The levels of major (Na, K, Ca and Mg), trace (Cu, Co, Cr, Mn, and Zn), and toxic (Cd and Pb)
metals in onion (Allium cepa L.) bulbs and irrigation water were determined by flame atomic absorption
spectroscopy (FAAS). Dissolution of onion samples was carried out by wet digestion with a total volume of 2 mL
HNO3 (69-72%) and 2 mL HClO4 (70%) mixture in a flask fitted with reflux condenser on Kjeldahl heating
apparatus. The levels of major metals were Na (208 and 121 µg/g), K (3127 and 3298 µg/g), Ca (599 and 550
µg/g) and Mg (516 and 407 µg/g) in onion irrigated with water from well and Lake Ziway, respectively. Among
the trace metals (µg/g dry weight), Zn was the highest (18 and 14) followed by Mn (8.8 and 13), Cr (4.9 and 6.6),
Cu (3.2 and 3.6), and Co (1.2 and 1.8) in onion irrigated with water from well and Lake Ziway, respectively. The
toxic metal Cd was 0.6 and 0.5 µg/g in onion irrigated with well and lake waters, respectively, while Pb was
below method detection limit. The levels of Na, K, Ca and Mg detected in well water and the Lake Ziway water
used for irrigation were (9.4, 4.6 mg/L), (43, 13 mg/L), (23, 10 mg/L) and (30, 8.6 mg/L), respectively. Higher
levels of Zn (0.08 mg/L) and Co (0.06 mg/L) were found in the lake water while higher Mn (1.1 mg/L) and Cr
(0.44 mg/L) in well water. The toxic metal Pb in both well and Lake Ziway water, and Cd in well water samples
were below the method detection limits. Mn in well water and Cr in both water samples exceeded the FAO limit
of maximum recommended level in irrigation waters.