The cytogenetic indication of irradiation in persons exposed to the action of the factors in the Chernobyl accident]

363 men who have been working under conditions of additional irradiation in terms from few hours to some months were cytogenetically examined to define individual irradiation. In 111 men with the known dose of irradiation (5-140 cGy), the results of cytogenetic evaluation indicated, as a rule, a less intensive irradiation than physical dosimetry. This could be caused by elimination of chromosome aberrations, individual sensitivity, peculiar irradiation situation, or in some cases by incorrect evaluation of dose. In 252 men with the unknown dose of irradiation a tentative level was determined as based on frequency of metaphases with chromosome type aberrations. According to the study the absorbed dose was below 25 cGy in 209 cases, 26-50 cGy in 39 cases, and reached 51-90 cGy in 4 cases.     

Stable chromosome aberrations in atomic bomb survivors: results from 25 years of investigation

Frequencies of stable chromosome aberrations from more than 3,000 atomic bomb survivors were used to examine the nature of the radiation dose response. The end point was the proportion of cells with at least one translocation or inversion detected in Giemsa-stained cultures of approximately 100 lymphocytes per person. The statistical methods allow for both imprecision of individual dose estimates and extra-binomial variation. A highly significant and nonlinear dose response was seen. The shape of the dose response was concave upward for doses below 1.5 Sv but exhibited some leveling off at higher doses. This curvature was similar for the two cities, with a crossover dose (i.e. the ratio of the linear coefficient to the quadratic coefficient) of 1.7 Sv (95% CI 0.9, 4). The low-dose slopes for the two cities differed significantly: 6.6% per Sv (95% CI 5.5, 8.4) in Hiroshima and 3.7% (95% CI 2.6, 4.9) in Nagasaki. This difference was reduced considerably, but not eliminated, when the comparison was limited to people who were exposed in houses or tenements. Nagasaki survivors exposed in factories, as well as people in either city who were outside with little or no shielding, had a lower dose response than those exposed in houses. This suggests that doses for Nagasaki factory worker survivors may be overestimated by the DS86, apparently by about 60%. Even though factory workers constitute about 20% of Nagasaki survivors with dose estimates in the range of 0.5 to 2 Sv, calculations indicate that the dosimetry problems for these people have little impact on cancer risk estimates for Nagasaki.     

The molecular and cellular consequences of the chernobyl accident

In this paper the results of research at 5–10 and 24 years after the Chernobyl accident are summarized. These results include the investigation of genomic instability, formation of the adaptive response, genome damage, and oxidative status. The studies were performed on cells in culture, mice, children and adults who lived in the contaminated areas, and liquidators of the consequences of the Chernobyl accident. Inhibition of cell proliferative activity, late cell death, and the increase in micronucleus and giant cell frequency were observed after the exposure of cells in culture in the accident zone followed by their culturing in laboratory conditions. In the progeny of the exposed cells, the effect of enhanced radiosensitivity was detected. Thus, it can be assumed that exposure of parental cells in culture in the area of the accident induced genomic instability that resulted in the development of various abnormalities in progeny cells. At the organism level, the Chernobyl zone exposure of mice caused an increase in radiosensitivity; as well, a decrease in the endotheliocyte density in the cerebral cortex and other brain tissues was observed. In the blood lymphocytes of children stimulated by PHA, a more than two times increase in micronucleus cell frequency was detected. A reduced number of individuals with significant adaptive response was found in both the juvenile and adult groups. In all investigated populations, an increased number of individuals with enhanced radiosensitivity were observed in response to low-dose radiation exposure. At 24 years after the accident liquidators were subjected to examinations, which revealed an increased frequency of cells with micronuclei and chromosome-type aberrations in blood lymphocytes, an elevated level of DNA double strand breaks, and a reduced level of reactive oxygen species compared to those of the control group. This means that the genomic instability that was accumulated by the residents of the contaminated regions and liquidators as a result of the accident leads to damage of the genetic apparatus, an increase in radiosensitivity, and hypoxia as late consequences that all are risk factors and increase the probability of the development of tumor and non-tumor diseases. The development of the above-mentioned pathological processes may occur in the distant future.

