Fetal dose assessment for the offspring of the Techa Riverside residents

Massive releases of fission products from the plutonium facility Mayak (Southern Urals, Russia) resulted in the contamination of the Techa river and its floodlands (1949–1956). The results of long-term studies of exposure populations have been used for different purposes of retrospective dosimetry. The riverside residents were exposed via various pathways and their progeny were exposed in utero both to external radiation and to internal radiation from radionuclides ingested by the mothers prior to conception and during pregnancy. Fetal doses due to ⁹⁰Sr from the maternal skeleton were estimated and compared with doses from other pathways. Individual red bone marrow (RBM) doses to the late fetuses were calculated on the basis of ⁹⁰Sr contents measured in the maternal skeleton and the ⁹⁰Sr transfer coefficients (TC) to the fetal skeleton were determined on the basis of the Techa river data. Two values of TC were assumed depending on the mothers’ maturation status in the period of maximum releases: TC=0.2 for group 1 (adulthood of mothers in 1950) and TC=0.02 for group 2 (mothers not yet in menarche age in 1950). Fetal doses in both groups that resulted from the different TC values varied by a factor of about 5–8. Furthermore, the fetal RBM doses due to ⁹⁰Sr from the maternal skeleton were found to depend on the distances from the site of release and the time after major ⁹⁰Sr intake. The average fetal RBM doses in the population of the upper, middle and lower Techa riverside regions were close to the ratio 3:2:1 and 20 years after the onset of contamination, the fetal doses have decreased by a factor of about 3–5. The distance from the site of release determined the relative contribution of different pathways to the fetal dose. For the settlements that are located closest to the site of release, the external exposure was of major concern up to the date of evacuation. For the non-evacuated settlements, the contribution of internal doses was higher and after 1956, external exposure is assumed to be negligible. From 1956 on, ⁹⁰Sr that has been transferred from the maternal skeleton was practically the single source of in utero exposure. Received: 8 December 2000 / Accepted: 1 July 2001     

Radioactive aerosols released from the Chernobyl Shelter into the immediate environment

The release of radioactive particles through large gaps in the containment of the destroyed Chernobyl reactor was assessed during two measurement periods. In 1996–1999, a total radionuclide flow rate of 274 Bq s⁻¹ or 8.64 × 10⁹ Bq year⁻¹ was determined. These releases were predominantly due to ¹³⁷Cs (78.5%), ⁹⁰Sr (21.1%), and ^239+240Pu (0.4%). The mean activity concentration in the aerosol measured directly at the gaps was about 240 mBq m⁻³ with an activity median aerodynamic diameter (AMAD) of 2.4 μm for ¹³⁷Cs, 120 mBq m⁻³ with an AMAD in the range 3.1–13 μm for ⁹⁰Sr, 1.8 mBq m⁻³ with an AMAD in the range 3.5–11 μm for ^239+240Pu, and 2.0 mBq m⁻³ with an AMAD of 1.5 μm for ²⁴¹Am. The resulting total inhalation dose rate calculated close to the gaps was about 100 nSv h⁻¹. In the near environment, the mean ¹³⁷Cs activity in the aerosol was 2.2 mBq m⁻³ with an AMAD of 2.2 μm, which gave rise to an inhalation dose rate of about two orders of magnitude lower than the corresponding dose rate at the gaps. Occasionally, however, dose levels were measured in the near environment that were similar to those at the gaps. In 2000–2003, lower activity concentrations were observed. The decrease was more pronounced at the gaps than in the near environment. The results indicate that effective dose due to inhalation must be considered for the dose assessment of construction workers who will be deployed at the Chernobyl site to reconstruct the old or to build the new Shelter, in the future.     

Pilot study of the Urals population by tooth electron paramagnetic resonance dosimetry

During 1949–1956, about 76 × 10⁶ m³ of radioactive liquid waste containing a total activity of 10¹⁷ Bq was discharged into the Techa River by the first Russian industrial nuclear facility Mayak. As a consequence, the population living in the river valley received considerable internal and external radiation doses. The results of a first application of electron paramagnetic resonance (EPR) of tooth enamel for a retrospective individual dose evaluation of the residents of the Techa riverside are presented. Three main contributions to the dose absorbed in tooth enamel have been considered: external exposure mainly from the Techa River sediments, internal exposure mainly due to ⁹⁰Sr; and background radiation including all other sources of exposure except the Techa River. The teeth of 86 inhabitants of the town Kamensk-Uralskii were analysed to determine the age-dependent contribution of the background radiation to the enamel dose. For 22 residents of the middle and lower Techa riverside, measurements of the ⁹⁰Sr whole-body content and EPR measurements of the absorbed dose in enamel were used to establish a correlation between these two quantities. Finally, absorbed doses in the enamel of five residents of the upper Techa riverside were determined by the EPR method. Contributions of the background radiation and the internal ⁹⁰Sr contamination were subtracted to determine the external exposure of the residents.     

