Dynamics of 134 + 137Cs accumulation in insects inhabiting the 30-kilometer zone of Chernobyl Nuclear Power Station

Accumulation of the specific activity of 134 + 137Cs in insects was investigated in the most typical biogeocenoses within the 30-km zone of the Chernobyl NPP. The studied biogeocenoses had different rates of the exposure doses. It was shown that the specific activity of 134 + 137Cs in the insects inhabiting forest biotops was of the same order that in the crown, whereas in the insects inhabiting open biotops the specific activity was higher than in plants. Two periods of the increased 134 + 137Cs content in insects were found: May and September. Along with seasonal activity variations, a tendency to decreasing and stabilization of 134 + 137Cs content was observed during the period of the study.     

Modeling of different types of size-effect in accumulation of 137Cs in fish from the cooling pond of the Chernobyl Power Plant

All known types of size-effect in accumulation of radiocesium in fish are described on the basis of the dynamic model of distribution and migration of the radionuclide in aquatic ecosystem. The time-dependent activity of 137Cs in different age classes of carp and pike-perch from the Chernobyl Nuclear Power Plant Cooling Pond is calculated. It is shown that during the first year after the accident the activity of 137Cs in the young generations of fish was higher (negative size-effect) owing to higher feeding rate of young fish. During the following years the increase of activity in the older fish generations takes place (positive size-effect). It is shown that size-dependence is more clear for the predatory species.     

Identification of processes governing long-term accumulation of 137Cs by forest trees following the Chernobyl accident

The regularities of ¹³⁷Cs distribution in trees (Pinus sylvestris and Betula pendula) growing in different types of forest ecosystems were investigated. High levels of heterogeneity of ¹³⁷Cs activity concentrations in different parts of the trees, resulting from their varied metabolism have been shown. The data obtained demonstrate a non-uniform character of ¹³⁷Cs distribution along the trunks, which can be explained by radio- nuclide fixation by the xylem vessel walls and by geometry changes along the tree trunk. It has been found that the radial distribution of ¹³⁷Cs in the tree trunk is dependent on the availability of ¹³⁷Cs in soil, which governs the transfer of this radionuclide via xylem sap and on the properties of the xylem. The accumulation of ¹³⁷Cs by trees was influenced by the vertical distribution and availability of ¹³⁷Cs in the soil as well as by the root biomass distribution in different soil horizons. A bioavailability factor, which takes into account the vertical distribution of radiocesium in soil, bioavailability of this radionuclide and distribution of root biomass in different soil horizons is proposed for comparative analyses of ¹³⁷Cs transfer from soil to trees in different types of forest ecosystems. Received: 8 February 2000 / Accepted: 1 December 2000     

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.     

The change in efficiency of protective measures for reduction of 137Cs accumulation by agricultural plants in various periods after the Chernobyl accident

Dynamics of 137Cs transfer factors to plants and the effects of protective measures on this radionuclide accumulation in the agricultural production is estimated on the example of the south-western regions of Bryansk District. Three periods in decreasing the 137Cs content in plants during 20 years after the Chernobyl accident are identified. The contribution of radionuclide decay, natural biogeochemical processes and protective measures aimed at reduction of the 137Cs accumulation in agricultural plants during various periods after radioactive fallout is shown. Maximum permissible levels of 137Cs contamination of cultivated lands, where crop products meeting current standards may be obtained, at different scopes of protective measures on radioactive-contaminated territories are forecasted. Periods after radioactive fallout, when crop and forage products meeting radiological standards are obtained, are assessed.     

Age specific formation of doses in children exposed to radioactive caesium following the accident in the Chernobyl Nuclear Power Plant

Individual measurement data on radiological surveillance of people residing in the territories most radioactively contaminated following the Chernobyl accident are analyzed to provide a comparison of doses from caesium radionuclides to children and adults. The external doses to children does not exceed those to adult inhabitants of the same settlement. By the results of surveillance in 1986 more than 80 thousand inhabitants of the western areas of Bryansk region, a specific activity of caesium radionuclides and corresponding internal radiation dose rate in a number of settlements appeared at children age under 3 years old exceeding the appropriate parameters for adult inhabitants. Among persons evacuated from the contaminated areas, such excess in day of departure from an area averaged 3.8 for surveyed pairs the child-parent.     

