Hot particles--a challenge within radioecology.
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Humans↗
Biomedical subjects
B Salbu
Publications and source records attributed to B Salbu.
Estimation of apparent rate coefficients for radionuclides interacting with marine sediments from Novaya Zemlya.
To assess the impact of radionuclides entering the marine environment from dumped nuclear waste, information on the physico-chemical forms of radionuclides and their mobility in seawater-sediment systems is essential. Due to interactions with sediment components, sediments may act as a sink, reducing the mobility of radionuclides in seawater. Due to remobilisation, however, contaminated sediments may also act as a potential source of radionuclides to the water phase. In the present work, time-dependent interactions of low molecular mass (LMM, i.e. species < 10 kDa) radionuclides with sediments from the Stepovogo Fjord, Novaya Zemlya and their influence on the distribution coefficients (Kd values) have been studied in tracer experiments using 109Cd2+ and 60Co2+ as gamma tracers. Sorption of the LMM tracers occurred rapidly and the estimated equilibrium Kd(eq)-values for 109Cd and 60Co were 500 and 20000 ml/g, respectively. Remobilisation of 109Cd and 60Co from contaminated sediment fractions as a function of contact time was studied using sequential extraction procedures. Due to redistribution, the reversibly bound fraction of the gamma tracers decreased with time, while the irreversibly (or slowly reversibly) associated fraction of the gamma tracers increased. Two different three-compartment models, one consecutive and one parallel, were applied to describe the time-dependent interaction of the LMM tracers with operationally defined reversible and irreversible (or slowly reversible) sediment fractions. The interactions between these fractions were described using first order differential equations. By fitting the models to the experimental data, apparent rate constants were obtained using numerical optimisation software. The model optimisations showed that the interactions of LMM 60Co were well described by the consecutive model, while the parallel model was more suitable to describe the interactions of LMM 109Cd with the sediments, when the squared sum of residuals were compared. The rate of sorption of the irreversibly (or slowly reversibly) associated fraction was greater than the rate of desorption of the reversibly bound fractions (i.e. k3 > k2) for both radionuclides. Thus, the Novaya Zemlya sediment are supposed to act as a sink for the radionuclides under oxic conditions, and transport to the water phase should mainly be attributed to resuspended particles.
Cadmium Radioisotopes↗
The impact of Pu speciation on distribution coefficients in Mayak soil.
To assess the long-term consequences when radionuclides are released into the environment, information on the source term, transport and transformation processes, interaction with soils (KD) and biological uptake (CF) is needed. Among the artificial radionuclides released to the environment by nuclear activities, the transuranium elements are a major concern, due to very long half-lives and their accumulation in bone as well as high radiotoxicity. Plutonium has been produced in greater quantity than other transuranic elements, however, environmental assessments are complicated by the complex environmental behaviour. Physico-chemical forms of Pu will determine the interactions with soils and, thus, the degree to which soils can act as a sink or a potential diffuse source of contaminants. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a 'Mayak soil-rainwater system' to obtain information on KD values. After a defined contact time, the samples where then sequentially extracted and results are used in a dynamic box model to estimate interaction and fixation rates. The interaction of all Pu-species with soils seems to be rapid and follows a two-step reaction. Up to contact times of a few weeks, the KD for Pu(III,IV) (730 +/- 240 l/kg) is approximately one order of magnitude higher than for Pu(V,VI) (90 +/- 20 l/kg) and Pu(III,IV)-organic (40-60 l/kg). After 3 months contact time, the KD in only the two organic-bound Pu-species were significantly lower. This shows that the initial association with the soil is dependent on the Pu-species in the rainwater. After only 1 h of contact, between 33 and 40% of the plutonium was strongly bound to the soil components, i.e. only extractable with strong HNO3. The extraction of soil-bound Pu followed a similar pattern for all the original species, suggesting that the next step of Pu interaction mechanism with soil was rather independent of the original species. For both the Pu(V,VI) and Pu-organic species, the rainwater-desorption extract gave consistently higher KD values than that calculated from the rainwater-sorption data; whereas for Pu(III,IV), desorption KD values were more similar to sorption KD values. This supports the suggestion that the observed difference in Pu adsorption to soils reflects Pu-speciation in the water soluble phase, and that actual soil-Pu interactions are rather independent of the original speciation. Modelling of the extraction data show a different in association rate for the different Pu species, where the Pu(III,IV) has the fastest association rate as expected.
