Individual variation of 90Sr deposition and its variability depending on the genotypic homogeneity of the sample

Individual peculiarities of 90Sr skeleton deposition in CBA mice were investigated. Differences in the radionuclide accumulation were not more than two times. Sex features in 90Sr deposition were not revealed. The range of individual variability of 90Sr deposition was analyzed in inbred mice in comparison with outbred stock and voles from natural population; it was found that variability in the radionuclide accumulation increased with sample genotypic heterogeneity.     

Comparison of the accumulation of 137Cs and 90Sr by six spring wheat varieties

The uptake of ¹³⁷Cs and ⁹⁰Sr by six varieties of spring wheat (Triticum aestivum) was compared in field trials on land contaminated by the Chernobyl accident. All the experimental varieties are officially adopted for agricultural use in Belarus and are used in large-scale production. Under identical conditions of nutrition, the productivity of the varieties varied significantly by a factor of 1.3. The extent of ¹³⁷Cs and ⁹⁰Sr accumulation by wheat grain, quantified as the concentration ratio, differed between the varieties by as much as a factor of 1.6, for both radionuclides. There was a significant linear positive correlation between the ⁹⁰Sr activity concentration in grain and straw, and the calcium concentration. The correlation between ¹³⁷Cs and potassium was not significant. The results suggest that certain varieties of spring wheat used in normal agricultural practice accumulate less ¹³⁷Cs and ⁹⁰Sr into grain than others. Some spring wheat varieties accumulated relatively less ¹³⁷Cs, but did not accumulate less ⁹⁰Sr. One variety, Quattro, had a significantly lower uptake of both ⁹⁰Sr (for grain) and ¹³⁷Cs (for both grain and straw) than that of the other varieties tested. The reduction efficiency achieved by the use of these varieties, however, is not as high as that achieved by soil amelioration techniques in the past. Nevertheless, since there are no additional costs or production losses associated with these varieties, their use in the contaminated areas is worth considering as a simple, practical, and effective contribution to reducing the uptake of both ⁹⁰Sr and ¹³⁷Cs and allowing farmers to produce food-grade grain.     

The content of 90Sr in the bone tissue of the population of the Soviet Union (1959 - 1971). (The basic laws of its accumulation and distribution).

On the basis of the results of long-term observations, general laws have been identified determining the dynamics of 90Sr concentration in the bone tissue of the population of the USSR in 1959-71, the peculiarities of 90Sr accumulation in different age groups and the connection and dependences between the intake and the contect of the isotope in human organism. It has been found that maximum 90Sr concentration occur in children born in the year when nuclear tests were carried out. The type of distribution of the frequency of occurrence of cases showing different levels of 90Sr content in uniform population groups was determined. Characteristic features of 90Sr distribution in different bones of the skeleton and its changes in the course of time were de monstrated.     

Strontium metabolism in teeth and enamel dose assessment: analysis of the Techa river data

People living on the banks of the Techa river were exposed to ⁹⁰Sr in the early 1950s. Data obtained by radiochemical measurements of extracted permanent teeth, ⁹⁰Sr autopsy measurements in bone and tooth samples, in vivo measurements of surface beta activity of the anterior teeth and whole-body counter (WBC) measurements of ⁹⁰Sr in the skeleton have been analyzed. Surface beta activity measurements indicate a biological half-life of ⁹⁰Sr of about 35 years in enamel. The WBC measurements have been performed since 1974 and a model for the age-dependent strontium retention in human bone has been used to extrapolate to previous time periods when the other measurement results were obtained. For the first decade after the intake, the ratio of the ⁹⁰Sr concentrations in teeth and bones were found to decrease with age at the time of major intake, from about 10 for 1-year-old children to about 0.3 for adults. There was a considerable variability of individual data within each age group. For adults, the correlation between ⁹⁰Sr in skeleton and teeth was not high at 0.47 according to radiochemical data for posterior teeth (molars and premolars) and 0.43 according to measurements of surface beta activity for anterior teeth. For children and adolescents there was no correlation between individual measurements in the skeleton and teeth. The absorbed dose in enamel due to ⁹⁰Sr in dentine has been calculated by Monte Carlo simulations of the electron transport. The results are in agreement with EPR measurements of the absorbed dose in the enamel of persons exposed, mainly due to ⁹⁰Sr ingestion. Received: 19 July 1999 / Accepted: 5 May 2000     

