Ibrahim et al. 2024 — Heavy metal contamination in staple foods, Jigawa State, northwest Nigeria
This cross-sectional study measured lead (Pb), cadmium (Cd), and total mercury (Hg) in 361 raw staple food samples — cereals (maize, rice, millet, sorghum) and legumes (cowpea, soybean) — collected from households in 4 local government areas of Jigawa State, northwest Nigeria, to investigate the association between food heavy metal contamination and chronic kidney disease burden in the region. Mercury contamination was the dominant finding: 97.8% of households had food Hg levels above the authors’ reference threshold (>0.02 mg/kg), while only 4.2% showed elevated Pb and all showed normal Cd. The study used atomic absorption spectrophotometry (AAS) for analysis.
Key numbers
Mercury (tHg) — dominant finding:
- 97.8% of households had elevated Hg in food (>0.02 mg/kg reference threshold)
- Overall median Hg: not reported as single median; Hadejia LGA had highest Hg (median 3.084 mg/kg, P<0.001)
- Households not cultivating their own food: median Hg 2.503 mg/kg (P=0.05 vs. cultivating households)
- Households not using fertilizer: median Hg 2.522 mg/kg (P=0.02)
- Households with farms outside their communities: median Hg 2.733 mg/kg (P=0.020)
- Households with prior history of kidney disease requiring renal replacement therapy: median Hg 2.54 mg/kg (P=0.05)
Lead (Pb):
- 4.2% of households had elevated Pb (>0.2 mg/kg reference threshold)
- Higher Pb concentrations: households not using fertilizer (median 0.027 mg/kg, P=0.007)
- Higher Pb concentrations: households primarily consuming rice (median 0.023 mg/kg, P=0.005)
- Hadejia LGA had higher proportion with elevated Pb (60.0%, P=0.008)
Cadmium (Cd):
- All 361 households had normal Cd levels (below the 0.2 mg/kg reference threshold)
- Highest Cd: Gumel LGA (median 0.021 mg/kg, P<0.001)
- Younger age group (18–24 years) had significantly higher Cd (median 0.015 mg/kg, P=0.02)
Reference thresholds used by authors: Cd ≤0.2 mg/kg, Pb ≤0.2 mg/kg, Hg ≤0.02 mg/kg (WHO-derived)
Methods (brief)
Cross-sectional survey in 4 LGAs of Jigawa State, Nigeria. Staple food samples collected in plastic containers from 361 households. Samples ground and sieved (100 µm). Digestion with concentrated nitric acid. Analysis by Atomic Absorption Spectrometer (AAS). Precision: 92%–103% recovery; measurements in triplicate. Sampling period: 30 April–21 May 2023. Ethical approval: Jigawa State Ministry of Health Research Ethics Committee (JGHREC/2022/086). Note: the extremely high Hg values (median up to 3.084 mg/kg) are anomalous compared to typical cereal Hg literature values and may reflect AAS method limitations, contamination during digestion, or local environmental Hg sources (gold artisanal mining in the region). The data should be interpreted with caution.
Implications
Certification: The anomalously high Hg findings (97.8% of samples above 0.02 mg/kg, with medians reaching 2.5–3.1 mg/kg) are far outside the range reported by Total Diet Studies for cereals globally and warrant methodological scrutiny before being used as occurrence data for certification standards. Cd findings (all normal) and modest Pb findings (4.2% elevated) are more plausible for subsistence-farmed African cereals.
Courses: The association between rice consumption and elevated Pb (P=0.005) is consistent with rice’s known tendency to accumulate Pb from contaminated paddy water. The LGA-level geographic variation (Hadejia highest for Hg and Pb) may reflect artisanal gold mining activity in the Hadejia River Basin, illustrating supply-chain geography as a contamination driver.
App: The cereal matrix here (raw unprocessed grains) is upstream of final food products. The data are relevant to risk scoring for Nigerian-origin sorghum, millet, maize, and rice ingredients, but the Hg values require verification against laboratory methods of higher specificity before application.