ESTIMATION AND PREDICTION OF 90 Sr AND 137 Cs RADIOACTIVE POLLUTION OF THE MEDITERRANEAN BASIN FROM THE BLACK SEA AFTER THE CHERNOBYL NPP ACCIDENT

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1 ESTIMATION AND PREDICTION OF 9 Sr AND 137 Cs RADIOACTIVE POLLUTION OF THE MEDITERRANEAN BASIN FROM THE BLACK SEA AFTER THE CHERNOBYL NPP ACCIDENT V.N. EGOROV, G.G. POLIKARPOV, N.A. STOKOZOV, N.YU. MIRZOYEVA The A.O. Kovalevsky Institute of Biology of the Southern Seas (IBSS), National Academy of Sciences (NAS) of Ukraine, Nakhimova Pr., 2, Sevastopol UA-9911, Crimea, UKRAINE; Phone: ; viktor@egorov.sebastopol.ua The work presents of estimation of the 9 Sr and 137 Cs inputs from the Black Sea to the Mediterranean Basin through the Bosporus Strait after the Chernobyl NPP accident. It is obtained that the 9 Sr and 137 Cs fluxes from the Black Sea to the Sea of Marmara decreased with an effective exponential half-lives (T 5 ) 9.5 years and 6.4 years, respectively. The estimations have shown that 11.2 TBq 9 Sr and 25.4 TBq 137 Cs in has delivered from the Black Sea to Mediterranean Basin after the Chernobyl NPP accident. The radioactive pollution of the Mediterranean Basin will continue during 5 half-lives, i.e years to 9 Sr and 32 years to 137 Cs. The total 9 Sr and 137 Cs inputs from the Black Sea to the Mediterranean Basin have been estimated as TBq and TBq, respectively. INTRODUCTION After the Chernobyl NPP accident, about PBq of 9 Sr and 37-1 PBq of 137 Cs were released to the environment. In May 1986 the atmospheric fallouts after the Chernobyl NPP accident were the main source of the 137 Cs input in the Black Sea. The atmospheric fallouts of 9 Sr and 137 Cs over the Black Sea were 1-3 TBq and TBq, respectively. The 9 Sr input to the Black Sea was caused by the atmospheric fallouts as well as with the Dnieper River (57.8 TBq) and the Danube River (32.8 TBq) runoff during the following years [1, 9]. The investigations are devoted to assessment of discharge fluxes of 9 Sr and 137 Cs from the Black Sea into the Mediterranean via the Bosporus Strait after the Chernobyl NPP accident. The results of determinations of the long-lived radionuclides ( 9 Sr and 137 Cs) contents in water at the layer of -5 m as well as assessments of the water fluxes from the Black Sea into the Sea of Marmora via the Bosporus Strait were used for calculations of the fluxes. MATERIAL AND METHODS Published data [1, 9] as well as the results of investigations at IBSS were utilized for assessment of radioactive pollution of the Black Sea. The collection of the IBSS data [3-7] were carried out in aboard of oceanographic vessels under support of National programs of Ukraine, EU programs EROS- and EROS-21, IAEA projects NR 74 RB and RER/2/3, and in collaboration with WHOI and EPA (USA). Intercomparison of 9 Sr and 137 Cs radioactivity measurements in water were fulfilled jointly with WHOI, RISO National Laboratory (Denmark), and by support of IAEA with profile laboratories of Bulgaria, Georgia, Romania, Russia and Turkey. Current intensity via the Bosporus Strait was assessed with account of water balance of the Black Sea and according to data of the Ukrainian Research Hydrometeorological Institute [1] with help of mathematical model of the water, salt and radioisotope balance of Black sea with annual averaged parameters [2].

