Radiological investigations in the surroundings of Bilibino, Chukotka, Russia

Abstract

This paper presents the results of radiological investigations in different parts of Chukotka comprising especially the Bilibino area. About 70 samples including sediments, soils, lichens, mosses, and reindeer meat and bones were measured. 137Cs ground contamination measured on several locations in Chukotka, NE Siberia, ranges between 586 and 1243 Bq/m2 (reference date 1 Sept 1994), with a mean of 850 Bq/m2 and a coefficient of variation (1 sigma) of 27%. No 134Cs was detected; from its lower level of detection, a possible contribution of Chernobyl releases to total 137Cs fallout of less than 48 Bq/m2 could be derived. 90Sr and 239,240Pu contaminations were found to be 510 ± 42% and 19 ± 47% Bq/m2, respectively. Natural radionuclides were determined to be 564 ± 15% Bq/kg dry soil for 40K, 29 ± 32% for 226Ra and 33 ± 25% for 228Ra, which is within normal levels. The highest plant contaminations were found in moss and lichen, with 137Cs up to 75 and 46 Bq/kg d.m. respectively, in remote areas, and 91 and 103 Bq/kg, respectively, in the vicinity of the Bilibino nuclear power plant (NPP). Near the NPP, significant traces of 60Co, 54Mn and 51Cr were also found in certain soil, plant and sediment samples, as well as enhanced levels of 137Cs, 90Sr and 239,240Pu. In sediments from the floodplain where the waste water of the NPP is discharged, 60Co and 239,240Pu contaminations up to 120 and 34 Bq/kg dm., respectively, and gamma dose rates up to 10 μSv/h were found, compared to a 0.1-0.2 μSv/h background level typical for the region. Two samples of reindeer meat (September 1994 harvest) showed 137Cs contaminations of 9.0 and 28.4 Bq/kg fresh weight. Taking into account that meat obtained from reindeer slaughtered in winter contains more 137Cs, 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 contamination of the region seems to be somewhat lower than expected from mean global 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 production to anthropogenic radionuclides can be anticipated. A rough calculation (after Strand et al., 1998) based on the reindeer samples and taking into account the well-known seasonal variation of reindeer contamination, dietary habits 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, depending on the amount of reindeer meat consumed (90-350 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 one tenth, viz. 6.6 mSv, and the dose rate today about 0.03 mSv/year. (C) 2000 Elsevier Science Ltd.