Heavy Metals and Essential Elements in Selected Medicinal Plants Commonly Used for Medicine in Tanzania

Several plants in Tanzania are known to be of potential therapeutic value and are used in traditional medicine system of the country. In this paper, two medicinal plants Moringa oleifera (leaves and roots), and Hibiscus sabsdariffa (rosella calyces) were analysed for elemental concentration. Essential and non-essential heavy metals like Mg, K, Mn, Fe, Ni, Cu, Zn, Cd and Pb were quantified in selected medicinal plants by EDXRF technique. The main purpose of this study is to document the presence and the levels of heavy metals in these herbs. High Potassium contents were observed to be 20882.20 ± 253.65 mg/kg in Moringa oleifera roots, in Hibiscus sabsdariffa (rosella calyces) 15732.03 ± 191.27 mg/kg, and 14541.08 ± 206.83 mg/kg in Moringa oleifera leaves. Magnesium was the second abundant element with concentration (5058.13 ± 115.80 mg/kg in Moringa oleifera leaves, 4328.86 ± 132.85 mg/kg Hibiscus sabsdariffa and 1400.59.59 ± 72.09 mg/kg in Moringa oleifera roots), followed by Iron (716.57 ± 48.05 mg/kg in Hibiscus sabsdariffa, 556.44 ± 11.77 mg/kg and 309.57 ± 8.96 mg/kg in Moringa oleifera roots and leaves respectively. Except Fe and Ni in all plant samples and Mg in leaves of Moringa oleifera and calyces of Hibiscus sabsdariffa as well as Mn in roots of Moring oleifera, the concentrations of other metals were below the permissible limits in plants set by FAO/WHO. The results presented that there is no risk associated with consumption of analysed medicinal plants. However, since Cd was not detected and it is highly toxic even at very low concentrations. Therefore, further analysis which will employ other analytical techniques and includes more samples is needed to have a definite statistical conclusion on the safety consumption of the analysed medicinal plants. The results also show that the analysed plant species are beneficial sources of appropriate and essential trace elements.