Heavy Metal Contamination of Irrigation Water, Soil, and Vegetables and the Difference between Dry and Wet Seasons Near a Multi-Industry Zone in Bangladesh

Ahmed et al. (2019) sampled irrigation water, soil, and vegetables at three sites adjacent to a multi-industry zone (textiles, dyeing, garments, pharmaceuticals, ceramics, paint, packaging) in Gazipur District, Bangladesh, comparing dry-season (Nov–Dec 2017) and wet-season (Jun–Jul 2015, drawn from the authors’ prior study) concentrations of Cr, Cu, Zn, As, Cd, and Pb. Heavy metal concentrations in irrigation water and vegetables exceeded FAO permissible levels in both seasons, while soil concentrations remained below EU permissible levels in both seasons except for As. Dry-season values were consistently higher than wet-season values across all three media. Hierarchical cluster analysis of metal co-occurrence suggested that vegetable contamination was sourced from irrigation water in the wet season and from soil in the dry season. Bioconcentration factors from soil to vegetable averaged 1.18 for Cd and 0.37 for Zn, indicating high transfer of these metals from soil into edible tissue.

Key numbers

Irrigation water — dry season means by area (mg/L; FAO permissible level in parentheses; n=12 per area):

• Cr: 1.1 (Banglabazar), 3.2 (Kashimpur), 2.1 (Chandra); FAO 0.1 — 11–32× over limit
• Cu: 1.8, 5.2, 6.85; FAO 0.2 — 9–34× over limit
• Zn: 12.8, 15.3, 17.5; FAO 2.0 — 6.4–8.8× over limit
• As: 0.63, 0.50, 0.44; FAO 0.1 — 4.4–6.3× over limit
• Cd: 0.012, 0.023, 0.022; FAO 0.01 — 1.2–2.3× over limit
• Pb: 2.04, 0.58, 0.83; FAO 5.0 — within limit in all areas

Irrigation water — wet season means by area (mg/L; n=12 per area):

• Cr: 0.45, 0.92, 0.85
• Cu: 1.4, 4.3, 6.0
• Zn: 8.6, 9.9, 13.7
• As: 0.62, 0.20, 0.16
• Cd: 0.007, 0.009, 0.009 — met FAO limit in wet season
• Pb: 1.75, 0.35, 0.36 — within FAO limit in all areas

Soil — dry season means by area (mg/kg; EU permissible level in parentheses; n=12 per area, each a 5-subsample composite from 0–15 cm):

• Cr: 65.6, 70.2, 66.8; EU 100 — within limit
• Cu: 57.1, 85.5, 40.9; EU 100 — within limit
• Zn: 169.2, 163.5, 186.9; EU 200 — within limit
• As: 16.8, 11.9, 10.5; EU 5 — 2.1–3.4× over limit (only soil metal that exceeded EU limit)
• Cd: 0.34, 0.28, 0.26; EU 1 — within limit
• Pb: 36.2, 32.8, 34.2; EU 60 — within limit

Soil — wet season means by area (mg/kg):

• Cr: 49.0, 56.7, 51.1
• Cu: 28.9, 40.4, 34.5
• Zn: 146.5, 145.2, 150.7
• As: 9.7, 8.4, 6.5 — still exceeded EU limit of 5
• Cd: 0.19, 0.17, 0.19
• Pb: 30.8, 26.3, 29.7

Vegetables — dry season means by area (mg/kg fresh-weight basis; FAO/WHO permissible level in parentheses; n=24 per area, mixed vegetable composite of radish, amaranth, red amaranth, spinach, Indian spinach, taro, bottle gourd, yard long bean, pumpkin):

• Cr: 22.60, 14.7, 20.71; FAO 1 — 14.7–22.6× over limit
• Cu: 15.7, 13.0, 15.7; FAO 30 — within limit
• Zn: 61.5, 59.9, 66.8; FAO 20 — 3.0–3.3× over limit
• As: 1.43, 1.33, 1.01; FAO 0.1 — 10.1–14.3× over limit
• Cd: 0.334, 0.299, 0.392; FAO 0.2 — 1.5–2.0× over limit
• Pb: 6.63, 5.50, 6.68; FAO 0.3 — 18.3–22.3× over limit

Vegetables — wet season means by area (mg/kg; n=9 per area, mixed composite of taro, kangkong, helencha, brinjal, sponge gourd):

• Cr: 4.34, 8.04, 4.39
• Cu: 12.9, 24.0, 12.9
• Zn: 54.1, 44.8, 56.4
• As: 1.07, 0.63, 0.69 — still exceeded FAO 0.1
• Cd: 0.143, 0.097, 0.147 — met FAO 0.2 in Kashimpur, near limit elsewhere
• Pb: 8.10, 5.03, 4.98 — Banglabazar wet-season Pb (8.10) exceeded dry-season Pb (6.63) in the same area, consistent with the cluster-analysis finding that wet-season vegetable contamination tracks irrigation water rather than soil

Vegetable-specific peaks (dry season, mg/kg):

• Taro root: Zn 113.89, Cr 39.84, Cu 20.81, Pb 14.72, As 4.61, Cd 0.31 — highest overall metal load
• Radish leaf: Cr 48.98, Cu 25.77 — highest among leafy vegetables
• Helencha (wet season): Zn 102.97 — Zn was the highest of the six metals within helencha, and helencha had the highest overall metal load among wet-season species (Figure 4b)

Bioconcentration factor (BCF, vegetable mg/kg ÷ soil mg/kg, dry season):

