Radon concentration in groundwater … Oni O.M. et al Nigerian Journal of Physics Vol. 25(1) June 2014 www.nipng.org 64 RADON CONCENTRATION IN GROUNDWATER OF AREAS OF HIGH BACKGROUND RADIATION LEVEL IN SOUTHWESTERN NIGERIA Olatunde Michael ONI + , Olukunle Olaonipekun OLADAPO ++ , Dauda Biodun AMUDA + Emmanuel Abiodun ONI +++ , Adetola Olufunke OLIVE-ADELODUN + Kemi Yemisi ADEWALE + and Mary Olawumi FASINA + + Department of Pure and Applied Physics Ladoke Akintola University of Technology, Ogbomoso, Nigeria ++ Deaprtment of Science Laboratory Technology Ladoke Akintola University of Technology, Ogbomoso, Nigeria +++ Department of Physics Oduduwa University, Ipetumodu, Nigeria Abstract For over two decades, groundwater has been the dominant source of drinking water in Nigeria. Despite the reported radiological risk associated with the exposure to radon and its progenies, the level of awareness of the presence of this carcinogenic radioisotope in drinking water in Nigeria is low. Water from underground sources is consumed and used for other various household activities without prior treatment, thereby may serve as a radiation source of concern if the concentration of radon in such water is high. A total of 112 samples of groundwater in areas of elevated background radiation level in some cities and towns in southwestern Nigeria were collected and assayed for the radon ( 222 Rn) concentration. The measurement was carried out using RAD7 (DURRIDGE Company Inc., USA). The result revealed a steady trend of variation in the concentration of 222 Rn in water samples from different sources. Highest concentration was found in water from borehole sources. The concentration of radon in all the water samples were found to be above the maximum contaminant level (MCL) presented by the Standards Organisation of Nigeria for radionuclide concentration in drinking water in Nigeria. The 222 Rn concentration from all the water from borehole sources were found to be higher than 11.1 Bq.L -1 stated by the United States Environmental Protection Agency as the MCL in states in the USA without radon monitoring policy and enhanced indoor air program. Irrespective of the sources, 62.8% of the samples collected had radon concentration above the 11.1 Bq.L -1 MCL, while 2.8% of the samples had a concentration above 100Bq.L -1 , a MCL recommended by European Union for measurement that warrants consideration of possible remedial actions. None of the measurements was up to 1000Bq.L -1 recommended by European Union as upper bound value above which remedial action is definitely required. Keywords: Radon in water; RAD7; Cancer of GIT and lung Introduction Radon is a radioactive noble gas soluble in water. It is the most important natural radionuclide contributing to the radioactivity in groundwater. There are three different isotopes of radon, but only radon-222( 222 Rn), with a half life of 3.8 days, formed within the uranium chain by decay of 226 Ra, is of interest as the other isotopes are very short-lived. Radon in water has been reported (EPA, 2003) to contribute significantly to the 222 Rn concentration in indoor air. This is due to the release of dissolved 222 Rn from household water during use. Inhalation of air-bound 222 Rn has been reported in most developed countries to be the second cause of lung cancer after cigarette smoking (EPA, 2003). Further internal exposure from progenies of radon disintegration has been evaluated and reported (Knutsson and Olofsson, 2002; Badhan et al., 2012) being responsible for cases of cancer of other parts of the internal organs, mostly that of the gastrointensinal tract (GIT). With these research findings, measurements of radon concentration in water samples have been carried out in many parts of United Kingdom, United States of America and other developed countries (EPA, 2003; Badhan et al., 2012; NAS 1999). Results of such research activities have led to the setting of limits of the concentrations of radon and other radionuclides in water (Table 1). Literature has it that the highest concentration of 222 Radon is found in groundwater and least in surface water. This concentration however varies from one geologic formation to the other. The peak radon concentration has been reported in granitic rock formation (Knutsson and Olofsson 2002).