XA9745822 RADIOECOLOGY OF THE VARDAR RIVER CATCHMENT AREA AFTER THE CHERNOBYL RELEASE

L. CVETANOVSKA Center for Application of Radioisotopes in Science and Industry "Skopje", Skopje, FYR of Macedonia

T. ANOVSKI University "St. Kiril and Metodij", Skopje, FYR of Macedonia

1. INTRODUCTION

Vardar river with its length of 301.6 km and its catchment area of 28,338 km^ covers almost 80% of the territory of the Republic of Macedonia Various usage of the surface and underground water flows of this hydro system (water supply, irrigation, etc.) to which gravitate cca 2/3 of the population of our Country, are subject of increased interest for their protection. In this sense, radioecological investigations (due to a presence of a local not well prospected uranium deposits and a factory for phosphate fertilisers) were in progressfl]. Immediately, after the first information for me Chernobyl disaster from the 26th of April, 1986, as a result of the accident at the Chernobyl Nuclear Power Plant, and the registered increased level of radioactive contamination of the environment of our Country, our research work as well as the activity in the Republical Institute for Occupational Hygiene and in the Institute for Veterinary, both, also from Skopje, have been intensified As a result of unusual high amount of precipitation, in May 1986, the contamination of the whole country was expected to be increased, and this fact was confirmed later on. According to this, appropriate recomendaiions and activities to the population were suggested, as well as adequate protective measures have been taken. The fi/st preliminary results of performed gamma-spectrometric analysis showed that besides many others, the following isotopes: 1-131,1-132, Cs-134, Cs-137 and Ru- 103, dominated into the investigated water, air and food samples[2]. Different from the concentration of 1-131 into the filtered Skopje air which was 12 Bo/m^ on the 5th of May, 1986, the concentration of Cs-137 was up to 15 Bq/m^ in air, 122 Bq/L in local precipitation, up to 800 Bq/kg in sediments and 0.29 Bq/L in the water samples from the Vardar river. During the realization of the planned investigations, following the Chernobyl accident, which were more or less systematic, valuable data for the distribution of individual isotopes within the Vardar river system , determining the level of radioactive contamination of different water, food, soil and other samples, have been collected On me basis of the obtained results, calculations for the Chernobyl disaster contribution to the effective equivalent dose for adults for the year 1986 and 1989-1992 period were performed

Financial support was provided by the Fund for Science and Technology of the Republic of Macedonia

138 2. RESULTS AND DISCUSSION

As a result of unusual high amount of precipitation, in May 1986 in some regions even more than 100 L/m^, the radioactive contamination of the whole country caused by the Chernobyl disaster, was increased The concentration of 1-131 and Cs-137 in various samples of milk during May, 1986, was in the range of 100-5000 Bq/L and 100-500 Bq/L, respectively. Certain results received by the performed systematic radioecological investigations, related with the determination of the distribution of various observed radionuclides in different environmental samples, for the period following the Chernobyl disaster, as average concentrations for the covered period are presented in Table I and Fig.1,

TABLE L DISTRIBUTION OF CERTAIN OBSERVED RADIONUCLIDES IN VARIOUS SAMPLES FROM THE CENTRAL PART OF THE VARDAR RIVER CATCHMENT AREA

Investigated Period Average cone. of observed radionuclides in Bq/kg or L sample Month/year Ru-103 Cs-134 Cs-137 1-131

May/-86 120+-14 70+-11 220+-16 84+-12 Dec/"86 / 69+-9 166+-11 / Uncultivated "87 / 76+-10 131+-11 / soil '89 / / 40+-5 / '90 / / 10+-3 / '91 1 1 15+-3 1

May/>86 174+-16 120+-20 221+-26 271+-8 Grasse '87 <10"2 19+-2 3S+-3 <10"2 '89 / / 20+-2 / '91 1 1 12+-2 1

May/"86 125+-17 122+-6 133+-8 197+-20 Milk •89 / / <1 / '90 / / <1 / '91 1 '

139 Bq/kgorL

100 T !Cs-137 in Vardar r. 90 in B q/b<1 00 80 H !C$-137inVardar river sediments in 70 Bq/kg 60 SO

40 hr'-T, 30 ".it 20 : rr-r 10 0 I 1986 1987 1988 1989 1990 1994

y ear of observation

FIG. 1. Cs-137 concentration in sediments and water samples from the Vardar river in Bq/kg or L for the period after the Chernobyl disaster

