Ecological half-time of radiocesium from Chernobyl debris and from nuclearweapons fallout as measured in a group of subjects from the South of Sweden

From 1960 to 1980 and between 1987 and 1994 the whole-body content of Cs-13 7, and when possible also Cs-134, was measured in a group of subjects livin g in the city of Lund, Sweden (55.7 degreesN, 13.2 degreesE). The results h ave been analyzed to estimate the effective ecological half-time of fallout radiocesium in humans living in the area. The Lund area (The Province of S kane) was subjected to a deposition of about 2 kBq m(-2) of pre-Chernobyl C s-137 from nuclear weapons testing and I kBq m(-2) of Cs-137 from Chernobyl fallout in May 1986. The radiocesium from the nuclear weapons tests in the 1950's and 1960's still gave a significant contribution to the total Cs-13 7 levels in humans in the post-Chernobyl study period (1987-1994) of about 0.4 Bq per kg body weight, which was about 10% of the peak post-Chernobyl c oncentration level of Cs-137 (3.5-4 Bq kg(-1)) in 1987. The effective ecolo gical half-time for Cs-137 from Chernobyl was found to be 1.8 +/- 0.2 y. Th e aggregate transfer factor from deposition to mean activity concentration in man was estimated to be 3.6 Bq kg(-1)/kBq m(-2). These values may be com pared with an effective ecological half-time of 1.3 y found in the referenc e group in the 1960's, and an aggregate transfer factor of 10 Bq kg-1/kBq m (-2). This difference is largely explained by the continuous nature of the global fallout leading to contamination on growing crops whereas the Cherno byl fallout occurred just prior to the South Swedish growing season, leadin g to less efficient transfer to crops and to human diet. The average commit ted individual effective dose (50 y) from ingested 137Cs from the Chernobyl fallout was estimated to be 0.02 mSv and from the nuclear weapons fallout (1945-1995) to be 0.20 mSv.