Risk assessment of natural radioactivity in surface water and sediments from a waterfall site in Osun State, Nigeria

Activity concentration of natural radionuclides in surface water and sediment from a waterfall site, Erin-Oke, Osun, Nigeria, has been determined by gamma spectrometry. The mean activity concentration of K-40, Ra-226, and Th-232 were estimated to be 61.015 +/- 15.50, 8.165 +/- 2.05 and 5.24 +/- 1.57 Bq/l, respectively in water samples and 172.023 +/- 35.433, 19.282 +/- 4.95, and 17.089 +/- 4.37 Bq/kg respectively in sediment samples. Total annual effective dose ingested by an individual ranges from 10.73 +/- 3.36 to 15.18 +/- 4.44 mSv/y, 2.50 +/- 0.80 to 3.58 +/- 0.96 mSv/y, and 2.30 +/- 0.72 to 3.23 +/- 0.93 mSv/y, with mean values of 13.25 +/- 3.89, 3.10 +/- 0.90, and 2.83 +/- 0.83 mSv/y for infants, children, and adults, respectively. These values are greater than International Commission on Radiological Protection (ICRP) and the World Health Organization's recommended limit of 1.0 and 0.1 msv/y, respectively. Mean activity concentrations in sediment are 172.023 +/- 35.433, 19.823 +/- 4.95, and 17.089 +/- 4.37 Bq/kg for K-40, Ra-226, and Th-232, respectively, with mean absorbed dose of 26.91 nGyh(-1). This value is lesser than UNSCEAR world average value of 55 nGyh(-1). Health hazard index and radium equivalent for sediments showed lower values than absorbable limits.