Agarwal et al. 2022 — Seasonal variation of Pb, Cd, Cr, Hg in vegetables from East Kolkata Wetlands, India
This study examines seasonal variation in bioaccumulation and translocation of Pb, Cd, Cr, and tHg in three food crops grown in the East Kolkata Wetlands (EKW), a Ramsar-listed site that doubles as a sewage-treatment and urban food-supply system for Kolkata, India. Vegetables sampled were bottle gourd (Lagenaria siceraria), ladies’ fingers/okra (Abelmoschus esculentus), and maize (Zea mays) from the Dhapa municipal solid-waste dumping site. Heavy metal concentrations in edible parts were substantially elevated relative to ambient soil, with the monsoon season producing the highest bioaccumulation and translocation factors across all species and metals.
Key numbers
- Soil biologically available concentrations (Dhapa site, ranges across seasons and years):
- Cr: 298.76–443.85 ppm (mg/kg)
- Pb: 12.02–45.22 ppm
- Cd: 1.69–7.68 ppm
- Hg: 0.98–1.81 ppm
- Metal concentrations in edible parts (all ppm dry weight; ranges across seasons 2016-2017):
- Bottle gourd (L. siceraria): Pb 23.59–35.45, Cd 5.88–13.98, Cr 2.04–7.63, Hg 0.88–2.04
- Ladies’ fingers/okra (A. esculentus): Pb 13.51–29.67, Cd 3.42–9.64, Cr 1.86–5.56, Hg 0.00–1.04
- Maize (Z. mays): Pb 31.78–42.33, Cd 11.93–18.43, Cr 9.83–17.21, Hg 0.45–3.52
- Metal accumulation order in edible parts: Pb > Cd > Cr > Hg for all three species
- Seasonal pattern: monsoon consistently showed highest bioaccumulation factor (BF) and translocation factor (TF) across all species and metals; premonsoon lowest
- Species accumulation ranking: Z. mays > L. siceraria > A. esculentus for total HM content
- Cd bioaccumulation factor (BF, edible parts/soil): highest among all four metals in all species and seasons, indicating preferential plant uptake
- Analytical method: AAS (PerkinElmer Model 3030) with graphite furnace atomizer; NIST SRM 2709/2710/2711 reference materials; recoveries 85–99%
- Note: all concentrations reported as ppm (mg/kg) dry weight; conversion to ppb (µg/kg) multiply by 1,000. Maize Pb values of 31,780–42,330 ppb (dry weight) indicate severe contamination from sewage-fed farming; these are site-specific extreme values, not representative of commercial corn.
Methods (brief)
AAS with graphite furnace (GFAAS) for all four metals. Vegetable samples oven-dried at 60°C, powdered, 1 g digested with HNO3/H2O2/HCl mixture. Soil samples extracted with 0.5 N HCl (weak acid, biologically available fraction). Samples collected at three seasonal points (premonsoon, monsoon, postmonsoon) in 2016 and 2017 from Dhapa, EKW. Two-way ANOVA for between-species and between-season comparisons.
Implications
Certification: Site-specific to heavily contaminated sewage-fed urban wetland agriculture. Values are extreme outliers not applicable to commercial supply chains; use as upper-bound evidence for what contaminated-soil irrigation can produce, not as representative food concentration data. Courses: Compelling case study for wastewater-irrigated urban agriculture as a heavy metal contamination pathway. Demonstrates how Cd bioaccumulation factors can exceed 1.0 (plant accumulates more Cd than soil biologically available fraction), which is the key metric for regulator attention. App: Not suitable as baseline app values. May be cited as “worst-case contaminated-site” scenario for educational context. Microbiome: Not addressed.