Answer to Question #11678 Submitted to "Ask the Experts"

I am female and 55, and I recently discovered I have a thyroid nodule. I am concerned about the lingering health effects from the aboveground testing and fallout conducted at the Nevada Test Site while I was in utero. Of course, I drank milk growing up. My mother developed myasthenia gravis a few years later and had to have a thyroid tumor removed.

I have read the 1 October 1997 testimony before the US Senate on "Radioactive Fallout From Nuclear Testing at Nevada Test Site, 1950–60." What further studies have been done to determine the health effects from the fallout from the testing? Is there any information, like a radiation map, that I can provide to my doctor to help estimate my exposure to this radiation?

You have asked a question that many others are interested in, i.e., the effects of atmospheric nuclear testing in Nevada on your health and in particular, on your thyroid gland. I appreciate that you are seeking clarification about this, and I will do my best to respond.

There are three important factors that could have affected how much radiation exposure you might have received from nuclear weapons testing fallout: (1) when you were born, (2) where you were born and lived as a young child, and (3) whether your diet as a child included significant quantities of fresh dairy products.

Based on your age, you must have been born around 1961. The reason your birth year is significant is because the most important form of radioactive iodine (iodine-131 or ¹³¹I) from nuclear tests has a short half-life, only about eight days, so the exposure of the public to ¹³¹I lasted only about one month after each nuclear test. The US nuclear tests in 1961 and afterwards were, for the most part, small compared to those conducted in earlier years. However, there were large nuclear tests conducted in other countries at that time.

Where you lived is important because not all parts of the United States were equally affected by fallout. Locations near southern Nevada and southern Utah and directly east of those areas received the highest exposure, though there was also significant exposure at locations in Idaho and Montana. A diet of fresh milk is an important factor because iodine is readily transferred through the environment into dairy products.

There have been several studies on the health risks of radioactive fallout on the thyroid among the U.S. public, though such studies are difficult to conduct and, for the most part, show only weak relationships between exposure and thyroid nodules and thyroid cancer. Two of the most important studies can be found summarized here: National Library of Medicine and National Institutes of Health. There is also a semitechnical publication on health and radioactive fallout that you might find of interest in a reprint from American Science.

The National Cancer Institute (NCI) has prepared material for the public to directly address your concerns and I recommend it to you highly. A page at that website will show you a map of exposure levels across the country. The NCI also has an online calculator for persons like you to estimate their own exposure.

I would like to emphasize that, even with your doctor's evaluation, it is very hard to relate an individual's medical condition, e.g., thyroid nodules, to radiation exposure that took place many tens of years ago. Thyroid disease occurs at relatively high rates even among people not exposed to radiation and in particular, in women (see the information from the American Cancer Society).

Steven L. Simon, PhD