2 RESULTS AND DISCUSSION The modern estimations [2] of water exchange between the Black Sea and the Mediterranean Basin via Bosporus Strait is based on results of Upper and Low Bosporus Currents investigations. Upper Bosporus Current passes low-salinity waters (18 / ) from the Black Sea to the Sea of Marmara, and Low Bosporus Current passes to the Black Sea high-salinity waters (35 / ), which are penetrated to the Black Sea water column into subsurface layers. Moreover the Upper Bosporus Current delivered to the Sea of Marmara high-radioactivity waters of the Black Sea -5 м layer. The investigations have shown that the Upper and Low Bosporus Currents discharges is ruled by seasonal changes of the Black Sea water balance. The [8] investigations have shown that sea level of the Black Sea has a maximum in May and minimum in October. Long-term investigations have been discovered annual increasing of Black sea level in order mm per year, which is agreement with general tendency to the World Ocean. The components of the Black Sea water balance (the data were obtained by Ukrainian Hydrometeorology Service from 1923) [1] are shown in Fig. 1. During investigation period the increasing of evaporation has been observed as a result of climatic changes. The annual water flux from the Azov Sea to the Black Sea has decreased due to increasing of water scoop from the Don and Kuban Rivers. At the same time, rivers runoff, outflow the Black Sea water to the Azov Sea, as well as the total water balance of the Black Sea have not changed. The water balance changes have been compensated by increasing of Upper Bosporus Current and decreasing of Low Bosporus Current. The relationship between Upper and Low Bosporus Currents discharges and total annual the Black Sea runoff are shown in Fig. 2 (the data were obtained by Ukrainian Hydrometeorological Service [1]. Fig. 2 show that the dependence between the Bosporus Currents and total annual rivers discharges can be described by liner functions. It allows to estimate annual Upper Bosporus Current discharge with a help annual river discharge data. The observations have shown, that during the first year after the Chernobyl NPP accident the 9 Sr and 137 Cs distribution in the Black Sea surface water was extremely non homogeneously due to non-uniformly of atmospheric fallouts [1, 7, 9]. Further, the more uniformly radionuclides distribution was observed as a result of physical water mixing processes. The 9 Sr and 137 Cs distribution in surface mixed layer of the Black Sea in are shown in Fig. 3. Vertical 9 Sr and 137 Cs distribution in center of the Black Sea Western cyclonic gyre (Fig. 4-5) have shown that up to 1987 quasi-uniformly distribution of these radionuclides in -5 m layer has been observed. In the subsequent period the gradients concentration of 9 Sr and 137 Cs within -5 m layer were inappreciable. It has allowed to calculate the annual radionuclides concentrations in water of the Upper Bosporus Current. Results of the calculations of radionuclides fluxes transferred out from the Black Sea via Bosporus Strait are shown in Table 1. Change of the flux of radionuclides migrated out of the Black Sea is illustrated by Fig. 6. The figure is shown, that in case of data presentation in logarithmic scale for ordinates axis, points can be approximated by direct line. For 9 Sr data a factor of determination (r 2 ) was estimated as.836 and for 137 Cs as.874. From these data it follows, that regularities of change of radionuclides transfer fluxes with a sufficient degree of adequacy are described by exponential function. This function can be used for predication estimations. It is obvious, that integration of these functions will allow to estimate total fluxes of radionuclides from the Black Sea to the seas of the Mediterranean Basin for the time intervals within the limits of integration.

3 Water balance River discharge Evaporations Precipitations Upper Bosporus current Lower Bosporus current Inflow from Sea of Azov 4 Inflow to Sea of Azov Years Fig. 1. The component of the Black Sea water balance.

4 6 Upper Bosporus current 4 Lower Bosporus current River discharge ( per year) Fig. 2. The relationship between Upper and Low Bosporus Current discharges and total annual the Black Sea runoff. According to ours data, the total fluxes for 9 Sr (Q 1 ) and 137 Cs (Q 2 ) are estimated as: Where, t time (year). b Q 1 = exp ( t ) dt, (1) a b Q 2 = 34.6 exp ( t ) dt, (2) a

5 47 46 a b Fig. 3. The 9 Sr (a) and 137 Cs (b) distributions in surface mixed layer of the Black Sea in 1998-

6 9 Sr, Bq m Depth, m Fig. 4. Vertical distributions of the 9 Sr in the Western Black Sea Central Basin in the period (circles and medium dashed line), them approximations (solid lines) and level of 9 Sr concentration in the -5 m layer before Chernobyl NPP accident (short dashed lines) 137 Cs, Bq m Depth, m Fig. 5. Vertical distributions of the 137 Cs in the Western Black Sea Central Basin in period (circles), them approximations (solid lines) and level of 137 Cs concentration in the - m layer before Chernobyl NPP accident (dashed lines)

7 Table 1. Assessments of the 9 Sr and 137 Cs fluxes from the Black Sea via Bosporus Strait after the Chernobyl NPP accident Years Upper Bosporus Strait flux - water outflow from the Black Sea to the Sea of Marmara (km 3. year -1 ) Average conc. in water layer -5 m +/- 1σ n (Bq m -3 ) 9 Sr Flux from the Black Sea via Bosporus Strait (TBq y -1 ) Average conc. in water layer -5 m +/- 1σ n (Bq m -3 ) 137 Cs Flux from the Black Sea via Bosporus Strait (TBq y -1 ) / / / / / / / / / / / / / / / / / / ТBq 2 r =.874 T = 6.4 y 5, Cs 2 r =.836 T = 9.5 y 5,1 9 Sr Years Fig. 6. Change of 9 Sr ( + ) and 137 Cs ( ) outflows from the Black Sea via Bosporus Strait