It is evident, that in the beginning the spectrum of the registered radiomiclides was larger. 1-131 and Ru-103 were between the first radioisotopes which disappeared within the few months after the accident As, by the end of 1986, Cs-137 was (due to its long half life) the dominant isotope into the investigated environmental samples within the Vardar river hydro system, in our further research work we pay to it a special attention. At present, as it can be seen from the Fig. 1, the concentration of Cs-137 in the water and sediment samples from the Vardar river are reduced to 0.045 Bq/L and 30 Bq/kg, respectively. Although, many other radionuclides migrate slowly into soil profile depths and as rule they are located in a soil layer with thickness up to 10 cm, the presence of Cs-137 in concentration range 30-60 Bq/kg in first 20 cm of uncultivated and 40 cm of cultivated soil sampels is registered up to present days. TTiis is in agreement with the experience, that the more distant from the Chernobyl Nuclear Power Plant, the greater is the share of mobile forms of Caesium in soils, recived by the scientists in the Republic of Belarus[3]. Thus, the radionuclides penetrated into the soil and involved in the migration processes will be present in the biological chain "soil-plant-animal-man" for a long time.

140 3. MODELLING

On the basis of the results obtained by the performed radioecological investigations of the Vardar river system and taking into the consideration many other relevant parameters, calculations for determination of the Chernobyl disaster contribution to the effective equivalent dose for adults for the year 1986 and 1989-1992 period, were done and respective values of 1.50 and 0.02 mSv/y were received By using of adequate mathematical model[4-7], evaluation of the effective equivalent dose to be received by the local population , due to me possible usage of contaminated river water for bom, irrigation and for water supply, was performed and values in good agreement with the previous, obtained on the basis of the field measurements, were received.

4. CONCLUSIONS

Apart from the obtained results throughout the performed radioecological investigations, in the period after the Chernobyl accident from one side and the applied technique of data evaluation, from the other, the following conclusions can be drown, - Period after the Chernobyl disaster, i.e. after me 26 of May '86, was characterized with an increased level of environmental radioactive contamination of our country. According to the radioactivity level in different samples and locality, appropriate recomendations and measures have been taken. - Correlation between the radioactivity of soil and grasse sampes, from one side and these in milk and meat samples, from the other, is evident, enabling us to use it successfully in evaluation the prediction of the efective equivalent dose to be received with time, by the local population. - Applied model for the evaluation of the effective equivalent dose for the local population, to be received due to the possible usage of river vater for both, irrigation and water supply, showed good agreement with the calculations based on the field measurements. - The contribution of Chernobyl disaster to the effective equivalent dose to the local population, at present days is very low, approaching the contamination level before the accident

REFERENCES

[ 1 ] ANOVSKI, T., et al. , "Detemination of Biogeochemical and Radioecological Characteristics of the Vardar River System", IAEA-TECDOC-229, Vienna (i 980).

[2] ANOVSKI, T., .NKOLOVSKA, L, NEDELKOVSKI, D., ADAMOV, M., "Increased Radioactive Contamination of the Environment in Republic of Macedonia as a Result of Chernobyl Accident", Proc. of the H Yugoslav Conference on Assessement of the Radiation Risk Due to the Present Radiation into the Environment/in Macedinian/, Kragujevac, 6-8 October (1986).

[3 j The Chernobyl disaster, its consequences and ways of overcoming in Belarus, The Chernobyl State Committee of The Republic Belarus, The National Report( 1993).

141 [4] ANOVSKI, X, Application of Isotope Technique in Pollution Study of Watter Flows, PhD Thesis, Faculty of Technology and Metallurgy, Univ.'Sv.Kiril AMetodij", Skopje(19S4).

[5] Algemine Verechungrundlagen fur die Bestimung der Strahlen exposition durch Radioactive einleitungen in oberflashangewaser, Der Bundesminuster der Innem, FR of Germany (1976).

[6] ANOVSKI, X, HADZIEVSKI, LJ., KACURKOV, D., MINCEVA, B., LELJFANOVA, L,, "Model for Assessement of Internal Exposure of the Man Due to the Usage of Contaminated Water Flows", XQI Yugoslav Symp.on Radiation Protection, Pula, 10-13. June(1985).

[7] HADZIEVSKI, LJ., ANOVSKLT..KACTJRKOV.D., MINCEVA, B..ANDONOVSKLB., NIKOLOVSKA, L., "Application of Computers in Evaluating the Distribution of Radionuclides Released into Surface Waters", Acta PhysicaHungarica, Vol.59, No: 1 -2 (1986)

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