PRELIMINARY REPORT ON RADON CONCENTRATION IN DRINKING WATERAND INDOOR AIR IN KENYA A.O. MUSTAPHA 1,∗ , J.P. PATEL 1 and I.V.S. RATHORE 2 1 Department of Physics, University of Nairobi, P.O. Box 30197, Nairobi, Kenya; 2 Department of Physics, Kenyatta University, P.O. Box 43844, Nairobi, Kenya ( ∗ author for correspondence: tel.: +254-2-447552; fax: +254-2-449616; e-mail: amidu_mustapha@hotmail.com) Received 21 January 2000; accepted in revised form 11 June 2002 Abstract. A screening survey has been carried out to determine activity concentrations of radon ( 222 Rn) in drinking water and indoor air in various locations in Kenya. The concentration of 222 Rn in water was measured using a liquid scintillation counter (LSC). Three different passive integrating devices were used in the measurements of 222 Rn in air. In the short-term measurements, radon is absorbed in activated charcoal and the analyses were carried out using either LSC or gamma ray spectrometry. The long-term measurements were carried out using solid-state nuclear track detectors (SSNTD). The mean and maximum values of 222 Rn concentrations in water are 37 and 410 Bq L -1 and 100 and 1160 Bq m -3 , respectively, in air. The highest values were obtained from groundwater sources and in the basements of buildings. When these values are compared with the internationally recommended reference levels, there are indications of existence of radon problems in some of the water sources and the dwellings tested in this survey. Key words: air, radioactivity, radon, water 1. Introduction Radon, atomic number 86, is a naturally occurring radioactive inert gas. There are “over twenty-six” isotopes of radon, but in terms of their radiological significance, the most important isotopes are 222 Rn (radon) and 220 Rn (thoron). Being decay products of the primordial radioactive elements, uranium and thorium, respectively, 222 Rn and 220 Rn are ubiquitous in all human environments. Most of the radon to which people are exposed emanates from soil and rock. The other sources of signi- ficance are building materials, potable water, and natural gas (UNSCEAR, 1993). The link between residential radon and lung cancer among the general public is not unequivocal (Letourneau et al., 1994; Ruosteenoja et al., 1996). However, in order to forestall risks of cancer among the general public, many national authorities and some international organizations (Ahmed, 1993; Colgan and Gutierrez, 1996) have already adopted reference levels for radon in air and water. This paper presents the results of a screening survey on the concentrations of radon in indoor air and in drinking water carried out in Kenya. The objective of the survey is to determine the range of radon levels in the environment and thereby es- tablish whether or not there is radon problem in Kenya. As a result of the analytical Environmental Geochemistry and Health 24: 387–396, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.