Levels of metals in commercially available Ethiopian black teas and their infusions

Abstract

K, Ca, Mg, Mn, Fe, Zn, Cu, Co, Cd and Pb contents of commercially available Ethiopian black tea (Wushwush, Gumero, and Black Lion) and their infusions were analyzed by flame atomic absorption spectrometry (FAAS). In black tea leaves the order of metal content was found to be: K (11503–13780 mg/kg) > Ca (3821–4419 mg/kg) > Mg (3219–3538 mg/kg) > Mn (1242–1421 mg/kg) > Fe (319–467 mg/kg) > Zn (20.2–21.6 mg/kg) > Cu (9.1–11.5 mg/kg). Co, Cd and Pb were too low to be detected by the method (FAAS). In tea infusion, prepared in a laboratory condition following Ethiopian tea making procedures, the range of metal contents was found as follows: K (110–124 mg/L) > Mg (14.5–16.3 mg/L) > Ca (10.0–10.7 mg/L) > Mn (8.5–13.4 mg/L) > Fe (0.98–1.56 mg/L) > Zn (0.098–0.100 mg/L) > Cu (0.038–0.063 mg/L). The metal contents of the black tea leaves were higher than those of tea infusions. The extraction was highest for K (47.1%) and lowest for Ca (12.5%).

KEY WORDS: Tea (Camellia sinensis), Black tea, Tea infusion, Heavy metals, Flame atomic absorption spectrophotometer (FAAS)

Bull. Chem. Soc. Ethiop. 2010, 24(3), 339-349.