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. In 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.