Levels of heavy metals in the raw and processed Ethiopian tobacco leaves

Tobacco (Nicotiana tabacum L.) is a commercial plant. Tobacco leaves naturally accumulate and concentrate relatively high levels of heavy metals and particular cadmium in leaves. Tobacco is one of the basic agricultural products, in Ethiopia, with social and economic importance. However, there is no report in the literature on the determination of levels of heavy metals in Ethiopian tobacco leaves. Hence this research is intended to determine the levels of heavy metals in the raw and processed Ethiopian Virginia tobacco leaves. Samples of raw Virginia tobacco leaves were collected from two different regions of Ethiopia (Billate and Shewa Robit). The three processed tobacco samples were collected from National Tobacco Enterprise, Addis Ababa, Ethiopia. The samples were wet-digested using 3 mL HNO3 (69-72 %) and 3 mL HClO4 (70 %) at 350 °C for 3.5 h and concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in the samples were determined by flame atomic absorption spectrometer. The mean metals concentrations (in µg/g dry weight) in the raw Virginia tobacco leaves from Billate and Shewa Robit, respectively, were: Cu (4.38, 7.30), Zn (53.7, 33.2), Cd (1.20, 1.30), Cr (ND, 1.45), Ni (ND, 1.90). The mean metals concentrations (in µg/g dry weight) in the processed tobacco from Billate and Shewa Robit, respectively, were: Cu (9.80, 12.8), Ni (2.35, 2.20) Cd (1.45, 1.90), Cr (1.65, 1.75), Zn (101, 83.8). The mean metals concentrations (in µg/g dry weight) in the processed tobacco Nyala (Ethiopian cigarette leaves) were: Cu (8.95), Cd (1.55), Cr (1.62), Ni (4.70), Zn (79.3). The concentrations of Cr and Ni in tobacco leaves from Billate and Pb in all the tobacco samples were below the detection limits. This study showed that the metal contents of tobacco leaves varied with the geographical origin in which the tobacco plant grows. The metal contents of processed tobacco were higher than the corresponding raw leaves. Pb was not detected in both the raw and processed Ethiopian tobacco leaves.