Assessment of 90Sr concentration in dental tissue using thin-layer beta-particle detectors and verification with numerical calculations

Electron paramagnetic resonance (EPR) measurements of tooth enamel can be used as an individual biological dosimeter for external dose assessment. However, the presence of 90Sr in the tooth tissues makes the task of interpreting EPR tooth dosimetry more complicated. The determination of the dose contribution of incorporated 90Sr in calcified tissue to the total dose measured by EPR is one of the main aspects of correct interpretation of EPR tooth dosimetry. In this work, experimental and numerical calculations were performed to convert the measured beta-particle dose rate to 90Sr concentration in calcified tissue. The cumulative beta-particle dose was measured by exposing artificially contaminated dentin and enamel to thin-layer alpha-Al2O3:C detectors in two different exposure geometries. Numerical calculations were performed for experimental exposure conditions using calculations of electron transport and secondary photons [Monte Carlo n-Particle Transport code version 4C2 (MCNP)]. Numerical calculations were performed to optimize the sample size and exposure geometry. The applicability of two different exposure conditions to be used in routine analysis was tested. Comparison of the computational and experimental results demonstrated very good agreement.     

Monte Carlo-based calculation of imaging plate response to <Superscript>90</Superscript>Sr in teeth: experimental validation of the required correction on sample thickness

Recently, a numerical method was proposed to correct the imaging plate (IP) response to ⁹⁰Sr concentration in tooth samples, depending on the sample thickness. This is important to quantify any ⁹⁰Sr concentration in teeth, which in turn is necessary to determine any ⁹⁰Sr incorporation of a person retrospectively. Although the final goal will be to evaluate the (inhomogeneous) spatial distribution of ⁹⁰Sr inside tooth samples precisely, the present study was restricted—as a first step—to the evaluation of ⁹⁰Sr in teeth assuming a uniform ⁹⁰Sr distribution. A numerical method proposed earlier was validated experimentally in the present study by measuring the IP response to standard sources of various thicknesses and ⁹⁰Sr concentrations. For comparison, the energy deposition of the β-rays emitted by ⁹⁰Sr in the IP—which is considered to be proportional to the IP luminescence signal—was calculated for the various sample thicknesses involved, by means of the MCNP-4C code. As a result, the measured IP response could be reproduced by the calculations within the uncertainties, depending on the thickness of the standard sources. Thus, the validity of the proposed numerical method to correct the IP response for sample thickness has successfully been demonstrated.     

Concentrations of 90Sr in the tooth tissues 60 years after intake: results of TL measurements and applications for Techa River dosimetry

This article focuses on the study of ⁹⁰Sr in the tooth tissues of Techa riverside residents 60 years after intake. The Techa River was contaminated by radioactive wastes in the 1950s. Contamination of the river system, including water, bottom sediment, floodplain soil, and grass, depended on the distance from the source of releases. Therefore, the average ⁹⁰Sr intake was different in different settlements located downstream the river. An additional factor influencing ⁹⁰Sr accumulation in the teeth is the rate of tissue mineralization at the time of intake which depended on the donor’s age at the time of releases. Measurements of ⁹⁰Sr concentration in various dental tissues (enamel, crown, and root dentin) of 166 teeth were performed about 60 years after the main intake using the method of thermoluminescence passive beta detection. The paper presents the current levels of tooth tissue contamination, and the tooth-to-tooth variability of ⁹⁰Sr concentration in tooth tissues was assessed for the tissues which were matured at the time of massive liquid radioactive waste releases into the Techa River. A model describing the expected levels of ⁹⁰Sr in matured dental tissues depending on age and intake has been elaborated for the population under study. The results obtained will be used for calculation of internal dose in enamel and for interpretation of tooth doses measured by means of the electron paramagnetic resonance method, among the population of the Techa River region.     

Intrapopulation variability of some meadow plant species with respect to their ability to accumulate 90Sr

Field and laboratory studies of different plant species revealed the presence of intraspecific polymorphism in respect of the ability to accumulate 90Sr. The populations consisted of the plants effectively and ineffectively accumulating 90Sr; the former were capable of two to thirty-seven times higher accumulation than the latter. The proportion of the plants with high accumulating ability can reach 10%. Judging by the high values of the coefficients of correlation between the laboratory and field data, the results of the 90Sr content analysis different plant species were highly concordant. Accumulation of 90Sr by plants is in direct relation to its content in soil, but within the limits of the same contamination density, and is controlled by the plant genotype.     

