To determine the current risk of internal radiation exposure after the Chernobyl accident, the (137)Cs body burden of the inhabitants of Bryansk Oblast, Russian Federation was evaluated, from 1998 to 2008. The study population is composed of 84 666 people who visited Bryansk No. 2 Hospital. A whole-body counter was used for measurement of (137)Cs body burden. (137)Cs concentration was significantly higher in the late period during the study and showed seasonal variation, suggesting that inhabitants may have consumed contaminated forest products. However, people with high annual exposure doses were quite rare during all years of the study. In conclusion, although internal radiation exposure from (137)Cs continues to this day in Bryansk Oblast, the annual exposure dose is low in almost all inhabitants. Because of the long half-life of (137)Cs, the long-term follow-up is necessary to monitor the health status and relieve the anxiety of the inhabitants around Chernobyl.

During the Chernobyl Nuclear Power Plant (CNPP) accident on 26 April 1986, large amounts of radionuclides were released and spread to vast areas. Inhabitants residing around CNPP have been exposed to external and internal irradiation due to the long half-life of (137)Cs (30 years). In this study, we screened for internal whole-body (137)Cs concentration using a whole-body counter in the Zhitomir state of Ukraine. The total number of participants was 144,972 (96,149 females and 48,823 males). The median body burden of (137)Cs per body weight decreased from 1996 to 2008. In particular, after 2003, more than half of subjects had internal exposure doses below the detectable level. A weak seasonal effect was found in measurement data from 1997 to 1999, but no such effects were observed in later years. We also calculated annual dose for each year and confirmed that doses have been decreasing gradually. In particular, after 2003, the annual effective dose decreased to 0.1 mSv y(-1) for 95% of the participants. Only two persons were found to have received more than 5 mSv y(-1) since 2007. Although the health effects of (137)Cs body burden due to the Chernobyl accident remain uncertain, further screening is needed to monitor the health status and to allay the anxiety of inhabitants in the contaminated areas around CNPP.