A Human Health Risk Assessment of Soil and Crops Contaminated by Heavy Metals in Industrial Regions, Central Iran

Overview

This Iranian soil-to-plant survey quantifies total cadmium (Cd), lead (Pb), nickel (Ni), and Fe in paired topsoil (0–20 cm) and edible crop samples (wheat grain, rice grain, onion bulb) collected from three Isfahan-province regions: Zarrinshahr (6–8 km east of Isfahan Steel Mill Company), Mobarakeh (12–14 km east of Mobarakeh Steel Mill Company), and Natanz (140–150 km from the steel mills; treated as the control region). Twenty-seven paired soil and crop composites (3 crops × 3 regions × 3 field replications) were digested by USEPA Method 3050B (soils) and wet HNO₃/H₂O₂ mineralisation (crops, per Lozano-Rodriguez et al. 1995), then quantified by graphite-furnace AAS (Perkin Elmer AAnalyst 800; Cd, Pb, Ni) and flame AAS (Fe). Mean industrial-region soil concentrations were Cd 1.85, Fe 35 894, Ni 64.5, and Pb 38 mg/kg vs. Natanz Cd 0.54, Fe 15 363, Ni 20, and Pb 19 mg/kg; industrial-region soils exceeded the EU 2000 sludge-soil ceiling for Cd (1.5 mg/kg) and the USEPA 1983 soil limit for Ni (40 mg/kg). Mean industrial-region crop concentrations across the three crops were Cd 0.25, Fe 55.7, Ni 1.80, and Pb 1.79 mg/kg dry weight; the three-crop means exceeded the Codex Alimentarius Commission 2001 maximum permitted concentrations (MPC) for Cd (0.20), Ni (0.6), and Pb (0.3 mg/kg) by 1.25×, 3.0×, and 6.0×. Total estimated daily intake (EDI) of Cd, Ni, and Pb in Zarrinshahr (2.08, 12.61, 14.46 µg/kg bw/day) and Mobarakeh (1.87, 12.37, 14.15) exceeded WHO 1993 TDIs of 1, 5, and 3.6 µg/kg bw/day by approximately 2×, 2.5×, and 4×; total target hazard quotient (THQ) sums for Pb and Cd from the three-crop pathway were greater than 1, indicating non-negligible non-carcinogenic health risk for inhabitants of the two industrial regions. The Natanz control region showed EDIs and THQs below tolerance.

Key numbers

Table 1 — Soil physicochemical properties (page 24, n=3 fields per region)

Range across all studied fields: pH 7.6–7.9; EC 1.3–4.7 dS m⁻¹; OC 5.03–26.5 g kg⁻¹; CEC 13–32 cmol+ kg⁻¹; texture predominantly loam.

Table 2 — Soil heavy-metal concentrations (mg kg⁻¹ dry weight; page 25)

Site LSD with asterisk denotes p < 0.001 between-region difference. Means in a column followed by the same letter are not significantly different at p < 0.05. The text §“Heavy Metal Concentrations in the Soils” (p. 9) summarises the industrial-region soil means as Cd 1.85, Fe 35 894, Ni 64.5, Pb 38 mg/kg, treating Zarrinshahr and Mobarakeh as a pooled industrial group; the Natanz pooled summary is Cd 0.54, Fe 15 363, Ni 20, Pb 19 mg/kg. The Pb values in the three regions (38.3, 37.7, 19.3 mg/kg) all exceed the EU 2000 sludge-soil ceiling of 10 mg/kg cited by the authors (the paper attributes the 10 mg/kg figure to the European Union 2000 Working Document on Sludge; the wiki page reports the figure as the authors cited it; see Verification notes regarding the EU vs. USEPA attribution in the table footer).