Absorption↗
The impact of plutonium speciation on the distribution coefficients in a sediment-sea water system, and radiological assessment of doses to humans.
When radionuclides are released from a source into the marine environment, the assessment of long term consequences to humans depends on information on the source term, transport in water, interactions with sediments (KD) and biological uptake (CF). Sensitivity analysis of assessment models demonstrates that KD is one of the most sensitive parameters contributing to large uncertainties in the assessment. Furthermore, the interaction of Pu-species with sediments is a time and temperature dependent process. The distribution coefficient, Bq kg(-1) sediment per Bq L(-1) sea water, increases with time until pseudo-equilibrium/equilibrium is reached (KD). Thus, the contact time between contaminated sea water and sediments should be taken into account in dispersion and dose assessment models. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a sediment-sea water system to obtain information on KD's. After a defined contact time, the samples have been sequentially extracted to determine mobile and bound fractions. The results indicate that the distribution coefficient, KD, for plutonium depends on Pu-species in question. Thus, sediments act as a sink for Pu(III, IV) (high KD), while Pu(III, IV)-organic and Pu(V, VI) should be considered more mobile (low KD). Furthermore, the interaction with inert fractions obtained from sequential extraction depends less on Pu-species but increase with time. For short time interactions, species-specific time functions rather than KD constants should be applied in assessment models. When the accepted KD (10(5) L kg(-1)) is implemented in the model, the estimated collective dose is about 8 x 10(-4) person-Sv, i.e., a factor of about 2 lower than for Pu(III, IV)-organic and Pu(V, VI). So changes in KD have an impact on the assessment of collective dose received from a potential release of plutonium from fallout, reactor accidents, etc., which underlines the need for more detailed studies on speciation, kinetics, and KD's in different sediment-sea water systems.
Acetates↗
Radioactive contamination from dumped nuclear waste in the Kara Sea--results from the joint Russian-Norwegian expeditions in 1992-1994.
Russian-Norwegian expeditions to the Kara Sea and to dumping sites in the fjords of Novaya Zemlya have taken place annually since 1992. In the fjords, dumped objects were localised with sonar and ROV equipped with underwater camera. Enhanced levels of 137Cs, 60Co, 90Sr and 239,240Pu in sediments close to dumped containers in the Abrosimov and Stepovogo fjords demonstrated that leaching from dumped material has taken place. The contamination was inhomogeneously distributed and radioactive particles were identified in the upper 10 cm of the sediments. 137Cs was strongly associated with sediments, while 90Sr was more mobile. The contamination was less pronounced in the areas where objects presumed to be reactor compartments were located. The enhanced level of radionuclides observed in sediments close to the submarine in Stepovogo fjord in 1993 could, however, not be confirmed in 1994. Otherwise, traces of 60Co in sediments were observed in the close vicinity of all localised objects. Thus, the general level of radionuclides in waters, sediments and biota in the fjords is, somewhat higher or similar to that of the open Kara Sea, i.e. significantly lower than in other adjacent marine systems (e.g. Irish Sea, Baltic Sea, North Sea). The main sources contributing to radioactive contamination were global fallout from atmospheric nuclear weapon tests, river transport from Ob and Yenisey, marine transport of discharges from Sellafield, UK and fallout from Chernobyl. Thus, the radiological impact to man and the arctic environment of the observed leakages from dumped radioactive waste today, is considered to be low. Assuming all radionuclides are released from the waste, preliminary assessments indicate a collective dose to the world population of less than 50 man Sv.
Aluminum Silicates↗
Radioactive contamination in the environment of the nuclear enterprise 'Mayak' PA. Results from the joint Russian-Norwegian field work in 1994.
A brief overview of the radioactive waste inventory of the 'Mayak' PA reprocessing plant, Chelyabinsk Region, Russia is given together with a description of the environmental contamination caused by its activities and the origins of contamination. The joint Russian-Norwegian field work in 1994 is described, together with the major analytical results. The field work was of a limited extent, and was not designed to include a complete mapping of the environmental contamination around the plant. The results are, however, in good agreement with the very extensive previous Russian investigations. The highest concentrations of radioactivity were found in Reservoirs 10 and 11 and at the floodplain of the upper Techa River (Asanov Swamp). Also high concentrations are found in biota, especially fish from Reservoir 10.
Arctic Regions↗
Transfer, pathways, enrichment, and discharge of 137Cs and 90Sr in the pulp industry.
