Sodium-22 in the food-chain: lichen-reindeer-man
Mattsson, L.J.
Health Physics 23(2): 223-230
1972
ISSN/ISBN: 0017-9078 PMID: 4644588 Document Number: 45126
The levels of atmospheric and biospheric 22Na rose after 1961, indicating an addition to the natural levels as a result of nuclear weapon testing. The isotope has a physical half-life of 950 days. Lichens (Cladonia alpestris) and reindeer whole blood, flesh (shoulder muscle) and bone were collected in central Sweden between 1961 and 1969.The 22Na level in lichen in June 1964 was 34 plus or minus 9 pCi/kg dry weight and the 22Na activity per unit mass of stable Na was 260 plus or minus 70 nCi/kg. The concentration of 22Na in reindeer flesh rose from between 1 and 10 to a maximum of 200 pCi/kg wet weight in late 1964. By early 1969 the value had fallen to 25 pCi/kg. There was rapid exchange of 22Na between blood and soft tissues. There was no significant seasonal variation in 22Na activity. The biological half-life of the isotope in reindeer food is estimated to be 2.5 years. Activity was measured in the proximal third of the reindeer humerus and a maximum of 600 pCi/kg wet weight was found in mid-1965. The biological half-life in bone was estimated to be 0.5 year.Annual measurements of whole-body radiation in Swedish Lapps indicate a 22Na body burden of less than 2 nCi at the time of assumed maximum. This suggests that the radiation dose from 22Na is insignificant compared with that from many other natural and artificial radionuclides. The 22Na:137Cs ratio for Swedish Lapps is only 10 to 20% of that for Alaskan Eskimos, indicating a higher intake of stable Na in the former.