The Relationship Between I131 Concentrations in Various Environmental Samples

Abstract

A study was made of the relationship between I131 concentrations in air, vegetation milk and cattle thyroids in the vicinity of Hanford during the period January 1961, through April, 1963. The study provides some insight into mechanisms of I131 passage down the food chain to man, and illustrates the rate at which I131 concentrations decrease following relatively acute depositions of fallout materials. The major source of the I131 was fallout of debris from nuclear weapons tests. Concentrations noted during periods of testing were 10–100 times those found when no testing was in progress. Fresh milk constituted the principal mode of intake of I131 for persons residing in the Hanford environs. Concentrations in milk samples collected from local dairy farms averaged about 50 pc I131/l, during 1961, and 40 pc/l. during 1962. The potential radiation dose received by a small child (with a 2 g thyroid) via milk consumption was estimated to be about 400 times that received via inhalation during the period under study. For an adult (with a 20 g thyroid) the ratio of thyroid exposure via milk to that via inhalation was estimated to be about 40 to 1.