻¹. The effects of non-local mixing were incorporated in a model to describe the temporal evolution of measured ⁹⁹Tc and ⁶⁰Co radionuclide sediment profiles in the eastern Irish Sea, influenced by radioactive waste discharged from the Sellafield reprocessing plant. Reworking conditions in the sediment column were simulated by considering an upper mixed layer, an exponentially decreasing diffusion coefficient, and appropriate biotransport coefficients to account for non-local mixing. The diffusion coefficients calculated from the ⁹⁹Tc and ⁶⁰Co cores were in the range 2-14 cm² y⁻¹, which are consistent with the values found by other workers in the same marine area, while the biotransport coefficients were similar to those obtained for a variety of macrobenthic organisms in controlled laboratories and field studies.     

Suitable gamma energy for gamma-spectrometric determination of U in surface soil samples of a high rainfall area in India

The paper presents a systematic study on suitability of various gamma lines for monitoring of ²³⁸U activity in soil samples around a uranium mineralized zone of Kylleng Pyndengsohiong Mawthabah (Domiasiat), Meghalaya in India. The area lies in a plateau region which recieves the highest average annual rainfall (12,000 mm) in the world. The geochemical behaviour of the uranium and its daughter products at such wet climatic conditions imposes restrictions to assess ²³⁸U through gamma lines of radon decay products. Soil samples were collected from nine locations around the uranium mineralization zone for analysis. The ratio of the concentration of uranium obtained from gamma energies of radium daughter products to the 63.29 keV of ²³⁴Th was found to vary from 1.01 to 2.07, which indicates a pronounced disequilibrium between uranium and radium daughters. The results obtained from various gamma energies were validated from the data generated by Instrumental Neutron Activation Analysis (INAA) technique. The ²³⁸U activities from the two analytical methods show a well fitted regression line with correlation coefficient 0.99 which validates the reliability of 63.29 keV energy for estimation of uranium in such conditions.     

Comparative study of natural radioactivity levels in soil samples from the Upper Siwaliks and Punjab,India using gamma-ray spectrometry

Natural radioactive materials under certain conditions can reach hazardous radiological levels. So, it becomes necessary to study the natural radioactivity levels in soil to assess the dose for the population in order to know the health risks and to have a baseline for future changes in the environmental radioactivity due to human activities. The natural radionuclide (²²⁶Ra, ²³²Th, and ⁴⁰K) contents in soil were determined for 26 locations around the Upper Siwaliks of Kala Amb, Nahan and Morni Hills, Northern India, using high-resolution gamma-ray spectrometric analysis. It was observed that the concentration of natural radionuclides viz., ²²⁶Ra, ²³²Th and ⁴⁰K, in the soil varies from 28.3 ± 0.5 to 81.0 ± 1.7 Bq kg⁻¹, 61.2 ± 1.3 to 140.3 ± 2.6 Bq kg⁻¹ and 363.4 ± 4.9 to 1002.2 ± 11.2 Bq kg⁻¹ respectively. The total absorbed dose rate calculated from activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K ranged from 71.1 to 162.0 nGy h⁻¹. The radium equivalent (R_eq) and the external hazard index (H_ex), which resulted from the natural radionuclides in soil, were also calculated and found to vary from 149.4 to 351.8 Bq kg⁻¹and from 0.40 to 0.95 respectively. These values in Upper Siwaliks area were compared with that from the adjoining areas of Punjab. The radium equivalent activities in all the soil samples were lower than the limit (370 Bq kg⁻¹) set in the Organization for Economic Cooperation and Development (OECD) report and the dose equivalent was within the safe limit of 1 mSv y⁻¹.     

Marked disequilibrium between 234Th and 230Th of the 238U natural radioactive decay chain in IAEA reference materials n. 312, 313 and 314

A new laboratory for the spectroscopy of natural radioactivity with a good energy resolution is presented. It consists of two distinct parts equipped, respectively, the first one with a HpGe γ-ray detector, whose setup has been already completed, and the second one with large area Silicon α-ray detectors and a radiochemical section for thin α-samples preparation, whose setup is yet in progress and will be the argument of a separate work.The γ-ray spectrometer was calibrated by means of IAEA Reference Materials n. 312, 313, 314 and 375. A large difference from the predictions of secular equilibrium emerged between the activities of ²³⁴Th and ²³⁰Th in Materials n. 312, 313 and 314.