Teferi et al. 2026 — Heavy metal contamination and health risks in honey from Kellem Wollega Zone, Ethiopia
Honey samples from three districts in the Kellem Wollega Zone of western Ethiopia were analyzed for seven metals (Cu, Fe, Mn, Ni, Zn, Cd, Pb) by ICP-OES after wet acid digestion. Cadmium concentrations (1.38–2.30 mg/kg) and lead concentrations (18.00–21.42 mg/kg) far exceeded the EU maximum limit for Cd in honey (0.05 mg/kg per Regulation (EU) 2023/915) and the Codex Alimentarius maximum for Pb (0.1 mg/kg). Non-carcinogenic hazard indices remained below 1.0 across all sites, indicating no immediate chronic toxic risk at typical honey consumption rates, but cumulative carcinogenic risk values (1.32 × 10⁻³ at Dambi Dollo) exceeded the 1 × 10⁻⁴ benchmark, with nickel as the dominant contributor to total cancer risk. The study is the first to provide a baseline heavy-metal dataset for honey from this zone, identifying artisanal gold mining in Anafilo and agricultural chemical use as primary contamination drivers.
Key numbers
All concentrations in mg/kg wet weight, mean ± SD, n = 3 composite samples (one per district).
| Metal | Dambi Dollo | Gawo Kebe | Anafilo | Codex/EU limit |
|---|---|---|---|---|
| Cu | 10.46 ± 0.01 | 6.36 ± 0.02 | 12.79 ± 0.01 | 5 µg/g (Codex) |
| Fe | 127.20 ± 0.39 | 99.58 ± 0.77 | 159.67 ± 0.57 | 15 mg/kg (Codex) |
| Mn | 16.08 ± 0.12 | 10.23 ± 0.06 | 16.73 ± 0.07 | — |
| Ni | 8.19 ± 0.01 | 6.05 ± 0.01 | 8.85 ± 0.02 | — |
| Zn | 88.02 ± 0.52 | 209.54 ± 1.01 | 75.71 ± 0.40 | — |
| Cd | 1.65 ± 0.01 | 1.38 ± 0.01 | 2.30 ± 0.02 | 0.05 mg/kg (EU 2023/915) |
| Pb | 20.15 ± 0.27 | 21.42 ± 0.18 | 18.00 ± 0.13 | 0.1 mg/kg (Codex) |
Concentration order across all sites: Zn > Fe > Pb > Mn > Cu > Ni > Cd.
Pb levels showed no statistically significant difference across sites (p > 0.05, one-way ANOVA); all other metals showed significant site differences (p < 0.05, Tukey HSD).
Method LOQ (ICP-OES): Cu 0.057 mg/L, Fe 7.157 mg/L, Mn 0.185 mg/L, Ni 0.114 mg/L, Cd 0.327 mg/L, Zn 3.735 mg/L, Pb 1.576 mg/L. Recovery rates 89.09–114.82%; %RSD 0.12–1.35%.
Health risk (adult, IR = 5.5 g/day, BW = 67 kg, ED = 70 yr):
- Hazard Index (HI): Dambi Dollo 8.10 × 10⁻¹, Gawo Kebe 7.94 × 10⁻¹, Anafilo 7.86 × 10⁻¹ (all < 1; non-carcinogenic risk not significant)
- Total Cancer Risk (∑TCR): Dambi Dollo 1.32 × 10⁻³, Gawo Kebe 1.21 × 10⁻³, Anafilo 9.08 × 10⁻⁴ (Dambi Dollo and Gawo Kebe exceed 1 × 10⁻³ threshold; classified as high risk by NYSDOH criteria)
- Ni dominates carcinogenic risk at all sites (TCR range 8.50 × 10⁻⁴ to 1.23 × 10⁻³); Cd secondary; Pb contributes primarily to non-carcinogenic hazard
Methods (brief)
Fifteen honey subsamples collected from five apiary points per district (five-point cluster sampling), composited into three samples. Wet acid digestion with HNO3/HClO4 (2:1.5 v/v) at 160–240 °C in Kjeldahl block, filtered through Whatman No. 41 paper, diluted to 100 mL. ICP-OES PerkinElmer Optima 8000, 1500 W RF, samples diluted 1:10 before measurement. No arsenic, mercury, or tin measurement; study limited to Cu, Fe, Mn, Ni, Zn, Cd, Pb. No speciation performed; all values are total metal.
Implications
Certification: Pb at 18–21 mg/kg and Cd at 1.38–2.30 mg/kg are 180–214× and 28–46× above the Codex Pb limit and EU 2023/915 Cd limit respectively. Honey sourced from mining-impacted regions of Ethiopia would fail any HMT&C threshold for these metals by a wide margin. This paper provides important geographic range data showing African artisanal mining zones as extreme honey contamination hotspots.
Courses: Demonstrates the biomonitoring utility of honey for regional environmental contamination assessment. The divergence between non-carcinogenic risk (safe at usual intake rates) and carcinogenic risk (elevated above thresholds) illustrates why different risk-assessment frameworks yield different conclusions for the same contamination level.
App: The extreme Pb and Cd values reported here are outliers on the high end of the global honey distribution; they should not be used as representative values for honey from low-contamination regions. The geographic qualifier on any honey contamination estimate matters substantially.