Hanford Animal Studies of Radioiodine

• Published in: Radiation protection dosimetry 1995-07, Vol.60 (4), p.295-305
• Main Author: McClellan (INVITED), R.O.
• Format: Article
• Language: English
• ISSN: 0144-8420; 1742-3406
• DOI: 10.1093/oxfordjournals.rpd.a082731

Very early in the Hanford nuclear project, 131I was recognised as a key radionuclide whose release from the nuclear fuel cycle would need to be closely controlled and monitored. Later, concern emerged for 131I as significant fallout radionuclide from nuclear weapons testing. To provide a scientific basis for controlling exposures, a major multifaceted research programme was conducted at Hanford. A major portion of the research programme focused on evaluating the radiotoxicity of 131I to domestic sheep because of their likelihood of receiving radioiodine exposure via ingestion of contaminated forage. The sheep studies involved multiple exposure levels and multigenerational studies conducted over a period of years and defined the effects of 131I from exposures producing acute effects down to minimal-effect levels and no-observed-effect levels. Other studies examined the influence of route of exposure (oral, inhalation, intravenous, subcutaneous, and dermal) on the disposition of 131I. In all cases, the patterns of uptake and distribution were quite similar, with rapid accumulation of 131I in the thyroid. Another study in which dairy cattle ingested 131I established the relationship among levels in the cow's diet, cow's thyroid, milk, and the thyroid of humans drinking the milk. Although the research was conducted over 30 years ago, it was innovative in its experimental design judged by today's standards and yielded results that will continue to be of substantial value in assessing the risks to animals and humans of 131I exposure as long as such concerns exist.