Health Risks of Ionizing Radiation: - Clark University
Health Risks of Ionizing Radiation: - Clark University
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,