Overview
Augustine and colleagues measured lead and cobalt in surface soils from an irrigated vegetable farmland near the Amba River in Lafia, Nigeria. The source is not utensils or finished-product occurrence evidence: it is upstream irrigation/farmland pathway evidence for metals in soil where vegetables are grown.
Key numbers
The sampling site was a vegetable irrigated farmland in Tundun Amba, close to the State Water Board intake in Lafia metropolis and near the Amba River. Three representative soil samples were collected at 0-15 m, 15-30 m, and 30-45 m from the irrigation-water source, using surface soil from 0-30 cm depth.
Soil physicochemical parameters in Table 2 were: pH-H2O 6.35, 5.81, and 5.60 for samples A, B, and C; pH-CaCl2 5.23, 5.35, and 4.78; electrical conductivity 100, 240, and 210 µS/cm; exchangeable acidity 0.83, 1.0, and 0.50 Meq/100g; organic carbon 1.40%, 1.49%, and 1.45%; organic matter 2.40%, 2.57%, and 2.50%; and texture classes sandy loam, sandy loam, and loamy sand.
Table 3 reports heavy-metal concentrations using aqua regia digestion, in mg/kg:
| Sample code | Distance | Pb | Co |
|---|---|---|---|
| A1 | 0-15 m | 1.473 +/- 0.0006 | 0.105 +/- 0.0001 |
| B1 | 15-30 m | 1.551 +/- 0.0003 | 0.089 +/- 0.0008 |
| C1 | 30-45 m | 1.573 +/- 0.0001 | 0.083 +/- 0.0009 |
Table 4 reports heavy-metal concentrations using nitric acid digestion, in mg/kg:
| Sample code | Distance | Pb | Co |
|---|---|---|---|
| A2 | 0-15 m | 1.451 +/- 0.0005 | 0.086 +/- 0.0006 |
| B2 | 15-30 m | 1.363 +/- 0.0002 | 0.060 +/- 0.0001 |
| C2 | 30-45 m | 1.512 +/- 0.0007 | 0.078 +/- 0.009 |
The results text summarizes aqua-regia-extractable Co as 0.083-0.105 mg/kg and lead (Pb) as 1.473-1.573 mg/kg, and nitric-acid-extractable Co as 0.060-0.086 mg/kg and Pb as 1.363-1.512 mg/kg. Pb ranked higher than Co under both digestion methods.
The authors attribute the higher Pb signal to activities carried out on the Amba River, including automobile washing, discharge into the water body from the Lafia water-works treatment plant, and other anthropogenic activities. The conclusion states that all measured Pb and Co concentrations were below the cited DPR-EGASPIN and US EPA farmland-soil limits.
Methods (brief)
Surface soils were air-dried for one week, pulverized, sieved through 2.0 mm mesh for pH and total-metal analysis, and further pulverized through 0.5 mm mesh for organic matter. Pb and Co were extracted in parallel by aqua regia digestion (30.0 mL HCl plus 10.0 mL HNO3 added to 1.0 g soil and left 24 h, then heated at 140 C) and nitric acid digestion (1.0 g soil with HNO3, heated to a clear solution). Concentrations were determined by atomic absorption spectrometry from calibration curves.
Related evidence
- Irrigation water and soil amendments as anthropogenic inputs to cropland
- Soil-to-plant transfer of heavy metals
- Source attribution and environmental burden apportionment
- Lead
- Cobalt
Update history
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