Katebe et al. 2024 — Trace metals in vegetables from Lubumbashi contaminated soils
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.