Concentration of lead and mercury in collected vegetables and herbs from Markazi province, Iran: a non-carcinogenic risk assessment

Overview

This Iranian cross-sectional field survey quantifies total lead (Pb) and total mercury (Hg) in ten species of green leafy vegetables and herbs, agricultural soil (0–15 cm), and irrigation water from five agricultural sites across Markazi province (an industrial-agricultural region of northwest Iran with aluminum, steel, petroleum, and automotive industries). Samples collected May–August 2014; analysis by ICP-OES (Varian Vista-MPX, Spectroacros EOP, with ultrasonic nebulizer). All vegetable Pb means exceeded the WHO/FAO 300 µg/kg leafy-vegetable Pb ceiling cited by the authors (range 990–1734 µg/kg dry weight across species). Hg means ranged 36–56 µg/kg dry weight; four species (Allium wakegi, Artemisia dracunculus, Lepidium sativum, Trigonella foenum-graecum) exceeded the 50 µg/kg drinking-water Hg “safety limit” the authors invoked. Soil and water Pb and Hg also exceeded WHO/FAO guidelines cited by the authors. Hazard Index (Pb + total mercury (tHg) THQ) for the combined 15–64 adult age range was 8.49 (urban) and 9.01 (rural); Pb contributed ~93 % and tHg ~7 % of HI; the authors concluded both urban and rural consumers face significant non-carcinogenic health risk from green leafy vegetable and herb consumption in this province.

Key numbers

Method validation (§3.1, Tables 1–2)

• Linear range Pb and Hg: 2.5–1000 µg/kg, with regression coefficients 0.9975 (Pb) and 0.9992 (Hg).
• Detection limits (LOD): Pb 2 µg/kg, Hg 0.35 µg/kg. Limits of quantification (LOQ): Pb 1.16 µg/kg, Hg 6.6 µg/kg. (See Verification notes for the LOD/LOQ swap and an LOQ-below-LOD inconsistency for Pb in the printed Table 2.)
• Recoveries (n=18 each, 6 spiking levels 15–750 µg/mL): Pb 96.2 % (soil), 106.8 % (vegetable), 113.5 % (water); Hg 98.2 % (soil), 104.3 % (vegetable), 115.1 % (water). RSD range 4.3–16.85 % across all matrices and analytes.

Table 3 — Mean Pb and Hg in vegetables (µg/kg dry weight), soil (µg/kg dry weight), and irrigation water (µg/L)

Across-vegetable pooled means (§3.2 text): Pb 1095 ± 722.07 µg/kg dw (range 990–1734); tHg 47.30 ± 23.35 µg/kg dw (range 36.12–56.14).

Standard limits cited by the authors: WHO/FAO leafy-vegetable Pb ceiling 300 µg/kg (Yahaya 2013); Hg “established safety limit” 50 µg/kg (Fawell et al. 2005 — note: the Fawell et al. reference is the WHO Mercury in Drinking-Water background document; the 50 µg/kg figure is a drinking-water-context value the authors apply to vegetables, with no explicit justification for the cross-matrix transfer). WHO irrigation-water Pb ceiling 0.01 mg/L = 10 µg/L cited at §3.2 (WHO 2007). All vegetable Pb means and the soil Pb mean exceed cited limits; the soil Hg mean is just above the 50 µg/kg threshold; the water Pb mean (494 µg/L) exceeds the 10 µg/L irrigation guideline by ~49-fold.

Table 4 — THQ for Pb and tHg and Hazard Index (HI) by age group, urban vs. rural Markazi consumers

THQ < 1 = no significant non-carcinogenic risk; THQ ≥ 1 = possible adverse effects; HI ≥ 10 = considerable non-carcinogenic risk (Lei et al. 2015 thresholds, §2.11.3). All Pb THQ values exceed 1; all Hg THQ values are below 1; all HI values exceed 1 (range 7.92–9.76). The authors state Pb is “14 times more than Hg” in HI contribution; from Fig. 3 caption: Pb accounts for 93 % and Hg for 7 % of HI.

Risk-assessment parameter set (§2.11.2)

• THQ formula (as printed, §2.11.2 Eq. 2): THQ = (EF × ED × FIR × C / RFD × WAB × TA) × 10⁻³. See Verification notes — the printed formula contains a typographic bracket-omission inconsistent with the standard USEPA THQ definition; the values in Table 4 are reconstructible with the standard interpretation THQ = (EF × ED × FIR × C) / (RFD × WAB × TA × 10⁶) where C is in µg/kg and RFD is in mg/kg/day.
• EF (exposure frequency): 365 days/year.
• ED (exposure duration): 70 years.
• TA (averaging time): 70 years (= 70 × 365 days).
• FIR (per-capita vegetable consumption): 250 kg/person/year = 684 g/person/day (FAO 2015 Iran figure).
• RFD: Pb 0.0004 mg/kg/day; Hg 0.0003 mg/kg/day (USEPA 2000).
• C: concentration of Pb or Hg in vegetable (µg/kg dry weight, as printed in Table 3).
• WAB (body weight): urban 64/71/74/74/72/69 kg for 15–24/25–34/35–44/45–54/55–64/15–64; rural 60/66/69/68/67/65 kg for the same age groups (Asgari et al. 2009 surveillance values).

