harms of routine screening for thyroid cancer and with research on communicating risk information to the public and the medical community.

  • Considered directions for further research.

The committee reached the following general conclusions in three subject areas.

Estimates of national, county, and individual exposure to iodine-131

  1. In attempting to fulfill its Congressionally mandated tasks, the NCI undertook a very difficult task that depended on limited data of uncertain reliability and validity. The NCI report represents a careful, detailed, and responsible effort to estimate iodine-131 exposure from the Nevada atomic weapons tests. The NCI's methods were generally reasonable, although specific elements can be questioned (Chapter 2).

  2. The estimate of the American people's collective dose from I-131 is consistent with the committee's analysis and is unlikely to greatly over- or understate the actual levels (Chapter 2 on Validation and Uncertainty in Collective or Average Dose Estimates).

  3. The levels of detail presented in the report, specifically, county-specific estimates of iodine-131 thyroid doses, are probably too uncertain to be used in estimating individual exposure. For the most part, direct measures of fallout for any particular weapons test were made for only about 100 places nationwide (except near the Nevada Test Site itself). Estimates of county-specific exposures may also have little relevance to specific individuals for whom exposure depends on such critical factors as varying individual consumption of milk and other foods and variations in the source of those foods (Chapter 2 ).

  4. Individual-specific estimates of past exposure to iodine-131 from the Nevada tests are possible but uncertain, often highly so, because critical data are often not available or of questionable reliability. A small minority of the population—those who were young children at the time of testing and who routinely drank milk from backyard cows or, especially, goats—had a significant exposure to I-131 (Chapter 2 on From Fresh Milk to Human Intake and Chapter 3 on Normal Thyroid Physiology).

Estimates of Cancer Risk

  1. Exposure to I-131 as a by-product of nuclear reactions can cause thyroid cancer as shown conclusively by the 1986 nuclear accident in Chernobyl, which resulted in high level exposure for many people. The NCI dose reconstruction model indicates that the level of exposure to I-131 was sufficient to cause and continue to cause excess cases of thyroid cancer. Because of uncertainty about the doses and the estimates of cancer risk, the number of excess cases of thyroid



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