MEASUREMENT OF RADON CONCENTRATION IN OFFICES WITHIN THREE HIGHER INSTITUTION CAMPUSES IN SOUTHWEST NIGERIA.

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.