RESUMO
Presently, the British-American Tobacco Company [BAT] located in Ibadan, Oyo State is the only tobacco producing company in Nigeria accounting for about nine different brands of cigarette tobacco smoked in the country. The tobacco leaves are produced from some farmlands located in Oke-Ogun area of Ibadan where special fertilizers are used for the growing of the tobacco leaves. The use of this fertilizer may enhance natural radionuclide contents in the farm soils and through root uptake be accumulated in the leaves. In this study, soil samples from three farmlands used for the production of the tobacco leaves were collected in order to determine the activity concentrations of [226]Ra, [232]Th and [40]K in the farm soil. Measurements for the determination of the activity concentrations were carried out using gamma-ray spectrometry comprising a lead-shielded 76 mm _ 76 mm NaI[Tl] detector crystal [Model 802 series, Bicron Nal] coupled to a Canberra series 10 plus multichannel analyzer [MCA] [model 1104] through an preamplifier base. Results of measurements showed that the average activity concentrations of the natural radionuclides in the soil samples across the three farms varied from 2550.4 +/- 154.6 to 3208.9 +/- 188.7 Bq kg[-1] for [40]K, 33.1 +/- 11.9 to 39.9 +/- 9.3 Bq kg[-1] for [226]Ra, while for [232]Th it varied between 51.98 +/- 8.4 and 56.08 +/- 17.51 Bq kg[-1]. The activity concentrations of these radionuclides and gamma absorbed dose rates due to the concentration of these radionuclides were found to be higher than world average values while those of the control farm values were lower to world averages and the tobacco leaf farms. From the results obtained the fertilizer type used on the farmlands for the tobacco leaf production was very rich in [40]K with typical values greater 2000 Bq kg-[1]. Also there may be possible high signatures of [210]Pb and [210]Po in the tobacco leaves and the cigarette samples smoked in the country. This is a subject for future research consideration given the fact that alpha radiation plays a major role in the etiology of lung cancer