brechignac_f_desmet_g_eds_equidosimetry_ecological_standardi

BEHAVIOR OF Cs-137 AND Sr-90 ON FISH PONDS IN UKRAINE

E.VOLKOVA, V. BELYAEV, Z. SHIROKAYA, V. KARAPYSH

Institute of Gidrobiology, NASU, 12, Prosp.Geroyiv Stalingrada, Kiev, 04210, UKRAINE

1.Introduction

Radiation monitoring and radioecological studies have also shown a high persistence of radionuclides in lakes located in a number of communities in the Ukraine[1, 2]. Contamination levels of fish in these lakes are very high and this pathway has become increasingly important in determining the overall dose to humans [3].

2.Results and discussion

The region incorporates several ponds and lakes, which are located within areas of different contamination intensities. Water bodies are distributed as follows: water bodies No. 1, 2 (Narodychi rayon)-the zone of obligatory evacuation, water bodies No. 5 (Dubrovizk rayon), 6 (Zarechensk rayon), 7 and 8 (Volodimerezk rayon), 10 (Rokitnyansk rayon) - the zone of optional evacuation, ; water body No. 3 (Ovruch rayon) - the zone of strict radiation control, water bodies 4 (Novograd-Volinsk rayon), 9 (Sarni rayon) - the clean zone.

137Cs levels in water bodies under study vary widely (more than 1 order of magnitude), however, the levels do not exceed contemporary permitted levels. 90Sr levels were found to be of more uniform pattern.

Levels of sediments-sorbed 137Cs and 90Sr were found to vary substantially - from 242 to 2470 Bq/kg and from 32 to 306 Bq/kg, respectively. At the same time there is no definite correlation between sediments' radionuclide levels and radionuclide levels in water. For example, the highest 137Cs level was registered in water body No. 7, while the highest level of specific radioactivity of sediments was registered in water body No.6. While analysing radionuclide distribution between soluble and sorbed forms, it is necessary to note, that 137Cs levels in water and 137Cs levels of sediments are almost equal (with some prevalence of soluble forms), while 90Sr is mainly represented by soluble forms (from 71 to 99%) of its overall concentrations in a water cross-section.

Bottom deposits are the prime radionuclide accumulators (this is especially true for 137Cs). Levels of bottom deposits' radioactive contamination depend on multiple factors, including, inter alia, types of bottom deposits, bottom shapes, currents, etc. (fig. 1). High water plants belong to the most important components of aquatic ecosystems (fig. 2). We selected the most common water plants for the study.

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In some cases, radionuclide contents in fish samples from the water bodies substantially exceeded permitted 137Cs levels in food products (approved by the Public Health Ministry of Ukraine). Moreover, these levels substantially differ from similar parameters, observed before the Chernobyl NPP accident.

3.Conclusion

It is necessary to note, that water bodies, affected by several radionuclide accumulation factors simultaneously, might become sources of human radionuclide consumption [4, 5]. Therefore, it is necessary to review permits for commercial/amateur fishing in every particular case.

4.References

1.E. N. Volkova, V.V.Beliayev, Z.O. Shyrokaya, N.L. Shevtsova, T.P. Prityka, V.A. Karapish. Particular feature of radioactive contamination of fish ponds of North part of Rivne region // Scientific papers of the Institute for nuclear research.-2001. – 3, N1. – P.156 – 160.

2.Belyaev V. Accumulation and elimination of Cesium-137 from the organism of hydrobionts : Summary of thesis for degree of Doctor of Philosophy by speciality 03.00.17 - hydrobiology. – Institute of Hydrobioljgy, National Academy of Sciences of Ukraine, Kyiv, 2001. – 18 p.

3.Modelling and study of the mechanisms of the transfer of radioactive material from terrestrial ecosistems to and in water bodies around Chernobyl, Final report EUR16529 en,1996.- 184 p.

4.Ye. N. Volkova, V.V.Beliayev, Z.O. Shyrokaya, V.G. Klenus, A.Ye. Kaglian, M.I. Kuzmenko, T.P. Prityka, V.A. Karapish. Radioactive contamination of water bodies of Ukrainian Polesye and forms of presence of radionuclides in some components of aquatic ecosistems // Hydrobiological Journal.- 2000. - 36, N4. – P.50 – 65.

