CONCENTRATIONS OF I-129 IN THE BIOSPHERE

In order to examine the worldwide distribution of the background I-129 , environmental levels of I-129 and I-127 have been measured by neutro n activation analysis on samples (thyroids from human and grazing live stock and soils) at locations in the northern and southern hemisphere remote from release points. Human thyroids collected in Lower Saxony ( Federal Republic of Germany) showed no change in a mean value of the I -129:I-127 isotope ratio of 2.5 X 10(-8) over a period of 11 years. Is otope ratios found in bovine thyroids taken from sites within the Euro pean Communities during 1979-1981 and from Lower Saxony (FRG) during 1 992-1993 exhibited I-129:I-127 values between 4.7 X 10(-9) and 8.2 X 1 0(-8) (mean value: 2.0 X 10(-8)) and between 1.3 X 10(-8) and 8.0 X 10 (-8) (mean values: 4.0 X 10(-8)) respectively. Human and bovine thyroi ds collected in Southern Chile (39-41 degrees South) between 1985 and 1986 showed mean values of the I-129:I-127 isotope ratio of 1.5 X 10(- 9) and 2.2 X 10(-9), respectively. Two pools of sheep thyroid fragment s taken from Victoria (Australia) in 1957 and 1989 exhibited isotope r atios of 6 X 10(-10) and 5 X 10(-10). All three species taken from sit es in the southern hemisphere showed concentrations of biospheric I-12 9 to be comparable with those established worldwide in the pre-nuclear age. Significantly higher values of the I-129:I-127 isotope ratio bet ween 1.2 X 10(-7) and 7.4 X 10(-6) (mean value: 9.1 X 10(-7)) were fou nd in surface soil samples collected in Chernobyl-contaminated areas u p to a distance of 420 km around the Chernobyl nuclear facility in Rus sia, Belarus and Ukraine. The locations examined showed Cs-137 ground deposition values between 6 and 250 kBq m(-2).