Abstract:
Indoor radon (222Rn) has been identified as the second leading cause of lung cancer after tobacco
smoking. In this study, one hundred solid state nuclear track detectors, CR-39 (Poly Allyl Di-
Gycol) purchased from Track Analysis System Limited were used to measure 222Rn levels in
selected offices within three higher institution campuses in South-Western Nigeria, from which
the annual effective dose, probability of lung cancer induction and expected mortality rate of the
occupants of the offices were estimated. The detectors were exposed for a period of three to four
months in the offices, after which they were retrieved, etched and the tracks were counted for
indoor radon concentration estimation. The mean indoor radon concentration for the selected
offices of Federal University of Technology Akure (FUTA), Ekiti State University (EKSU) and
Federal University Oye-Ekiti (FUOYE) were estimated to be 215.67 ± 43.43 Bq m-3, 153.14 ±
29.83 Bq m-3, 297.47 ± 59.74 Bq m-3 respectively. The mean radon concentration observed in
these institutions were within the recommended action level value of World Health Organization
(WHO) 100 to 300 Bq m-3. The mean annual effective dose equivalent for FUTA, EKSU, and
FUOYE were estimated to be 3.49 ± 0.70 mSv y-1, 2.48 ± 0.48 mSv y-1, and 4.82 ± 0.96 mSv y-1
respectively, which are within the range of the recommended International Commission on
Radiological Protection (ICRP) level of 3 - 10 mSv y-1. The estimated risk probability of lung
cancer induction increases with increase in the age at which the occupants were exposed to each
radon level. For the three institutions, the probability of lung cancer induction at age 70 years
with respect to age of exposure ranged between 1.58x10-7 and 6.24x10-5. The expected mortality
rate due to exposure to a radon concentration ranging from 6.88 to 1357.70 Bq m-3 was estimated
to range from 0 to 44 deaths among the population of 10000 persons. According to these
findings, the chances of dying from lung cancer due to exposure to 222Rn increases with increase
in concentration.