5.Ye. N. Volkova, V.V.Beliayev, Z.O. Shyrokaya, T.P. Prityka, V.A. Karapish. 137Cs and 90Sr in water

bodies of Rivne region // International conference “Fifteen Years after the Chernobyl Accident. Le ssons Learned”. Abstracts proceeding. - Kyiv, 2001. – P. 2-79.

GENETIC EFFECTS OF CHRONIC GAMMA-IRRADIATION AT A LOW DOSE RATE:

EXPERIMENTAL STUDY ON CBA/LAC MICE

A.N. OSIPOV, A.L. ELAKOV, P.V. PUCHKOV, V.D. SYPIN

Moscow Scientific and Industrial Association “Radon”, 7th Rostovsky lane 2/14, Moscow, 119121, RUSSIA;

E-mail: aosipov@radon.ru

M.D. POMERANTSEVA, L.K. RAMAIYA, V.A. SHEVCHENKO

N.I. Vavilov Institute of General Genetics, Russian Academy of Sciences Gubkin str. 3, , Moscow, 119991, RUSSIA.

1. Introduction

In contrast to high doses of ionizing radiation, the negative effect of which is beyond doubt, the question of whether the action of low doses is harmful or useful remains open. As follows from literature data [1-3] and the results of our studies [4,5], low-dose ionizing radiation induces a complex of biochemical and biophysical reactions in the animals’ organism. However, it is not clear whether these changes are the result of adaptation of the organism to an increased radiation background and whether the action of low doses leads to significant genetic consequences.

In the present work we have studied the level of DNA strandbreaks in spleen lymphocytes, the percentage of normochromatic erythrocytes (NCE) with micronuclei (MN) in peripheral blood as well as the frequency of abnormal sperm heads (ASH) in mice exposed to continuous low dose-rate gamma-radiation.

2. Materials and methods

12-14 g CBA/lac mice (3-4 weeks old) purchased from Stolbovaya (Russian Academy of Medical Sciences) were used for this experiment. The animals were housed in plastic cages 7 days before irradiation. Food and sterile water were provided ad libitum. The control and experimental animals were maintained under identical conditions (20ρ2θɋ, 50ρ10% relative humidity, 12-hr light/dark cycle).

The mice were irradiated using a UOG-1 device (course Cs-137, dose rate 0.17 cGy/day) during 80, 120, 210 and 365 days. The dose-rate of radiation was controlled with a DRG-O1T radiometer (Russia). The irradiation was 24 h a day with a short break (10-15 min) to attend to the animals. The total dose received by the animals made up 13.6, 20.4, 35.7 and 63,5 cGy respectively. Dosimetry was performed using FLi detectors ɌLD-100 (Sweden) and DTG-4 (Russia). The measurements were made using RE-1 (RADOS, Finland) and DTF-01 (Russia) devices.

At the 80, 120, 210 and 365th day the animals were decapitated and the spleen and testes were removed. The suspension of spleen cells in PBS with 3 mM NaN3, and cooled to 4°ɋ, was filtered through a nylon net. The concentration of cells was counted in a Goryaev’s chamber.

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Alkaline single cell gel electrophoresis (comet assay) was carried out as described by Singh et al. [6]. According to this assay, the level of single-strand DNA breaks will be in direct proportion to the amount and migration distance of DNA after alkaline electrophoresis of single cells immobilized in agarose. The fluorescent dye Hoechst 33258 was used for DNA staining. The DNA comets were analyzed with a fluorescence microscope Lumam I-2 (LOMO, Russia). 100 comets for each slide were counted. Depending on an appearance of comets (i.e. tail length, head diameter and intensity), the comets were assigned to one of five classes from 0 to 4 (0 – undamaged, 4 – maximally damaged). This method of visual estimation was proposed by Collins et al. [7] and is considered to be suitable for studying DNA damage [8]. The results obtained with this method were confirmed with the help of a computer analytical system Kinetic Imaging, Liverpool, UK. The number of comets in each category was counted and an average index of DNA comets was calculated as

ACI= (0·n0 + 1·n1 + 2·n2 + 3·n3 + 4·n4)/Ȉ,

where n0 - n4 is the number of comets in categories 0–4 and Ȉ is the sum of all counted comets.