Natural and artificial radionuclides are transferred from terrestrial ecosystems via the forest industry to coastal sea water. The material processed, i.e., wood, fresh water, and bark, have low levels of radionuclides, but large amounts of raw materials are processed annually. Thus the annual flux of radionuclides is substantial. The purpose of this investigation was to study transfer, redistribution, enrichment, and discharges of 137Cs and 90Sr in pulp industry employing the sulphate process. 137Cs and 90Sr were measured by means of Ge-detectors and a low level liquid scintillation spectrometer, respectively. 137Cs was highly enriched in the recovering process for sodium, while 90Sr was enriched in the recovering system for calcium compared to concentration levels in raw materials. The concentrations of 137Cs and 90Sr in bark were almost ten times the concentration level in conifer wood. No 137Cs or 90Sr could be identified in atmospheric discharges from the combustion processes. The products contained very low levels of these radionuclides. Only 5% of the annual input of 137Cs and 90Sr were found in the products. Discharges of radionuclides from this particular pulp production plant is nearly 40% of the annual 137Cs and 90Sr input. The contribution of 137Cs and 90Sr to coastal seawater is probably of minor importance providing that wood or fresh water from highly contaminated areas are not utilized.
Cesium Radioisotopes↗
The mobility of 137Cs and 90Sr in agricultural soils in the Ukraine, Belarus, and Russia, 1991.
Results are presented from studies concerning the behavior of the Chernobyl-derived radionuclides 137Cs and 90Sr in soil-plant agricultural systems in the Ukraine, Belarus, and Russia during 1991. The sites, representing ploughed and natural pastures, were located at varying distances between 50 and 650 km and varying directions from the Chernobyl reactor site. The 137Cs activity concentrations in the upper 0-5 cm soil layer ranged from 25-1,000 kBq m-2 and were higher in natural pastures as compared to ploughed pastures. For 90Sr, activity levels ranged from 1.4-40 kBq m-2, and the highest 90Sr deposition was observed in the Gomel Region, Belarus. The highest 90Sr: 137Cs ratio was also observed in the Gomel soils, i.e., 15% as compared to between 0.72 and 7.4% in the other soils. The mobility of radionuclides was studied by means of sequential extraction. For all soils, between 60 and 95% of the 137Cs was found to be strongly bound to soil components. In the Russian and Ukrainian soils, between 40 and 98% of the 90Sr was found in the easily extractable fractions, and the distribution of 137Cs and 90Sr followed that of the naturally occurring stable isotopes of cesium and strontium. However, in the Gomel soils, between 20 and 50% of the 90Sr was easily extractable and the distribution of 90Sr within the extraction fractions did not follow that observed for stable strontium. These results are thought to reflect the association of 90Sr with fuel particles deposited in the Gomel Region. The mobility of 90Sr is expected to increase with time (as the particles weather) in these soils.
Cesium Radioisotopes↗
Mobility of dichlorprop in the soil-water system as a function of different environmental factors. I. A batch experiment.
Batch experiments were conducted to study the mobility of 14C-labelled dichlorprop in different soil types. Soils rich in organic carbon showed high sorption capacity compared to sand soil with low content of organic C. Soil to soil variations decreased when corrected for different content of organic C (Kd normalized to Koc). Data obtained in batch experiments fit into linear as well as Freundlich sorption isotherms (17 degrees C). Desorption of [14C]dichlorprop in the soil-water system increased with pH. A significant amount of dichlorprop may be considered as 'non-available' in soils with high organic C, even at relatively high pH-values. The octanol/water partitioning coefficient (Kow) for dichlorprop was inversely related to pH. In the pH range 4-7, the Kow-value varied from 114 to 0.6. The relationship between Koc and pH was similar to the relationship between Kow and pH and the data fitted the following equation: log Koc = 0.5 log Kow + 0.2 (r2 = 0.986).
2,4-Dichlorophenoxyacetic Acid↗
Applications of nuclear analytical techniques in environmental research. Plenary lecture.