Table 3 — Crop edible-portion heavy-metal concentrations (mg kg⁻¹ dry weight; page 26, n=3 fields per crop × region)

Letters within a column denote LSD groupings at p < 0.05 (Duncan-equivalent ANOVA post-hoc). Asterisks on LSD values: *p < 0.05, ***p < 0.001. The text §“Heavy Metal Concentrations in the Crops” (p. 10) provides two parallel pooled summaries:

• Industrial-region three-crop pooled means (Zarrinshahr + Mobarakeh): Cd 0.25, Fe 55.7, Ni 1.80, Pb 1.79 mg/kg dw.
• Natanz three-crop pooled means: Cd 0.05, Fe 12.8, Ni 0.23, Pb 0.24 mg/kg dw.
• Crop-specific pooled-industrial Pb means: wheat grain 2.05, onion bulb 2.01, rice grain 1.31 mg/kg dw (the text uses these three figures).
• Crop-specific pooled-industrial Cd means: wheat grain and onion bulb 0.29 (sic — see Verification notes; Table 3 implies 0.30 wheat / 0.29 onion); rice grain 0.16 mg/kg dw.
• Three-crop pooled-industrial Ni 1.80 and Pb 1.79 are 3.0× and 5.97× the Codex 2001 MPC for cereals (0.6 and 0.3); pooled-industrial Cd 0.30 wheat and 0.29 onion are 1.5× the FAO/WHO 2001 food MPC of 0.20.

Table 4 — Pearson correlation coefficients (r) between soil and crop heavy metals (page 27, n=27)

*Significant at p < 0.01, n = 27. The text (p. 12) reports diagonal same-metal correlations as 0.98 (Fe), 0.95 (Pb), 0.94 (Ni), and 0.97 (Cd); the wiki page tabulates the full 4 × 4 matrix per the table.

Bio-accumulation factor (BAF) — Figure 2 (page 30)

All-sample pooled mean BAF (C_plant / C_soil): Cd 0.116, Pb 0.036, Ni 0.022, Fe 0.001. Descending order: Cd > Pb > Ni > Fe.

Regional Cd BAF means across the three crops: Zarrinshahr 0.136, Mobarakeh 0.130, Natanz 0.081 (text p. 13). Crop-specific BAF readings from Figure 2 (chart-extracted; precision ±0.005):

Wheat and onion are characterised as stronger Cd and Pb accumulators than rice. Reported reference point: Li et al. 2012 Pearl River Estuary rice grain BAFs were Cd 0.206, Pb 0.006, Ni 0.059 (text p. 13).

Table 5 — Estimated daily intake (EDI, µg kg⁻¹ day⁻¹ bw; page 28)

ᵃ TDI, WHO 1993. ᵇ PMTDI, FAO/WHO 2007. EDI computed as (C_metal × W_food) / B_w with C_metal in µg g⁻¹ dry weight, W_food per local Isfahan-region adult consumption (wheat 265 g day⁻¹, rice 187 g day⁻¹, onion 35 g day⁻¹; authors’ local investigation, p. 7), B_w = 60 kg adult.

In Zarrinshahr and Mobarakeh, total EDIs for Cd, Ni, and Pb were ≈ 2×, 2.5×, and 4× the WHO 1993 TDIs respectively; in Natanz all four total EDIs fell well below the tolerable limits. Fe EDIs in both industrial regions were below the FAO/WHO 2007 PMTDI of 800 µg kg⁻¹ day⁻¹ bw. EDI rank-orders by metal in the industrial regions (text p. 14): wheat and onion crops Fe > Pb > Ni > Cd; rice Fe > Ni > Pb > Cd.

Contamination Load Index (CLI) — Figure 3 (page 31)

CLI = C_crop / MPC (Codex Alimentarius 2001 MPCs for crops: Cd 0.2, Ni 0.6, Pb 0.3 mg kg⁻¹). CLI > 1 indicates the crop is contaminated with the metal.

Text-reported regional three-crop mean CLI values (p. 14):

Per-crop CLI extracted from Figure 3 (chart-extracted; precision ±0.2):

All industrial-region crops except rice in Zarrinshahr (Cd CLI ~0.9 < 1) and rice in Mobarakeh (Cd CLI ~0.8 < 1) showed CLI > 1 for all three metals; the Natanz crops sat at CLI < 1 across the board (the wheat Pb chart reading near 1.0 in Figure 3 is the only Natanz value approaching unity).

Target Hazard Quotient (THQ) — Figure 4 not shown, text p. 15

THQ formula (Chien et al. 2002): THQ = (EF × ED × FI × MC) / (RfDo × BW × AT) × 10⁻³.

