The radioactive contamination dynamics of water body ecosystems of different types in the Chernobyl atomic station alienation zone in Belarus

The long-term (1986-2005) gamma-activity dynamics in dominating zoobenthos species and the bottom sediments in the inlet of Pripyat river and the non-flowing Perstok lake within the Chernobyl alienation zone was determined. Immediately after the accident (1986-1987) zoonehthos y-activity achieved the maximal values (up to 300-1100 kBq/kg) and after that began to decline steadily due to natural decay of man-caused radionuclides of "Chernobyl origin". Up to summer 2005 gastropod mollusks gamma-activity (Lymnaea stagnalis, Viviparus viviparus) approached to the natural level (less than 6 Bq/kg) in the inlet of Pripyat river, but it remained at the very high level up to 979-1638 Bq/kg in the Perstok lake. The positive correlation between gamma-activity of mollusks and bottom sediments has been established. In turn, the long-term variations of atmospheric precipitate amounts which wash down radionuclides from surrounding territories to water bodies and the amounts of annual flow of the Pripyat river as well as shoreline position changes in water bodies within the Chernobyl alienation zone influence on these values too.     

Participation of the lipid peroxidation processes in the adaptation mechanism of Muridae like rodents to the radioactive contamination of the Chernobyl NPP zone

Results of the comparative analysis of the complex investigation of rodent population state caught at areas with different levels of contamination in the accident zone of the Chernobyl NPP during 1986-1993 and 2007, at areas with a practically normal radiation background in the neighborhood of the Kiev City in 1993 and at areas with the normal and increased radiation background in Ukhta region of Komi Republic in 1993-2008 are presented. It is shown that the absence of the linear dependence in changes of the lipid peroxidation (LPO) regulatory system parameters in rodent tissues on the dose of the external gamma-radiation at areas of their trap persists for a long time. Different ability to normalization of the studied indices and nonlinearity of their dose dependences allow us to suggest that changes of the scale and direction of interrelations between the reciprocal parameters of the LPO regulatory system in norm in tissues of rodents which were caught in the accident zone and at areas with an increased radiation background should be the information signal determining selection of the strategy of adaptation to the chronic radiation factor action.     

Evaluation of the effect of the radioactive contamination of hydrobionts in the 30-kilometer control zone of the accident at the Chernobyl AES]

A study was made of hydrobionts, particularly fishes, living within the thirty-kilometer control zone of Chernobyl NPP and northern part of the Kiev basin, after the disaster. Out of 31 fish species living in the NPP cooling pond some were identified which were mostly affected by radioactive contamination. They were predators belonging, with respect to reproduction and development, to a lithophilous group. Peculiarities of reproduction of Hypophthalmichthys molitrix kept in stews of the cooling pond before the accident were studied. After a three-year exposure to ionizing radiation (cumulative dose of 8-9 Gy) no reduction in the reproductive capacity of mature fishes was observed.     

The possibility of using the preparation MIGI-K in districts exposed to radioactive contamination following the accident at the Chernobyl AES]

A preparation from mussels, MIGI-K, used as an additive to the diet of people working at the Chernobyl power plant has proved to be efficient in increasing the total resistance of the body, including the resistance to ionizing radiation. In experiments with animals, MIGI-K has been shown to accelerate excretion of 45Ca and 86Rb from the body. The combination of these properties of MIGI-K permits us to consider it an efficient drug to be used within the regions affected by the Chernobyl disaster.     

The role of small mammals and birds in transport of matter through the shore zone of lakes

An attempt was made to estimate the role of small mammals and birds in the cycling of nutrients in the littoral zone of lakes. We estimated the approximate amounts of food, organic matter and elements ingested and egested during the breeding season by waterfowl. Small mammal densities were estimated, and their movements studied between different patches of a mosaic landscape, including the lake's shore region. Studies on passerine birds were aimed at determining the territories of some species in alder forest. Special attention was paid to the range of penetration of the reed belts by forest species.     