Genetic effects in the liquidators of consequences of Chernobyl Nuclear Power Plant accident

The purpose of the present research was the estimation of probable genetic consequences at the liquidators of the consequences of Chernobyl accident in 1986-1987. The research is made on two groups of the liquidators. The first group included the liquidators taking place on the account in the branch register and working now at the enterprises of a nuclear industry. The second group included 902 liquidators of consequences of Chernobyl accident in 1986 constantly living in the Ryazan area and which are taking place on permanent observation the account in regional hospital. For an estimation of probable genetic effects analyzed the data on frequency and outcomes pregnancy of the wives of the liquidators, on condition and on diseases of newborn, on switching intrauterine development defects (IDD). The analysis carried out depending on dozes of an irradiation: up to 5 cGy; 5-10 cGy and 10-25 cGy. Received materials testify, that at the liquidators, at a doze of an external irradiation 10-25 cGy, the determined effects--period long sterility, kept at a part them till 3 years come to light. The set of the received data, such as depending from the dose increase of frequency of spontaneous abortions and of inherent defects of development of newborn, the increase of frequency diseases of newborn and share newborn with low weight, allows to make a conclusion about an induction of genetic effects in sexual cells of the liquidators of consequences of Chernobyl accident at dozes of an external irradiation more than 10 cGy. Taking into account high biological efficiency of alpha-radiation (K = 20), and of beta-radiation (K = 2-4), the equivalent effective doze male gonads (testes) in 3-5 times is higher, than estimated only from external gamma-radiation.     

An estimation of 137Cs accumulation in forest fungi by the soil properties

A method of calculation of radiocaesium uptake by forest mushrooms as a function of soil properties is presented. Calculated value of 137Cs transfer factor for Xerocomus badius in the contaminated area of Bryansk Province of Russia is in a good agreement with experimental data.     

Vertical Distribution and Estimated Doses from Artificial Radionuclides in Soil Samples around the Chernobyl Nuclear Power Plant and the Semipalatinsk Nuclear Testing Site

For the current on-site evaluation of the environmental contamination and contributory external exposure after the accident at the Chernobyl Nuclear Power Plant (CNPP) and the nuclear tests at the Semipalatinsk Nuclear Testing Site (SNTS), the concentrations of artificial radionuclides in soil samples from each area were analyzed by gamma spectrometry. Four artificial radionuclides (²⁴¹Am, ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Co) were detected in surface soil around CNPP, whereas seven artificial radionuclides (²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, ⁹⁵Zr, ⁹⁵Nb, ⁵⁸Co, and ⁶⁰Co) were detected in surface soil around SNTS. Effective doses around CNPP were over the public dose limit of 1 mSv/y (International Commission on Radiological Protection, 1991). These levels in a contaminated area 12 km from Unit 4 were high, whereas levels in a decontaminated area 12 km from Unit 4 and another contaminated area 15 km from Unit 4 were comparatively low. On the other hand, the effective doses around SNTS were below the public dose limit. These findings suggest that the environmental contamination and effective doses on the ground definitely decrease with decontamination such as removing surface soil, although the effective doses of the sampling points around CNPP in the present study were all over the public dose limit. Thus, the remediation of soil as a countermeasure could be an extremely effective method not only for areas around CNPP and SNTS but also for areas around the Fukushima Dai-ichi Nuclear Power Plant (FNPP), and external exposure levels will be certainly reduced. Long-term follow-up of environmental monitoring around CNPP, SNTS, and FNPP, as well as evaluation of the health effects in the population residing around these areas, could contribute to radiation safety and reduce unnecessary exposure to the public.     

