Wijeyaratne & Kumari 2021 — Cd, Cr, Pb in Alternanthera sessilis (Sri Lanka)
Alternanthera sessilis (known locally as mukunuwenna) is a protein-rich green leafy vegetable consumed raw across South Asia; this study measured Cd, Cr, and Pb concentrations in roots, leaves, and root-zone soils from organic and non-organic cultivation sites in Sri Lanka’s North Central Province, a region with elevated chronic kidney disease of unknown etiology (CKDue) prevalence. All leaf and root concentrations of Pb, Cd, and Cr exceeded WHO/FAO safe limits for human consumption, and bioconcentration factors greater than 1 for Cd confirmed hyperaccumulation potential; however, target hazard quotients (THQ) for each metal were below 1 for both adults and children, indicating negligible individual-metal health risk at average consumption rates, though the hazard index (HI) for adults at non-organic sites was 1.2, suggesting potential cumulative risk.
Key numbers
- Leaf concentrations (mg/kg dry weight), non-organic sites:
- Pb: 2.65–3.43 (dry season and rainy season)
- Cr: 10.10–13.85
- Cd: 1.87–2.15
- Leaf concentrations (mg/kg dry weight), organic sites:
- Pb: 3.20–3.40
- Cr: 6.26–6.70
- Cd: 0.67–0.68
- WHO/FAO safe limits for human consumption: Pb 0.3 mg/kg, Cr 2.3 mg/kg, Cd 0.2 mg/kg — all exceeded in both organic and non-organic leaf samples.
- Root concentrations (mg/kg dry weight), non-organic: Pb 4.72–4.94, Cr 17.88–18.86, Cd 1.98.
- Root zone soil concentrations: Pb 5.17–6.44 mg/kg, Cr 18.67–28.65 mg/kg, Cd 0.37–1.03 mg/kg — all below EU agricultural soil critical levels.
- Bioconcentration factor for Cd > 1 at all sites in both seasons (range 1.7–2.0): confirms Cd hyperaccumulator status.
- THQ < 1 for all three metals for both adults and children in all sites.
- Hazard index (HI) for adults at non-organic sites: 1.2 (cumulative risk > 1, indicating potential adverse non-cancer health effects with lifetime exposure).
- Organic farming significantly reduced Cd and Cr concentrations in leaves and roots vs. non-organic sites; Pb did not differ significantly between farming methods.
Methods (brief)
Atomic absorption spectrophotometry (Analytic Jena novAA 400p) in graphite furnace mode following APHA procedures; acid digestion with concentrated HNO3 (plant tissue) and EDTA (soil); MDL 0.02 mg/L for all metals; CRM 023 sandy loam (soil) and BCR 485 (plant tissue) as reference materials; recovery 95.1–96.2% for all matrices and metals. ANOVA with Tukey’s pairwise comparison for seasonal and spatial differences.
Implications
Certification: Demonstrates that a commonly consumed South Asian leafy vegetable can hyperaccumulate Cd and accumulate Pb and Cr at leaf concentrations exceeding WHO/FAO limits even when grown in soils below EU agricultural critical levels — illustrating the gap between soil-limit compliance and plant-tissue exceedances. Organic cultivation reduced Cd and Cr in leaves significantly but did not eliminate exceedances.
Courses: Illustrates crop-uptake mechanisms (bioconcentration, translocation factors) and the distinction between soil compliance and food-tissue safety. The Cd hyperaccumulation finding is relevant to understanding why certain green leafy vegetables concentrate specific metals independently of soil total burden.
App: South Asian leafy vegetables and herbs, particularly Alternanthera sessilis, should be flagged as potential Cd, Cr, and Pb accumulator matrices; organic sourcing reduces but does not eliminate the risk.