     

The significance of cytogenetic investigation for the estimation of Chernobyl accident consequences

The results of the cytogenetic investigation of people, which were exposed to radiation in the result of the Chernobyl NPP accident, were presented. Also the possibilities of the application of cytogenetic findings for dose estimations and for the prediction of the radiation influence consequences were examined. During the period of time since 1986 till 2004 the cytogenetic investigations of 1724 liquidators participating in the liquidation works after the Chernobyl accident were carried out. The radiation dose estimated by the frequency of dicentrics in 1986 was about 0.16 Gy. The doses for liquidators were determined by the frequency of translocations (FISH method) during the period from 1992 till 1995. For liquidators who worked in Chernobyl only in 1986 the average dose of radiation was about 0.19 Gy and for liquidators who worked repeatedly during the period from 1986 till 1995 - 0.39 Gy. There was shown that during the whole period of investigation (1986-2004) the frequency of dicentrics in peripheral blood lymphocytes was significantly higher than the control level. The cytogenetic investigation of Bryansk region inhabitants which was carried out in 1992-1994 discovered heightened value in 5 times than the control one. Findings are of great importance for the prediction of ill effects of radiation and for the development of sensitive criterions for early exposure disturbances in state of health.     

The distribution of individual radiation doses in liquidators of Chernobyl accident using cytogenetic analysis

The cytogenetic screening was carried out in 100 Chernobyl clean-up workers (liquidators) with registered doses during 1 year after exposure. The bayesian analysis has been applied for constructing the individual distribution of probability density for biological doses estimated from dicentric and centric ring yields in liquidators. The coincidence of the biological and registered dose has been found in 25% of cases; among the rest persons the documented doses exceeded the biological estimations in 25% of cases and the cytogenetic doses were higher than registered ones in 50% of cases. The total distribution of biological doses was constructed by pooling the individual data in 50 mGy dose intervals. The distribution obtained had the maximum at 300-350 mGy and contained 68% of probability density in the dose range 0-1000 mGy. The probabilistic approach in cohort biodosimetry showed the necessity of corrections in radiogenic risk assessment for Chernobyl liquidators. The advantages of bayesian technique for biodosimetrical treatment of cytogenetic data in conditions of small number of cells scored and low aberration yields induced by low dose irradiation were discussed.     

The characteristics of the realization of cytogenetic damage in mammalian and plant cells exposed to low doses of radiation]

A complicated character of the cytogenetic injury dependence upon radiation dose was revealed after low-level gamma irradiation of Vicia faba seedlings and Chinese hamster fibroblasts. The dependence was linear with low-level secondary exposure to 70 GeV protons. The authors discuss a threshold nature of induction of the cytogenetic damage repair responsible for a high outcome of damages under the effect of low-level gamma radiation.     

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.     

The assessment of accumulated internal irradiation doses of the inhabitants of the populated areas in Republik Belarus after Chernobyl accident

A new system of evaluation methods has been developed for the assessment of the accumulated internal irradiation doses in the inhabitants of the populated areas of the Republic of Belarus that were contaminated by the Chernobyl radionuclides. The system is based on the results of WBC measurements. The model is based on the WBC-results of the State Dosimetric Register for the period of 1987-2010. The dose assessment model is based on the classification of the populated areas, on the regional features of the soils through which 137Cs can enter into the locally grown and produced foods. The model is also based on building the regressive correlations of accumulated internal doses to the contamination density of the territory of a populated area. Such regressive correlations are made for each region. The influence of indirect factors of dose forming was taken into consideration in the dose assessment. Among these factors are the population of the area, and the amount of forested territory around it, which were taken as correction coefficients. The coefficients were determined from the regressive correlation of the correction coefficients to a specific area of forest for each region. So called "countermeasure factor" was used for specification of other model results.     

Characteristics of the development of radiation sickness in guinea pigs exposed to non-uniform irradiation in highly lethal doses

Certain peculiarities have been revealed in the development of radiation sickness in guinea pigs subjected to nonuniform irradiation with superlethal doses. With electron and gamma-neutron radiation LD50/1.5 was 116.11 and 114.48 Gy respectively, when delivered to whole body, and 133.40 and 111.72 Gy when delivered to the posterior part of the body.     

