226Ra In Sediments Research Articles

Assessing radiation dosimetry for microorganisms in naturally radioactive mineral springs using GATE and Geant4-DNA Monte Carlo simulations.

Mineral springs in Massif Central, France can be characterized by higher levels of natural radioactivity in comparison to the background. The biota in these waters is constantly under radiation exposure mainly from the α-emitters of the natural decay chains, with 226Ra in sediments ranging from 21 Bq/g to 43 Bq/g and 222Rn activity concentrations in water up to 4600 Bq/L. This study couples for the first time micro- and nanodosimetric approaches to radioecology by combining GATE and Geant4-DNA to assess the dose rates and DNA damages to microorganisms living in these naturally radioactive ecosystems. It focuses on unicellular eukaryotic microalgae (diatoms) which display an exceptional abundance of teratological forms in the most radioactive mineral springs in Auvergne. Using spherical geometries for the microorganisms and based on γ-spectrometric analyses, we evaluate the impact of the external exposure to 1000 Bq/L 222Rn dissolved in the water and 30 Bq/g 226Ra in the sediments. Our results show that the external dose rates for diatoms are significant (9.7 μGy/h) and comparable to the threshold (10 μGy/h) for the protection of the ecosystems suggested by the literature. In a first attempt of simulating the radiation induced DNA damage on this species, the rate of DNA Double Strand Breaks per day is estimated to 1.11E-04. Our study confirms the significant mutational pressure from natural radioactivity to which microbial biodiversity has been exposed since Earth origin in hydrothermal springs.

Behaviour and mobility of U and Ra in sediments near an abandoned uranium mine, Cornwall, UK.

Sediment samples were collected from the vicinity of the abandoned South Terras uranium mine in south-west UK and analysed for uranium and (226)Ra to explore their geochemical dispersion. The radioactivity concentrations in the sediment samples were measured using alpha spectrometry for uranium, and gamma spectrometry for radium. Sequential chemical extraction was applied to selected sediments in order to investigate the speciation of the radionuclides and their association with stable elements. The activity ratio of the uranium isotopes was used to explore the mobility of uranium, and scanning electron microscopy (SEM) and electron microprobe analysis (EMPA) were used to characterise the sediments. The radiochemical results identified two locations with enhanced radioactivity, so two samples from these locations were further investigated. The geochemical distribution of the radionuclides in these two samples varies within the five operationally-defined fractions. In one sample, the majority of the uranium was released from the 'carbonate' fraction, followed by the organic fractions. Similarly, in the second sample, the uranium was mainly resealed from the carbonate fraction, although a considerable percentage associated with the resistant fraction. The fractionation trend of radium noticed to show some similarities to that of barium, as expected from the similarity in their chemistries. Geochemical distributions of the stable elements, such as Mn, Ti and As, were different in the enhanced radioactivity samples. The activity ratio of (234)U/(238)U shows different trends in the two sediments, signifying the impact of organic matter and/or the exchange between water and sediment. SEM and EMPA analysis identified uranium-bearing phases in association with potassium, calcium, iron, manganese and arsenic.

Comparative characterization of hydrocarbon structures and 232Th and 226Ra concentrations in Caspian Sea sediments

An integrated study of the hydrocarbon composition of bituminous substances has been performed, and the amount of the natural radionuclides 232Th and 226Ra in the surface layer of Caspian Sea sediments has been determined. The 226Ra concentration in the sediment increases with the increasing bitumen content. A comparative analysis of the amount of bitumen hydrocarbon structures in sediments and the 232Th and 226Ra natural radionuclides has shown that the 232Th and 226Ra concentration in the sediment increases with increasing amount of aromatic structures in chloroform-extracted bitumen. The concentration of 226Ra in the sediments increases with the increasing amount of polycyclic aromatic structures and decreases with an increase in the amount of monocyclic substituted aromatics. This fact indicates the preferential accumulation of 226Ra in sediments with a less reduced organic matter, which is typical of modern sediments in the early stages of diagenesis.

