Overview
This study measured Pb, Cu, and Zn in soil and kale grown near the KIWASCO sewage treatment plant in Obunga slum, Kisumu County, Kenya.
Key numbers
Source units are ppm.
- Sample frame: 60 samples total, 30 soil samples and 30 kale samples, drawn from five plots around the KIWASCO treatment plant over January-June 2018.
- Mean Pb: soil 0.41298 +/- 0.102; kale 0.37098 +/- 0.105.
- Mean Zn: soil 0.34676 +/- 0.095; kale 0.2302 +/- 0.085.
- Mean Cu: soil 0.1051 +/- 0.002; kale 0.08666 +/- 0.003.
- Plot-level kale Cu ranged from 0.07 +/- 0.001 (plot 2) to 0.0995 +/- 0.003 (plot 1).
- Plot-level soil Zn ranged from 0.2791 +/- 0.001 (plot 4) to 0.4226 +/- 0.005 (plot 5); plot-level kale Zn ranged from 0.1423 +/- 0.002 (plot 2) to 0.3622 +/- 0.003 (plot 5).
- The authors report Pb, Cu, and Zn in both soil and kale below KEBS/WHO/FAO standards and no immediate human-health risk in the analyzed samples.
Methods
Soil samples were taken from the upper 20 cm with a stainless-steel scoop; kale leaves were collected with a razor blade. Plant samples were washed, oven-dried for 48 hours, ground in a porcelain mortar, and passed through a 2 mm sieve. Soil samples were air-dried for 72 hours, disaggregated, sieved through 2 mm, then oven-dried for 2 hours. A 2.0 g aliquot of each sample was digested on a hot plate: plant samples in a 20 mL tri-acid mixture of HNO3:HCl:H2SO4 (5:1:1), soil samples in HCl:HNO3 (3:1). Digests were filtered, diluted to 50 mL with deionized water, and analyzed for Pb, Zn, and Cu by atomic absorption spectrometry. ANOVA was run in Minitab 16.
Implications
The source supports vegetable/kale context for Pb, Cu, and Zn under sewage-sludge irrigation conditions. Soil and kale values should remain separate matrices.
Related evidence
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