The influence of exogenous melanin on the development of female Wistar rats' posterity of first generation exposed to low doses at different dose rates during embryogenesis

To research a radio-protective effect of melanin on the reproductive system during its creation the development of first generation posterity (900 descendants) of 125 pubertal female Wistar rats was examined after the single gamma-irradiation with a dose of 1 Gy (mean dose rate of 0.03 mGy/h), which they have been exposed to on the day ten of pregnancy, and the chronic gamma-irradiation with a total dose of 1 Gy (mean dose rate of 5.31 mGy/h) which they have been being exposed to during the first 10 days of pregnancy. The melanin of natural animal origin has the anti-radial effectiveness with the single irradiation increasing the number of alive newborn descendants in a litter and doubling their survival during the first 30 days after the birth. The melanin's effect is less expressed with the chronic irradiation.     

External and internal irradiation of a Rural Bryansk (Russia) population from 1990 to 2000, following high deposition of radioactive caesium from the chernobyl accident

In 1990, a joint Nordic-Russian project was initiated in order to make independent estimations of the effective dose to selected groups of inhabitants in a highly contaminated area around the city of Novozybkov in the western Bryansk region of Russia. The inhabitants were living in six villages with initial contamination levels of ¹³⁷Cs between 0.9 and 2.7 MBq m⁻². Some villages had been decontaminated, others not. Both school children and adults participated in the study. The external irradiation of 100–130 inhabitants was determined during 1 month in September-October each year from 1990 to 2000 (except 1999), using individual thermoluminescent dosemeters. The body burden of ^137,134Cs was determined by in vivo measurements in about 500 inhabitants annually from 1991 to 2000, and for a subgroup also with analysis of the ¹³⁷Cs concentration in urine. The mean effective dose (E) from external and internal irradiation due to ^137,134Cs deposition varied between 2.5 and 1.2 mSv per year between 1990 and 2000. The total mean E decreased, on average, by 9% per year, while the mean external dose decreased by 16% per year. The dose rate from internal radiation decreased more slowly than the dose rate from external radiation, and also showed an irregular time variation. The contribution from the internal dose to the total E was 30–50%, depending on the village. Predictions for the long-term changes in the effective dose to people living in the areas are presented. The cumulated E for the 70 years following the accident was estimated to be about 90 mSv with the assumption that both internal and external dose decrease by 2% per year after year 2000. The highest E during a life-time received by single individuals living in the area may amount to around 500 mSv considering the individual variations in E.     

The activation of the immunosorptive properties of blood during its UV irradiation at therapeutic doses

UV irradiation of donor rhesus-positive blood in apparatus, applied in Soviet hospitals for autotransfusion of UV-irradiated blood produces a 2-fold increase of the blood capacity to bind antirhesus antibodies in blood or serum from sensibilized women. The above data can be used for increase in therapeutic effect of blood exchange transfusion in children with rhesus-conflict hemolytic disease.     

The chromosomal radiosensitivity of children whose parents were exposed to antitumor radiochemotherapy]

The effect of gamma radiation was studied on routine stained chromosomes from lymphocytes of children born to Hodgkin's disease patients after cancer therapy (CP) in comparison to children from healthy parents (HP). Irradiation (0, 0.25, 0.50, 1.00, 1.50 Gy) of the whole blood was performed in culture medium. Metaphases were obtained from 52-h cultures. Chromosomal aberrations were used as an endpoint. Aberrations of both chromosomal and chromatid types were scored in 150-200 metaphases for estimation of spontaneous level of cytogenetic injuries and in 100 metaphases of induced one. It is found that chromosomes of CP children are more radiosensitive than chromosomes of HP ones, the spontaneous frequency of chromosome aberrations being equal in both groups.     

Frequency of stable chromosomal aberrations determined by FISH in 49 Chernobyl nuclear accident liquidators exposed to various doses of radiation

FISH technique was tested on the 49 liquidators of the Chernobyl Accident. Groups were formed according to average group exposure doses and/or individual ones determined by the method of EPR. The essential variability of spontaneous and irradiation-induced frequencies of reciprocal translocations was observed. In groups with the lowest EPR-doses (below 25 cGy) the average cytogenetic dose was considerably higher then doses determined by EPR-method. The best coincidences between average in-group EPR- and FISH-doses were in the group with 25-50 cGy doses for "acute irradiation" model and in the group with 50-100 cGy and higher for "chronic irradiation" model.