Radiological investigations in the surroundings of Bilibino, Chukotka, Russia

This paper presents the results of radiological investigations in different parts of Chukotka comprising especially the Bilibino area. About 70 sample s including sediments, soils, lichens, mosses, and reindeer meat and bones were measured. Cs-137 ground contamination measured on several locations in Chukotka, NE Siberia, ranges between 586 and 1243 Bq/m(2) (reference date 1 Sept 1994), with a mean of 850 Bq/m(2) and a coefficient of variation (1 sigma) of 27%. No Cs-134 was detected; from its lower level of detection, a possible contribution of Chernobyl releases to total Cs-137 fallout of les s than 48 Bq/m(2) could be derived. Sr-90 and Pu-239,Pu-240 contaminations were found to be 510 +/- 42% and 19 +/- 47% Bq/m(2), respectively. Natural radionuclides were determined to be 564 +/- 15% Bq/kg dry soil for K-40, 29 +/- 32% for Ra-226 and 33 +/- 25% for Ra-228, which is within normal level s. The highest plant contaminations were found in moss and lichen, with Cs- 137 up to 75 and 46 Bq/kg d.m. respectively, in remote areas, and 91 and 10 3 Bq/kg, respectively, in the vicinity of the Bilibino nuclear power plant (NPP). Near the NPP, significant traces of Co-60, Mn-54 and Cr-51 were also found in certain soil, plant and sediment samples, as well as enhanced lev els of Cs-137, Sr-90 and Pu-239,Pu-240. In sediments from the floodplain wh ere the waste water of the NPP is discharged, Co-60 and Pu-239,Pu-240 conta minations up to 120 and 34 Bq/kg dm., respectively, and gamma dose rates up to 10 mu Sv/h were found, compared to a 0.1-0.2 mu Sv/h background level t ypical for the region. Two samples of reindeer meat (September 1994 harvest) showed Cs-137 contami nations of 9.0 and 28.4 Bq/kg fresh weight. Taking into account that meat o btained from reindeer slaughtered in winter contains more Cs-137, the mean activity concentration in meat calculated for 1 year of production is 74 Bq /kg f.w. Apart from the vicinity of the NPP, the anthropogenic radioactive contamina tion of the region seems to be somewhat lower than expected from mean globa l fallout levels typical for the geographical latitude according to UNSCEAR data, but is in good accordance with AMAP figures (Strand et al., 1998). Due to the tundra food-chain. a certain exposure of the local population to anthropogenic radionuclides can be anticipated. A rough calculation (after Strand ct al., 1998) based on the reindeer samples and taking into account the well-known seasonal variation of reindeer contamination, dietary habit s of the indigenous population and, finally, external radiation resulted in an individual committed effective dose of 18-70 mSv (integrated from 1950 to infinite time) from atomic bomb fallout for the indigenous population, d epending on the amount of reindeer meat consumed 190-350 kg/year per person ). The individual dose rates today are about 0.1-0.4 mSv/year. For the non- indigenous people, the individual committed effective dose is only about on e tenth, viz. 6.6 mSv, and the dose rate today about 0.03 mSv/year. (C) 200 0 Elsevier Science Ltd. All rights reserved.