ABSTRACT
A total of one hundred and twenty-five atmospheric, surface, near-surface, and
underground tests were conducted at the Nevada Test Site (NTS) between
1951 and 1963.These tests resulted in fallout of many different kinds of radio-
active isotopes, including cesium, strontium, and iodine, exposing millions of
Americans to radioactive contamination [1, 2]. The most extensive analysis of
radioactive fallout from U.S. nuclear weapons testing concentrated on radio-
iodine, or I-131, which has a half-life of eight days [1]. An analysis performed by
the National Cancer Institute (NCI) found that nuclear weapons tests released
about 150 million curies of I-131 [1]. Virtually every county in the United States
received some I-131 fallout. The highest levels of I-131 fallout were deposited
immediately downwind from the NTS. The main pathway of exposure to humans
was from consumption of fresh milk. Although in some groups (e.g., Native
Americans), exposures may also have resulted from eating wild game and fish
[3]. While the NCI study estimated doses of I-131 fallout, subsequent estimates
were made of the risks of I-131 exposure, with particular emphasis on thyroid
cancer. Estimates of thyroid cancer risk are questionable because of the many
uncertainties associated with the actual levels of fallout deposited, individual
exposures and doses (including the relative biological effectiveness of I-131),
and the dose-response function. The possible excess thyroid cancers from the
I-131 fallout have been estimated to range from 11,300 to 212,000, with a central
estimate of 49,000.
