Large populations of people around the world live in areas that expose them to high levels of terrestrial background radiation. Several populations live in areas with monazite sands containing radioactive thorium: about 90,000 people in Yangjiang, China, are exposed to у doses of about 4 mSv per year, and 100,000 people in Kerala, India, are exposed to median doses of 4 mSv/yr and up to 70 mSv/yr in some cases (2, 14). Long-term epidemiological studies of these popula­tions have not shown any significant cancer risk from these higher background doses of radiation (14). The Guarapari coastal region of Brazil has monazite sands that expose some 30,000 people to dose rates of 5 mSv/yr. Around 7 million resi­dents of the wine country of central France live in granitic areas and get annual doses of 1.8 to 3.5 mSv. A small population of about 2,000 people in Ramsar, Iran, get an average annual dose of 6 mSv with a smaller number getting up to 20 mSv. The 2,740 residents of Leadville get 5.25 mSv/yr. In none of these cases is there evidence that the risk of cancer is increased from these high background doses of radiation (15).

When you add up all of the pieces, the students coming to Colorado State University end up with an average annual background dose of 4.2 mSv, nearly three times what it would be in Florida or Texas, excluding medical exposure (Figure 8.6).

Should they be worried? One way to answer the question is to see whether people in Colorado have a higher than average rate of cancer. In fact, Coloradans have the fourth lowest incidence of cancer of any state in the United States, in spite of the fact that we have the highest level of background radiation of any state in the country, and we have the third lowest incidence of lung cancer in

spite of the high level of radon (16). Clearly, this high rate of background radia­tion is not causing a lot of excess cancers in Coloradans—quite the reverse. Of course, one reason for a lower incidence of cancer is the lifestyle of people in Colorado, who tend to be quite active and do not smoke a lot. Still, it is clear that people living in Colorado do not have to worry about the high back­ground radiation they are exposed to. This is a very important factor when considering the exposure of people to radiation from storage of nuclear waste in a repository, for example, or after a nuclear accident. If the doses are less than background levels that people are exposed to naturally with no negative consequences, then it is not worth worrying about. Simply understanding this elemental fact should remove much of the worry that people have about expo­sure to radiation from nuclear reactors. We are all exposed to radiation—you can’t avoid it—but being exposed to radiation from nuclear waste storage or even a nuclear accident is no different from exposure to natural or medical radiation. It is all about the dose!