Parameters: EF = 365 d y⁻¹; ED = 70 y; FI = food ingestion rate (g person⁻¹ d⁻¹); MC = heavy-metal concentration in food (µg g⁻¹); RfDo = oral reference dose (mg kg⁻¹ day⁻¹) = 1E−03 (Cd), 2E−02 (Ni), 7E−01 (Fe), 4E−03 (Pb) per USEPA IRIS 2003/2007 and Nadal et al. 2008; BW = 60 kg adult; AT = 365 × 70 d.

Reported THQ values in Zarrinshahr (p. 15):

• Cd: wheat 1.3, rice 0.64, onion 0.3; sum 2.24.
• Pb: total across the three crops 4.14.
• Ni: total 0.74.
• Fe: total 0.8.

Combined THQ values for Pb and Cd via crops consumption are > 1 in the industrial regions, indicating relatively high non-carcinogenic health risk. The text identifies Pb as the dominant contributor, followed by Cd. The paper does not tabulate per-crop / per-region THQ; the wiki page reports the four sums and the Cd per-crop trio as the text states them.

Method-quality figures (page 6)

• Method detection limits (MDL): Fe 0.15 mg kg⁻¹; Ni 0.0035 mg kg⁻¹; Cd 0.0008 mg kg⁻¹; Pb 0.003 mg kg⁻¹.
• Spike recovery: Cd 96 %, Fe 98 %, Pb 98 %, Ni 97 %.

Local Isfahan-region adult-consumption inputs (text p. 7)

Authors’ local investigation: wheat 265 g day⁻¹, rice 187 g day⁻¹, onion 35 g day⁻¹; adult body weight 60 kg.

Methods (brief)

Study design. Cross-sectional paired soil–crop survey. Two industrial regions (Zarrinshahr, Mobarakeh; 6–8 km and 12–14 km east of the Isfahan Steel Mill Company and Mobarakeh Steel Mill Company, respectively) and one control region (Natanz; 140–150 km from the steel mills). Three crops × three regions × three field replications = 27 paired soil and edible-portion crop samples. Each composite formed from five differing parts of each field.

Soil sampling. Topsoil (0–20 cm) per region per crop field. Air-dried, crushed, and passed through a 2 mm sieve. pH measured in saturation paste; EC measured in saturated extracts; organic C by Walkley–Black; CEC by ammonium acetate; particle size by pipette (Gee & Bauder 1986).

Soil digestion. 1 g of soil + HNO₃ + H₂O₂ per USEPA Method 3050B (1996).

Crop preparation. Edible portions rinsed with double-distilled water, dried at 70 °C, powdered. 1 g of crop powder + 10 mL concentrated HNO₃ + 2 mL H₂O₂ at 70 °C in a hot black digester (Lozano-Rodriguez et al. 1995 wet-mineralisation protocol); diluted to 50 mL with distilled water.

Instrumentation. Graphite-furnace atomic absorption spectrometry (Perkin Elmer AAnalyst 800) for Cd, Pb, and Ni on a dry-weight basis. Flame atomic absorption spectrometry for Fe.

Calibration & QC. Method detection limits: Fe 0.15 mg kg⁻¹, Ni 0.0035, Cd 0.0008, Pb 0.003 mg kg⁻¹. Spike recovery: Cd 96 %, Fe 98 %, Pb 98 %, Ni 97 %. Double-distilled water used throughout. All analyses performed at the central laboratory of Islamic Azad University, Isfahan (Khorasgan) Branch. No certified reference material (CRM) reported; recovery is the sole accuracy control.

Speciation. Total Cd, total Pb, total Ni, total Fe. No arsenic (As)/mercury (Hg) panel; no species fractionation.

Reporting basis. Crop concentrations on a dry-weight basis (per Methods §“Soil and Crop Analysis”). Risk-assessment EDIs are computed in µg kg⁻¹ bw day⁻¹ using local Isfahan adult consumption (wheat 265, rice 187, onion 35 g day⁻¹) and a 60-kg adult body weight; consumption inputs are stated as raw, not as-consumed, but the paper does not explicitly state a wet-to-dry conversion, so the Table 5 EDIs are best interpreted as derived from the dry-weight crop concentrations and the as-purchased consumption figures (see Verification notes).

