Radiation Exposure and the Nevada Test Site

Exposure to ionizing radiation is one of the major risk factors for thyroid cancer. Living in Southern Nevada and having a diagnosis of thyroid cancer always raises questions about our proximity to the Nevada Test site and possible exposure to radiation as a result of where we live. This article will attempt to review some of this information.

The Chernobyl Accident

Much of what we’ve learned about the effects of radioactive fallout from nuclear reactors in the modern era has been learned over the last 2 decades from the Chernobyl nuclear reactor accident in the former Soviet Union (Pripyat, Ukraine). On April 26, 1986 the Chernobyl reactor exploded and resulted in a massive release of radiation into the atmosphere, equivalent to 400 times the amount of radiation delivered by the atomic bombing of Hiroshima. The cloud of radiation disseminated over a wide geographic area and was detectable around the world. Heaviest contamination occurred in Belarus, Ukraine and Russia, but there was also significant contamination of Western Europe and Eastern North America. It is estimated that 60% of the fallout occurred in Belarus. Exposure to radiation from the Chernobyl accident caused a dramatic incidence in thyroid cancer and thyroid cancer deaths. It is estimated that this incident resulted in approximately 4000 new cases of thyroid cancer, especially in children and adolescents exposed at the time of the accident. We have learned that patients with significant exposure to ionizing radiation should have close surveillance of the thyroid using high resolution ultrasound by an experienced thyroidologist. Fine needle aspiration biopsy of suspicious nodules to enable early detection and treatment of thyroid cancer is crucial.

The Nevada Test Site

From 1951 to 1962 the Nevada Test Site (NTS) was the primary site used by the US Government for both above and below ground testing of nuclear weapons. During this time period 100 tests were conducted (86 above or near ground level and 14 below ground tests) which resulted in significant release of radiation into the atmosphere. The heaviest atmospheric contamination appears to have occurred in 1952, 1953, 1955 and 1957. This radioactive contamination came primarily in the form of I131, which is taken up and stored in the thyroid gland. Estimates suggest that fallout from the NTS may produce 10,000 to 75,000 cases of thyroid cancer; estimates of up to 22,000 other radiation-induced cancers and 2000 deaths from radiation-induced leukemia may arise in the US from the NTS and global fallout.

Predicting NTS Exposure

Individuals exposed to radiation from the NTS, referred to as ‘downwinders’, may need special surveillance of their thyroid. Surprisingly enough, exposure to radioactive fallout in Southern Nevada was relatively low due to atmospheric conditions and prevailing winds which pushed the radioactive cloud north and east of the NTS. As a result, a high rate of exposure due to fallout is found in western Utah, northern Idaho, western Montana, and the Midwestern states (especially the Dakotas, Nebraska and Kansas). Detailed maps of fallout exposure can be seen at the website for the National Cancer Institute.

Mechanism of Exposure

Nuclear explosions result in the release of large amounts of iodine 131 (I131), a radioactive isotope of iodine. As iodine falls from the atmosphere and settles on vegetation, dairy cows consume large amounts of I131 and then secrete it in milk. I131 is ingested by humans (especially children) through contaminated milk. This iodine is then stored in the thyroid gland and used to make thyroid hormone. Iodine deficient individuals are at higher risk for exposure. Ingestion of large amounts of iodine by downwinders can saturate iodine stores in the body so that I131 is not stored in the thyroid gland. Some explosions sent radioactive material over 6 miles into the stratosphere, where the radiation can remain suspended for years before being deposited around the globe uniformly in what is known as global fallout (global fallout also occurs from other sources of radiation release into the atmosphere: Chernobyl, nuclear testing from other nations, etc).

It is possible to calculate one’s estimated exposure from the Nevada Test Site using this website. There is a direct relationship between the severity of the exposure and the risk of cancer. Age of exposure is also important in determining risk, with childhood exposure being the most dangerous.

Summary

The risk of exposure to significant amounts of ionizing radiation from the NTS is quite low for people currently living in Southern Nevada. Residents of Southern Nevada during the 1950’s and 1960’s may have slightly higher exposure to radioactive fallout, but his is probably does not require systematic screening of the thyroid for most individuals unless they were downwinders during childhood or adolescence. Individuals that have significant exposure to radioactive fallout or exposure to ionizing radiation as a result of radiotherapy for medical problems do require evaluation and monitoring by an experienced thyroidologist.

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