The estimation of 90Sr and 137Cs excretion parameters from the organism of wild and laboratory small mammals in vivo, after natural contamination of them in the Chernobyl zone

In the course of laboratory experiment, parameters of 90Sr and 137Cs excretion were estimated in individuals of bank vole Clethrionomys glareolus, captured at one of the most contaminated sites of the Chernobyl zone. The animals were kept under laboratory conditions using "clean" feed during 50 days. The similar investigation was carried out with laboratory mice Mus musculus (Big Blue line) during a longer period (184 days). The measurements of 90Sr content in the animals' body were in vivo carried out, using a specially designed beta-spectrometer with appropriate software, and 137Cs one--by the gamma-spectrometer. During the experiment, the animals had lost less 0.4% of activity due to physical decay of radionuclides. The organism was depurated mainly through biological excretion. In accordance with parameters of one-component exponential decay equation, 99.3% of 137Cs initial content in vole was excreted with half-life period of 2.18 days, and mice--4.4 days (99%). 90Sr excretion had longer half-life period: 11.7 days (56%) in voles, and 49.9 days (87%) in laboratory mice. The rest radionuclides amount of given model was considered as non-excreted from the organism during the observation period. It was determined on the example of voles that 90Sr and 137Cs loss in males was faster than in females, and among females more intensive excretion was in lactating females. 137Cs excretion from the body of bank vole is mainly with urine (74.7%), whereas 90Sr one--with feces and urine in approximately equal amounts. Due to the birth of babies and consequent feeding female lose appreciably less amount of radionuclides body burden than at daily loss with urine and feces.     

Cytogenetic studies on submerged plants from the Yenisei River area in the zone of radioactive contamination

Cytogenetic studies on three species of submerged plants from different parts of the Yenisei River area subjected to radioactive impact of the Krasnoyarsk Mining-and-Chemical Plant and the Electrochemical Factory have been conducted. A high level of irregularities in ana-telophase and metaphase of mitoses has been revealed in test samples compared to the control: agglutination and fragmentation of chromosomes, lagging chromosomes, bridges, fragments, misdivisions, and others. The nature of the disorders indicates that they are related in part to the direct damage to the chromosome structure and in part to damage to the spindle.     

Thyroid cancer incidence among Chernobyl emergency workers: follow-up period 1986-2003

A vast amount of research articles devoted to the increase in childhood thyroid cancer incidence in the most contaminated by radionuclides territories of Belarus, Russia and Ukraine affected by the Chernobyl accident were published recent years. However, the amount of research studies of thyroid cancer incidence among the Chernobyl emergency workers (liquidators) is quite scanty. In the article results of the study of thyroid cancer incidence in the cohort of the Chernobyl liquidators (103427 persons) residing in 6 administrative regions of Russia (North-West, Volgo-Vyatsky, Central-Chernozemny, Povolzhsky, North-Caucasus and Urals) are described and discussed. For the period 1986-2003 eighty seven cases of thyroid cancer were detected in the cohort. Statistically significant excess of the incidence among liquidators over baseline incidence, SIR = 3.39 (95% CI: 2.73; 4.16), among men of Russia has been found. The highest thyroid cancer incidence (SIR = 6.49) was registered among liquidators who had been involved in mitigation works during April-July 1986. At the same time no statistically significant relationship between the incidence rate and external radiation dose, ERR = 1.68 (95% CI: -0.95; 6.46), was detected.     

Historical mutation rates predict susceptibility to radiation in Chernobyl birds

Extreme environmental perturbations are rare, but may have important evolutionary consequences. Responses to current perturbations may provide important information about the ability of living organisms to cope with similar conditions in the evolutionary past. Radioactive contamination from Chernobyl constitutes one such extreme perturbation, with significant but highly variable impact on local population density and mutation rates of different species of animals and plants. We explicitly tested the hypothesis that species with strong impacts of radiation on abundance were those with high rates of historical mutation accumulation as reflected by cytochrome b mitochondrial DNA base‐pair substitution rates during past environmental perturbations. Using a dataset of 32 species of birds, we show higher historical mitochondrial substitution rates in species with the strongest negative impact of local levels of radiation on local population density. These effects were robust to different estimates of impact of radiation on abundance, weighting of estimates of abundance by sample size, statistical control for similarity in the response among species because of common phylogenetic descent, and effects of population size and longevity. Therefore, species that respond strongly to the impact of radiation from Chernobyl are also the species that in the past have been most susceptible to factors that have caused high substitution rates in mitochondrial DNA.     

The demonstration of environmental radioactive contamination by its gametocidal action

Two Viola matutina Klok. populations growing in two areas of the thirty-kilometer zone of Chernobyl varying in gamma radiation background have been studied. Stable, repeated (during a period of 1987-1988) differences between the populations with respect to the amount of sterile pollen and the pattern of anther distribution curves have been revealed. It is suggested that the increased radiation loading is the cause of the increased occurrence of sterile pollen in one of the populations.     

