Overview
Ojekunle and colleagues measured cadmium (Cd), lead (Pb), and Cu in soil and tree bark around a mechanic village in Abeokuta, Nigeria, comparing the results with a farmland control. This is in-scope supply-chain and mitigation evidence because it documents a source-attribution pathway from mechanic activity to soil and plant tissue, not cashew-nut occurrence.
Key numbers
Table 1 reports mean soil metal concentrations in mg/kg:
| Location | Cd (mg/kg) | Pb (mg/kg) | Cu (mg/kg) |
|---|---|---|---|
| Farmland control | 0.062 | 0.000 | 0.018 |
| Mechanic village | 0.069 | 2.959 | 0.137 |
Table 2 reports soil concentration ranges and regulatory limits:
| Metal | Soil concentration range (mg/kg) | Regulatory limit (mg/kg) |
|---|---|---|
| lead (Pb) | 0.00-24.34 | 600 |
| cadmium (Cd) | 0.06-0.08 | 100 |
| Cu | 0.00-1.20 | 100 |
The text states that the maximum statistical value for Pb in mechanic-village soil was 24.34 mg/kg at a high-activity point. The authors interpret this as evidence of higher mechanic activity at that location, while still below the soil guideline they cite.
Table 3 reports mean concentrations in plant bark, compared with source-cited food/heavy-metal standards:
| Metal | WHO/FAO (mg/kg) | EC/CODEX (mg/kg) | Mean concentration in plant bark (mg/kg) |
|---|---|---|---|
| cadmium (Cd) | 0.05-0.10 | 0.200 | 0.042 |
| Cu | 0.10 | 0.300 | 0.052 |
| lead (Pb) | 0.10 | 0.300 | 0.299 |
Table 4 reports percentage uptake efficiency:
| Plant | Cd (%) | Pb (%) | Cu (%) |
|---|---|---|---|
| Neem | 36.63 | 0.77 | 33.67 |
| Mango | 38.37 | 13.63 | 75.32 |
| Cashew | 34.37 | 33.70 | 44.24 |
The conclusion states that heavy-metal uptake efficiency in the three species followed Mango > Cashew > Neem. The authors recommend mango where copper pollution is the main target and neem where multiple metals occur in similar proportions.
Methods (brief)
Soil was collected 10 m from the base of sampled trees at 0-15 cm and 15-30 cm depths, air dried, sieved, digested with concentrated sulphuric acid/selenium solution and hydrogen peroxide, and analyzed by Thermo S4 AAS. Bark was cut from the top, middle, and bottom of trunks with a nitric-acid-washed stainless knife, oven dried at 105 degrees C, digested with sulphuric, perchloric, and nitric acids, and analyzed by AAS. Samples were run in triplicate and reported as mean values.
Related evidence
- Soil-to-plant transfer of heavy metals
- Source attribution and environmental burden apportionment
- Remediation evidence — drivers and interventions
- Lead
- Cadmium
- Copper
Update history
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