Evaluation of cloud and precipitation parameterization using a single-column model: A TWP-ICE case study

Cloud and precipitation parameterization schemes are evaluated, and their sensitivity to the method and/or parameters used to determine cloud physical processes is examined using a singlecolumn version of the Unified Model (SCUM). In the experiment for TWP-ICE, cloud fraction is overestimated (underestimated) in the upper (lower) troposphere due to the wet (dry) bias. The precipitation rate is well simulated during the active monsoon period, but overestimated during the suppressed monsoon and clear skies periods. In the moist convection scheme, trigger condition and entrainment process affect the lower tropospheric humidity through the impact on convective occurrence frequency and intensity, respectively. Strengthening the trigger condition and using the adaptive entrainment method alleviate the low-level dry bias. In the microphysics scheme, more large-scale precipitation is produced with prognostic rain, due to rain sedimentation considering vertical velocity of rain drop, than with diagnostic rain. Less ice/snow deposition with the prognostic two-ice category results in lower ice water content and upper-level cloud fraction than with the diagnostic splitting method for the twoice category. In the cloud macrophysics scheme, the prognostic cloud fraction and cloud/ice water content scheme produces a larger cloud fraction and more cloud/ice water content than the diagnostic scheme, mainly due to detrainment from moist convection (cloud source) that surpasses the effect of convective heating and drying (cloud sink). This affects temperature by influencing the radiative, convective, and microphysical processes. The experiment with combined modifications in cloud and precipitation schemes shows that interaction between modified moist convection and cloud macrophysics schemes results in more alleviation of the cold bias not only at the lower levels but also at the upper levels.

The formation of acid rain in the atmosphere, adjacent to the TTP with the joint-condensing of sulfur dioxide and water vapor

Presents the results of mathematical simulation of the condensation process of sulphur dioxide and water vapor on the condensation nuclei surface under the action of natural factors. Numerical investigations were carried out for the summer at a moderate speed of the wind. The influence of the parameter of condensation on the speed of the process of sulfuric acid drops formation in the air space was analyzed. Time ranges, sufficient for the formation of the acid rain sedimentation in the atmosphere, adjacent to the areas of thermal power station work were established. It is shown that the speed of air masses movement effects on the process of acid anthropogenic admixtures dispersion in the atmosphere. Approbation of the obtained results was carried out by checking the difference scheme conservative and solution of test problems.

Bioaccumulation and lack of oxidative stress response in the ragworm H. diversicolor following exposure to 226Ra in sediment

The main effluent from oil and gas production, produced water, from some platforms in the North Sea contains elevated concentrations of 226Ra. The aim of this study was to investigate whether 226Ra in sediment would accumulate in and affect sediment-dwelling organisms. In addition, we wanted to determine if the bioavailability would be modulated by the presence of a scale inhibitor which is used during oil and gas production. Hediste diversicolor was therefore exposed to different levels of 226Ra (30–6600 Bq kg −1) in combination with scale inhibitor in the sediments in a flow through system. The levels of radioactivity in the exposures were close to levels that can be measured in proximity to oil/gas production facilities. 226Ra spiked to natural sediment partitioned into pore water and accumulated in the sediment-dwelling polychaete following a four-week exposure period. The results suggest that 226Ra did not bind strongly to sediment (low sediment:water partitioning coefficient), but it was not shown to bioaccumulate in any great extent (bioaccumulation factors of 0.019–0.022). Exposure of H. diversicolor in sediments with up to 6600 Bq kg −1 226Ra had no measurable effect on the total oxyradical scavenging capacity of the organisms compared to control. So although they accumulated the alpha-emitter, the treatments did not appear to cause oxidative stress in polychaete tissues.

Speciation of 226Ra in seabed sediments formed in hydrothermal cold fluid zones (Deryugin Deep, Sea of Okhotsk)

Specific features of the behavior of Ra in seabed sediments from hydrothermal cold fluid zones were considered. It was shown that increased content of 226Ra in sediments is associated with accumulation of fine-grained Mn hydroxides in the surface oxidized layer of the sediment. These hydroxides, formed in the zone of contact of reduced Mn with bottom water, act as the sorption matrix with which 226Ra is efficiently removed from bottom water to be further accumulated in the surface layer of the sediments. It was found that 75% of 226Ra in the sediment is that sorbed from seawater with Mn hydroxide. The proportion of 226Ra coprecipitated with Ba does not exceed 4%.