Sensitivity of soil bacteria isolated from the alienated zone around the Chernobyl Nuclear Power Plant to various stress factors

Seventy strains of chemoorganotrophic bacteria isolated by our group in 1993-1994 from soil sampled in the zone around the Chernobyl Nuclear Power Plant (ChNPP) were studied with respect to their sensitivity to various stress factors damaging DNA. Bacillus subtilis, B. cereus (both spores and vegetative cells), Methylobacterium extorquens, M. mesophilicum, and unidentified pigmented bacteria were found to be the most resistant to ultraviolet (UV) radiation, exhibiting LD90 values of 40 to more than 211 J/m2. The same bacteria, as well as Bacillus polymyxa, were tolerant to hydrogen peroxide (lethal concentrations of H2O2 ranged from 0.3 to 1.0 M); i.e., UV-resistant strains were also tolerant to hydrogen peroxide and vice versa. Fluorescent pseudomonads were the most sensitive to both UV radiation and H2O2, showing LD90 from 6 to 18 J/m2 and a lethal concentration of H2O2 lower than 0.1 M. All of the soil samples collected in the alienated zone around the ChNPP, where the radioactivity of the soil had decreased from 1000 to 2 microCi/kg soil over the period from 1987 to 1995, contained not only resistant bacteria but also a small number of bacteria sensitive to UV radiation and H2O2.     

DNA damage evaluated by the comet assay in lymphocytes of children with 137Cs internal contamination caused by the Chernobyl accident

The comet assay is one of the most versatile and popular tools for evaluating DNA damage. Its sensitivity to low dose radiation has been tested in vitro, but there are limited data showing its application and sensitivity in chronic exposure situations. The influence of the internal contamination caused by the Chernobyl accident on the level of DNA damage was evaluated by the comet assay on lymphocytes of 56 Ukrainian children. The study was performed during 2003 on children with demonstrable 137Cs internal contamination caused by food consumption. The children were selected for the study immediately after a 137Cs whole body counter measurement of internal contamination. The minimal detectable amount of 137Cs was 75 Bq. The control group included 29 children without detectable internal contamination, while in the exposed group 27 children with measured activity between 80 and 4037 Bq and committed effective dose between 54 and 3155 microSv were included. Blood samples were taken by a finger prick. The alkaline version of the comet assay was used, in combination with silver stained comets and arbitrary units (AU), for comet measurement. Factors such as disease, medical treatment, surface contamination of children's living location, etc., were considered in the study. Non-significant differences (p > 0.05) in DNA damage in control (9.0 +/- 5.7 AU) versus exposed (8.5 +/- 4.8 AU) groups were found. These results suggest that low doses of 137Cs internal contamination are not able to produce detectable DNA damage under the conditions used for the comet assay in this study. Further studies considering effects of high exposure should be performed on chronically exposed people using this assay.     

The simulation of 137Cs distribution in forest ecosystems and prediction of its accumulation by forest products

A mathematical model of 137Cs migration in forest ecosystem is presented, which describes the behaviour of this radionuclide in the forest litter-soil system, trees, understory and forest animals. The model's parameters for different types of forest ecosystems are estimated and model's adequacy is tested through the use of independent experimental data. The sensitivity of the model's output variables is analyzed to variations in the most significant parameters. The differences in the seasonal and mean annual dynamics of 137Cs concentration in muscles of roe deers and mooses are shown to be defined by specific features of the diets of these animals and variations in 137Cs content in the main diet components.     

Role of non-radiation factors in forming cytogenetic effects in evacuees from a 30-km zone of the Chernobyl Nuclear Power Plant

The time-effect relationship for chromatid type aberrations, chromosome type fragments, hyperploidy and polyploidy levels in peripheral blood lymphocytes were investigated in inhabitants of t. Pripiat' and nearby villages, who were departured from the Chernobyl NPP 30-km exclusive zone during first days after the Chernobyl catastrophe. The time-course changes of the mentioned cytogenetic indices in evacuees were displayed as a gradual decline of chromosomal rearrangements and genome abnormality frequencies from the statistically elevated level in the first 1-2 years after the accident to the subcontrol meanings at the end of the 14-years observation period. In early terms after exposure the frequency of chromatid exchanges in adult men and the polyploidy level in women aged 23-35 years were sufficiently increased comparing with other evacuee subgroups. Some peculiarities of the fragment aberration frequency dynamics were shown for persons with different terms of the departure from the Chernobyl zone. The role of the combination of mutagenic factors acted in the accidental situation at Chernobyl for inducing the elevated level of cytogenetic damage in evacuees is discussed.     

