Measurements of 129I in Human and Bovine Thyroids in Europe-transfer of 129I Into the Food Chain

Abstract

Bovine thyroid glands from different countries in Europe and human thyroid glands from Lower Saxony (Federal Republic of Germany) show isotopic 129I/127I ratios of 2.1 X 10(-9) to 8.2 X 10(-8) for cattle and 2.1 X 10(-9) to 8 X 10(-8) in humans. These values give information about the concentration of fallout 129I in Europe since most of these glands were collected in areas without nuclear facilities. Some of the human thyroids were collected after the Chernobyl accident between May 1986 and February 1988. Results obtained from human thyroids taken in some locations of Lower Saxony show no significant increase of the 129I during this time. Higher concentrations of 129I were only found in cattle grazing in the vicinity of a reprocessing plant in Mol, Belgium. Samples of soil, vegetation, milk, and water from this area contained higher than normal concentrations of 129I. The long-term transfer of radioiodine from the soil to the plant and the translocation within the soil were studied using a soil monolith with a 129I-contaminated surface. During the 4 y of the experiment, the transfer factor plant/soil decreased from 0.3 to 2.2 X 10(-3). Soil samples taken in 5-cm steps to a depth of 30 cm then at 40 and 50 cm depths showed that the transport of radioiodine to lower layers proceeds very slowly. The top 5-cm layer contained about 80% of the total radioactivity 52 mo after contamination. In an in-vivo study with a dairy cow, the transfer of radioiodine from feed to milk to cow meat and to pig thyroid gland was followed for 53 d using 129I-labeled pasture grass contaminated via roots. A part of the milk obtained from the cow was fed to a pig as a substitute for humans. The mean value of the transfer factor milk/feed was 2.4 X 10(-3) d kg-1. The values of the transfer factor cow meat/feed obtained for different muscle cuts and organs (excluding thyroid) ranged between 3.0 X 10(-4) (kidney) and 5.4 X 10(-2) d kg-1 f.w. The transfer factors pig thyroid/milk (as pig feed) and pig thyroid/cow feed exhibited values of 1.2 and 8.7 X 10(-3) d kg-1 f.w., respectively.