NATURAL RADIOACTIVITY IN DRINKING WATER FROM DIFFERENT SOURCES IN SOME PARTS OF ONDO STATE, SOUTHWESTERN, NIGERIA.

Abstract

In order to determine the natural activity concentrations of 226Ra, 232Th and 40K in water from different sources in some parts of Ondo State Southwestern Nigeria, fifty samples of water were collected from dug- wells, boreholes, ponds, streams and rivers. The measurement was done using a well-calibrated gamma-ray spectrometry system with high-purity germanium detector. The calculated activity concentrations for 226Ra, 232Th and 40K were used with their ingested dose conversion factors to estimate the annual effective doses for the International Commission on Radiological Protection (ICRP) age groups 0-1 y, 1-2 y, 2-7 y, 7-12 y, 12-17 y and >17 y. The activity concentration values of 40K, 226Ra, and 232Th varied from 0.72±0.04 to 8.02±0.35 Bq/l , 0.20±0.01 to 1.12±0.10 Bq/l and 0.60±0.04 to 1.45±0.06 Bq/l respectively in dug well water samples. Also, the activity concentration values of 40K, 226Ra and 232Th in Borehole water samples varied from 0.94±0.06 to 5.90±0.15 Bq/l, 0.18±0.01 to 1.06±0.14 Bq/l and 0.52±0.04 to 1.04±0.05 Bq/l respectively . In Pond water samples, the activity concentration values of 40K, 226Ra and 232Th varied from 0.25±0.05 to 3.6±0.21 Bq/l, 0.15±0.01 to 0.82±0.04 Bq/l and 0.52±0.10 to 1.64±0.20 Bq/l respectively. The values of activity concentrations of 40K, 226Ra and 232Th in Stream water samples varied from 0.37±0.09 to 4.95±0.12 Bq/l, 0.15±0.01 to 0.34±0.03 Bq/l and 0.52±0.04 to 0.90±0.04 Bq/l . In River water samples, the activity concentration values of 40K, 226Ra and 232Th varied from 0.46±0.02 to 5.38±0.10 Bq/l, 0.17±0.01 to 0.23±0.04 Bq/l and 0.56±0.02 to 1.38±0.20 Bq/l respectively. The calculated annual effective doses equivalent for different age groups due to consumption of water from different sources were below the ICRP recommended limit 1 mSv/y except from the dug wells (0.46 to 1.78 mSv/y) and is common in 0-1 y age group (babies). The severe hereditary and cancer risk effects to adult (>17 y) per year due to ingestion of radionuclides in water from different sources are above the range of acceptable risk values recommended by the United State Environmental Protection Agency (USEPA).