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 131I (half-life 8.06 d) measured between 21 and 72 d following the nuclear accident at Chernobyl on 26 April 1986. Nine years later 129I (half-life 1.57 x 10(7) y) fission product and natural 127I were measured in the same thyroids. The mass ratios, 129I/131I 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 129I/131I(-1) ratio never exceeded 30. The observed ratio of 129I to natural 127I in thyroids ranged from 5 to 200 times the ratio before the accident, except that the Norwegian thyroids had 129I/127I ratios which were less than the ratios of pre-Chernobyl thyroids from Ulm. These studies show the 129I and 131I from the Chernobyl accident were accumulated with natural 127I in animal thyroids but the isotope ratios, calculated to the release date, had wide ranges. The 131I radioactive exposure might be estimated from a fission product mixture by measuring 129I in thyroids long after the exposure to 131I, 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 131I and 129I in thyroid glands during the first 3 mo after the Chernobyl accident.