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Health Risks of Ionizing Radiation: - Clark University

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2<br />

BACKGROUND RADIATION<br />

2.1 Introduction<br />

Exposures to ionizing radiation that result from<br />

human activities such as nuclear testing <strong>of</strong>ten receive<br />

significant popular attention. However, the largest<br />

proportion <strong>of</strong> radiation around the world is emitted<br />

by natural sources. Most <strong>of</strong> the exposure typically<br />

received by the public is produced by cosmic rays,<br />

terrestrial radiation, and internally deposited natural<br />

radionuclides (Samet 1997). According to Hoel<br />

(1995), radon alone, one source <strong>of</strong> background<br />

radiation that enters indoor environments from<br />

the soil and irradiates the lung through inhalation,<br />

accounts for over fifty percent <strong>of</strong> the world’s total<br />

estimated effective dose <strong>of</strong> radiation.<br />

While these exposures are termed “natural<br />

radiation” this does not indicate an inherently<br />

benign nature. It is necessary to look further into<br />

the health effects <strong>of</strong> background radiation because<br />

“there is a mistaken tendency to assume that natural<br />

radiation is harmless” (Caufield 1989). Claims that<br />

man-made exposures are the same or only a fraction<br />

higher than natural radiation levels imply that the<br />

effects are insignificant, and this is a false assurance.<br />

A substantial body <strong>of</strong> research suggests that natural<br />

radiation can be harmful, and as we increase<br />

our exposure through intensified dependence on<br />

mineral processing, airplane flights, phosphate<br />

and potassium fertilizers and fossil fuels, we also<br />

increase our exposure and related health risks.<br />

Outcomes associated with background radiation<br />

include chromosomal aberrations and childhood and<br />

adult cancers including leukemia, osteosarcoma, and<br />

melanoma (Henshaw et al. 1990). Indeed, as <strong>of</strong> 1989<br />

according to Caufield, “most scientists believe[d]<br />

that natural radiation cause[d] about one per cent <strong>of</strong><br />

all fatal cancers”.<br />

Estimates <strong>of</strong> average annual background<br />

radiation exposure center around 0.003 Sv (3 mSv),<br />

about two-thirds <strong>of</strong> which comes from radon. There<br />

is considerable variability in individual annual<br />

exposure according to geology, elevation, and<br />

other factors. Smokers, for example, are exposed<br />

to roughly twice as much radiation as nonsmokers<br />

due to radionuclides in tobacco smoke 1 . These are<br />

within the range <strong>of</strong> doses that would be considered<br />

low, although a lifetime dose can exceed our cut<strong>of</strong>f<br />

(as we have defined it,

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