Overview
This study measured As, Cd, Cr, Cu, Fe, Ni, Pb, and Zn in corn (Zea mays) grain and surface soil from five farmlands in the vicinity of the Obajana Cement Plant (OCP), the largest cement-manufacturing plant in sub-Saharan Africa, located in Kogi State, Nigeria. The key finding is that Pb concentrations in corn from the three downwind farmlands (F2, F3, F4) ranged from 0.23 to 0.38 µg/g dry weight, exceeding the FAO/WHO maximum limit of 0.2 µg/g for grains, while Cr concentrations (2.08–3.56 µg/g dry weight) were several-fold above the normal cereal range of 0.01–0.41 µg/g across all farmlands including the upwind control. All health hazard indices (HHI) for corn consumption were less than 1, suggesting no immediate non-carcinogenic risk under typical Nigerian corn intake rates, but the spatial gradient for Pb — with downwind values six to 35 times higher than upwind values — clearly implicates cement plant emissions and vehicular traffic as contamination drivers. This is the first reported health hazard assessment for corn grown near OCP.
Key numbers
Corn grain element concentrations, mean ± SEM in µg/g dry weight, by farmland:
| Element | FC (control, n=19) | F1 (upwind, n=20) | F2 (downwind, n=24) | F3 (downwind, n=12) | F4 (downwind, n=14) |
|---|---|---|---|---|---|
| As (total) | 0.01 ± 0.00 | 0.01 ± 0.00 | <0.01 | <0.01 | 0.01 ± 0.00 |
| Cd | <0.01 | <0.01 | <0.01 | BDL | <0.01 |
| Cr | 3.56 ± 0.65 | 2.31 ± 0.07 | 2.20 ± 0.18 | 2.08 ± 0.17 | 2.57 ± 0.17 |
| Cu | 3.13 ± 0.48 | 2.36 ± 0.16 | 2.21 ± 0.18 | 2.79 ± 0.25 | 2.27 ± 0.18 |
| Fe | 42.0 ± 3.1 | 40.0 ± 3.7 | 35.2 ± 3.6 | 41.1 ± 4.4 | 44.3 ± 6.4 |
| Pb | 0.02 ± 0.00 | 0.01 ± 0.00 | 0.23 ± 0.03 | 0.30 ± 0.03 | 0.38 ± 0.02 |
| Ni | 2.10 ± 0.28 | 1.45 ± 0.05 | 1.46 ± 0.08 | 1.33 ± 0.11 | 1.70 ± 0.11 |
| Zn | 28.4 ± 1.2 | 23.9 ± 1.1 | 13.5 ± 1.3 | 6.32 ± 1.11 | 18.2 ± 2.1 |
Median values given in parentheses in the source. Sampling period: harvest season 2017.
FAO/WHO grain limit for Pb: 0.2 µg/g. All downwind farmland corn means exceed this limit. Normal cereal Cr range 0.01–0.41 µg/g; all farmlands exceed the upper end of this range by 5–8-fold.
Cadmium was at or below LOD (0.001 ng/g) in most corn samples. Total arsenic was uniformly low (0.01 µg/g or below) across all sites.
Methods (brief)
Corn grain (oven-dried, ground to flour) and surface soil (0–15 cm, oven-dried, <2 mm, ball-milled): HNO3/H2O2 digestion (microwave for corn, block digester for soil). Measurement by ICP-MS (Agilent 7900) for As, Cr, Cd, Cu, Ni, Pb; MP-AES (Agilent 4100) for Fe and Zn. Method is total metals (not speciated — no As speciation; Cr is total chromium, not Cr-VI). CRM validation: CRM-CM-A (corn meal), NIST 2709 and NIST 2711 (soils); percent recovery 78–120%. LODs: Cd 0.043 ng/g (soil), 0.001 ng/g (corn); Zn 0.150 ng/g. Ninety-one samples total (89 reported; 5 farmlands, 19–24 samples each). Basis: dry weight throughout.
Implications
Certification: Lead in corn grain is directly relevant to HMT&C food ingredient monitoring. The downwind values (0.23–0.38 µg/g dw = 230–380 ppb dw) substantially exceed the FAO/WHO grain limit and are noteworthy as a geographically scoped industrial-contamination finding. These values are not representative of global corn but define an upper bound for industrial-vicinity production. The chromium data are total Cr; Cr-VI data are absent. Cadmium in corn near this facility was effectively undetectable, consistent with cement-specific emission profiles rather than mining or smelter sources.
Courses: Illustrates how industrial proximity (cement, not mining) can drive Pb and Cr exceedances in staple cereals via atmospheric deposition, with a clear upwind/downwind spatial signal.
App: Corn grain Pb from industrial-vicinity origins may warrant elevated risk flagging. Standard-supply corn (no industrial proximity declaration) should use global occurrence surveys rather than this dataset.
Microbiome: Not applicable.
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Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and 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.
| Commit | Date | Change | Description |
|---|---|---|---|
| a8052bb | 2026-08-09 | major | 6 sections added; narrative text revised |