Transfer of 85Sr and 134Cs from diet to reindeer foetuses and milk

Sr-85 and ¹³⁴Cs in aqueous solution of the chlorides were administered daily to four pregnant reindeer during the last part of gestation. Radionuclide concentrations were determined in calves sacrificed at birth, and secretion of the nuclides was measured in milk. Although the gastrointestinal absorption of ⁸⁵Sr was low, an apparently higher transfer of the absorbed fraction of ⁸⁵Sr than ¹³⁴Cs from the mother to the foetus led to similar accumulation of ⁸⁵Sr and ¹³⁴Cs in foetuses. At birth 1.4–1.6 and 1.5–2.5% of the total administered activities of ⁸⁵Sr and ¹³⁴Cs, respectively, were present in the calves‘ bodies. Transfer coefficients (F _m) for ⁸⁵Sr and ¹³⁴Cs from feed to milk were estimated at 0.0218±0.0026 and 0.185±0.025 day kg⁻¹, respectively, and the observed ratio (OR_milk-diet) for ⁸⁵Sr was 0.124±0.037. Transfer of radiostrontium to reindeer milk was in agreement with previously reported relationships between Ca intake and radiostrontium transfer in ruminants. These relationships suggest that the transfer of radiostrontium to foetuses and milk of free-ranging reindeer can be 3–4 times higher than observed in this experiment (due to lower Ca intake with natural forage), but the transfer to milk will not be as high as that of ionic ¹³⁴Cs. The concentrations of ⁸⁵Sr in milk suggested that the does mobilized skeletal stores of Ca and ⁸⁵Sr for milk production, although the diet appeared to satisfy the Ca requirements. In reindeer with radiostrontium intake during the whole year, radiostrontium concentrations in milk will therefore be higher than indicated by the F _m value observed in our study. No differences in half-times for ⁸⁵Sr and ¹³⁴Cs secretion in milk were detected. Both nuclides were secreted with short- and long-term half-times of 1–2 and 12–19 days, respectively. For ⁸⁵Sr, 80–90% of the activity was excreted with the short half-time, whereas the corresponding value for ¹³⁴Cs was 30–50%.     

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.     

Radiocesium in mushrooms from selected locations in the Czech Republic and the Slovak Republic

In this paper, activity concentrations of radiocesium in mushrooms from various locations in the Czech Republic and the Slovak Republic in the years 2000–2004 are presented. Summary reports of Czech regulatory bodies have judged the average activity concentrations in mushrooms to be remarkably below the maximum permissible level of contamination. However, there are certain regions where radiocesium activities have approached the maximum permissible level for contamination of basic foodstuff. For example, the highest activity concentration of ¹³⁷Cs measured by gamma-spectrometry was 2,263 Bq kg⁻¹ (on a dry mass basis), in Xerocomus badius from Staré Ransko (a locality in the Czech-Moravian Highlands, Czech Republic). The highest activity concentration of ¹³⁷Cs measured in Slovakia was 966 Bq kg⁻¹ (on a dry mass basis), for Suillus luteus from Senica. For comparison, the corresponding activity concentration in a sample taken within the 30 km zone around Chernobyl was measured to be 6,000 Bq kg⁻¹ (on a dry mass basis). Our results have also demonstrated remarkably lower activity concentrations of ¹³⁷Cs in Slovakia compared to those in the Czech Republic.     

Mapping the distribution of (90)Sr in teeth with a photostimulable phosphor imaging detector

The present communication describes the technical aspects of the first application of an imaging plate for visualization of (90)Sr deposited in human teeth. The teeth were obtained from Techa River area residents who were exposed as a result of releases of radioactivity into the Techa River by the first Soviet nuclear plant Mayak in the early 1950s. The investigations form the basis for an experimental procedure for accurate mapping of the distribution of (90)Sr in teeth with an imaging plate. This new method can be used as an individual indicator of radionuclide intake. Its advantages are its high sensitivity (0.02 Bq/g mm(-2) of (90)Sr), it ability to examine small detectable cross-sectional areas of dental tissue (dentin) contaminated with (90)Sr (from 0.01 mm(2)), the nondestructive method of analysis, and the simplicity of use. The combined application of this method with EPR tooth biodosimetry can provide more accurate dose reconstruction and may lead to more effective radiation risk assessment.     

