Food Safety Assessment: Trace Metal Concentrations in Onion (Allium cepa L.) from Kewot District, North Shoa, Ethiopia

The present investigation focused on assessing the concentrations of heavy metals in onion bulb samples collected from two kebeles (townships) within North Shewa, Ethiopia, a region known for extensive cultivation of onions (Allium cepa L). Onion bulbs (Allium cepa, L.) were randomly collected from the farms in Yelen Kebele and Kewot District Terre. Following appropriate pre-treatment, ICP-MS was used to determine the concentration levels of selected metals. The optimum parameters of 240oC digestion temperature, (3mL of 69% HNO3, 2mL of 37% HClO4, and 0.5ml of 30% H2O2) volume of reagents and 3 hours’ digestion time were employed. The results obtained showed that the average concentrations of Zn, Cu, Pb and Cd in onion bulb samples were in the range of 2.15-3.05 mg/kg, 0.10-0.125 mg/kg, 0.03-0.04 mg/kg, 0.0001 mg/kg respectively. The percentage relative standard deviations were 17.0 to 19.9%, 3.4 – 3.5%, 7.0 t0 9.5% and 10.0% for Zn, Cu, Pb and Cd, respectively. The accuracy of the method, expressed as percentage recovery, was in the range of 95.3 -113.5%, with corresponding %RSD (n = 3) values ranging from 1.7–6.5% being obtained. Results of comparison of the level of metals with WHO/FAO standard limits revealed that the level of all analyzed heavy metals were below the corresponding metals permitted values for vegetables. Health risk assessment of onions from Terre and Yelen revealed very low estimated daily intakes and target hazard quotients for Zn, Cu, Pb, and Cd, with cumulative hazard indices well below the safety threshold of 1. This indicates negligible non-carcinogenic health risks from consuming these onions. Therefore, onions from both kebele are considered safe regarding heavy metal contamination.