179 Radiation Protection Dosimetry Vol. 89, Nos 3–4, pp. 179–182 (2000) Nuclear Technology Publishing AGE-DEPENDENT DYNAMICS OF CAESIUM RADIONUCLIDE CONTENT IN INHABITANTS OF THE BRYANSK REGION, RUSSIA: A SEVEN-YEAR STUDY T. Jesko², I. Zvonova², M. Balonov², C. Thornberg‡, S. Mattsson², E. Wallstrom§, R. Vesanen§ and M. Alpsten§ ²Institute of Radiation Hygiene Mira str.8, 197101, St Petersburg, Russia ‡Lund (Malmo) University, Sweden §Goteborg University, Sweden Abstract — From 1991 to 1998, workers from Russia and Sweden performed measurements to estimate the internal exposure of the inhabitants in some villages of the Bryansk region which were severely contaminated with 134 Cs and 137 Cs after the Chernobyl Nuclear Power Plant accident in 1986. The measurements of the radionuclide content in the human bodies were performed with two techniques: whole-body counting and an indirect method based on measurement of 137 Cs and creatinine concentration in urine samples. The measurement results have shown that 134 Cs and 137 Cs content in rural inhabitants depends both on natural and social factors. It is also shown that caesium radionuclides content in children increases with age and reaches the maximum values in adults. Mean whole body content of 134 Cs and 137 Cs in men is higher by a factor of 1.7 than in women. The method of selective measurement of caesium radionuclides concentration in collective urine samples may be successfully applied for estimation of average whole body content in groups of persons. INTRODUCTION After the accident at the Chernobyl nuclear power plant in 1986, the western part of the Bryansk region of Russia with a population of more than 100,000 persons was severely contaminated with radionuclides at the level above 0.5 MBq.m -2 of 137 Cs. After the decay of short-lived radionuclides by autumn of 1986, 137 Cs and 134 Cs consumed with local food became the main sources of the internal whole-body exposure in the inhabitants of the rural area (1,2) . The task of internal exposure monitoring of a large number of people arose from that time. In 1986, the Institute of Radiation Hygiene, St Peters- burg, developed a method using portable scintillation gamma radiometers and monochannel spectrometers of different types for in vivo monitoring of incorporated gamma emitters in inhabitants of the contaminated territories (3) . With decreased activity in the human body the pre- cision of whole-body measurements using portable equipment is considerably reduced. When the levels of the caesium internal burden get close to the level of the devices’ sensitivity, an indirect method using the measurement of caesium and creatinine concen- tration in the urine was used to estimate the radio- nuclides in the body. Urine samples are easily col- lected from a large number of people and are treated in the laboratory for measurement in a low back- ground environment. This method has been tested in the Bryansk region. MATERIAL AND METHODS Between 1991 to 1998, workers from the Institute of Radiation Hygiene, St. Petersburg, Russia, and from the Universities of Goteborg and Lund (at Malmo), Sweden, performed measurements to estimate the whole-body content (WBC) of 137 Cs and 134 Cs in inhabitants of ten villages of the Bryansk region where the 137 Cs soil con- tamination varies between 0.1 and 2.8 MBq.m -2(4) . The annual measurements were performed in September but samplings have also been made in April during 1992 and 1993. The measurements of the radionuclide contents were performed in about 2800 inhabitants of different ages (from 1 to 80 years old). The estimation of 137 Cs and 134 Cs burden was performed with two tech- niques: whole-body counting and one based on measurement of radionuclide and creatinine concen- tration in urine samples. About 700 samples of urine were collected from persons undergoing whole-body content measurements and analysed for caesium radionuclides content; 350 of them were analysed for creatinine concentration as well. The measurements of 137 Cs and 134 Cs body burden were performed with portable one-channel scintillation gamma spectrometers (RFT-20046, Robotron, Germany, and NC-482B, Hungary), both equipped with 63 mm 3 63 mm NaI(Tl) crystal detectors manufactured in the USSR. The third type of device was a whole-body coun- ter installed in a mobile radiometric laboratory using 50 cm 3 80 cm 3 10 cm plastic scintillators in the form of a stove bench (5) . The whole-body measurements using portable