Does the cortical bone resorption rate change due to <Superscript>90</Superscript>Sr-radiation exposure? Analysis of data from Techa Riverside residents

The Mayak Production Association released large amounts of ⁹⁰Sr into the Techa River (Southern Urals, Russia) with peak amounts in 1950–1951. Techa Riverside residents ingested an average of about 3,000 kBq of ⁹⁰Sr. The ⁹⁰Sr-body burden of approximately 15,000 individuals has been measured in the Urals Research Center for Radiation Medicine in 1974–1997 with use of a special whole-body counter (WBC). Strontium-90 had mainly deposited in the cortical part of the skeleton by 25 years following intake, and ⁹⁰Sr elimination occurs as a result of cortical bone resorption. The effect of ⁹⁰Sr-radiation exposure on the rate of cortical bone resorption was studied. Data on 2,022 WBC measurements were selected for 207 adult persons, who were measured three or more times before they were 50–55 years old. The individual-resorption rates were calculated with the rate of strontium recirculation evaluated as 0.0018 year⁻¹. Individual absorbed doses in red bone marrow (RBM) and bone surface (BS) were also calculated. Statistically significant negative relationships of cortical bone resorption rate were discovered related to ⁹⁰Sr-body burden and dose absorbed in the RBM or the BS. The response appears to have a threshold of about 1.5-Gy RBM dose. The radiation-induced decrease in bone resorption rate may not be significant in terms of health. However, a decrease in bone remodeling rate can be among several causes of an increased level of degenerative dystrophic bone pathology in exposed persons.     

Dynamics and distribution of radiocaesium in broiler chicken

The distribution and biological half-life of radiocaesium (¹³⁷Cs) in broiler chickens after three oral applications (in course of 1 day at the age of 14 days) of artificially contaminated feed mixture were studied. There was a rapid uptake of the orally administered ¹³⁷Cs (within a few hours) and also a rapid loss of ¹³⁷Cs which varied in the different organs (the initial biological half-life was: liver 0.6 day, intestine 0.6 day, breast meat 2 days, leg meat 1.2 days). More than one-half of the total administered ¹³⁷Cs activity (55%) was excreted from the body within the 1st day after dosage, and after 14 days more than 90% had been excreted. The highest accumulation of ¹³⁷Cs occurred in meat (50%–90%), and the proportion of total activity in breast and leg meat varied during decontamination. The transfer of radiocaesium from feed into the chicken body (measured as ratios of the ¹³⁷Cs activity concentrations in the organ to the ¹³⁷Cs activity concentration in the applied dose) 1 day after application was: 0.0220, 0.0294, 0.0216 and 0.0195 for breast meat, leg meat, intestine and liver, respectively. Significant differences between the values were demonstrated (P<0.05) except between those of breast meat and intestine. For the first 3 days there was a higher proportion of ¹³⁷Cs activity in leg meat, whereas from the 4th day a greater part of total activity was found in breast meat. The latter results were confirmed in a subsequent study. Data from this study suggest that if broiler chickens are contaminated by radiocaesium to a level of 5 kBq/chicken in the course of 1 day at the age of 14 days, then immediate feeding with uncontaminated feed mixture for 18 days should be effective in decontaminating the chicken's meat below the intervention levels for radiocaesium in animal products, i.e. below 1000 Bq ⋅ kg^–1. Received: 30 December 1996 / Accepted in revised form: 13 May 1997     

Leukemia incidence among people exposed to chronic radiation from the contaminated Techa River, 1953–2005

Beginning in 1950, people living on the banks of the Techa River received chronic low-dose-rate internal and external radiation exposures as a result of releases from the Mayak nuclear weapons plutonium production facility in the Southern Urals region of the Russian Federation. The Techa River cohort includes about 30,000 people who resided in riverside villages sometime between 1950 and 1960. Cumulative red bone marrow doses range up to 2 Gy with a mean of 0.3 Gy and a median of 0.2 Gy. Between 1953 and 2005, 93 first primary cases of leukemia, including 23 cases of chronic lymphatic leukemia (CLL), were ascertained among the cohort members. A significant linear dose–response relationship was seen for leukemias other than CLL (P < 0.001), but not for CLL. The estimated excess relative risk per Gy is 4.9 (95% confidence interval (CI): 1.6; 14.3) for leukemias other than CLL and less than 0 (95% upper bound 1.4) for CLL.     