Determination of 226Ra in sediments by ICP-MS: A comparative study of three sample preparation approaches

Three protocols (Method I: ion chromatography (IC) and extraction chromatography (EC), Method II: precipitation followed by IC, and Method III: adsorption onto MnO2 followed by IC-EC) were investigated to determine their applicability for the separation and pre-concentration of 226Ra in sediments. 226Ra recoveries, measured using the isotope dilution method with 228Ra as yield tracer, and the removal of spectral and non-spectral interferences were evaluated. The formation of polyatomic interferences at m/z = 226 from elements found in the matrix of sediments was also investigated to assess the level of separation required. Methods I and III were found to be the most effective with respect to recoveries and interference removal. The efficiency of a rapid microwave based protocol for the complete digestion of 1 g of sediment is also described. The method was tested and 226Ra concentrations in the millibecquerel range (fg) were determined in a standard reference material and sediment cores collected from Lake Baikal.

A Microphysical Bulk Formulation Based on Scaling Normalization of the Particle Size Distribution. Part I: Description

Abstract The authors address the problem of optimization of the microphysical information extracted from a simulation system composed of high-resolution numerical models and multiparameter radar data or other available measurements. As a tool in the exploration of this question, a bulk microphysical scheme based on the general approach of scaling normalization of particle size distribution (PSD) is proposed. This approach does not rely on a particular functional form imposed on the PSD and naturally leads to power-law relationships between the PSD moments providing an accurate and compact PSD representation. To take into account the possible evolution of the shape/curvature of the distribution, ignored within standard one- and two-moment microphysical schemes, a new three-moment scheme based on the two-moment scaling normalization is proposed. The methodology of the moment retrieval included in the three-moment scheme can also be useful as a retrieval algorithm combining different remote sensing observations. The developed bulk microphysical scheme presents a unified formulation for microphysical parameterization using one, two, or three independent moments, suitable in the context of data assimilation. The effectiveness of the scheme with different combinations of independent moments is evaluated by comparison with a very high resolution spectral model within a 1D framework on representative microphysical processes: rain sedimentation and evaporation.

Sequential extraction of 226Ra in sediments from an estuary affected historically by anthropogenic inputs of natural radionuclides

Riverbed sediments from an estuary historically affected by wastes discharged by several phosphate fertiliser plants and enriched in uranium-series radionuclides were operationally speciated using a Tessier-based method. In each selective fraction the 226Ra content was determined by alpha-particle spectrometry after radiochemical isolation and electrodeposition onto stainless steel planchets. These studies were performed in 226Ra-polluted estuarine sediments collected one year after anthropogenic discharges had ceased in order to obtain useful information about the operational forms in which this radionuclide remains associated with the sediments at this time. The results obtained revealed that one year after 226Ra inputs had stopped, the radionuclide was associated mostly with the more refractory forms. Consequently, it is possible to foresee little potential remobilisation of 226Ra contamination from sediments to the aqueous phase in the future under normal environmental conditions.

Environmental characterization and radio-ecological impacts of non-nuclear industries on the Red Sea coast

The Red Sea is a deep semi-enclosed and narrow basin connected to the Indian Ocean by a narrow sill in the south and to the Suez Canal in the north. Oil industries in the Gulf of Suez, phosphate ore mining activities in Safaga—Quseir region and intensified navigation activities are non-nuclear pollution sources that could have serious radiological impacts on the marine environment and the coastal ecosystems of the Red Sea. It is essential to establish the radiological base-line data, which does not exist yet, and to investigate the present radio-ecological impact of the non-nuclear industries to preserve and protect the coastal environment of the Red Sea. Some natural and man-made radionuclides have been measured in shore sediment samples collected from the Egyptian coast of the Red Sea. The specific activities of 226Ra and 210Pb ( 238U) series, 232Th series, 40K and 137Cs (Bq/kg dry weight) were measured using gamma ray spectrometers based on hyper-pure germanium detectors. The specific activities of 210Po ( 210Pb) and uranium isotopes ( 238U, 235U and 234U) (Bq/kg dry weight) were measured using alpha spectrometers based on surface barrier (PIPS) detectors after radiochemical separation. The absorbed radiation dose rates in air (nGy/h) due to natural radionuclides in shore sediment and radium equivalent activity index (Bq/kg) were calculated. The specific activity ratios of 228Ra/ 226Ra, 210Pb/ 226Ra, 226Ra/ 238U and 234U/ 238U were calculated for evaluation of the geo-chemical behaviour of these radionuclides. The average specific activity of 226Ra ( 238U) series, 232Th series, 40K and 210Pb were 24.7, 31.4, 427.5 and 25.6 Bq/kg, respectively. The concentration of 137Cs in the sediment samples was less than the lower limit of detection. The Red Sea coast is an arid region with very low rainfall and the sediment is mainly composed of sand. The specific activity of 238U, 235U and 234U were 25.3, 2.9 and 25.0 Bq/kg. The average specific activity ratios of 226Ra/ 228Ra, 210Pb/ 226Ra and 234U/ 238U were 1.67, 1.22 and 1.0, respectively. The relationship between 226Ra/ 228Ra activity ratio and sample locations along the coastal shoreline indicates the increase of this ratio in the direction of the Shuqeir in the north and Safaga in the south where the oil exploration and phosphate mining activities are located. These activities may contribute a high flux of 226Ra. The concentration and distribution pattern of 226Ra in sediment can be used to trace the radiological impact of the non-nuclear industries on the Red Sea coast.

