Journal of Radioanalytical and Nuclear Chemistry, Vol. 260, No. 3 (2004) 503508 02365731/2004/USD 20.00 AkadØmiai Kiad, Budapest ' 2004 AkadØmiai Kiad, Budapest Kluwer Academic Publishers, Dordrecht Activity concentrations of selected artificial and natural radionuclides in water and sediment samples from the North Western Black Sea, 1999 D. C. Breban,* N. Paunescu, J. Moreno-Bermudez,** R. Margineanu National Institute for Physics and Nuclear Engineering, IFIN-HH, P.O. Box MG-6, Bucharest, Romania (Received June 16, 2003) Radioactive concentrations of several artificial and natural radionuclides were determined in water and sediment samples collected from various locations in the NW Black Sea in December 1999. For water samples, 90 Sr and 137 Cs activity concentrations were of approximately 11 mBq/l and 26.341.2 mBq/l, respectively. The concentration of tritium ranged from 7 to 24 T.U. In sediment samples, maximum concentrations of 137 Cs, 239+240 Pu and 241 Am were found of 128–6 Bq . kg 1 , 1.8–0.1 Bq . kg 1 and 0.05–0.04 Bq . kg 1 , respectively. For U and Th radionuclides, the concentrations ranged from 2080 Bq . kg 1 and 3050 Bq . kg 1 , respectively. The results were consistent with those reported in earlier research for the Black Sea. Introduction Due to its geographical position, the Black Sea has received radioactive contamination both from atmospheric fallout and rivers discharges. The studies on the radioactivity contamination of the Black Sea are very important to assess the environmental impact derived from the presence of alpha-, gamma- and beta-emitting radionuclides with long-half lives (e.g., actinides, 137 Cs and 90 Sr). Extensive work have been published on the Black Sea radioactivity 15 since the Chernobyl accident and most researchers have focused on 137 Cs and 90 Sr. In the last years information on Pu radionuclides content in sediment samples from the Romanian and Bulgarian Coast of the Black Sea were presented. 1,3,6 The international expedition of the Professor Vodyanitskiy research vessel in the NW Black Sea, in December 1999, provided samples of water and sediment which were investigated for natural and artificial radioactivity and thus, a follow up of earlier investigations in the area. Experimental Sample collection and preparation The cruise covered the region of the Danube River, the Crimean coastal waters and offshore areas. The description of the collection sites is presented in Table 1. Water samples Between 50 and 70 liters of unfiltered water were collected to analyze 137 Cs and 90 Sr. During the * E-mail: domnica@ifin.nipne.ro ** On leave from the International Atomic Energy Agency, IAEAs Laboratories Seibersdorf, A-2444, Austria, E-mail: mor@rad.chemie.tu-muenchen.de expedition, Cs and Sr were preconcentrated from water samples as Cs ammonium phosphomolybdate and Sr oxalate salts, respectively, after previous addition of carriers. Further analytical treatment was carried out in the laboratory 7,8 where the Cs-AMP was dissolved in NaOH, re-precipitated as Cs-AMP and subjected to gamma-spectrometric analysis of 137 Cs. The 90 Sr determination procedure is described below. Sediment samples Bottom sediments were collected with an EPA Box corer from different layers from the surface to a depth of 30 cm. The samples were dried at 105 C, grounded through a 2 mm sieve and homogenized. Approximately 100 g of dry sample was subjected to gamma- spectrometry. For the radiochemical analyses the samples were ashed at 600 C. Radioactivity analyses Gamma-spectrometry: The content of 137 Cs was determined by -ray spectrometry using a Canberra MCA S100 system equipped with a Ge(Li) detector, with 15% efficiency and 2.2 keV energy resolution (FWHM) at the 1332.5 keV line. The spectra were analyzed with SAMPO 90, a dedicated computer code for the use with high-resolution -spectrometry systems. The IAEA 375 reference material was used for quality control purposes. Tritium analyses: About 100 ml of water was distilled in the presence of KMnO 4 and measured with a Tricarb 1600 TR liquid scintillation analyzer. 9 Some of the samples were also measured at the Isotope Hydrology Laboratory of the IAEA using a liquid scintillation analyzer 1550 CA. 10