Prediction of 137Cs behaviour in the soil-plant system in the territory of Semipalatinsk test site

A mathematical model of 137Cs behaviour in the soil-plant system is presented. The model has been parameterized for the area adjacent to the testing area Ground Zero of the Semipalatinsk Test Site. The model describes the main processes responsible for the changes in 137Cs content in the soil solution and, thereby, dynamics of the radionuclide uptake by vegetation. The results are taken from predictive and retrospective calculations that reflect the dynamics of 137Cs distribution by species in soil after nuclear explosions. The importance of factors governing 137Cs accumulation in plants within the STS area is assessed. The analysis of sensitivity of the output model variable to changes in its parameters revealed that the key soil properties significantly influence the results of prediction of 137Cs content in plants.     

The dose estimation to the population as a result of radioactive contamination of the Semipalatinsk Test area

The results are presented from estimation of spatial distribution of 137Cs and 90Sr contamination densities in the areas of horses and sheep grazing within the Semipalatinsk Test Site. Dose burdens to various cohorts of the population living within the STS and consuming contaminated animal products are predicted. Doses of shepherds in the most contaminated pasture areas have been found to exceed the accepted limit (1 mSv/y). The conclusion is made about the need for further studies on the risk assessment of the STS population exposure above the accepted limits.     

Radiobiological effects on plants and animals within Semipalatinsk Test Site (Kazakhstan)

The Semipalatinsk Test Site (STS) was the main place of nuclear devices tests in the former Soviet Union. From 1949 to 1989 about 460 nuclear explosions have been carried out at STS. Radioactive contamination of STS territory has the extremely non-uniform character. The main dose-forming radionuclides are 137Cs, 90Sr, 152Eu, as well as 154Eu, 60CO, 239,240Pu and 241Am. The greatest specific activity of 137Cs and 239,240Pu in ground are n x 10(3) kBk/kg, 152Eu - 96 kBk/kg, 154Eu - 10.4 kBk/kg, 60Co - 20.5 kBk/kg, 241Am - 15 kBk/kg. However, up to now, within STS sites exists where gamma-dose rate comes to 60 microGy/h, that is enough for induction reliable biological effects in animals and plants. Inhabiting territory of STS plants and animals are characterized by increased level of mutagenesis, changes of morpho-anatomic indices and parameters of peripheral blood, by the increase of asymmetry bilateral indices, change of composition and structure of communities.     

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.     

Radiocaesium variability within sheep flocks: determination of 137Cs intake in free-ranging sheep

A study is described in which ¹³⁷Cs intake by free-ranging sheep was estimated at two farms in the area of west Cumbria (northwest England) which received some of the highest amounts of fallout from the Chernobyl accident within the United Kingdom. The faecal excretion of ¹³⁷Cs was estimated from faecal ¹³⁷Cs activity concentrations and the use of intraruminal controlled release devices containing Cr₂O₃ to determine faecal dry matter output. The intake of ¹³⁷Cs was estimated by assuming an apparent absorption coefficient appropriate to the herbage grazed. The methodology has the advantage that sampling of herbage representative of that ingested by study animals is not required. Caesium-137 dietary intake explained >60% of the observed variability in the ¹³⁷Cs activity concentration determined in the muscle of sheep. Resultant transfer coefficient (F _f ) values to describe the transfer of ¹³⁷Cs from the diet to muscle were in agreement with previously reported values. At one farm, there was a positive correlation between the ¹³⁷Cs activity concentration in muscle and F _f whilst at the other farm there was a negative correlation between F _f and ¹³⁷Cs dietary intake. Potential reasons for these observations are discussed. Received: 6 April 2000 / Accepted: 25 May 2000     

Mortality from cardiovascular diseases in the Semipalatinsk historical cohort, 1960-1999, and its relationship to radiation exposure

