Quantification and health risk assessment of heavy metals in milled maize and millet in the Tolon District, Northern Ghana

Abstract

This study was conducted to quantify the levels and measure the health risk of selected heavy metals (Fe, Zn, Pb, Mn, Cr, Ni) in milled millet and maize from 10 communities in the Tolon District, northern region of Ghana. Control samples of maize and millet were also prepared in order to identify whether the sources of the heavy metals were limited to the milling process or otherwise. The heavy metals present in the collected milled samples were quantified using an AAS Varian Spectra 220 FS. The average concentrations of the selected heavy metals in the milled maize samples were the following: Fe = 1.3392 ± 0.4341 mg/kg, Ni = 0.9502 ± 0.2696 mg/kg, Pb = 2.2177 ± 0.0534 mg/kg, Cr = 0.4359 ± 0.3574 mg/kg, Zn = 0.6809 ± 0.0534 mg/kg, and Mn = 0.3550 ± 0.1042 mg/kg. Milled millet samples recorded mean concentration of the heavy metals as Fe = 1.9467 ± 1.0597 mg/kg, Ni = 0.9520 ± 0.1218 mg/kg, Pb = 2.2780 ± 0.0221 mg/kg, Cr = 0.3421 ± 0.1498 mg/kg, Zn = 0.8540 ± 0.1139 mg/kg, and Mn = 0.4241 ± 0.0859 mg/kg. All selected heavy metals concentrations were below standards in food except Pb. Locally made mill plates were found to leach heavy metals in the milled flours due to the direct contact of the grains with the mill plates. However, the comparison of milled to pounded flour (control samples) indicated other potential sources of heavy metals aside from the disk attrition mill. The health risk assessment revealed no potential hazards nor cancer risk in both children and adults.

Keywords: disk attrition mill; heavy metals; metal leach; mill plates; milled millet and maize.