Modelling of fish contamination with 90Sr in relation to the calcium concentrations in water

A set of data on the equilibrium concentration factors of 90Sr in fish in relation to the Ca concentrations in water was collected and analyzed. An empiric relationship was obtained on the basis of statistical processing of this dataset: CF(90Sr, Bq/kg w.w.) = 3940(1770-6110)/[Ca, mg/L]water. The range of observed data on the concentration factors of 90Sr in fish is from 20 to 4000 L/kg (about 200 times). The statistical relationship obtained in the paper allows one to reduce this uncertainty by more than 50 times. The formula adequately describes equilibrium concentration factors of 90Sr both in freshwater and in marine fish. A dynamics model approach is described for the cases of accidental contamination of water bodies, when the equilibrium approaches are not appropriate.     

Current radiation status of the ecosystem of the Lake Bolshoi Igish situated along the axial part of the East-Urals radioactive trace

Data on the current radioecological status of lake Bolshoi Igish in the Middle Ural are presented in the paper. The lake is situated on the central axis of the East-Urals radioactive trace which was formed as a result of the 1957 nuclear accident at the Mayak Production Association. The distribution of 90Sr and 137Cs in the major components of the water basin is shown. Seasonal dynamics of the specific activity of radionuclides in water and in bottom deposits has been investigated. The current community of the higher water plant species has been studied. The paper discusses the concentration of 90Sr and 137Cs in the macrophyts of lake Bolshoi Igish depending on their species.     

The cytogenetic consequences of chronic irradiation in rodent populations inhabiting the Eastern Urals Radioactive Trace zone

In bone marrow cells of rodents (Apodemus (Sylvaemus) uralensis Pall., 1811, Apodemus agrarius Pall., 1771) inhabiting the Eastern Urals Radioactive Trace (EURT) zone (Kyshtym radiation accident 1957) and adjacent areas of Urals, the chromosome instability and 90Sr accumulation in bones were investigated. Intensive mutagenic process in both species from impact plots (the soil pollution by 90Sr 2322-16690 kBq/m2) was found. Significant positive correlation of aberrant cells frequencies and 90Sr was shown. Possible causes of the lack of resistance to long-term mutagenic factor (over 100 generations since 50 years from the accident) such as migration of animals and specific configuration of the EURT zone (narrow extended territory with sharply falling gradient of radionuclide pollution), which considerably decrease the probability that certain changes will be fixed and inherited in a series of generations of rodents, are discussed.     

Experimental evidence for the adaptive value of sexual reproduction

It is generally believed that recombination by sexual reproduction is unfavourable in constant environments but is of adaptive value under changing environmental conditions. To test this theory, experimental populations of yeast (Saccharomyces cerevisiae) were set up and maintained at different levels of environmental heterogeneity. Recombination was estimated by determining sporulation rates. Sporulation rates first increased in populations living in highly variable environments, but after some time began to decrease. The decrease started last and was slowest in populations which were maintained under the same conditions for a sufficiently long time, to allow some adaptation of the gene pool to the respective environment. Patterns of genotypic variability could not be interpreted in such simple terms, but there was a statistically significant correlation between sporulation rate and genotypic variability. This correlation is to be expected because recombination generates genotypic variability. Summing up, recombination by sexual reproduction is advantageous in changing environments if the population can track the changes in the environment by changing its genotypic structure.     

The features of radioactive contamination of small birds in Chernobyl zone in 2003-2005

