Levels of essential and non-essential metals in Rhamnus prinoides (Gesho) cultivated in Ethiopia

Abstract

The objective of this study was to assess the levels of essential and toxic metals in leaf and stem of Rhamnus prinoides which are used for bitterness of local alcoholic beverages in Ethiopia and as traditional medicine in some African countries. Levels of essential metals (Ca, Mg, Cr, Mn, Fe, Co, Ni, Cu and Zn) and toxic metals (Cd and Pb) in the leaves and stems of Rhamnus prinoides (Gesho) cultivated in Ethiopia were determined by flame atomic absorption spectroscopy. Known weights (0.5 g) of dried samples were digested with the optimized mixture of HNO₃, H₂O₂ and HClO₄ on a Kjeldahl apparatus with a reflux condenser. The efficiency of the optimized procedure was validated by spiking experiment and the percentage recovery for all the metals was in the range of 92–103% for leaf samples and 91–103% for the stem samples. The levels (mg/kg) of the metals were found to be: Ca (6304–22236), Mg (3202–5706), Cr (5.08–20.6), Mn (8.12–17.9), Fe (47.9–187), Co (22.2–42.1), Ni (12.8–27.3), Cu (6.5–73.0), Zn (12.2–43), Cd (0.81–3.10), and Pb (17.7–25.0) in the leaf samples and Ca (3601–5675), Mg (2635–5528), Cr (ND–16.3), Mn (2.16–3.98), Fe (22.0–124), Co (18.7–91.7), Ni (9.68–19.2), Cu (16.8–233), Zn (17.4–28.2), and Cd (ND–1.56) in the stem samples. However, the levels of Cr and Cd in stem samples at one and two sample sites, respectively, and the levels of Pb in stem samples at all sample sites were below the method detection limit. This study showed that the leaf and stem of R. prinoides (Gesho) are good sources of essential minerals and virtually free from toxic metal Cd but not from Pb in the leaf.

KEY WORDS: Rhamnus prinoides, Gesho, Leaf, Stem, Minerals, Alcoholic beverages, Ethiopia

Bull. Chem. Soc. Ethiop. 2012, 26(3), 329-342.

DOI: http://dx.doi.org/10.4314/bcse.v26i3.2