129I and 137Cs fission products in thyroids of animals, 1984-1991

Iodine is intensely concentrated in the thyroid of animals, while 137Cs is not. In this study, 129I and 137Cs concentrations were determined in animal thyroids from selected areas during 1984-1991. The thyroids were from deer killed within the Savannah River Site (SRS) in South Carolina; from the environs of Oak Ridge (OR), Tennessee; West Tennessee; and Florida. Thyroids from sheep slaughtered routinely in Birmingham, England (UK), were also tested. The glands were analyzed by x-ray spectroscopy using a high-purity germanium well detector. 129I concentrations of 1 to 102 Bq 129I (g thyroid)-1 were found in 6.8% of deer thyroids from SRS. Eighty-nine percent of the thyroids from SRS and 38% of those from OR contained 129I concentrations of 0.01 to 1.0 Bq 129I g-1. No thyroids from West Tennessee or Florida had more than 4 mBq 129I g-1. Cesium was found to be distributed differently; 38% of the thyroids from SRS contained 0.1 to 0.65 Bq 137Cs g-1, and the highest concentrations appeared periodically, during November and December. Ten to 100 mBq of 137Cs were found in 60% of thyroids from SRS, 79% of those from Florida, 52% of those from OR, and 22% of those from West Tennessee. Inmore » thyroids from SRS and Florida, most of the 137Cs has been from worldwide fallout on sandy soil which permits 137Cs-rich vegetation; if a fraction of the 137Cs is from other sources, it has not been defined. The unique finding of this report is the high incidence and persistence of > 0.01 Bq 129I (g thyroid)-1 in deer from OR and SRS. 129I is a marker for fission products, but it is not a radiological hazard because of its very slow radioactive decay and its continual dilution by additions of nonradioactive iodine to the environment.« less