Assessment of Radiological Risks, Radiogenic Heat and Natural Radioactivity in Kamukuywa River Sediments in Mt. Elgon Bungoma County, Kenya

The activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K in sediments from the Kamukuywa River in Bungoma County were determined using a NaI(Tl) detector at South Eastern University Kenya, Physics Department in order to obtain the radium equivalent, absorbed dose rate, annual effective dose rate, hazard indices, radioelement concentrations (RC) and radiogenic heat production (RHP). The average activity concentrations for ²³⁸U, ²³²Th and ⁴⁰K were 31 ± 2 Bq·kg⁻¹, 51 ± 3 Bq·kg⁻¹, and 57 ± 3 Bq·kg⁻¹, respectively. The average activity concentrations of ²³⁸U and ⁴⁰K were less than the global limits of 35 Bq·kg⁻¹ and 400 Bq·kg⁻¹. The average activity concentration of ²³²Th exceeded the international limit of 50 Bq·kg⁻¹. The activity concentration ranged from 19 ± 1 to 48 ± 2 Bq·kg⁻¹ for ²³⁸U, 17 ± 1 - 89 ± 4 Bq·kg⁻¹ for ²³²Th and 35 ± 2 - 90 ± 5 Bq·kg⁻¹ for ⁴⁰K. Radioelement concentrations ranged from 1.5 - 3.9 ppm for ²³⁸U, 4 - 21 ppm for ²³²Th and 11 - 28 ppm for ⁴⁰K, with averages of 2.5 ppm, 12 ± 1 ppm and 18 ± 1 ppm for each. The RHP for ²³⁸U, ²³²Th and ⁴⁰K was 0.001 µW·m⁻³ with a range of 0.001 µW·m⁻³ - 0.002 µW·m⁻³, 0.009 µW·m⁻³ with a range of 0.003 µW·m⁻³ - 0.016 µW·m⁻³ and 0.013 µW·m⁻³ with a range of 0.008 µW·m⁻³ - 0.021 µW·m⁻³. The average radiogenic heat production (RHP) for all radionuclides was 0.08 µW·m⁻³, lower than the global average of 4 µW·m⁻³ and ranging from 0.05 - 0.14 µW·m⁻³. Radium equivalent averaged 109 ± 6 Bq·kg⁻¹, with a range of 55 ± 3 to 173 ± 9 Bq·kg⁻¹. The internal and external hazard indices averaged at 0.2 mSv·y⁻¹, with a range of 0.1 mSv·y⁻¹ - 0.4 mSv·y⁻¹ and 0.3 mSv·y⁻¹, respectively. The extra lifetime cancer risk averaged 0.5 × 10⁻⁴ mSv·y⁻¹, while the annual gonadal equivalent dosage averaged at 330 ± 17 mSv·y⁻¹. The average exposure rate was 47 ± 2 nGy/h, with an annual effective dose rate of 0.1 mSv·y⁻¹ for both indoors and outdoors. All samples had radium equivalent, hazard index and annual effective dose rate values that were less than the globally accepted limits of 370 Bq·kg⁻¹ and 1 mSv·y⁻¹, respectively. As a result, sediment samples collected from Kamukuywa River pose low health risks to the general public. The heat flow (Hf) averaged at 7 mW·m⁻² and ranged from 4 to 11 ± 1 mW·m⁻². The Hf and RHP levels indicate that geothermal exploration in Bungoma County’s Kamukuywa River is possible.