Yohannes et al. 2024 — Heavy metals in edible vegetable oils, Gondar, Ethiopia

This study measured five metals (Fe, Cu, Zn, Pb, Cd) in 17 edible vegetable oil samples from Gondar City, Northwest Ethiopia, using flame atomic absorption spectroscopy (FAAS) after microwave digestion. The study found that 25% of samples exceeded the WHO/FAO Codex limit for cadmium (0.05 mg/L as reported) and 17% exceeded the limit for lead (0.1 mg/L as reported), with exceedances described by the authors in some locally produced vegetable oils. This is the first comprehensive heavy metals investigation of vegetable oils from this region.

Note on evidence tier: downgraded from A to B. The license is CC BY-NC-ND 4.0 (restricts adaptation), the sample size is small (n=17 across oil types, with sparse type-level replication), no health risk assessment was performed, and the LOQ values (0.94–4.95 mg/L) are relatively high for cadmium.

Key numbers

Median concentrations in unspiked samples (mg/L as reported; Table 7 labels these as p50 ± interquartile range; concentrations appear to reflect the digested extract solution, not necessarily mg/kg wet weight of the oil — unit conversion was not provided in the paper):

• Fe: median 0.15 ± 0.12 mg/L; range 0.01–0.80 mg/L
• Pb: median 0.07 ± 0.07 mg/L; range 0.003–0.27 mg/L
• Cu: median 0.015 ± 0.9 mg/L; range 0.002–0.06 mg/L
• Zn: median 0.25 ± 0.9 mg/L; range 0.07–0.80 mg/L
• Cd: median 0.96 ± 0.04 mg/L; range 0.08–0.18 mg/L

Note: Cd median of 0.96 appears inconsistent with the range of 0.08–0.18; Cu and Zn interquartile-range values also appear inconsistent with their maxima. These are likely reporting/table errors in the paper. The range values are retained as the more interpretable values for screening.

Regulatory exceedances:

• Cd: 25% of samples exceeded 0.05 mg/L (FAO/WHO Codex limit)
• Pb: 17% of samples exceeded 0.1 mg/L (FAO/WHO Codex limit)

Kruskal-Wallis test showed significant differences among oil types for Cu (p=0.0244) and Zn (p=0.0084), but not for Cd (p=0.087), Fe (p=0.1225), or Pb (p=0.6595).

LOD (method): Pb 0.4 mg/L, Fe 1.485 mg/L, Zn 0.16 mg/L, Cu 0.47 mg/L, Cd 0.3 mg/L. LOQ: Pb 1.33 mg/L, Fe 4.95 mg/L, Zn 0.523 mg/L, Cu 1.56 mg/L, Cd 0.94 mg/L. Recovery: 81.6–120% in Table 5, although the abstract/results narrative summarizes recovery as 81–115%. RSD: below 15%.

Methods

FAAS (210VGP model, flame atomic absorption spectroscopy) with air-acetylene flame. Microwave digestion: 0.5 g sample + 5 mL HNO3 (69–72%) + 2 mL HCl (37%) plus H2O2 (optimized digestion condition totals 8 mL reagent volume) at 180°C for 55 min. Triplicate analysis. Results reported in mg/L of extract solution; the paper does not clearly state the dilution factor or provide a conversion to mg/kg wet weight of oil, which limits comparability with other studies. Study period: May–July 2021. n=17 samples across oil types.

Limitation: Method LOD/LOQ values are high relative to several reported unspiked ranges. Pb results (0.003–0.27 mg/L) are below the Pb LOQ (1.33 mg/L), and the Cd range (0.08–0.18 mg/L) is below both the Cd LOD (0.3 mg/L) and Cd LOQ (0.94 mg/L), even though the paper reports Cd exceedances against a 0.05 mg/L reference level. Treat this source as contextual regional evidence rather than standards-calculation data.

Implications

Certification: The regional data (Gondar, Ethiopia; locally produced oils from small-scale operations) is contextually important for understanding production-setting risk. Reported Cd and Pb exceedances in some locally produced oils should be interpreted alongside the method LOD/LOQ limitations above.

Courses: Case study on how outdated extraction equipment, absence of refining/bleaching, and inadequate quality control are discussed as potential contributors in small-scale edible-oil production.

App: Limited utility for ingredient-level contamination profiling due to unit reporting ambiguity, source-internal QC inconsistencies, and small sample size. Use as contextual regional data only.

Wiki pages this source may touch

• vegetable-oils
• sunflower-oil
• soybean-oil
• cooking-oils-other
• lead
• cadmium
• copper
• iron
• zinc

Verification notes

• Source identity checked against DOI 10.1186/s12889-024-19695-0 and the Marker extraction at raw/markdown/FM_11323368/FM_11323368.md.
• Source reports total Pb, Cd, Cu, Fe, and Zn by FAAS; no speciation issue is present.
• niger-seed-oil and mixed-vegetable-oil are source-specific matrix descriptors; no ingredient pages for those exact oil categories exist in the current taxonomy snapshot.
• Table 7 contains internal inconsistencies (especially Cd median vs range), so this page preserves the source’s values and explicitly marks the inconsistency rather than normalizing the data.
• Cross-vendor audit (Codex, 2026-05-17) corrected one unit statement from mg/kg to mg/L because the source reports Table 6/7 and exceedance thresholds in mg/L; no mg/kg conversion is provided.
• Method validation caveat: the source’s LOD/LOQ table conflicts with several reported unspiked concentration ranges, especially Cd, so this page should not feed standards calculations without independent re-analysis.
• products/cooking-oils-other exists as a local product page used for oil/condiment routing even though it is absent from the GPT taxonomy snapshot.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.