SYNOPSIS

Ecogenetic analysis of long-term after-effects of the Totsky nuclear explosion in 1954 in Orenburg region, Russia (facts, models, hypotheses) / A.G. Vasil'ev, V.M. Boev, E.A. Gileva et al./. - Yekaterinburg: "Yekaterinburg", 1997. 192 p.

ISBN 5-88464-051-X

Editor: A.G. Vasil'ev, Dr.Sc. (Biology); Reviewer: O.A. Zhigalsky, Dr.Sc. (Biology)

The book contains total results of studies of the large author group about long-term after-effects of the Totsky nuclear explosion (TNE) which took place on September 14, 1954 in the Orenburg region (Russia). 45 thousand persons were present on the Totsky military range (TMR) during military trainings (TMT) at the moment of A-explosion and the aborigines were evacuated in minimal extent. At present 31.3 % of the former participants of the TMT are officially recognized as the invalids. Many of them suffer from malignant tumours or illnesses of blood with early development of complicated atherosclerosis.

The book's authors carried out complex study of natural environment in areas suffered from the TNE by means of radiochemical, radioecological, cytogenetic, phenogenetic and medico-ecological methods.

Radioecological study of terrestrial and aquatic ecosystems shows that at present the radioecological situation in the region is close to normal, however in separate areas in a zone of potential influence of the TNE an increase of the contents of ¹³⁷Cs and ^239,240Pu in soil is found. ¹³⁷Cs contamination density of sites of soil and vegetation cover near all examined localities is 1.5 - 3 times greater than global level. Pu-isotope concentration in a superficial turf layer of soil varies within interval 4.1-82.6 Bq/kg and the respective values of contamination density of this layer vary from 42 to 5284 Bq/m². According to reconnaissance data the contents of Pu in a soil-vegetation cover in examined territory of the Orenburg region is 1.5 - 5 times greater than global level and fits in limits of values marked for localities situated at a distance of 3-500 km from Chernobyl accident zone and sometimes increases these values too.

Populations of indicator species (the bank vole - Clethrionomys glareolus Schreb., the house mouse - Mus musculus L., the east-european vole - Microtus rossiaemeridionalis Ognev) inhabiting zone of potential influence of the TNE and outside of it were used as an ecotoxicological models for study of probable long-term after-effects of the TNE.

Two species of rodents inhabiting near TMR display the increased frequency of chromosomal damages in metaphases cells of bone marrow. In the synanthropic house mouse the frequency of structural chromosomal aberrations is 1.7-2 times larger than in the control group and in the east-european vole - 8-15 times respectively. In the house mouse population located along the axial part of the Totsky radioactive trace (TRAT) specific cytogenetic markers of the ionizing radiation influence (stable and unstable aberrations of the chromosomal type) are revealed. At the same time in the East-european vole population located outside of the TRAT heritable genome changes are shown. These facts indicate the influence of some mutagenic factors on the previous generations of the rodents. Some facts point out to existence in the impact areas of system of heritable genetical instability which was revealed earlier in the common vole (Microtus arvalis Pall.) on the territory contacting with the East-Ural radioactive trace (EURT) in the Chelyabinsk region. When extrapolating these results on human population it seems rather probable the occurrence of the similar system of heritable genetic instability both in people. This is agree with data of cytogenetic analysis of people from the impact areas, for example with sharp increase of unstable chromosomal aberrations in children of 9-15 years old (the generations of "grandsons" of eye-witnesses).

The authors suggest that people from examined localities near TMR are exposed to the high genetical risk which at least partly is connected with ionizing radiation influence in the past and may be at present.

Phenogenetic analysis of populations of radiophore-species (the bank vole) displays the unusual for Ural populations high concentration of serious innate anomalies in the skull structure of mutational and teratogenic origin and also many less significant malformations of the normal process of individual development. These facts are considered as long-term radiation-induced stochastic effects which according to recommendations of ICRP (International Committee of Radiation Protection) can be referenced to multifactorial category. The possible initial influence of the TRAT on formation of the anomalies of development is indirectly confirmed by significantly higher contents of the ?-active substances in ashes rests of bone and mussel tissues of rodents in populations from the impact zone (the axial part of the TRAT). In the Totskoe population of the bank vole which was the first experiencing the direct effect of the TNR some typical abnormalities in palatine bone structure marking a delay of ossification process are revealed. Similar abnormalities were found in the population of the red vole (Clethrionomys rutilus Pall.) in the EURT zone in the Sverdlovsk region. From 1982 to 1996 significant increase of frequency of this type abnormalities is revealed in Totskoe population of the bank vole. In 1997 60 % individuals captured in the epicentral zone of the TNE display this anomaly of development. It is almost on the order more than in populations of the bank vole located outside of the TRAT. A spectrum of unique serious abnormalities which is found in the control sample is not less than in the impact ones. So, this suggests that the TNE affected not only the narrow strip of territory along the TRAT, but also wider contacting zone.

Based on results of the prior study we can conclude that in the suffered districts of the Orenburg region (Krasnogvardeisky and Totsky) characters of long-term ecogenetical after-effects on population level are revealed which are probably connected with the TNE in 1954. Carefully extrapolating all these data on people one can reach the following conclusions: prolongated residing of people at the territories even with rather low levels of radionuclide contamination can result in accumulation of genetically caused minor morphological uglinesses and morphogenetic aberrations and an increase of their number in the subsequent generations of people. However, the absence of strong press of natural selection in human population (for the known reasons) would not result in adaptive genetic changes in the direction of radioresistance increase contrary to populations of the model rodent species where this press is enough strong (Ilienko, Krapivko, 1993). Received materials allow the authors to assume reasonably that prolongated radiation in low doses can result in the long-term after-effects expressed as disturbances of processes of individual development not only in the model indicator species but also in people too. These effects are expressed as heritable decrease of general resistance to illnesses, increase of level of total sickness rate and number of innate morphological uglinesses in the impact zones.

Serious confirmation of the made prognosis is a modern condition of children health in the impact areas of the Orenburg region. V.M. Boev with colleagues found the increase of illness rate of newborns: the increase of innate anomalies in 1.6 times, innate pneumonies in 2.3 times, intrauterine hypoxies and asphixia in delivery in 2.9 times. The innate anomalies make up 22.1 % in structure of the newborn mortality. The authors note enough high level of general mortality of people which is higher than that in rural population of the Orenburg region and Russian Federation as a whole. At the same time the mortality of people from neoplasms increases from 1960 to 1994 in 2.3 times (the rate of growth make up 129.2 %). In the impact areas the level of people mortality is higher than in rural population in the Orenburg region as a whole. Cytogenetic study of people in the impact areas displays the increase of the frequency of exchanges of chromosomal type in persons inhabiting the epicentral zone of TNE in comparison with the control ones. The frequency of unstable chromosomal aberrations (circular chromosomes) in examined children group ("grandsons" of eye-witnesses of TNE) is 3 times higher than in the parent generation and in the eye-witnesses with the persons of the same age. Therefore it becomes clear that ecogenetic prognosis of long-term after-effects of the TNE based on study of the model rodent species unfortunately begins to be realized in the human population.

Reconnaissance data about individual absorbed doses of radiation in aborigines-eye-witnesses of the TNE by means of EPR dozimetry method on tooth enamel are received (the maximal individual absorbed dose make up 3 Gy). These facts demand to consider the probability of the occurence of heritable genetic instability system (according to hypothesis of E.A.Gileva) in offsprings of eye-witnesses of TNE and inhabitants of TRAT zone more seriously and result in a necessity to continue the ecological and genetical study of Totsky problem.