The data on risk of mortality from cardiovascular disease due to radiation exposure at low or medium doses are inconsistent. This paper reports an analysis of the Semipalatinsk historical cohort exposed to radioactive fallout from nuclear testing in the vicinity of the Semipalatinsk Nuclear Test Site, Kazakhstan. The cohort study, which includes 19,545 persons of exposed and comparison villages in the Semipalatinsk region, had been set up in the 1960s and comprises 582,656 person-years of follow-up between 1960 and 1999. A dosimetric approach developed by the U.S. National Cancer Institute (NCI) has been used. Radiation dose estimates in this cohort range from 0 to 630 mGy (whole-body external). Overall, the exposed population showed a high mortality from cardiovascular disease. Rates of mortality from cardiovascular disease in the exposed group substantially exceeded those of the comparison group. Dose-response analyses were conducted for both the entire cohort and the exposed group only. A dose-response relationship that was found when analyzing the entire cohort could be explained completely by differences between the baseline rates in exposed and unexposed groups. When taking this difference into account, no statistically significant dose-response relationship for all cardiovascular disease, for heart disease, or for stroke was found. Our results suggest that within this population and at the level of doses estimated, there is no detectable risk of radiation-related mortality from cardiovascular disease.     

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.     

A Spatially Explicit Model to Predict Radiocesium Body Burdens of White-Tailed Deer on the U.S. Department of Energy's Savannah River Site

We developed a spatially explicit exposure model to interpolate and predict radiocesium (¹³⁷Cs) body burdens found in white-tailed deer (Odocoileus virginianus) on the U.S. Department of Energy's (USDOE) Savannah River Site (SRS) to gain insight into and differentiate between the main contributing sources of this radionuclide for use in harvest management strategies that focus on minimizing human risk. Hunting has been allowed from permanent stands as a mechanism to manage the deer herd since 1965. All animals are monitored in the field for gross beta and gamma activity levels, providing a spatially explicit dataset. The models described here use the relative locations of the hunt-stands to predict ¹³⁷Cs exposure distributions. We used kriging to create an interpolation surface using average white-tailed deer body burdens. Cross-validations of the kriged surfaces differentiated between sources of ¹³⁷Cs and where deer reside on the SRS. The kriged surfaces, coupled with additional regression analyses, provide a comprehensive assessment of deer's ¹³⁷Cs body burdens with predictive capability that quantifies the scale at which such investigations can be conducted. Although the models are local in scale, the methods presented here can be used as a template for other large areas that are being monitored for radioactive fallout.     

Radionuclide Contamination at Kazakhstan's Semipalatinsk Test Site: Implications on Human and Ecological Health

A delegation of five scientists participated in a U.S. National Research Council program to review the status of research on the health and environmental impacts of nuclear testing at the Semipalatinsk Test Site (STS) in the eastern region of the Republic of Kazakhstan. From 11 August through 25 August 2000, we visited several research institutes in Kazakhstan and consulted with numerous Kazakh researchers from academic disciplines ranging from radioecology to public health and medicine. We focused on reviewing data on the health and environmental impacts resulting from the testing. The health effects caused by the testing at STS have received a fair amount of study, and research using modern techniques such as fluorescence in situ hybridization and nuclear magnetic resonance will likely increase the reliability of dose reconstruction. However, the extent to which the STS is contaminated has not been adequately characterized, and the potential exposure to nomadic peoples and ecological receptors at the uncontrolled test site is not known. Additional research in these areas, and development of administrative controls for the site, appears warranted.     