Among nuclear analytical techniques, neutron activation analysis (NAA) is particularly useful for environmental studies. It affords low detection limits for many elements, high specificity and few sources of systematic error, which means that high accuracy is attainable. Neutron activation analysis is particularly useful for trace and ultra-trace analysis of environmental samples (water, soils, rocks and biological material). In trace element work associated with pollution, instrumental NAA is a powerful technique for multi-element surveys, in particular when combined with other spectroscopic techniques. Nuclear techniques, as with most analytical techniques, cannot be used to distinguish between different physico-chemical forms of an element per se. When used in combination with appropriate separation techniques, however, nuclear techniques can provide valuable information about trace element speciation in environmental and biological systems. From dynamic tracer experiments, i.e., addition of chemically well defined labelled compounds to environmental systems, valuable information can be obtained on the distribution of species and on microchemical processes influencing the physico-chemical forms. In these laboratories, speciation studies on trace elements in natural waters have been carried out by using instrumental NAA in combination with physical separation techniques, such as dialysis and ultrafiltration, in situ and in the laboratory. Dynamic radiotracer experiments have provided important information about processes influencing the speciation of trace elements in aquatic systems. Sequential extraction techniques have proved to be useful in studies on sediments and soils when combined with NAA. Sequential extractions also provide significant information about the physico-chemical behaviour of radionuclides supplied to natural soils from the Chernobyl accident.
Environmental Pollution↗
Determination of aluminium-26 using a low-level liquid scintillation spectrometer.
The lack of a suitable tracer has severely limited the use of radioisotope tracer experiments in environmental and biological studies on aluminium. The only aluminium radioisotope with a half-life greater than 10 min is the long-lived positron emitter 26Al (t1/2 7.2 x 10(5) years). The exposure of this nuclide and the difficulty in attaining sufficiently low determination limits with standard radioanalytical techniques have restricted its application as a radioactive tracer. The development of a simple method for the routine determination of 26Al using Cerenkov counting and a Quantalus 1220 low-level liquid scintillation spectrometer is reported. For a 300 min counting time, determination limits of about 60 mBq in water samples and 120 mBq in biological (fish gill) samples can be attained. With these levels of determination, the use of 26Al as a tracer is a viable technique for the study of aluminium in environmental and biological systems.
Aluminum↗
Determination of plutonium-239 + plutonium-240 and plutonium-241 in environmental samples using low-level liquid scintillation spectrometry.
A radiochemical method for the simultaneous determination of 239Pu + 240Pu and 241Pu in environmental samples has been developed. In the course of the analysis a 236Pu tracer was used for estimating the chemical yield of plutonium isotopes. After suitable pre-treatment of the sample, the plutonium nuclides in solution were coprecipitated with iron(III) hydroxide and calcium oxalate and isolated further from impurities and interfering radionuclides by means of anion-exchange chromatography. Plutonium isotopes in the eluate (NH4I-HCI) were converted into nitrate form and then extracted with 20 ml of 5% bis(2-ethylhexyl) hydrogen phosphate extractive cocktail. The final organic solution was measured spectrometrically using an ultra-low-level liquid scintillation spectrometer, Quantulus (LKB, 1220 Wallac). The chemical yields of plutonium range from 25 to 50% for 100 I of sea-water and 30 to 60% for 40 g of dried soil sample. The counting efficiencies are nearly 100% for 239Pu + 240Pu and 48.8% for 241Pu, respectively. The detection limits were estimated to be 0.20 mBq for 239Pu + 240Pu and 2.2 mBq for 241Pu, respectively. The proposed procedure has been tested for the simultaneous determination of 239Pu + 240Pu and 241Pu in sea-water (Irish Sea, North Sea) and soils (Cumbrian coast, UK; Byelorussia, USSR).
Europe↗
Radionuclide mobility and bioavailability in Norwegian and Soviet soils.
A sequential extraction procedure has been applied to study the speciation of Chernobyl-derived radionuclides (137Cs and 90Sr) in soils from Norway, and from Byelorussia and the Chernobyl region in the USSR. Most 137Cs (greater than 80%) was strongly associated with soil components, whereas 90Sr was more mobile, up to 70% being found in the easily extractable fractions. The 90Sr: 137Cs ratio decreased with the distance from the reactor, reflecting the higher proportion of hot particles deposited in the regions close to the reactor, and the easily extractable fraction of 90Sr was significantly lower in the soils collected from the Chernobyl area. The distribution of stable Cs and stable Sr in the extraction fractions was similar for the various sites. Therefore, the location-specific differences in the distribution of 90Sr and, to a lesser extent, 137Cs arise because of fallout speciation rather than because of local environmental factors.
Accidents↗
Availability of caesium isotopes in vegetation estimated from incubation and extraction experiments.
