Overview
Okeke and colleagues compared heavy-metal concentrations in soils affected by palm oil mill effluent, spent engine oil effluent, and an uncontaminated control site in Ebonyi State, Nigeria. This is in-scope a3 source-attribution and soil-pathway evidence for agro-industrial and automotive effluents, not palm oil occurrence.
Key numbers
Table 1 reports mean soil concentrations as mg/kg:
| Metal | Palm oil mill effluent soil | Spent engine oil soil | Control soil | WHO reference (mg/kg) |
|---|---|---|---|---|
| Zn | 0.05a +/- 0.061 | 0.33a +/- 0.365 | 0.08a +/- 0.077 | 300 |
| nickel (Ni) | 17.69a +/- 16.504 | 27.07a +/- 25.955 | 3.48a +/- 0.556 | 50 |
| mercury (Hg) | 0.24a +/- 0.002 | 0.17a +/- 0.173 | 0.16a +/- 0.018 | 1.0 |
| Mn | 1.12a +/- 1.298 | 3.86a +/- 4.209 | 2.87a +/- 2.674 | 2000 |
| lead (Pb) | 0.00a +/- 0.000 | 0.01a +/- 0.012 | 0.23b +/- 0.046 | 85 |
| Fe | 0.63a +/- 0.724 | 2.41a +/- 2.781 | 0.65a +/- 0.207 | 50,000 |
| Cu | 0.56a +/- 0.618 | 3.07a +/- 3.479 | 0.57a +/- 0.632 | 100 |
| Co | 0.06a +/- 0.069 | 0.51a +/- 0.59 | 0.39a +/- 0.464 | 19 |
| chromium (Cr) | 0.10a +/- 0.114 | 0.25a +/- 0.046 | 0.24a +/- 0.11 | 100 |
| cadmium (Cd) | 0.05a +/- 0.058 | 1.84a +/- 3.24 | 0.31a +/- 0.338 | 3 |
The authors state that soil contaminated with spent engine oil had higher mean Zn, nickel (Ni), Mn, Fe, Cu, Co, chromium (Cr), and cadmium (Cd) than the palm oil mill effluent and control sites. They report mercury (Hg) as higher in palm oil mill effluent soil than in spent-engine-oil or control soil. lead (Pb) was highest in the control soil, and the authors describe this as a site-specific exception to the broader trend.
Methods (brief)
The study was conducted at Ebonyi State University’s Presco Campus in Abakaliki, Nigeria. The paper says it assessed soil metal concentrations across palm oil mill effluent, spent engine oil effluent, and control sites. The methods section also contains insect-assessment language that does not explain the soil-metal analytical workflow; this page therefore treats Table 1 as measured soil-context evidence but does not infer unreported digestion, instrument, or sampling details.
Related evidence
- Soil-to-plant transfer of heavy metals
- Source attribution and environmental burden apportionment
- Irrigation water and soil amendments as anthropogenic inputs to cropland
- Nickel
- Lead
- Cadmium
- Mercury, Total
- Chromium
Update history
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