137Cs示踪技术研究坡耕地黑土侵蚀和沉积特征

准确地测定研究区137Cs背景值,建立137Cs流失量与土壤再分布速率之间的定量模型是137Cs示踪技术的关键。通过野外选择参照样地和利用热核爆炸源137Cs背景值模型来确定研究区137Cs的背景值,在此基础上用体现耕作迁移的质量平衡模型估算黑土坡耕地不同地貌部位的土壤再分布速率,并对主要参数进行敏感性分析。结果表明(1)研究区实测的137Cs背景值为2376.81±108.46Bq/m2,模型预测值为2318.4Bq/m2,模型预测远离西北核试验基地的地区较为准确。(2)研究区中坡位(坡肩和坡背)137Cs含量最低,侵蚀最为强烈,平均侵蚀速率为33.56t/(hm2·a)和21.67t/(hm2·a);坡麓和坡足则明显表现沉积,平均沉积速率为-4.93t/(hm2·a)和-24.61t/(hm2·a)。(3)模型预测的侵蚀速率与耕层质量深度(d)、张驰深度(H)正相关,而与137Cs年沉降易被迁移的比例(γ)和颗粒校正因子(P)反相关。并且,模型对参数d、p的敏感性分别高于参数H和γ。     

Monte-Carlo prediction of changes in areas of west Cumbria requiring restrictions on sheep following the Chernobyl accident

Following the 1986 Chernobyl accident radiocaesium levels in sheep meat in some upland areas of the United Kingdom were above the national intervention limit. West Cumbria was one of these areas and restrictions are currently still in place. In addition to deposition from the Chernobyl accident, Cumbria has been subject to radiocaesium deposition from atmospheric nuclear weapons tests, the 1957 Windscale accident and routine releases from the Sellafield nuclear reprocessing plant. A Monte-Carlo approach has been used to try to predict areas in west Cumbria where radiocaesium activity concentrations in lamb meat would require the imposition of restrictions at different times after the Chernobyl accident. The approach models the transfer of radiocaesium from soil to vegetation, based upon soil organic matter, and from vegetation to lamb meat. Spatial inputs are soil organic matter and total post-Chernobyl (137)Cs and (134)Cs deposition; a ratio of Chernobyl (137)Cs to (134)Cs deposition has been used to differentiate Chernobyl and pre-Chernobyl (137)Cs deposition. Comparisons of predicted radiocaesium transfer from soil-vegetation and the spatial variation in lamb (137)Cs activity concentrations are good and predicted restricted areas with time after Chernobyl compare well to the restricted areas set by UK government. We predict that restrictions may be required until 2024 and that in some areas the contribution of pre-Chernobyl (137)Cs to predicted lamb radiocaesium activity concentrations is significant, such that restrictions may only have been required until 1994 as a consequence of Chernobyl radiocaesium deposition alone. This work represents a novel implementation of a spatial radioecological model using a Monte-Carlo approach.     

Cytogenetic abnormalities of the descendants of permanent residents of heavily contaminated East Kazakhstan

More than 400 nuclear explosion tests were conducted at the Semipalatinsk Nuclear Test Site (SNTS) and significant radioactive substances were released. The long-term consequences of the activities at the SNTS and the appearance of any hereditary effects remain insufficiently studied about 25 years after the test site was closed. The population living in villages near the SNTS are considered to have been heavily exposed to external and internal radiation. This study aims to perform an assessment and comprehensive cytogenetic analysis of the inhabitants living near the SNTS, and their first-(F1) and second-(F2) generation children. Residents of the East Kazakhstan region living in the area covered by the former SNTS were included in the study. To evaluate the hereditary effects of nuclear testing, comprehensive chromosome analyses were performed in lymphocytes using conventional Giemsa and fluorescent in situ hybridization methods in 115 F1 and F2 descendants in the villages of Dolon and Sarzhal, which were heavily contaminated. The parents of the subjects had permanently lived in the villages. A higher number of stable-type chromosome aberrations such as translocations was found in these residents than in 80 residents of the control area, Kokpecty, which indicates the possibility that radiation had biological effects on the exposed subjects.     

The transfer of 90Sr and of 137Cs radionuclides in the chain of soil-fodder-animal products in the area contaminated as a consequence of the Chernobyl AES accident

The database on 137Cs and or 90Sr transfer factors in the soil-fodder-animal products chain compiled in the framework of the project "Radioecological Consequences of the Chernobyl Accident" under the French-German Initiative was analyzed. The 137Cs transfer factors were determined into 10 fodder types for farm animals. The 137Cs and 90Sr transfer from daily diet to milk is practically independent from milk yield and season and is about 0.83% and 0.16%. 137Cs transfer factor into beef (adult animals) is about to 2.4% from the daily uptake with fodder per 1 kg meat.     

