Health Risks of Ionizing Radiation: - Clark University

adiation due primarily to radioactive elements in the
soil. These include Kerala, South India; Yangjiang,
China; Guarapari, Brazil; and Ramsar, Iran (Figure
2-2). Chromosome aberrations, evidence of DNA
damage that could also lead to cancer, are often
measured to assess the potential risk associated with
an exposure, and several rudimentary explorations
of chromosome aberrations in these areas have been
made. In Guarapari, an area with 10-100 times the
normal background exposure, researchers found
an increase of about 30% in chromosome breaks
compared to a control area (Barcinski et al. 1975).
In Kerala exposure has been estimated to be 15-30
times higher than surrounding areas. Kochupillai
et al. (1976) found a significant increase in some
types of aberrations but not others 2 . Preliminary
assessments of Ramsar and Yangjiang have not
detected increases in aberrations compared to local
control areas (Ghiassi-nejad et al. 2002, Hayata et
al. 2000). A series of papers published following
a collaboration between Chinese and Japanese
researchers assessed possible health effects
Background Radiation 15
Figure 2-2. Areas around the world having high external exposure to terrestrial radiation (mSv/yr) (http://www.angelfire.
com/mo/radioadaptive/ramsar.html).
attributable to high background radiation rates in
Yangjiang. This study did not detect an elevated
cancer risk (Sun et al. 2000, Tao et al. 2000, Zou et
al. 2000). A simple cross-sectional survey conducted
in Kerala, in panchayats with background exposures
as high as 70 mGy/yr, did not find a correlation
between cancer incidence and exposure (Nair et al.
1999). Although radiation measurements were made
in over 60,000 houses, the correlation analysis was
made on the panchayat level and did not address any
potential confounding factors.
Radon. As we mentioned above, radon is the
major source of background radiation exposure.
Studies of radon in homes and in mines are hard to
compare with other studies of radiation because of
the nature of radon and the exposure terminology
associated with it. Radon exposure is in truth
exposure to both radon and airborne decay products
of radon, or radon daughters. Radon in mines is
typically measured in working level months (WLM),
a unit that is described in more detail in the section
on miners (section 8). Radon in homes is commonly
2 There was a roughly 2-fold increase in chromatid-type aberrations (not significant) and a significant 10-fold increase
in chromosome-type aberrations.