Levels of Natural Radionuclides in Khat (Catha Edulis) Leaves and Soils in Selected Areas in Embu County, Kenya
Ngari, Vindesio Njagi
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Environmental data and information on levels of accumulation of radionuclides is crucial towards putting in place mitigation measures to ensure a safe environment. Over the past years, khat (Catha edulis) has been the major cash crop grown in some parts of the Eastern side of Kenya especially in Embu and Meru areas. The khat grown in Embu which is the study area is mainly the Muguka variety while the variety grown in Meru is the Miraa. The leaves from this plant are chewed for their stimulating effect. However, some studies have reported detrimental effects on the users of khat. In spite of its extensive use which extends to the Arabian Peninsula and the European markets, research on radionuclide concentrations in khat and in soils where it is grown has not been done. This therefore necessitated this research in order to provide public awareness on natural radiation levels. This research established the level of human exposure due to radiation by natural sources in the khat growing areas of Embu County by measuring the specific activities of 238U, 232Th and 40K, estimate the dose rate absorbed and obtain the hazard indices due to these radionuclides. Thirty samples were collected from different areas distributed throughout Embu County. The samples were then prepared and analyzed using the NaI(Tl) detector. The mean activities for khat leaves were obtained as 875.8±11, 10.1±1 and 51.1±4 Bq/kg for 40K, 238U and 232Th respectively. The activities of soil in the same region were however lower than the world average at 344±12, 22±11 and 33±5 Bq/kg for 40K, 238U and 232Th respectively. The mean absorbed dose rates obtained for soil was 44±0 nGyh-1 which is lower than the admissible dose standard of 1500 nGy/h. The AED for ingested radionuclides for khat had an average of 0.45±0.19 mSv/y. The average values of hazard indices for soil were 0.26, 0.32, 0.70 and 0.76 for external index, internal index, gamma index and ELCR respectively. All the indices in this work were within the safe. Results from this study therefore reveal that the khat grown in the Embu County poses no significant risk to the consumers and the general populace. The soils from the area are also safe for humans.