RADON CONCENTRATION IN GROUNDWATER OF AREAS OF HIGH BACKGROUND RADIATION LEVEL IN SOUTHWESTERN 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.