Overview
Katebe et al. assessed the effectiveness of organocalcareous amendments (chicken droppings, sawdust, and agricultural lime) in reducing transfer of trace metals from mine-contaminated soils to four vegetable species grown in Lubumbashi, DRC, where copper–cobalt mining has severely contaminated urban agricultural soils (Cu: 204–1355 mg/kg; Pb: 20–221 mg/kg; Cd: <0.05–45 mg/kg across three market gardens). The primary finding for food safety is that cobalt in vegetables from even the least-contaminated garden exceeded the FAO/WHO daily intake limit by 0.5 to 8.45 times, while Cd, Cu, and Pb daily consumption indices remained below FAO/WHO limits in the low-contamination garden. Organocalcareous amendments improved germination and reduced metal transfer only in low-contamination soil; in high and medium Cu-contaminated soils plant survival was too poor to assess metal transfer effectively.
Key numbers
Soil contamination (baseline before amendment):
- Kashamata (low Cu): Cu 204 mg/kg, Pb 20 mg/kg, Cd <0.05 mg/kg, Zn 60 mg/kg
- Manoah Kinsevere (medium Cu): Cu 535 mg/kg, Pb 81 mg/kg, Cd <0.05 mg/kg, Zn 394 mg/kg
- Chem-Chem (high Cu): Cu 1355 mg/kg, Pb 221 mg/kg, Cd 45 mg/kg, Zn 1470 mg/kg
- WHO soil toxicity thresholds cited: Cu 100 mg/kg, Cd 2 mg/kg, Pb 100 mg/kg, Zn 300 mg/kg, Co 30 mg/kg
Daily vegetable consumption index (low-contamination garden, Kashamata): Cobalt 0.029–0.465 mg/60 kg body weight/day, i.e., 0.5–8.45× FAO/WHO limit. Cd, Cu, and Pb daily consumption indices were below FAO/WHO limits for this garden.
Vegetable biomass metal concentrations: Specific per-species concentrations are reported in the paper’s results tables (not reproduced in the available markdown excerpt); detection limits for AAS analysis were Zn 0.010, Cu 0.10, Co 0.05, As 0.05, Cd 0.05 µg/g (dry weight). Analytical method: HNO3/HClO4 digestion (7:1 v/v) followed by AAS (VARIAN 220, Agilent). Soil total TME measured by portable XRF (Olympus Delta Classic Plus); exchangeable TME by 0.01 M CaCl2 extraction and AAS.
Methods
Greenhouse pot experiment at University of Lubumbashi Faculty of Agronomic Sciences, 2019. Completely randomized factorial design: five amendment levels × three soil contamination levels × four vegetable species × four replications. Sixty days cultivation. Four vegetable crops: Brassica chinensis (pak choi), Amaranthus vulgaris (amaranth), Beta vulgaris (beet), Brassica carinata (Ethiopian mustard). Soil TME: XRF (total), AAS (exchangeable via 0.01 M CaCl2). Plant TME: HNO3/HClO4 digestion, AAS for Zn, Cu, Co, As, Cd. Basis: dry weight for plant tissue. Pb measured in soil but not reported in plant tissue in available text; As and Cd measured in plant tissue. This paper is part of a series on Lubumbashi urban agriculture metal contamination (companion to Mununga Katebe et al. 2023).
Implications
Certification: Documents severe baseline contamination levels in DRC urban agricultural soils. Cobalt exceedances in edible greens even from the least-contaminated garden illustrate why geographic provenance of ingredients from mining regions carries elevated risk that standard multi-metal testing may undercount if Co is not included.
Courses: Illustrates the soil-to-plant transfer pathway for Cu, Co, Cd, Pb in tropical mining-region urban agriculture; soil amendment limited in utility at high contamination levels. Context for why ingredient sourcing geography is a material variable in supply-chain risk.
App: DRC-origin leafy greens and brassicas carry high Co and context-dependent Cu, Cd risk from mining region soils. This data point is geographically specific and should not be generalized to non-mining-region production.
Related evidence
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