The main radionuclides and dose formation in fish of the Chernobyl NPP exclusion zone

The results of the researches of spices-specificity, accumulation dynamics and distribution of 90Sr, of 137Cs and of transuranic elements in fish of the Chernobyl NPP exclusion zone are analysed. The data of estimations of absorbed doze rate from incorporated radionuclides for pray fish and predatory species are given. For the fish from the lake of the left-bank floodplain of the Pripyat River the increase of 90Sr specific activity is registered which is presumably connected with the dynamics of the physical-chemical forms of the radionuclide in soils and their wash out in water bodies from the catchment basin. Now about 90% of internal dose rate of fish from closed aquatic ecosystems within the Chernobyl NPP exclusion zone is caused by 90Sr incorporation.     

Antibmicrobial susceptibility of Serratia marcescens isolated from hospitalized patients in 2003 - 2005

500 strains of Serratia marcescens isolated in 2003-2005 were examined for drug susceptibility. By using several phenotypic methods it was shown that 67.6% of these strains produced ESBLs. Strains ESBL(-) and ESBL(+) were compared, paying special attention to their susceptibility to various antibiotics. It was revealed that strains ESBL(+) were much more resistant to majority of the investigated drugs. The biggest differences were in the case of amikacin and gentamicin, sensitive about 50% of ESBL(-) and 10% of ESBL(+), ciprofloxacin, sensitive 42% of ESBL(-) and 6.3% of ESBL(+) and trimethoprim/ sulphametoxazole, sensitive 45.8% of ESBL(-) and 9.4% of ESBL(+). Strains ESBL(-) retained a high susceptibility to ceftazidime (68.9%) and cefepime (71%). All strains ESBL(-) as well as ESBL(+) were susceptible to imipenem and meropenem. 78.9% of ESBL(-) and 67.3% of investigated ESBL(+) were susceptible to piperacillin/ tazobactam.     

Cytogenetic and population effects in oligochaeta from the Chernobyl zone

Research on intensity and character of reproduction of Oligochaeta (Dero obtusa, Nais pseudobtusa and Nais pardalis) was carried out in 1995-1996 in two water-bodies: a) in the Chernobyl NPP zone near Yanov Village, with a dose rate of 14 microGy h-1 on the surface of the bottom sediment; b) at the Uzh River area (the control water-body). The changes in both intensity and reproduction type were observed in worms at the radioactively polluted water-body. Stimulation of paratomic division in D. obtusa as well as activation of sexual reproduction in two other species were found out along with increasing of amount of cytogenetic damages in somatic cells.     

Species richness and abundance of forest birds in relation to radiation at Chernobyl

The effects of low-level radiation on the abundance of animals are poorly known, as are the effects on ecosystems and their functioning. Recent conclusions from the UN Chernobyl forum and reports in the popular media concerning the effects of radiation from Chernobyl on animals have left the impression that the Chernobyl exclusion zone is a thriving ecosystem, filled with an increasing number of rare species. Surprisingly, there are no standardized censuses of common animals in relation to radiation, leaving the question about the ecological effects of radiation unresolved. We conducted standardized point counts of breeding birds at forest sites around Chernobyl differing in level of background radiation by over three orders of magnitude. Species richness, abundance and population density of breeding birds decreased with increasing level of radiation, even after controlling statistically for the effects of potentially confounding factors such as soil type, habitat and height of the vegetation. This effect was differential for birds eating soil invertebrates living in the most contaminated top soil layer. These results imply that the ecological effects of Chernobyl on animals are considerably greater than previously assumed.     

Mitochondrial DNA heteroplasmy in laboratory mice experimentally enclosed in the radioactive Chernobyl environment

Mitochondrial DNA heteroplasmy using the protein-coding cytochrome b (Mtcyb) gene was assessed in laboratory mice (C57BL/6 and BALB/c) exposed to the Chernobyl environment. Subacute to subchronic (30-40 days) exposure resulted in a cumulative radiation dose of 1.2-1.6 Gy ( approximately 0.04 Gy/day). Mice were sampled prior to introduction into the enclosures and again after removal from the enclosures. Nucleotide variation (site heteroplasmy) in 306 pre-exposure Mtcyb gene copies (122400 base pairs) was compared to variation in 354 postexposure gene copies (141600 base pairs). Five mutant copies, each characterized by a single nucleotide substitution, were observed (four in the pre-exposure samples, one in a postexposure sample). The frequencies of mutant gene copies and nucleotide substitutions in pre-exposure and postexposure samples were not significantly different. This suggests that this type of exposure (i.e. low dose rate) does not pose a significant mutation risk to the Mtcyb gene in digit tissue. Furthermore, no significant radiation risk to analogous human tissues may exist when occupational exposures involve low dose rates such as these. Finally, linear, cumulative models of genetic risk currently used to estimate radiation-induced effects are likely to be inappropriate for low-dose-rate exposures and need to be re-evaluated critically.