Levels of Trace and Other Selected Metals in Mixed Teff Grain Samples

Teff (Eragrostis tef (Zuccagni)) is a hugely important crop to Ethiopia both in terms of production and consumption. In terms of production, teff is the dominant cereal by area coverage and second only to maize in production and consumption. The principal use of teff grain for human food in Ethiopia is in the form of Injera, a soft porous thin pancake with a sour taste. In this study, the levels of some selected essential and trace metals in the mixed teff grain samples were determined in the samples collected from the three selected sampling areas (Bure, Debre Markos, and Bahir Dar) of Ethiopia. After proper sample pretreatment, 5 mL HNO₃: 1 mL HClO₄, 240°C, and 2:30 h were the optimized digestion conditions. Then using the optimized conditions sample preparation was made and the levels of metals were determined by the Micro-Plasma Atomic Absorption Spectroscopy (MP-AES). The overall mean concentrations determined (mg/kg, dry weight) were in the ranges of Al (713-832) >Fe (252-694) >Ca (253-286) >Zn (69-87) >Mn (24-36) >Cu (13) >Pb (1.8-2.8) >Cd (1.8). The results indicated that mixed teff grain is a good source of essential metals but not free from the toxic metals Cd and Pb, the concentrations of Cd and Pb were higher than the WHO guidelines (0.1 and 0.2 mg/kg, respectively). The accuracy of the optimized procedure was evaluated by analyzing the digest of the spiked samples with a standard solution and the percentage recoveries varied from 92 to 104%, which is good and is in the allowed range of 90% ±10. ANOVA indicated that there is no significant difference between the mean concentrations of Cd and Pb among the mixed teff samples, but a significant difference for the other studied metals at a 95% confidence level.