Getu et al. 2022 — Heavy metals in cereals from Debre Markos market, Ethiopia
This paper measured Cr, Cu, Pb, and Cd in four cereal types (barley, tef, wheat, and maize) purchased from local market in Debre Markos, Northwest Ethiopia, by MP-AES after dry ashing digestion. Lead and cadmium were found above the FAO/WHO permissible limits in all four cereal types, while chromium and copper were below their respective limits. The study highlights heavy metal contamination in a key Ethiopian staple food supply linked to chemical fertilizer use (diammonium phosphate and urea) in the region.
Key numbers
Concentrations as mean ± SD (mg/kg dry weight) by MP-AES (Agilent 4210):
Lead (FAO/WHO limit 0.2 mg/kg):
- Barley: 0.49 ± 0.031 mg/kg (490 ± 31 ppb dw)
- Tef: 0.34 ± 0.121 mg/kg (340 ± 121 ppb dw)
- Wheat: 0.52 ± 0.029 mg/kg (520 ± 29 ppb dw)
- Maize: 0.37 ± 0.15 mg/kg (370 ± 150 ppb dw)
- All four cereals exceed the FAO/WHO permissible limit of 0.2 mg/kg by 1.7–2.6x
Cadmium (FAO/WHO limit 0.1 mg/kg):
- Barley: 2.01 ± 1.73 mg/kg (2010 ± 1730 ppb dw)
- Tef: 1.84 ± 1.60 mg/kg (1840 ± 1600 ppb dw)
- Wheat: 1.95 ± 1.69 mg/kg (1950 ± 1690 ppb dw)
- Maize: 1.93 ± 1.67 mg/kg (1930 ± 1670 ppb dw)
- All four cereals exceed the FAO/WHO permissible limit of 0.1 mg/kg by 18–20x; high variability (SDs comparable to means) indicates significant batch-to-batch variation
Chromium (FAO/WHO limit 2.3 mg/kg):
- Barley: 2.20 ± 0.072 mg/kg; Tef: 2.22 ± 0.061 mg/kg; Wheat: 1.57 ± 0.48 mg/kg; Maize: 1.84 ± 0.26 mg/kg
- All below limit; barley and tef near baseline
Copper (FAO/WHO limit 30 mg/kg): all samples 1.28–2.94 mg/kg, well below limit
Recovery test: 85.6–112.8% (within accepted 80–120% range). Correlation coefficients R² 0.9966–0.9983.
Methods (brief)
Dry ashing at 550°C; dissolution in 6M HCl; filtration and dilution to 50 mL. MP-AES (Agilent 4210) with wavelengths 425.433 nm (Cr), 324.754 nm (Cu), and associated Pb and Cd lines. Triplicate digestion and triplicate analysis. Standard solutions prepared from 1000 ppm stock solutions. Samples collected October 2019–August 2020 from composite bulk samples of 40 merchants per cereal type.
Implications
Certification: Ethiopian cereal supply shows markedly elevated Pb and especially Cd, likely reflecting fertilizer-derived contamination. Pb values 1.7–2.6x above FAO/WHO limits and Cd values 18–20x above limits are substantial. Origin traceability for Ethiopian grain sourcing warrants lot-level metals testing.
Courses: illustrates how agricultural chemical inputs (phosphate fertilizers) contribute to Cd accumulation in cereals globally, and the relevance of geographic origin.
App: barley, wheat, and maize from Ethiopia flag as elevated risk for Pb and Cd based on available literature.