Natural Radioactivity, Transfer Factor and Associated Radiological Risk in Commercially Cultivated Yam (Dioscorea Rotundata) in Northcentral Nigeria

Abstract

Human food chain can become contaminated either by direct radionuclide deposition, absorption from radionuclide-polluted soil and water by plant roots and direct ingestion of polluted plants, soil or water by animals. In this study, activity concentrations of primordial radionuclides in soil and yam (Dioscorea rotundata) samples from a commercially cultivated yam farm in northcentral Nigeria were analyzed using a 3″ × 3″ NaI(Tl) gamma detector. Results show that mean specific activities of ²³⁸U, ²³²Th and ⁴⁰K in soil and yam samples were 40.36 ± 3.97, 14.71 ± 0.80, 385.63 ± 16.54 Bq kg⁻¹, and 31.11 ± 4.00, 11.82 ± 0.72, 466.96 ± 27.20 Bq kg⁻¹ respectively, which are within limits of safety set by the United Nations Scientific Committee on the Effect of Atomic Radiation. The average absorbed dose for soil samples was 43.63 nGy h⁻¹ with corresponding mean annual effective dose of 0.05 mSv y⁻¹. Yam samples recorded mean absorbed dose rate of 42.61 nGy h⁻¹ with corresponding mean annual effective dose of 0.05 mSv y⁻¹, which were within international safety limits. Computed average soil-to-yam transfer factor was 0.70, 0.83 and 1.23 respectively for ²³⁸U, ²³²Th and ⁴⁰K. Transfer factors for ²³⁸U and ²³²Th were below unity, while for ⁴⁰K was significantly moderate, showing that bioaccumulation of natural radionuclides in the Nigerian grown yam does not pose any immediate radiological threat for public consumption. The yam tubers are therefore fit, not just for consumption, but also for export to other nations from a radiological perspective. Routine radiological checks of food crops are however encouraged in compliance with the ALARA provisions.