NATURAL RADIOACTIVITY AND PHYSICOCHEMICAL PROPERTIES OF WATER FROM SELECTED WATER SOURCES IN AKURE, SOUTHWEST, NIGERIA

Abstract

The quantity and quality of water are prime factors in the selection of any source of water supply. Water samples from streams, hand-dug wells, sachet and bottled water (from different factories), boreholes and rain at selected locations within Akure were collected in order to determine the activity concentrations of 238U, 232Th and 40K in them as well as their physicochemical characteristics. The activity concentrations of 238U, 232Th and 40K, the physicochemical parameters such as temperature, pH, nitrate, sulphate, and total hardness as well as the concentration level of heavy metals such as Cd, Pb, Cr and Fe were evaluated in the water samples in order to determine the quality of water from these sources and their suitability for drinking and domestic uses. Measurements of radioactivity in the water samples were carried out using high-purity (HPGe) detector coupled to Canberra Multichannel Analyzer system. Standard chemical/microbiological methods were used for the determination of physicochemical parameters while the concentration heavy metals were determined using Flame Atomic Absorption Spectrometry (FAAS). In all the water samples analyzed, 40K has the highest mean activity concentration which ranges from 4.99 to 13.09 Bq l-1 followed by Thorium with a range of 0.38 to 1.17 Bq l-1 and Uranium has the lowest concentration with range of 0.25 to 0.82 Bq l-1. The concentration of Pb in water samples ranges from 0 to 0.059 μg l-1, Cd varies from 0 to 0.010 μg l-1 and Cr is below the detectable limit. These results are below the World Health Organization (WHO) and United State Environmental Protection Agency (USEPA) guidelines of 15 μg l-1, the water samples for the selected locations is below the contamination level, and with reference to the National Drinking Water Quality (NDWQS) guidelines, the samples are suitable for drinking because they do not exceed the 10 μg l-1 threshold. The total annual effective dose for age group (0-1yr) from 1.44 × 10−4 to 5.14 × 10−4 mSv y-1, (1-2yr) from 3.58 × 10−5 to vii 1.02 × 10−4 mSv y-1, (2-7yr) from 2.57 × 10−5 to 7.83 × 10−5 mSv y-1, (7-12yr) from 4.73 × 10−5 to 1.24 × 10−4 mSv y-1, (12-17yr) from 2.77 × 10−5 to 7.26 × 10−5 mSv y-1 and (>17yr) from 9.55 × 10−5 to 3.18 × 10−4 mSv y-1. The total annual effective dose for each of the age group is below the ICRP and WHO recommended limit of 1mSv y-1 and 0.1mSv y-1 respectively. The results showed that Adults (>17 yr.) are less susceptible to radiation. The highest concentration of the total annual effective dose was found in bottled water samples while the least was found in stream water.