Determination of Selected Heavy Metals in Tobacco Leaves and Their Farmland Soils of Assosa District, Benshangul Gumuz Regional State, Ethiopia

Abstract

Tobacco is a commercial plant that can accumulate heavy metals in its leaves. In this study, the levels of selected heavy metals (Mn, Cu, Zn, Cd, and Pb) were determined in tobacco leaves and its farmland soils from Assosa District, Benshangul Gumuz Regional State, Ethiopia. All samples were collected from five tobacco farmlands. The samples were digested before quantitative determinations of the metals via inductively coupled plasma optical emission spectroscopy (ICP-OES). Repeatability and recovery studies were used to evaluate the efficiency of the method. Repeatability was evaluated by analyzing replicate samples and expressed as relative standard deviations (RSD%) were below 10.0. Recovery or percent recovery (R%) studies which were performed by spiking known concentrations of the metals into the samples from 85.67 -111.33% and 84.25 -114.00% for tobacco leaves and soil samples, respectively, indicating that the employed method is valid for the analysis of the metals. The concentrations of metals in tobacco leaf samples were 0.75 1.18 mg/kg, Mn; 0.11 -0.21 mg/kg, Cu; 0.58 -1.16 mg/kg, Zn; and not quantified -0.01 mg/kg, Cd whereas their concentrations in soil samples were 1.59 -8.04 mg/kg, Mn; 0.32 -0.38 mg/kg, Cu; and 0.29 -1.26 mg/kg, Zn; and 0.17 -0.31 mg/kg, Pb. Except in one tobacco leaves sample, Pb concentration was below LOQ. Similarly, in all soil samples, the concentration of Cd concentration was below LOQ. The findings indicated that the concentrations of the studied heavy metals in both tobacco leaf and soil samples were below the critical limits.