In order to detect characteristic regional differences or temporal changes of I-129 concentrations in the biosphere, thyroids from humans, grazing livestock, and herbivorous wildlife species (reindeer and roedeer) were collected in various areas of the world which are not affected by reprocessing plants. For reasons of comparison, all samples were analyzed for their I-129:I-127 atom ratios. Human and bovine thyroids taken from the 10th region in Southern Chile (39-degrees-41-degrees South) indicated values of the I-129:I-127 atom ratio between 1.1 x 10(-9) and 2.0 x 10(-9) and between 1.2 x 10(-10) and 9 x 10(-9), respectively. They showed no significant increase in the concentration of biospheric I-129 in comparison with that established in the pre-nuclear age. Atom ratios found in human thyroids collected in Lower Saxony (Federal Republic of Germany), which is a region not directly affected by reprocessing plants, exhibited I-129:I-127 values between 8 x 10(-9) and 6 x 10(-8) from February 1988 to September 1990. Thyroid glands of reindeer and roedeer as well as heather, moss, and lichen were taken from the Vilhelmina, Heby, and Gavle communes in Sweden and analyzed for I-129 and I-127. All three communes were found to be seriously contaminated by fallout from the Chernobyl accident. Highest I-129:I-127 atom ratios between 3.5 x 10(-7) and 1 x 10(-6) were found in the Gavle commune (approximately 150 km northwest of Stockholm) where the highest Cs-137 ground deposition (70-80 kBq m-2) was measured. Two soil samples taken from Krasnaya Gora and Mirny locations in Russia (approximately 200 km northeast of Chernobyl) exhibited ratios of about 1 x 10(-6). These locations showed a Cs-137 ground deposition of 370 and 1,300 kBq m-2, respectively.
