Sultana et al. 2022 — Heavy metals in root and leafy vegetables, Dhaka, Bangladesh
This study measured concentrations of eight heavy metals (Cr, Cd, Pb, Ni, Cu, Zn, Fe, Mn) in four root vegetables (beet, radish, carrot, turnip) and five leafy vegetables (mustard, cabbage, spinach, coriander, mint) purchased at Kawran Bazar, Dhaka’s largest fresh produce market, across four seasonal sampling phases. Leafy vegetables consistently showed higher metal concentrations than root vegetables, with several analytes exceeding FAO/WHO maximum permissible limits (MPL), particularly Cr, Cd, and Ni. Average daily intake (ADI), hazard quotient (HQ), and hazard index (HI) calculations indicated that four of five leafy vegetables posed potential health risks (HI > 1) versus one of four root vegetables.
Key numbers
All concentrations are on a dry weight (dw) basis.
Root vegetables (mg/kg dw; mean across 4 seasonal phases):
| Vegetable | Cr | Cd | Pb | Ni |
|---|---|---|---|---|
| Beet | 1.20 (range 0.60–0.90 phases 1–2) | 0.20 | 0.00 | 0.58 |
| Radish | 1.53 | 0.23 | 0.00 | 1.60 |
| Carrot | 1.58 | 0.30 | 0.75 | 0.38 |
| Turnip | 13.50 (max single phase: 49.60) | 0.08 | 0.25 | 1.40 |
FAO/WHO MPL for root vegetables (dw): Cr 2.30 mg/kg, Cd 0.20 mg/kg, Pb 0.30 mg/kg, Ni 2.70 mg/kg.
Turnip exceeded the Cr MPL in all phases; the maximum single-phase Cr value (49.60 mg/kg dw in the 4th phase) is anomalously high and the authors attribute it to late-season use of preservatives. Beet, radish, and carrot exceeded the Cd MPL.
Leafy vegetables (mg/kg dw; mean):
| Vegetable | Cr | Cd | Pb | Ni |
|---|---|---|---|---|
| Mustard | 4.70 | 0.20 | 1.70 | 3.23 |
| Cabbage | 1.35 | 0.10 | 0.75 | 0.68 |
| Spinach | 2.23 | 0.50 | 0.67 | 0.73 |
| Coriander | 3.88 | 1.13 | 2.00 | 3.05 |
| Mint | 6.18 | 0.20 | 2.25 | 1.45 |
FAO/WHO MPL for leafy vegetables (dw): Cr 2.30 mg/kg, Cd 0.20 mg/kg, Pb 0.30 mg/kg, Ni 2.70 mg/kg. Mustard, coriander, and mint exceeded Cr MPL; coriander exceeded Cd MPL in all phases (max 1.80 mg/kg); spinach Cd was 0.50 mg/kg (above 0.20 MPL); Pb exceeded MPL in all leafy vegetables by late season.
Hazard index (HI) values (all metals combined):
- Root vegetables: turnip 1.54, beet 0.56, carrot 0.34, radish 0.36
- Leafy vegetables: mint 2.83, spinach 2.11, coriander 1.93, mustard 1.66, cabbage 0.38
ADI exceedances: Cr for turnip consumption 0.202 mg/person/day (vs. PMTDI 0.20); Fe for mint 19.681 mg/person/day (vs. PMTDI 17.0). Assumption: 166.1 g fresh vegetables/person/day, 60 kg body weight.
Methods (brief)
Vegetables collected from Kawran Bazar, Dhaka, in 4 phases with minimum 14-day intervals over 2 months (early, mid-time, and late harvesting). Composite samples (3 replicates per vegetable per phase). Samples washed, dried at 65°C for 90 hours, ground and sieved at 0.20 mm. Acid digestion: 1 g dry weight in 10 mL concentrated HNO3 + 2 mL HClO4 at 150–200°C on hot plate. Analysis by Atomic Absorption Spectrophotometry (Varian AA 240) at wavelengths 357.9 nm (Cr), 228.8 nm (Cd), 283.3 nm (Pb), 232 nm (Ni), 324.7 nm (Cu), 213.9 nm (Zn), 248.3 nm (Fe), 279.5 nm (Mn). No speciation performed; total metals only. Note that reported LODs for Pb are 100 µg/L (AAS flame), which is high for Pb; non-detected Pb in several root vegetable samples is consistent with this instrumental limitation. Study does not report inorganic arsenic, tAs, tHg, Sn, Al, or U.
Implications
Certification: Cr and Cd exceedances in market vegetables from Dhaka are relevant to ingredient risk profiling for leafy greens and root vegetables used in global supply chains. The anomalously high Cr in turnip (49.60 mg/kg dw) warrants note; it exceeds the MPL by over 20-fold and would be flagged in any lot-level testing. Cd in coriander consistently exceeds MPL across all seasons, relevant to herbs sourced from South Asia.
Courses: Demonstrates the seasonal harvesting-period effect on metal concentrations and that late-season vegetables may carry higher loads, relevant to supply-chain timing and lot-sampling considerations.
App: Leafy vegetable risk scoring for South Asian sourcing should weight Cr, Cd, and Pb higher than for other origins. Root vegetable risk is lower overall, though carrot and radish show Cd above MPL.