Radioactive contamination of small birds (484 individuals, 44 species) was investigated in the Chernobyl zone (Ukraine) in 2003-2005. Values variation of 90Sr and of 137Cs activity concentration reached 3-4 orders of magnitude even in one site, and maximum values amounted to hundreds Bq/g at the central plots of the zone. The biggest contamination is appropriate to birds in breeding season and to settled species, whilst migrants are the "cleanest". Change of contamination within a year reflects seasonal and short-term changes in birds diet and in behaviour. During breeding season females have higher activity concentration of 90Sr, while on 137Cs accumulation sexual differences are absent. In other seasons radioactive contamination of male and female does not differ if they live in similar conditions and have similar migratory behavior. Young birds during fledging and just after, as a rule, have higher levels of 90Sr contamination than adults, and actually do not differ on 137Cs accumulation. On a set of own and published data, it was assumed, that in small birds the half-life period of 137Cs extraction amounts to 1-2 days, and 90Sr- 5-10 days, and dynamic equilibrium of the radionuclides turnover in organism is reached over 4-7 and 17-34 days, respectively, after the birds arrival on the contaminated site. Among 44 studied species, those who search invertebrates in soil top layer or forest litter (thrushes). have noticeably higher accumulation of 90Sr and of 137Cs. Specific differences of radionuclides accumulation for the rest birds were not revealed due to small sample sizes of the species.     

Sarcomere length effects on the Sr2+- and Ca2+-activation curves in skinned frog muscle fibres.

1. A procedure recently described to produce rapid changes in [Ca2+] and [Sr2+] within the whole cross-section of skinned muscle preparations (Moisescu, D.G. (1976) Nature 262, 610--613, and Moisescu, D.G. and Thieleczek, R. (1978) J. Physiol. 275, 241--262) has enabled us to obtain whole Ca2+- or Sr2+-activation curves at different sacromere lengths with the same preparation. 2. The maximal isometric force response was found to be very similar in Ca2+-and Sr2+-buffered solutions for otherwise identical conditions. 3. The change in sarcomere length between approx. 2.2 and 2.6 micron reversibly shifted both the Ca2+- and the Sr2+-activation curves by approx. 0.1 log units towards lower concentrations of the activator, without affecting their shape. However, the change in sarcomere length in the range above 2.6 micron did not have an effect upon the relative isometric force response-pCa (and -pSr) relationship. 4. All the Ca2+- and Sr2+-activation curves present a similar steepness and indicate that the relative isometric force increases from approx. 10 to 90% if the concentration of the activator is increased 3-fold. 5. The half time for force development in these experiments did not appear to be influenced by the length of the sarcomeres. 6. A potentiometric method for determining the apparent affinity constants of Ca2+, Mg2+ and Sr2+ to EGTA and ATP under various conditions is described.     

Polymorphism of THBS1 rs1478604 A>G in 5-untranslated region is associated with lymph node metastasis of gastric cancer in a Southeast Chinese population

Thrombospondin-1 plays an important role in cancer development and progression. This study investigated if a correlation exists between single-nucleotide polymorphisms (SNPs) in the Thrombospondin-1 gene (THBS1) and gastric cancer. We conducted a case-control study on a randomly recruited population of 283 patients and 283 healthy individuals from the city of Fuzhou in Southeast China. Individuals were genotyped for four SNPs (rs1478604 A>G, rs2228261 C>T, rs2292305 T>C, and rs3743125 C>T) in THBS1 using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. THBS1 genotypic distributions between the case and control groups were tested for correlations with cancer development. Comparisons between the case and control groups showed no significant differences in the genotypic distributions of rs1478604 A>G, rs2228261 C>T, and rs3743125 C>T. However, we found a statistically significant association between homozygous CC of THBS1 rs2292305 T>C and development of highly differentiated carcinoma (HDC). The rs1478604 A>G variant was found to be associated with invasion and lymph node metastasis in gastric cancer. After logistic regression and stratification analysis, rs1478604 A>G was more strongly associated with lymph node metastasis in HDC gastric cancer. The power to detect an effect for rs1478604 A>G in HDC was 90%. These findings indicate that the THBS1 rs1478604 A>G variant is linked with differential risks for gastric cancer nodal metastasis. These results support further investigation of THBS1 as a potential therapeutic target in gastric cancer.     

Determination of cefepime and cefpirome in human serum by high-performance liquid chromatography using an ultrafiltration for antibiotics serum extraction

The aim of this study was to describe a high-performance liquid chromatography (HPLC) assay for the determination of cefepime and cefpirome in human serum without changing chromatographic conditions. The assay consisted to measure cefepime and cefpirome which were unbound to proteins having a molecular mass of 10 000 or more by ultrafiltration followed by HPLC with a Supelcosil ABZ+ column and UV detection at a wavelength of 263 nm. The assay was been found to be linear and has been validated over the concentration range 200 to 0.50 μg/ml for both cefepime and cefpirome, from 200 μl serum, extracted. In future, the assay will support therapeutic drug monitoring for cefepime and cefpirome in neutropenic patients in correlation with microbiological parameters such as MIC₉₀ (minimal inhibitory concentration of antibiotic which kills 90% of the initial bacterial inoculum) and clinical efficacy.     