The accumulation of radionuclides 137Cs and 90Sr by different kinds and grades legumes crops

The decision of protein problem on contaminated by radionuclides territories as a result of the accident on Chernobyl NPP is not possible without increase of the sowing areas legumes crops (peas, lupine, soybean). Introduction in agricultural manufacture of grades with a low level of accumulation radionuclides (peas--Aist, Polesskay, Gomelskay Agat; soybean--Severnaya zvezda, Mageva) will allow to receive agricultural production adequate "Republican allowable levels of the contents of 137Cs and 90Sr in agricultural raw material and forages" on arable lands at their higher density of radioactive contamination: 137Cs--1300-1480 kBq/m2 (35.0-40.0 Ci/km2): 90Sr--18.5-37.0 kBq/m2 (0.50-1.00 Ci/km2).     

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 effect of gamma-radiation and desiccation on the viability of the soil bacteria isolated from the alienated zone around the Chernobyl Nuclear Power Plant

Methylobacterium extorquens, M. mesophilicum, and Bacillus subtilis strains were found to be resistant to gamma-radiation, irrespective of whether they were isolated from the alienated zone around the Chernobyl Nuclear Power Plant or outside this zone. The LD90 of Methylobacterium and B. subtilis strains with respect to gamma-radiation was 2.0-3.4 and 3.7-4.4 kGy, respectively, whereas their LD99.99 values were 4.5-6.9 and more than 10 kGy, respectively. The high threshold levels of gamma-radiation for Methylobacterium and B. subtilis imply the efficient functioning of DNA repair systems in these bacteria. Unlike Bacillus polymyxa cells, the cells of M. extorquens, M. mesophilicum, and B. subtilis were also resistant to desiccation. Pseudomonas sp., Nocardia sp., and nocardioform actinomycetes were sensitive to both gamma-radiation and desiccation. Similar results were obtained when the bacteria studied were exposed to hydrogen peroxide and ultraviolet radiation. The results obtained indicate that the bacteria that are resistant to gamma-radiation are also resistant to desiccation, UV radiation, and hydrogen peroxide. The possibility of using simple laboratory tests (such as the determination of bacterial resistance to UV light and desiccation) for the evaluation of bacterial resistance to gamma-radiation is discussed.     

90Sr and 137Cs in higher aquatic plants of the Chernobyl nuclear plant exlusion zone]

The content of radionuclides 90Sr and 137Cs in higher aquatic plants of water objects within Chernobyl NPP exclusion zone has been analysed. Biodiversity of phytocenose was studied and species-indicators of radioactive contamination were revealed. The seasonal dynamics of radionuclide content in macrophytes was studied and the role of main aquatic plant clumps in processes of 137Cs and 90Sr distribution in abiotic component of biohydrocenose was demonstrated.     

137Cs distribution and accumulation in organs and tissues of sheep in the event of chronic consumption of contaminated fodder in the area of the Chernobyl NPP accident

The regularities of 137Cs distribution and accumulation in organs and tissues of sheep on a farm located in the Chernobyl accidental zone were experimentally estimated. The distribution pattern of 137Cs concentration in organs and tissues is found to depend on the duration of the radionuclide uptake with the ration. During the first 24 h the highest 137Cs concentration is reported in the parenchymal organs; starting from day 30 muscular tissue and kidneys rank first, whereas in the other organs and tissues 137Cs concentration is 1.5-2 times lower. By 137Cs content and accumulation rate the study organs are arranged in a declining order as follows: muscles > > skin > liver > kidneys > heart > spleen. The mathematical models were devised describing the dynamics of increasing with time in 137Cs concentration in muscles, liver and skin. The methodology is suggested for the prediction of levels of 137Cs contamination of the muscular tissue of sheep. The time periods were regulated for sheep feeding with 137Cs contaminated fodder that ensure the production of mutton the radionuclide concentration in which meets the sanitary-hygienic standards.