Cesium-137 sediment depth profiles and inventories in Adirondack Lake sediments

Depth distributions and inventories of¹³⁷Cs (mCi km²) were determined in sediment from several fresh water lakes in the New York State Adirondack Preserve. Included were Big Moose and Darts Lakes, part of the North Branch of the Moose River system, as well as North, Sagamore, South, and Woods Lakes and the seepage pond, Tamarack Lake. Comparisons were made between the¹³⁷Cs inventories in these lakes and large inpoundments in the Adirondacks (Hinkley, Great Sacandaga, Stillwater and Cranberry Lake Reservoirs) and other large impoundments and lakes located in various regions of the U.S., especially Cayuga Lake, Ithaca, NY.None of the Adirondack Lakes had¹³⁷Cs distributions with depth in sediment that closely resembled the deposition pattern of weapons testing as a function of time. All of the natural lakes and small impoundments, including the seepage pond, were found to have significantly lower inventories of¹³⁷Cs than expected; while the large reservoirs were generally enhanced in¹³⁷Cs. We suggest that more than one mechanism may be responsible for the low sediment inventories: for the majority of lakes, flushing of¹³⁷Cs out of the lakes during periods of thermal stratification and ice thaw; and for the seepage pond, remobilization of¹³⁷Cs into the water column due to biological recycling.     

利用137Cs技术研究黑土坡耕地土壤再分布特征

利用¹³⁷Cs示踪技术和不同的理论模型研究典型的东北漫岗地形的黑土土壤再分布状况.通过野外采样和模型分析,得出研究区¹³⁷Cs背景值为2 232.75 Bq·m^-2,介于长江三角洲和黄土高原背景值之间,表明¹³⁷Cs沉降与纬度和降水相关.研究区各地貌部位¹³⁷Cs含量在水平方向和深度分布上有很大的分异.坡肩部位¹³⁷Cs含量最低,土壤侵蚀最为强烈;坡顶和坡背侵蚀较为微弱;坡脚和坡足基本上表现土壤沉积.¹³⁷Cs分布深度从坡肩20 cm到坡足80 cm土层,表现出该区经历了强烈的侵蚀和沉积过程.文中采用4种常用的¹³⁷Cs土壤侵蚀模型估计研究区的土壤侵蚀速率,结果表明,PM模型明显低估了土壤侵蚀速率,MBM-1明显高估了土壤侵蚀速率,MBM-2和MBM-3估计的结果较为相近的合理结果.     

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.     

Reconstruction of local fallout composition and gamma-ray exposure in a village contaminated by the first USSR nuclear test in the Semipalatinsk nuclear test site in Kazakhstan

After the disintegration of the USSR in end of 1991, it became possible for foreign scientists to visit Kazakhstan, in order to investigate the radiological consequences of nuclear explosions that had been conducted at the Semipalatinsk nuclear test site (SNTS). Since the first visit in 1994, our group has been continuing expeditions for soil sampling at various areas around SNTS. The current level of local fallout at SNTS was studied through γ-spectrometry for ¹³⁷Cs as well as α-spectrometry for ^239,240Pu. Average values of soil inventory from wide areas around SNTS were 3,500 and 3,700 Bq m^?2 for ¹³⁷Cs and ^239,240Pu, respectively, as of January 1, 2000. The average level of ¹³⁷Cs is comparable to that in Japan due to global fallout, while the level of ^239,240Pu is several tens of times larger than that in Japan. Areas of strong contamination were found along the trajectories of radioactive fallout, information on which was declassified after the collapse of the USSR. Our recent efforts of soil sampling were concentrated on the area around the Dolon village heavily affected by the radioactive plume from the first USSR atomic bomb test in 1949 and located 110 km east from ground zero of the explosion. Using soil inventory data, retrospective dosimetry was attempted by reconstructing γ-ray exposure from fission product nuclides deposited on the ground. Adopting representative parameters for the initial ¹³⁷Cs deposition (13 kBq m^?2), the refractory/volatile deposition ratio (3.8) and the plume arrival time after explosion (2.5 h), an absorbed dose in air of 600 mGy was obtained for the 1-year cumulative dose in Dolon village, due to the first bomb test in 1949. Considering possible ranges of the parameters, 350 and 910 mGy were estimated for high and low cases of γ-ray dose in air, respectively. It was encouraging that the deduced value was consistent with other estimations using thermal luminescence and archived monitoring data. The present method can be applied to other settlements affected by local fallout from SNTS.     