A rapid and inexpensive incubation and extraction technique for estimating the available low molecular weight and potentially bioavailable fraction of Cs isotopes in vegetation has been developed. Samples of contaminated vegetation (grass, herbage and fungi) and litter were exposed to rumen liquid from sheep, by in vitro incubation or by placing nylon bags in the rumen of sheep (in sacco). The results were compared with laboratory extractions using rumen buffer, NH4OAc, CsCl and de-ionized water. The release of low molecular weight 137Cs species after in vitro incubation with rumen liquid for 4-8 h was 75-85% for grass, herbage and fungi, 30% for lichen and 10% for litter. The reproducibility of the method was 5% for digestible matrices and 10-20% for litter where the fraction of Cs isotopes released was small. Extractions with NH4OAc and CsCl released 75 and 80% of the Cs isotopes in grass, respectively. Significantly lower extraction yields were obtained with de-ionized water and buffer. During in sacco incubation, 90-100% of the Cs isotopes in vegetation was released within 1 h; however, potentially available low molecular weight forms and Cs-bearing colloidal material could not be differentiated. The results obtained by incubation with rumen liquid and by extraction with NH4OAc or CsCl were in good agreement with published data from a 3 week feeding trial. For practical reasons extraction with NH4OAc or CsCl rather than incubation with rumen liquid is recommended for estimating the fraction of available low molecular weight Cs species.(ABSTRACT TRUNCATED AT 250 WORDS)
Accidents↗
Winter transport of Chernobyl radionuclides from a montane catchment to an ice-covered lake.
The amounts of 137Cs and 90Sr have been determined in the inflows and outflows of the Norwegian sub-alpine lake, Ovre Heimdalsvatn, in March/April during the period of ice-cover, when discharge is extremely stable. The lake is situated in an area contaminated by Chernobyl fallout. The transported course particulate plant material has been collected in traps; the particles and colloids have been removed from water samples by cross-flow ultrafiltration. On the basis of radionuclide inputs and outputs, lake budget calculations have been made for 137Cs and 90Sr during the period of ice-cover. Daily transport of radionuclides is considerably less than that observed during the spring snowmelt period when discharges are high. Size distribution patterns of Cs and Sr observed during winter are compared with previously published data from the same lake during the spring spate. The retention of 137Cs is similar in winter and spring, but retention of 90Sr is greater in winter.
Accidents↗
Size and charge fractionation of aqueous aluminium in dilute acidic waters: effects of changes in pH and temperature.
In natural waters, aluminium occurs in different physico-chemical forms, depending on pH, temperature and the presence of inorganic and organic ligands. Conventional methods for fractionation of AI species do not fully succeed in separating monomeric, i.e., low relative molecular mass (Mr) AI species, from polymeric colloidal AI species. In the present work, hollow-fibre ultrafiltration and acid digestion steps are introduced prior to the ordinary Barnes-Driscoll procedure. By this method, a colloidal AI fraction is separated from the particulate fraction, i.e., the fraction that is able to precipitate by the force of gravity. Both the monomeric and colloidal AI fractions are characterized according to Mr and the chemical properties such as hydroxyquinoline-isobutyl methyl ketone-extractability and Amberlite IR-120 cation exchangeability. Changes in pH and/or temperature were found to be critical for the analytical results of AI. By combining size and charge fractionation techniques, increased information concerning AI species in dilute freshwaters was obtained. One important investigation is the presence of high Mr AI species in the operationally defined monomeric AI fractions.
Aluminum↗
Use of an aluminium-26 tracer to study the deposition of aluminium species on fish gills following mixing of limed and acidic waters.
Results are presented from an experiment designed to investigate the deposition of Al species onto fish gills following the mixing of limed and acidic natural waters. The natural waters were labelled with 26Al and the distribution between high and low molecular weight forms was determined by ultrafiltration of water samples. In labelled acidic waters, the 26Al was present predominantly in low molecular weight forms, whereas in labelled limed waters the major fraction of 26Al was present in a high molecular weight form. In mixing experiments, 26Al was only detectable on fish gills when the 26Al was initially present in a low molecular weight form (i.e., in labelled acidic waters). Aluminium-26 was not detected on the gills of fish exposed to labelled limed waters. These results support the hypothesis that Al on fish gills arises from polymerization of low molecular weight species and that, within mixing zones, the high molecular weight species do not play a significant role in the precipitation of Al onto the gill surface.
Aluminum↗
Measurements of radionuclides after the Chernobyl accident. XXVII CSI pre-symposium. June 6-8, 1991, Bergen, Norway.
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Accidents↗