Abstract:
The aim of this study was to determine the levels of selected heavy metal (Fe, Mn, Zn,
Cu, Pb and Cd) of the onion bulbs, the wastewater used to irrigate the crops, and the
soil on which the crops were grown, using Inductively Coupled Plasma Optical
Emission spectroscopy (ICP-OES). The digestion procedure was employed to solubilise
the metals from the samples. The validation was performed by spiking the samples with
a standard solution of each metal having a known concentration and the percentage
recovery values of studied metals were in the range of 89– 120% for soil, 80–119% for
wastewater, and 78–113% for onion bulb samples. And the validation was performed by
precision in terms of RSD values were ≤11% for all the mean concentrations metals,
except Cu (BLD) in wastewater and the limit of detection (LOD) and limit of
quantification (LOQ) values were low for all studied heavy metals determined, except
for Pb, (= 0.099 and 0.33 mg/kg) for soil, (= 0.012 and 0.04 mg/kg) for wastewater
and= 0.042 and 0.14 mg/kg) for onion bulb, respectively. These showed the method was
reliable and accurate. And also the analytical curves presented good linearity with
squared regression coefficients (R2) higher than 0.99 for all the metals studied. The
average concentrations (mg kg-1) of the heavy metals in the wastewater samples were:
BDL for Cu, 5.94 for Fe, 0.401 for Mn, 0.286 for, 0.056 for Pb and 0.016 for Cd and the
study revealed that the levels of all selected heavy metals, except for Cu (BDL), were
found to be higher than the permissible limit set by WHO and USEPA. Similarly,
average concentrations (mg kg-1) of the metals in the soil samples were: 18.95 for Fe,
463.62 for Mn, 57.27 for Zn, 3.10 for Cu, 17.98 for Pb and 1.60 for Cd and the study
revealed that the level of Mn, were found to be above the standard limits set by (WHO).
The following average concentrations (mg kg-1) of the metals were found in the edible
parts of the onion bulbs: Fe (13.8), Mn (21.24), Zn (20.41), Cu (5.29), Pb (22.05) and
Cd (0.476). The study revealed that the levels of Pb and Cd in the onion bulbs that were
grown in KARC were found to be above the safe limits set by FAO/WHO for
consumption, posing a serious health hazard to humans. Therefore, regular monitoring
of malting wastewater, soils, and vegetables are essential to prevent excessive
consumption onion. Hence, regular monitoring of wastewater, soils, and vegetables are
essential to prevent excessive metal contamination of wastewater and soil for irrigation
