Key Points What is radioactive fallout? Radioactive fallout refers to a variety of airborne radioactive particles that fall to the ground during and following aboveground nuclear weapons tests. (Question 1) What is iodine 131 (I-131)? Iodine 131 is a radioactive isotope of iodine -- an altered form of the element that is chemically the same as the naturally occurring element but is radioactive. I-131 is found in fallout from atmospheric nuclear bomb explosions, along with a variety of other radioactive substances such as strontium-90. (Question 2) How were people exposed to I-131? For most people, the greatest I-131 exposure came from drinking contaminated milk. I-131 fell on pastures, and cows ate the vegetation, contaminating their milk. People received smaller levels of exposure from breathing contaminated air and eating other contaminated dairy products, eggs, and leafy vegetables. (Question 3) Am I still being exposed? Because I-131 has a short half-life, less than 1 percent remained 80 days after most nuclear tests. (Question 4)

1.  What is radioactive fallout?

Radioactive fallout refers to a variety of airborne radioactive particles that fall to the ground during and following aboveground nuclear weapons tests. People and animals may ingest these particles in their food or inhale them from the air.

2.  What is iodine 131 (I-131)?

Iodine 131 is a radioactive isotope of iodine -- an altered form of the element that is chemically the same as the naturally occurring element but is radioactive. I-131 is found in fallout from atmospheric nuclear bomb explosions, along with a variety of other radioactive substances such as strontium-90. I-131 has been of greatest concern because it concentrates in the thyroid, particularly in children, and may increase the risk for thyroid cancer. There appears to be little risk of thyroid cancer for people exposed to radiation as adults. Because iodine concentrates in the thyroid, high doses of I-131 are used to treat some types of benign thyroid disease as well as thyroid cancer.

3.  How were people exposed to I-131?

For most people, the greatest I-131 exposure came from drinking contaminated milk. I-131 fell on pastures, and cows ate the vegetation, contaminating their milk. People received smaller levels of exposure from breathing contaminated air and eating other contaminated dairy products, eggs, and leafy vegetables.

4.  Am I still being exposed?

Because I-131 has a short half-life, less than 1 percent remained 80 days after most nuclear tests.

5.  How common is thyroid cancer and how treatable is it?

Thyroid cancer is relatively uncommon compared with other forms of cancer, accounting for 1.6 percent of all cancers diagnosed in the United States. An estimated 20,700 cases will be diagnosed in 2002. The number of new cases is about 16 times the number of deaths, which is estimated to be 1,300 for 2002. Thyroid cancer occurs more than twice as often in women as in men. The rate of new cancers (invasive) for 1999 -- the most recent year available -- was 10.4 per 100,000 women and 3.8 per 100,000 men. Thyroid cancer death rates for 1999 were 0.5 deaths per 100,000 women and 0.4 deaths per 100,000 men. The lifetime risk of invasive thyroid cancer is estimated at 0.82 percent (1 in 122) for women and 0.30 percent (1 in 333) for men. Thyroid cancer is also highly curable. The five-year relative survival rate is 96 percent.

6.  What should people do who are concerned about cancer risk from fallout exposure?

Anyone who is concerned about cancer risk from fallout should request a thyroid exam as part of his or her next visit to a physician.

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