8 It is obtained by integration of equations (1) and (2) for the period , that the 9 Sr outflow via Bosporus Strait is estimated as 126. TBq, and 137 Cs TBq during 18 years. Calculations have shown, that the half-lives for the 9 Sr flow (T 5,1 =.693/.723) occurs in 9.5 years, and 137 Cs ((T 5,2 =.693/.175) - in 6.4 years. It is widely accepted, the dynamic process is considered to be completed in 5 periods of flow half-lives. Thus, as qualitative prediction of estimations it is possible to conclude that radioactive pollution of the Mediterranean Basin by 9 Sr will proceed still about 47 years, and 137 Cs - 32 years. By integrating of equation (1) on scale of 47 years and equation (2) on scale 32 years we are obtained that total outflow of 9 Sr in the seas of the Mediterranean Basin will achieve TBq, that will be % of the shortterm fallouts of this radioisotope on the Black Sea surface after the Chernobyl NPP accident. Total flux of 137 Cs release into the Mediterranean during 32 year is assessed as equaled to TBq, or % of its atmospheric fallouts on the Black Sea surface in 1986 after the Chernobyl NPP accident. References 1. K.O. Buesseler, H.D. Livingston. Time-series profiles of 134 Cs, 137 Cs and 9 Sr in the Black Sea. In Sensitivity to change: Black Sea, Baltic Sea and North Sea. Eds. Ozsoy, E. and Mikaelyan A. Dordrecht: Kluwer Academic. P (1997). 2. V.N. Egorov, G.G. Polikarpov, L.G. Kulebakina, N.A. Stokozov and D.B. Yevtushenko. Model of large-scale contamination of the Black Sea with the long-lived radionuclides 137 Cs and 9 Sr resulting from the Chernobyl NPP accident. Water Resources, 2 (3), P (1993). (in Russian). 3. V.N. Egorov, G.G. Polikarpov, N.A. Stokozov, L.G. Kylebakina, G.E. Lazorenko. Distribution of artificial radionuclides in water, bottom sediments and hydrobionts of the Black Sea following the Chernobyl NPP accident and assessment of 137 Cs input to the seas of the Mediterranean basin through the Bosporus. // European Сomission Radiation Protection 7: The radiological Expo-sure of the population of the European Community to radioactivity in the Mediterranean Sea. MARINA-MED project. Proc.of a seminar held in Rome Nuclear Energy Agency headquarters from 17 to 19 May P (1994). 4. V.N. Egorov, G.G. Polikarpov, N.A. Stokozov, L.G. Kulebakina, N.Yu. Mirzoyeva. Some data of the fate of 9 Sr in the aquatic system, including the region of Chernobyl NPP accident, the Black Sea and the Aegean Sea.// see publication 5. P (1994). 5. V.N. Egorov, P.P. Povinec, G.G. Polikarpov, N.A. Stokozov, S.B. Gulin, L.G. Kulebakina and I. Osvath. 9 Sr and 137 Cs in the Black Sea after the Chernobyl NPP accident: inventories, balance and tracer applications. J. of Environ. Radioactivity. 49 (3), P (1999). 6. Egorov V.N., Polikarpov G.G., Stokozov N.A., Gulin S.B., Mirzoyeva N.Yu. Assessment of the Black Sea response time-scale to pollution with 9 Sr and 137 Cs following the Chernobyl NPP accident. 36- th CIESM Congress Proceeding, Monte-Carlo. 36, - P (1). 7. G.G. Polikarpov, L.G. Kulebakina, V.I. Timoshchuk and N.A. Stokozov. 9 Sr and 137 Cs in surface waters of the Dnieper River, the Black Sea and the Aegean Sea in 1987 and J. Environ. Radioactivity, 13 (1), P (1991). 8. Practical Ecology of the Sea Regions. The Black Sea. Kiev: Naukova Dumka. 245 p. (199) (in Russian). 9. A.I. Nikitin, V.I. Medinets, V.B. Chumichev, V. M. Katrich, S.M. Vakulovsky, A.I. Kozlov and V.I. Lepeshkin. Radioactive contamination of the Black Sea in consequence of the Chernobyl NPP accident, as measured in October Atomic Energy, 65 (2), P (1988). (in Russian). 1. O.V. Voitsekhovitch, V.V. Kanivets, B.F. Kristhuk et al. Project RER/2/3 Status Report of the Ukrainian Research Hydrometeorological Institute for p. (1998).