Nitrogen and energy requirements of the short-tailed fruit bat (Carollia perspicillata): fruit bats are not nitrogen constrained

 Nitrogen (N) and energy (E) requirements were measured in adult Carollia perspicillata which were fed on four experimental diets. Bats ate 1.3–1.8 times their body mass ⋅ day^-1 and ingested 1339.5–1941.4 kJ ⋅ kg^-0.75 ⋅ day^-1. Despite a rapid transit time, dry matter digestibility and metabolizable E coefficient were high (83.3% and 82.4%, respectively), but true N digestibility was low (67.0%). Mass change was not correlated with E intake, indicating that bats adjusted their metabolic rate to maintain constant mass. Bats were able to maintain constant mass with digestible E intake as low as 1168.7 kJ ⋅ kg^-0.75 ⋅ day^-1 or 58.6 kJ ⋅ . Metabolic fecal N and endogenous urinary N losses were 0.87 mg N ⋅ g^-1 dry matter intake and 172.5 mg N ⋅ kg^-0.75 ⋅ day^-1, respectively, and bats required 442 mg N ⋅ kg^-0.75 ⋅ day^-1 (total nitrogen) or 292.8 mg N ⋅ kg^-0.75 ⋅ day^-1 (truly digestible nitrogen) for N balance. Based on E and N requirements and digestibilities, it was calculated that non-reproductive fruit bats were able to meet their N requirements without resorting to folivory and without over-ingesting energy. It was demonstrated that low metabolic fecal requirements allowed bats to survive on low-N diets. Accepted: 23 June 1996     

Reconstruction of the contamination of the Techa River in 1949–1951 as a result of releases from the “MAYAK” Production Association

More accurate reconstruction of the radioactive contamination of the Techa River system in 1949–1951 has been made on the basis of refined data on the amounts and the rate of discharge of radionuclides into the Techa River from the Mayak Production Association; this has led to the development of a modified Techa River model that describes the transport of radionuclides through the up-river ponds and along the Techa River and deposition of radionuclides in the river-bottom sediments and flooded areas. The refined Techa River source-term data define more precisely the time-dependent rates of release and radionuclide composition of the releases that occurred during 1949–1951. The Techa River model takes into account the time-dependent characteristics of the releases and considers (a) the transport of radionuclides adsorbed on solid particles originally contained in the discharges or originating in the up-river ponds as a result of stirring up of contaminated bottom sediments and (b) the transport of radionuclides in soluble form. The output of the Techa River model provides concentrations of all source-term radionuclides in the river water, bottom sediments, and floodplain soils at different distances from the site of radioactive releases for the period of major contamination in 1950–1951. The outputs of the model show good agreement with historical measurements of water and sediment contamination. In addition, the river-model output for ⁹⁰Sr concentration in the river water is harmonized with retrospective estimates derived from the measurements of ⁹⁰Sr in the residents of the Techa Riverside villages. Modeled contamination of the floodplain soils by ¹³⁷Cs is shown to be in agreement with the values reconstructed from late measurements of this radionuclide. Reconstructed estimates of the Techa River contamination are being used for the quantification of internal and external doses received by residents of the Techa Riverside communities.     

Reconstruction and forecast of doses due to ingestion of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr after the Chernobyl accident

The assessment doses due to ingestion of ¹³⁷Cs and ⁹⁰Sr for the population suffering from the Chernobyl accident was performed on the basis of the new mechanistic ecological model for assessment of radiological consequences of agricultural lands contamination (EMARC). The EMARC model allows estimation of internal doses based on ecological factors influencing the contamination of foodstuff, for the post-accidental years in the countries of the former Soviet Union. The EMARC model allows estimation of all quantities required in radiation hygiene practice. For example, the proposed analytical method may be used for both retrospective dose reconstruction and prospective estimates of annual dose and integrated “life-time” dose, for different age intervals. According to the EMARC model, estimated reference “life-time” doses for adults are between 7 and 269 μSv kBq⁻¹ m² for ¹³⁷Cs, and between 25 and 235 μSv kBq⁻¹ m² for ⁹⁰Sr. Maximal doses were estimated for persons who were 3, 9 and 11 years old, at the time of the accident and these doses exceed those for adults by a factors of 1, 5 for ⁹⁰Sr, and 1.4 for ¹³⁷Cs.     

