129I, 131I and 127I in animal thyroids after the Chernobyl nuclear accident.

A small number of animal thyroids from Bad Hall, Austria; Ulm, Germany; and Steinkjer, Norway had 131 I (half-life 8.06 d) measured between 21 and 72 d following the nuclear accident at Chernobyl on 26 April 1986. Nine years later 129 I (half-life 1.57 x 10 7 y) fission product and natural 127 I were measured in the same thyroids. The mass ratios, 129 I/ 131 I were calculated to the date of the Chernobyl accident and they ranged between 13 and 71. These ratios are compared to the expected ratios within an operating nuclear reactor during 2 y of operation, where the 129 I/ 131 I -1 ratio never exceeded 30. The observed ratio of 129 I to natural 127 I in thyroids ranged from 5 to 200 times the ratio before the accident, except that the Norwegian thyroids had 129 I/ 127 I ratios which were less than the ratios of pre-Chernobyl thyroids from Ulm. These studies show the 129 I and 131 I from the Chernobyl accident were accumulated with natural 127 I in animal thyroids but the isotope ratios, calculated to the release date, had wide ranges. The 131 I radioactive exposure might be estimated from a fission product mixture by measuring 129 I in thyroids long after the exposure to 131 I, but the results would probably show a wide range of possibilities. The determining variables should be evaluated. We know of no previous data regarding both 131 I and 129 I in thyroid glands during the first 3 mo after the Chernobyl accident.