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

Abstract

Tobacco is a commercial plant that can accumulate heavy metals in its leaves. In this study, we investigated the levels of selected heavy metals (Mn, Cu, Zn, Cd, and Pb) in tobacco leaves and their growing soils from Assosa District, Benshangul Gumuz Regional State, Ethiopia. Both 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 metals into the samples, ranged 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 (NQ) - 0.01 mg/kg, Cd. In soil samples, their concentrations 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 leaf sample, Pb was below the limit of quantification (LOQ). Similarly, in all soil samples, the concentration of Cd was below LOQ. The findings indicate that the concentrations of the studied heavy metals in both tobacco leaves and soil samples are below their WHO permissible limits in soil and plants. However, the levels of Zn in Amba and Basha tobacco leaves were higher than the WHO permissible limit in plants.

Keywords

• Tobacco leaves
• Soils
• Heavy metals
• Digestion

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