To study the induction of DNA damage in spleen lymphocytes by hydrogen peroxide the cell suspension in PBS (1x106 cells/ml) was incubated with 0.5 mM and 5 mM H2O2 for 30 min at 37°ɋ. The number of single-strand DNA breaks was determined using the fluorimetric assay of DNA unwinding [9]. According to this procedure, the increase of DNA breaks is estimated by the decrease of double-strand DNA fragments after controlled alkaline unwinding of DNA of the analyzed cells.

The frequency of peripheral blood NCE with MN was counted by the conventional procedure [10]. 2000 NCE were analyzed for each animal.

The ASH frequency was analyzed on epididymis smears [11]. 200 to 500 spermatozoa were counted from each male. Statistical processing of the results of measurements was performed using Student’s t-test. The samples from each animal were treated separately. Data are presented as the mean ρ standard error.

3. Results and discussion

The level of single-strand DNA breaks (SSB) was estimated by the fluorimetric assay of DNA unwinding (FADU) and alkaline single cell gel electrophoresis (comet assay). It was found that beginning from the 120th day of the experiment a significant (ɪ<0,05) increase was observed in the number of SSB registered by the comet assay but not by the FADU (Table 1). This fact is further proof of a higher sensitivity of the comet assay as compared to the FADU. So, in accordance with Singh et al., the lower limit of sensitivity of a standard modification of the comet assay is α 3 cGy for acute irradiation (α 30 SSB per nucleus) [12]. In addition to a high sensitivity, this method makes it possible to estimate the distribution of the total cell population by the level of DNA damage.

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Figure 1 shows the distribution of the cell population by the level of DNA damage. It is seen that at the 80th day of exposure a shift for one category is observed in the distribution of spleen lymphocytes in the direction of increasing number of cells with an elevated level of DNA strandbreaks. At the 120 and 210th days of the experiment subpopulations of cells with a high level of DNA damage and apoptotic cells were registered, but their number was insignificant (~2-4 %). Thus, the results obtained indicate that a long-term low dose-rate irradiation induces an increase in the general level of DNA breaks.

It is known that in normally functioning mammalian cells there is always a background level of DNA breaks present. These breaks are always divided in two classes:

-breaks, formed upon DNA damage by free radicals resulting from cell oxygen metabolism;

-breaks, formed in the course of chromatin functioning. This group includes breaks of enzymatic nature necessary for the processes of replication, repair, transcription, condensation, decondensation of chromatin, etc.

Mammalian cells have defense mechanisms of neutralization of free radicals in which such enzymes as superoxide dismutase, catalase, glutathion peroxidase, etc. (enzymatic defence systems) and such antioxidants as vitamin E, glutathione, taurine etc. (non-enzymatic defence systems) are involved. The heterogeneity in the distribution of DNA breaks observed in our work could suggest the exhaustion of the defense

antioxidant mechanisms of cells protecting from the damaging action of low levels of “by-products” of normal oxygen metabolism (O2-, OH•, H2O2, etc.).

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Fig. 1. The distribution of lymphocytes by the level of single-strand DNA breaks obtained in the course of analysis of alkaline DNA comets of spleen lymphocytes of mice exposed to continuous low dose-rate gamma-radiation.

To determine the antioxidant status of spleen lymphocytes of irradiated mice, we studied the indication of DNA damage in these cells by hydrogen peroxide. Hydrogen peroxide is a product of normal cell metabolism which in the presence of metal ions of variable valence (mainly Fe2+) leads to the formation of a highly toxic hydroxyl radical.

A slight increase of sensitivity of spleen lymphocytes of irradiated mice to hydrogen peroxide was noted on the 80th day of the experiment (Fig. 2). This fact can be explained by the exhaustion of the antioxidant potential of the cells. Continuation of irradiation of the animals probably leads to the activation of the defence systems of spleen lymphocytes, which is expressed as a decrease of their sensitivity to the action of H2O2 at the 120 and 210th days of the experiment. This effect can be due to the development of adaptation processes with the accumulation of a certain dose.