Radiocesium activity reduction in boar meat by brining

Meat of wild boar with an intial ¹³⁷Cs activity concentration of 103 Bq kg⁻¹ of fresh mass was treated by brining. Dry-salting reduced the ¹³⁷Cs activity only by about 12–18%. Subsequent brining was done by using both pure sodium chloride and a mixture of sodium chloride and potassium nitrate. After double-brine exchange, the ¹³⁷Cs activity concentration was reduced by at least 72%. The double-brine exchanges were done for two time intervals (the first each 24 h and the second each 7 days). There were no differences in the ¹³⁷Cs activity reduction for these two time intervals. From the technological point of view, the repeated exchange of the brine solution represents a relative easy method of ¹³⁷Cs activity reduction in contaminated pork meat.     

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.     

Reconstruction of 90Sr intake for breast-fed infants in the Techa riverside settlements

The Techa River (Southern Urals, Russia) was contaminated as a result of radioactive releases by the Mayak plutonium production facility during 1949-1956. The persons born after the onset of the contamination have been identified as the "Techa River Offspring Cohort" (TROC). The TROC has the potential to provide direct data on health effects in progeny that resulted from exposure of a general parent population to chronic radiation. The purpose of the present investigation is the estimation of (90)Sr intake from breast milk and river water in the period from birth to 6 months of life, necessary for an infant dose calculation. The investigation is based on all available data concerning radioactive contamination due to global fallouts and Mayak releases in the Southern Urals where extensive radiometric and radiochemical investigations of human tissues and environmental samples were conducted during the second half of the twentieth century. The strontium transfer factor from mother's daily diet to breast milk was estimated as 0.05 (0.01-0.13) d L(-1). Based on this transfer factor and data on (90)Sr water contamination, the average total (90)Sr intake for an infant born in the middle Techa River region was found to be equal to 60-80 kBq in 1950-1951. For the same period, calculations of (90)Sr intake using ICRP models gave values of 70-100 kBq. From 1952 onwards, the differences in intakes calculated using the two approaches increased, reaching a factor of 2-3 in 1953. The Techa River data provide the basis for improving and adapting the ICRP models for application to Techa River-specific population.     

Chronic low-dose exposure in the Techa River Cohort: risk of mortality from circulatory diseases

The aim of the present study was to analyze the mortality from circulatory diseases for about 30,000 members of the Techa River cohort over the period 1950–2003, and to investigate how these rates depend on radiation doses. This population received both external and internal exposures from ⁹⁰Sr, ⁸⁹Sr, ¹³⁷Cs, and other uranium fission products as a result of waterborne releases from the Mayak nuclear facility in the Southern Urals region of the Russian Federation. The analysis included individualized estimates of the total (external plus internal) absorbed dose in muscle calculated based on the Techa River Dosimetry System 2009. The cohort-average dose to muscle tissue was 35 mGy, and the maximum dose was 510 mGy. Between 1950 and 2003, 7,595 deaths from circulatory diseases were registered among cohort members with 901,563 person years at risk. Mortality rates in the cohort were analyzed using a simple parametric excess relative risk (ERR) model. For all circulatory diseases, the estimated excess relative risk per 100 mGy with a 15-year lag period was 3.6 % with a 95 % confidence interval of 0.2–7.5 %, and for ischemic heart disease it was 5.6 % with a 95 % confidence interval of 0.1–11.9 %. A linear ERR model provided the best fit. Analyses with a lag period shorter than 15 years from the beginning of exposure did not reveal any significant risk of mortality from either all circulatory diseases or ischemic heart disease. There was no evidence of an increased mortality risk from cerebrovascular disease (p > 0.5). These results should be regarded as preliminary, since they will be updated after adjustment for smoking and alcohol consumption.     