• Cd: 1.18 (highest; >1 indicates accumulation above soil concentration)
• Zn: 0.37
• Cu: 0.29
• Cr: 0.27
• Pb: 0.17
• As: 0.09 (lowest)
• Per-vegetable BCF: radish 0.61, red amaranth 0.61, amaranth 0.47, spinach 0.47, taro 0.44, bottle gourd 0.35, pumpkin 0.29, Indian spinach 0.22, yard long bean 0.11
• All vegetables except yard long bean exceeded the FAO/WHO 0.20 BCF threshold for “high health risk” classification

Statistical tests: one-way ANOVA across metals F=97.6–110.1, df=5, p<0.05 (water); F=189.5–222.6, df=5, p<0.05 (soil); F=90.6–202.2, df=5, p<0.05 (vegetables). Paired t-test for dry vs wet season significant at p<0.05 for all three media (water t=2.4–5.0 df=35; soil t=3.2–6.3 df=35; vegetables t=0.18–5.15 df=26). Two-way ANOVA across the three industrial areas was non-significant for soil and vegetables.

Methods (brief)

Irrigation water: 500 mL grab samples filtered through paper filter, acidified with HNO₃ (65%) to pH<2, stored at 4 °C in acid-washed 20 mL plastic bottles. Sampled at 12 randomly selected points per area.

Soil: 0–15 cm topsoil; 5 subsamples per point composited; air-dried, ground, sieved (2 mm); digested per US EPA Method 3050B.

Vegetables: separated into root (taro, kangkong), stem (taro, kangkong, amaranth), fruit (brinjal, sponge gourd, yard long bean), and leaf (taro, kangkong, helencha, radish, amaranth, red amaranth, spinach, Indian spinach, bottle gourd, pumpkin). Washed with tap then deionized water, air-dried, oven-dried at 60 °C for 48 h, milled. Digested at 120–130 °C for 14–16 h with concentrated HNO₃ and 30% H₂O₂; filtered through 4 µm paper filter (No. 5B, Advantec, Toyo Roshi Kaisha, Japan) and diluted to fixed volume.

Instrumentation: ICP-MS (Agilent 7500ce) at the Center of Advanced Instrumental Analysis, Kyushu University. Statistical analysis in Excel 2016, Origin Pro 8, and SPSS v21.

Limitations: total As reported, not speciated to inorganic vs organic. Vegetable concentrations reported as composite means by area rather than individual replicates per species in the main tables (Figure 4 reports per-vegetable means with standard error). Wet-season data drawn from the authors’ prior 2015 study, so dry-vs-wet comparisons span a two-year interval during which the authors state factory and discharge-point counts were unchanged.

Verification notes

Merge-enhanced 2026-05-18 from prior 2026-05-14 version. Changes:

• raw_handle corrected from legacy placeholder papers-cube to the canonical PCMF handle PCMF_article-2-copy-2.
• Added access_url (DOI link).
• Expanded metals: to include Cu and Zn (the paper reports both throughout; prior version omitted them despite Cu peaking at 6.85 mg/L in water and Zn at 186.9 mg/kg in soil).
• Expanded ingredients: from [leafy-vegetables] only to the broader vegetable scope the paper covers (leafy + root + umbrella vegetables, plus spinach which has its own page and is explicitly reported in Figure 4). Did NOT add ingredient pages that do not exist (amaranth, taro, helencha, kangkong, pumpkin, gourd) per the auto-stub policy.
• Expanded matrices: from [irrigation-water, soil, vegetable] to include agricultural-soil, leafy-vegetable, and root-vegetable for routing precision.
• Added wet-season irrigation-water and soil means by area, full vegetable BCF table per species, and FAO/WHO and EU permissible levels alongside reported values (prior version stated some limits but omitted the EU soil reference and the FAO vegetable limits).
• Corrected the As-direction note: prior version said “As 0.44–0.63” for dry season water; the correct area order is Banglabazar 0.63, Kashimpur 0.50, Chandra 0.44 (descending). The range was correct; the area attribution is now explicit.
• Added the paper-internal observation that Banglabazar wet-season Pb in vegetables (8.10 mg/kg) exceeded its dry-season value (6.63), reinforcing the cluster-analysis finding that wet-season uptake tracks irrigation water rather than soil.
• Removed legacy ## Implications section (certification / courses / app translation) per Wiki/HMTc firewall (Part 2): source pages report what the paper found, not how it applies to the certification program or consumer apps.
• Removed legacy ## Wiki pages updated on ingest section (not part of current source-page schema; routing is now the system’s responsibility per Part 5b).
• No brand names appear in this paper (only generic vegetable species and the analytical instrument vendor), so no brand-firewall application was needed.

Audit subagent (2026-05-18, verdict PROMOTE) flagged three minor concerns; all three verified against source and applied:

• sample_n: 99 was ambiguous in a 3-medium 2-season design (99 happened to equal total vegetable samples 72 dry + 27 wet, but the field semantic was unclear). Updated to 243 (water 72 + soil 72 + vegetables 99) with a per-medium breakdown in sample_population.
• “Helencha (wet season): Zn 102.97 — highest wet-season Zn” reworded to “Zn was the highest of the six metals within helencha, and helencha had the highest overall metal load among wet-season species (Figure 4b)” to mirror the paper’s p.7 framing.
• Water-storage bottle material corrected from “polyethylene” (invented detail) to “plastic” per paper §2.2 wording.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.