Data-analysis indices. Bio-accumulation Factor BAF = C_plant / C_soil. Contamination Load Index CLI = C_crop / MPC, with Codex Alimentarius Commission 2001 MPC values (Cd 0.2, Ni 0.6, Pb 0.3 mg kg⁻¹ for crops). Estimated Daily Intake EDI = (C_heavy_metal × W_food) / B_w with B_w = 60 kg adult. Target Hazard Quotient THQ = (EF × ED × FI × MC) / (RfDo × BW × AT) × 10⁻³ per Chien et al. 2002, with USEPA IRIS RfDo values (Cd 1E−03, Ni 2E−02, Fe 7E−01, Pb 4E−03 mg kg⁻¹ day⁻¹).

Statistics. One-way ANOVA for between-region soil comparison; two-way ANOVA for crop concentrations across regions. Means compared by least-significant-difference (LSD) test at p < 0.05. Pearson correlation between soil and crop heavy-metal concentrations. SAS 9.1 for Windows.

Geographic and exposure context. Isfahan province, central Iran, climate arid (annual precipitation ~110 mm, mean temperature ~16 °C). Prevailing wind west-to-east, with cultivated fields east of the steel mills. Cultivated lands on alluvial plains of the Zayandehrood river in Isfahan; Natanz on young low-level terraces. Major soil types Typic Calciargids, Typic Calcigypsids, Calcic Argigypsids, Typic Torriorthents, Chromic Haplotorrerts, Haplocambids. Regional cultivated areas: wheat ~670 ha, rice ~2000 ha, onion ~50 ha. Regional fertilizer application: urea 300–400 kg ha⁻¹, triple superphosphate 100–150, potassium sulphate 150–200 for wheat and rice; urea 200–250, triple superphosphate 300–350, potassium sulphate 300–350 for onion. Steel mills active for ≈ 40 years at the time of writing. The paper does not state the sampling year.

Implications

This source contributes paired Iranian soil-and-crop occurrence data for total Cd, Pb, Ni, and Fe from two industrial regions (Zarrinshahr, Mobarakeh) downwind of the Isfahan Steel Mill Company and Mobarakeh Steel Mill Company, plus a distant control region (Natanz). Its principal contributions to the wiki evidence pool:

