Assessment of Heavy Metal Profiles (Pb, Cd, Cu, Zn, As, and Hg) in Onion Bulbs Using Atomic Absorption Spectroscopy
Yusuf Ismail Koleleni *
Department of Physics, Muslim University of Morogoro, P. O. Box 1031, Morogoro, Tanzania.
*Author to whom correspondence should be addressed.
Abstract
This study assessed the concentrations of selected elements in onion (Allium cepa L.) bulbs collected from four onion-producing regions of Tanzania: Morogoro, Iringa, Singida and Dodoma. The elements assessed were lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), arsenic (As) and mercury (Hg). Samples were washed with deionised water, oven-dried, homogenised and subjected to acid digestion before analysis using atomic absorption spectroscopy (AAS). Inductively coupled plasma mass spectrometry (ICP-MS) was described as a complementary technique where required. The reported Pb concentrations were 4.20, 3.20, 2.00 and 3.50 mg/kg in Morogoro, Iringa, Singida and Dodoma, respectively, with Morogoro recording the highest value. Cadmium ranged from 0.03 to 0.07 mg/kg, while Zn ranged from 70.0 to 105.3 mg/kg according to the tabulated results. Arsenic concentrations ranged from 0.08 to 0.14 mg/kg. Mercury was reported at 0.02 mg/kg in Morogoro and 0.01 mg/kg in both Iringa and Dodoma, but was not detected in Singida. Comparisons with the thresholds stated in the manuscript suggested potential food-safety concerns, particularly for Pb. These regional differences support further monitoring of onion bulbs and verification of the analytical results, including reported discrepancies between the tables and narrative text. The findings provide region-specific observations but do not establish the sources of metal accumulation or quantify dietary exposure.
Keywords: Onion bulbs, Allium cepa, atomic absorption spectroscopy, mineral profiling, heavy metals, lead, cadmium, zinc, arsenic, food safety