Meteorological Evaluation of the Sources of Iodine-131 in Pasteurized Milk

Abstract

An examination of possible sources of radioiodine found in samples of milk in the midwestern states during May and early June 1962 shows that atmospheric testing at Christmas Island was the principal contributor to incidents of significant concentrations of iodine-131 in milk (exceeding 300 picocuries per liter). Underground testing at Nevada played at most only a minor role during this period. There is a cause-and-effect relationship between the penetration of thunderstorms into high concentrations of nuclear debris in the lower stratosphere and the subsequent amount of iodine-131 in milk. Analyses of samples of rainwater confirm the importance of this "scavenging" mechanism. The relative contributions of atmospheric and underground testing to the iodine-131 found in milk samples from September 1961 to December 1963 has been reviewed and only one incident in which the amount of iodine-131 exceeded 300 picocuries per liter could be attributed to an underground test.