• Bulk wheat-grain Pb occurrence in an Iranian industrial context: 2.00 mg/kg dw (Zarrinshahr), 2.10 (Mobarakeh), 0.29 (Natanz). The industrial-region values are ≈ 7× the Codex Alimentarius 2001 cereal MPC of 0.3 mg/kg; Natanz sits at ≈ 1× MPC. Adds to the upper tail of bulk-grain Pb occurrence data alongside other regional Iranian surveys (Hamadan in Heshmati 2020; Kermanshah in Ataee 2016).
• Bulk rice-grain Pb occurrence: 1.41 mg/kg dw (Zarrinshahr), 1.21 (Mobarakeh), 0.17 (Natanz). Industrial-region values ≈ 4× the Codex MPC. Substantially exceeds the Cao et al. 2010 Jiangsu industrial-zone rice-grain Pb baseline of 0.054 mg/kg cited in the paper’s discussion (p. 11).
• Onion-bulb Pb occurrence: 2.12 mg/kg dw (Zarrinshahr), 1.90 (Mobarakeh), 0.26 (Natanz). Useful upper-tail Pb evidence for the onions ingredient page and the root-tuber-vegetables product page.
• Bulk wheat-grain, rice-grain, and onion-bulb Cd occurrence: industrial-region wheat 0.31 / 0.28, rice 0.17 / 0.15, onion 0.30 / 0.28 mg/kg dw (Zarrinshahr / Mobarakeh); control Natanz 0.06 / 0.03 / 0.05. Wheat and onion industrial-region means exceed the Codex MPC of 0.20 mg/kg by ≈ 1.5×; rice means sit below the MPC but well above Natanz and the Cao et al. 2010 Jiangsu industrial-zone rice-grain Cd baseline of 0.014 mg/kg cited in the paper’s discussion (p. 11). Li et al. 2012 Pearl River Estuary is cited in the source only for rice-grain BAFs (Cd 0.206, Pb 0.006, Ni 0.059), not for mg/kg concentrations.
• Bulk crop Ni occurrence in an Iranian industrial setting: wheat 1.42 / 1.25, rice 1.65 / 1.70, onion 2.05 / 2.65 mg/kg dw in the two industrial regions vs. 0.21 / 0.20 / 0.28 in Natanz. All industrial-region values exceed the Codex MPC of 0.6 mg/kg by ≈ 2–4×. Contributes Ni occurrence data to the metals/nickel evidence pool.
• Soil-to-plant Cd transfer evidence: Cd BAF mean across all samples 0.116, with Cd > Pb > Ni > Fe descending order. Wheat and onion are stronger Cd and Pb accumulators than rice in the industrial regions. Regional Cd BAF (0.136 Zarrinshahr, 0.130 Mobarakeh, 0.081 Natanz) supports the soil-pollution-driven hypothesis: BAF rises modestly in contaminated soils despite the well-documented “dilution” tendency at high soil concentrations.
• Soil–crop Pearson correlation coefficients (n=27, all p < 0.01): diagonal same-metal r-values 0.98 (Fe), 0.95 (Pb), 0.94 (Ni), 0.97 (Cd). Strong soil-to-crop transfer signal for all four metals — useful as a reference for downstream synthesis claims about agricultural-pathway contamination upstream of food.
• Adult exposure burden in industrial-region Iran: total Cd EDI 2.08 / 1.87 µg kg⁻¹ day⁻¹ bw (Zarrinshahr / Mobarakeh) ≈ 2× WHO 1993 TDI of 1; Ni EDI 12.61 / 12.37 ≈ 2.5× TDI of 5; Pb EDI 14.46 / 14.15 ≈ 4× TDI of 3.6. Three-crop combined THQ for Pb (4.14) and Cd (2.24) > 1 in Zarrinshahr, indicating relatively high non-carcinogenic health risk from the cereal-and-onion pathway in industrial-region Isfahan adults.
• Industrial-region soil baselines: pooled industrial Cd 1.85, Fe 35 894, Ni 64.5, Pb 38 mg/kg vs. Natanz 0.54, 15 363, 20, 19 mg/kg. Industrial soils exceed the EU 2000 sludge-soil ceiling for Cd (1.5 mg/kg) and the USEPA 1983 soil ceiling for Ni (40 mg/kg); the authors also report all three regions’ Pb soil values (38.3, 37.7, 19.3) as exceeding a 10 mg/kg ceiling that they attribute to the EU 2000 Working Document on Sludge.
• Methodological reference point: GF-AAS (Perkin Elmer AAnalyst 800) with USEPA 3050B soil digestion and Lozano-Rodriguez 1995 wet-mineralisation crop digestion; MDLs of 0.0008 mg/kg (Cd) and 0.003 mg/kg (Pb); spike recoveries 96–98 %. No CRM-anchored accuracy validation; this is the principal contributor to B-tier evidence grading.

Sample size is small (n = 3 fields per region per crop, n = 27 paired soil–crop composites total). Single-year-unspecified sampling window, adult-only 60-kg single-cohort exposure cohort, three-crop intake aggregation that excludes other dietary sources, lack of CRM-anchored accuracy validation, and the absence of an arsenic or mercury panel limit the paper’s standalone authority; pools with other Iranian and regional vegetable/cereal surveys rather than anchoring any standalone characterisation. The strong soil–crop Pearson correlations and the clear industrial-vs-control gradient (≈ 3–5× concentration jumps across all four metals) make this a defensible point of evidence for the agricultural-pathway contamination mechanism in industrial-region Iran.

Related evidence

• Cadmium
• Lead
• Nickel
• Iron
• Wheat
• Rice
• Onions
• Cereals
• Other grain products (oat, millet, quinoa, barley)
• Rice (white, brown, wild — bulk grain)
• Root and Tuber Vegetables
• Codex Alimentarius — Maximum Levels for Cadmium in Food
• EPA IRIS — Cadmium Oral Reference Doses
• EPA IRIS — Lead, Oral RfD and Carcinogenicity Assessment
• EFSA — Nickel Tolerable Daily Intake (13 µg/kg b.w./day)

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