Reconnaissance of submarine groundwater discharge at Ubatuba coast, Brazil, using 222Rn as a natural tracer

Submarine groundwater discharge (SGD), which includes fresh groundwater and recycled seawater, has been recognized as a widespread phenomenon that can provide important chemical elements to the ocean. Several studies have demonstrated that SGD may approach or even exceed freshwater sources in supplying nutrients to coastal zones. This work reports preliminary results of a study carried out in a series of small embayments of Ubatuba, São Paulo State, Brazil, covering latitudes between 23°26′S and 23°46′S and longitudes between 45°02′W and 45°11′W. The main aims of this research were to set up an analytical method to assess 222Rn and 226Ra activities in seawater samples and to apply the excess 222Rn inventories obtained to estimate SGD. Measurements made during the summer of 2001 included 222Rn and 226Ra in seawater, 226Ra in sediment, seawater and sediment physical properties, nutrients and seepage rates. A continuous 222Rn monitor was also used to determine in situ collection of data to study short-term changes at one location. All methods indicated significant inflow of subsurface fluids at rates in excess of several cm per day.

Biogeochemistry of 226Ra in contaminated bottom sediments and oilfield waste pits

Solubility of 226Ra in sediments contaminated by produced water discharges was investigated using integrated microcosm, geochemical modelling and field sampling techniques. These studies strongly indicate that the biogeochemical control on 226Ra solubility in these sediments is coprecipitation with barite (BaSO 4). The role of barite was confirmed by selective extractions of contaminated sediments, geochemical measurements of solution saturation, theoretical coprecipitation calculations, and direct measurement of barite using X-ray diffraction. Despite elevated activities that are three orders of magnitude higher than background, fluxes of 226Ra from these contaminated sediments are of the same order of magnitude as those measured in natural systems. Remobilization of 226Ra was observed in the Humble Bayou sediment under anaerobic, sulfate-reducing conditions. Management of these contaminated sites will involve understanding the role of barite solid-solution chemistry on the fate and mobility of 226Ra.

210Pb based trace element fluxes in the nearshore and estuarine sediments off Bombay, India

Seven sediment cores from the Thana creek-Bombay harbour complex (THC) have been studied for excess 210Pb ( 210Pb exc, that portion of 210Pb not supported by decay of 226Ra in sediment), C org, Mn, Fe, Co, Ni, Cu, Zn and Al. The sediment accumulation rates based on 210Pb depth profiles decrease from 1.9 cm/yr, in the northern segment of the THC, to 0.4 cm/yr, in the southern segment. The calculated inventories of 210Pb exc increase from 16 dpm/cm 2, for the core from the southern area, to 187 dpm/cm 2, for the northernmost core, which was much higher compared to the atmospheric fallout inventory of 40–50 dpm/cm 2. The inner creek acted as a sink for 210Pb while active winnowing prevailed in the southern segment. Trace elements depth profiles in sediments did not exhibit signatures of significant environmental pollution. Variations in metal concentrations, metal/Al ratios and low excess metal inventories, suggested that the majority of the anthropogenic metals were either exported beyond the creek and nearshore region thus making the THC a passive link between the land and the sea for trace metals or largely removed prior to their entering the THC proper.