137Cs and 90Sr distribution peculiarities in soil and accumulation by pine tree wood and bark depending on edaphotops

The range of researches was made on 137Cs and 90Sr distribution regularities in pine tree plantations depending on different edaphic conditions. It is shown that total radionuclide amount in the forest litter depends on its thickness and is thought to be 10 to 70% for 137Cs and 20 to 60% for 90Sr. When soil fertility come increases from trophotop "A" to "C", 137Cs and 90Sr transfer factors for wood reduce. Soil humidity increase for each grade of trophic net results in increase of 137Cs transfer factors to wood and decrease for 90Sr. Total activity of 37Cs and 90Sr in pine wood plantation depends on plantation productivity and radionuclide transfer factors depending on different plantation conditions. In the most prevailing edaphotops pine wood accumulates 1-3% of 137Cs and 6-11% of 90Sr from total activity of radionuclides in biogeocenosis.     

Accumulation of 90Sr in field crops in conditions of radioactive pollution of agricultural lands

In the field experiment the influence of manure, peat, lake silt and their combinations on the uptake of 90Sr by barley, corn and potatoes was studied. Saturation of soil with organic substance, the decrease in soil acidity resulted in the lower accumulation of 90Sr by plants. In the beginning of the experiment, the specific activity of barley grain was from 75 to 132 Bq/kg. After three years of application of fertilizers the content of 90Sr in the barley grain decreased to 39 Bq/kg. There were no increase in 90Sr accumulation by the basic field crops with time.     

Intrapopulation Variability of Some Meadow Plant Species in Respect of Their Ability to Accumulate 90Sr

Field and laboratory studies of different plant species revealed the presence of intraspecific polymorphism in respect of the ability to accumulate ⁹⁰Sr. The populations consisted of the plants effectively and ineffectively accumulating ⁹⁰Sr; the former were capable of two to thirty-seven times higher accumulation than the latter. The proportion of the plants with high accumulating ability can reach 10%. Judging by the high values of the coefficients of correlation between the laboratory and field data, the results of the ⁹⁰Sr content analysis in different plant species were highly concordant. Accumulation of ⁹⁰Sr by plants is in direct relation to its content in soil, but within the limits of the same contamination density, and is controlled by the plant genotype.     

Biokinetics of <Superscript>90</Superscript>Sr after chronic ingestion in a juvenile and adult mouse model

The aim of our study was to define the biokinetics of ⁹⁰Sr after chronic contamination by ingestion using a juvenile and adult murine model. Animals ingested ⁹⁰Sr by drinking water containing 20 kBq l⁻¹ of ⁹⁰Sr. For the juvenile model, parents received ⁹⁰Sr before mating and their offspring were killed between birth and 20 weeks of ingestion. For the adult model, ⁹⁰Sr ingestion started at 9 weeks of age and they were killed after different ingestion periods up to 20 weeks. The body weight, food and water consumption of the animals were monitored on a weekly basis. Before killing and sampling of organs, animals were put in metabolic cages. ⁹⁰Sr in organs and excreta was determined by liquid scintillation β counting. Highest ⁹⁰Sr contents were found in bones and were generally higher in females than in males, and ⁹⁰Sr retention varied according to the skeletal sites. An accumulation of ⁹⁰Sr in the bones was observed over time for both models, with a plateau level at adult age for the juvenile model. The highest rate of ⁹⁰Sr accumulation in bones was observed in early life of offspring, i.e. before the age of 6 weeks. With the exception of the digestive tract, ⁹⁰Sr was below the detection limit in all other organs sampled. Overall, our results confirm that ⁹⁰Sr mainly accumulates in bones. Furthermore, our results indicate that there are gender- and age-dependent differences in the distribution of ⁹⁰Sr after low-dose chronic ingestion in the mouse model. These results provide the basis for future studies on possible non-cancerous effects during chronic, long-term exposure to ⁹⁰Sr through ingestion in a mouse model, especially on the immune and hematopoietic systems.