Transfer of 137Cs from water to fish is not linear in two northern lakes

Empirical data on the behavior of radionuclides in the biosphere are needed for validating radioecological models. In this study, data collected from two lakes in Northern Finland were used to investigate the transfer of ¹³⁷Cs from lake water into fish during a 20-year period after the Chernobyl nuclear power plant accident. The results indicated that transfer of ¹³⁷Cs in the food chains investigated is nonlinear: the water-to-fish concentration ratios (CRs) decreased with increasing ¹³⁷Cs concentration in water. Major deviation from linearity (constant CR) commonly assumed in radioecological modeling was observed only at low ¹³⁷Cs concentrations in water. Other findings of potential importance for radioecological models were that ¹³⁷Cs concentrations were threefold higher in piscivores than in non-piscivores and that no differences in ¹³⁷Cs uptake were found between the two piscivorous species (pike and perch) studied or between three non-piscivorous species (vendace, white fish, and roach) representing different feeding habits (planktivore, benthivore, and mixed diet).     

Radiostrontium contamination of soil and vegetation within the Semipalatinsk test site

The Semipalatinsk nuclear test site (STS) in the Republic of Kazakhstan was an important site for testing atomic bombs and other civil and military nuclear devices of the former Soviet Union. Results are presented from investigations on the extent of radiostrontium contamination in soils and vegetation at the technical areas of the STS, where the tests were conducted and in pastures used by farmers for grazing animals or for hay production. Our data are compared with those reported largely in the recent Russian language literature that has been reviewed. The extent of ⁹⁰Sr contamination of soil is highly variable over the STS with the highest values associated with the technical areas, particularly the Degelen mountains. Recently measured values in both the present data and the Russian language literature confirm the relatively high current contamination of soil and vegetation in the vicinity of tunnels and associated watercourses in the Degelen area. The proportion of ⁹⁰Sr in soil which could not be extracted with 6 M HCl was only an average of 20%, which is low compared to other test site areas and possibly indicates a relatively high mobility in this area, because the ⁹⁰Sr is derived from leakage from explosion tunnels along watercourses rather than being associated with fused silicates. A comparison of relative activity concentrations in soil and vegetation suggests that the transfer of ⁹⁰Sr to vegetation on the STS is high compared to that of ¹³⁷Cs and plutonium.     

Deposition and transport of radionuclides within an upland drainage basin in mid-Wales

The deposition of radiocaesium from nuclear weapons testing and the Chernobyl accident upon the Llyn Llygad Rheidol catchment in mid-Wales is described. Inventories of soil cores from the catchment support estimates of total atmospheric fallout. The mean inventory of weapons testing ¹³⁷Cs in lake sediment cores is broadly similar to that in soil cores. The inventory of Chernobyl fallout in sediment cores is significantly lower and raises questions concerning the residence time of ¹³⁷Cs in the catchment soils and lake waters. ¹³⁷Cs and ²⁴¹Am activities in a sediment core record the 1963 peak of fallout from nuclear weapons testing. The association of the peak activities of ¹³⁷Cs and ²⁴¹Am in the sediments with the falloot maximum is confirmed by ²¹⁰Pb dating. The ²¹⁰Pb dates also reveal a significant increase in sediment accumulation rates over the past 20 years.