Bone mineral density in residents of radioactive territories of Chelyabinsk Region

Operation of the Mayak plutonium production association resulted in radioactive contamination of a part of Chelyabinsk Region in the 1950–1960s. Significant gas-aerosol emission of ¹³¹I occurred since 1948; in 1957, a radiation accident resulted in ⁹⁰Sr contamination of large territories. This paper presents comparison of the bone mineral density of persons who lived on territories with different levels of ⁹⁰Sr-soil contamination with that of a control group. It was found that in 1970–1975, the bone mineral density, estimated from the mineral content in bone samples, in residents of contaminated areas born in 1936–1952 was significantly lower compared to the control group. For persons born in 1880–1935, such differences were not found. It was shown that the decrease in the bone mineral density was not related to ⁹⁰Sr exposure of osteogenic cells in the dose range from 0.1 to 1300 mGy: the coefficient of correlation between individual ⁹⁰Sr doses and bone mineral contents is not significant. The decrease in bone mineral density of persons born in 1936–1952 may be associated with exposure of the thyroid and parathyroid glands (systemic regulators of calcium metabolism) to ¹³¹I from gas-aerosol emissions from Mayak. The highest levels of gas-aerosol emissions occurred in 1948–1954 and coincided with the growth and development of the thyroid gland, characterized by intensive accumulation of ¹³¹I, and with the growth and maturation of the skeleton of persons born in the given calendar years.     

137Cs mobility in soils and its long-term effect on the external radiation exposure

To predict the external gamma-dose rate of Chernobyl-derived ¹³⁷Cs for a period of about 100 years after its deposition, the vertical distribution of radiocesium in several meadow soils in the Chernobyl area and in Germany was determined, and the corresponding residence half-times of this radionuclide in the various soil layers were evaluated using a compartment model. The resulting residence half-times were subsequently used to calculate the vertical distribution of ¹³⁷Cs in the soil as a function of time and finally to predict the external gamma-dose rates in air for these sites at various times. A regression analysis of the data obtained showed that the time dependence of the relative gamma-dose rate in air D(t) at the Chernobyl sites can be described by an exponential equation D(t) = a + b ⋅ exp(–t/c), where t is the time after deposition. For the ten German sites the best fit was obtained using the two-exponential equation D(t) = a ⋅ exp(–t/b) + c ⋅ exp(–t/d). The gamma-dose rate of ¹³⁷Cs at the Chernobyl sites decreases significantly more slowly with time than at the German sites. This means that after e.g. 30 years the mean relative gamma-dose rate at the German sites will have decreased from 100% (corresponding to an infinite plane source on a smooth surface) to 9% (95% confidence interval 8%–10%), while at the sites in the Chernobyl area it will have decreased only to 21% (20%–23%). This difference is the result of the longer residence half-times of ¹³⁷Cs in the soils at the Chernobyl sites. All results are compared with estimates from earlier studies. Received: 16 October 1996 / Accepted in revised form: 28 November 1996     

Comparative Effects of Superoxide Anion and Hydrogen Peroxide on Microsomal and Cytosolic Glutathione <Emphasis Type="Italic">S</Emphasis>-Transferase Activities of Rat Liver

Three hundred sixty healthy Ross×Ross 1-day-old broilers were used to study the effects of zinc glycine chelate (Zn-Gly) on growth performance, hematological, and immunological characteristics. All broilers were randomly assigned into six treatments. Diets were as follows: (1) control (containing 29.3 mg Zn kg⁻¹ basic diet [0–3 weeks] and 27.8 mg Zn kg⁻¹ [4–6 weeks]); (2) basic diet plus 30 mg Zn kg⁻¹ from Zn-Gly; (3) basic diet plus 60 mg Zn kg⁻¹ from Zn-Gly; (4) basic diet plus 90 mg Zn kg⁻¹ from Zn-Gly; (5) basic diet plus 120 mg Zn kg⁻¹ from Zn-Gly; (6) positive control, basic diet plus 120 mg Zn kg⁻¹ from zinc sulfate (ZnSO₄). After the 21- and 42-day feeding trials, the results showed that both of Zn-Gly and ZnSO₄ could improve the growth performance of broilers, with the greatest average daily feed intake observed in the broilers fed 90 mg Zn kg⁻¹ from Zn-Gly, but the greatest average daily gain observed with 120 mg Zn kg⁻¹ from Zn-Gly (0–3 weeks) and 90 mg Zn kg⁻¹ from Zn-Gly (4–6 weeks). Adding additional Zn-Gly improved the levels of immunoglobulins (IgA, IgM, and IgG) and the contents of total protein and Ca in serum and increased the immune organs index especially with 90 mg Zn kg⁻¹ as Zn-Gly. However, there were no significant differences in responses to complements (C3 and C4) and albumin in serum among the treatments.