Transfer factor (TF) interpretation (§3.2)

• All Pb TFs are below 1 (range 0.19–0.34): vegetables and herbs are weak Pb accumulators from this contaminated soil, with Spinacia oleracea the highest (0.34).
• Four Hg TFs exceed or approach 1: Allium wakegi 1.05, Artemisia dracunculus 1.07, Lepidium sativum 1.04, Trigonella foenum-graecum 1.02; the authors note this likely reflects atmospheric Hg deposition rather than soil-root uptake (Cao et al. 2010).
• The authors conclude the rank order of HI across age groups in both urban and rural Markazi areas is 15–24 > 25–34 > 55–64 > 45–54 > 35–44 (Conclusions §4); the youngest adult cohort carries the highest risk, driven primarily by Pb intake relative to body weight.

Methods (brief)

Study design. Cross-sectional vegetable, soil, and water survey across five agricultural sites in Markazi province, Iran (34° 05′ 30.26″ N, 49° 41′ 20.98″ E), May–August 2014. Ten leafy-vegetable/herb species collected per site (~1 kg each); 100 total vegetable composites (10 species × 10 samples). Five sites × six sample plots = 30 soil samples. 30 irrigation-water samples (in triplicate). Total n=160 sample units across the three matrices.

Vegetable/herb preparation. Samples washed with tap water, rinsed twice with deionized water, oven-dried 60–70 °C for 24 h, ground to small particle size, stored in polyethylene bags for ≤6–12 months prior to digestion. ~1 g powder + 15 mL acid mixture HNO₃ (70 %) + H₂SO₄ (65 %) + HClO₄ (70 %) in 5:1:1 v/v ratio in test tubes (Shakya & Khwaounjoo 2013 method).

Soil preparation. 10–15 cm depth samples, oven-dried 60–70 °C for 12–24 h, powdered. Digestion with 6 mol/L HNO₃; filtered under vacuum through Whatman No. 42 paper.

Water preparation. Collected from agricultural site irrigation in pre-cleaned polyethylene bottles (10 % HNO₃ soak overnight, two rinses with deionized water; Chary et al. 2008 protocol). Direct ICP-OES injection.

Instrumentation. ICP-OES EOP, Spectroacros, Varian Vista-MPX (Germany); ultrasonic nebulizer; argon carrier (99.999 % purity grade 5; 0.7 L/min for modified Lichte nebulizer, 13 L/min coolant); 4-channel peristaltic pump at 60 rpm pre-flush (45 s) and 30 rpm analysis; power 1400 kW (Marin et al. 2011 protocol).

Calibration. Stock solutions 10 µg/mL Merck; spiked calibration standards at 2.5–1000 µg/L equivalent in blank vegetable, soil, and water matrices. Recovery determined at six spiking levels (15, 25, 75, 150, 250, 500, 750 µg/mL — note: this is seven levels as listed, but the table reports six; the discrepancy is a paper-internal inconsistency).

Speciation. ICP-OES measures total elemental Pb and total elemental Hg. No methyl-/inorganic-Hg fractionation; no Pb species partitioning. source metadata metals: reflects total-Pb and total-Hg ([Pb, tHg]); methylmercury (MeHg) is not reported.

Statistics. Means, SDs, min/max via SPSS v.22; one-way ANOVA; p-value threshold 0.05; data reported as normal-distributed enabling parametric tests. Figures generated in Excel 2016.

Risk-assessment formulas. THQ per Chien et al. 2002 (Eq. 2, with the bracket-typography caveat); HI = THQ_Pb + THQ_Hg per Fakhri et al. 2017–2018 (Eq. 3). Thresholds per Lei et al. 2015: THQ ≥ 1 = possible adverse effects; HI ≥ 10 = considerable risk.

Implications

This source contributes Iranian field-survey occurrence data for total Pb and total Hg in ten species of green leafy vegetables and herbs, agricultural soil, and irrigation water across one industrial-agricultural province (Markazi). Its principal contributions to the wiki evidence pool:

• Bulk leafy-vegetable and herb Pb occurrence (µg/kg dw) in a heavily industrialized Iranian province: range 990 (A. ampeloprasum) to 1734 (S. oleracea) across species means; soil Pb 4994 µg/kg dw; irrigation water Pb 494 µg/L. All vegetable Pb means exceed the 300 µg/kg WHO/FAO leafy-vegetable Pb ceiling cited by the authors; the water Pb mean exceeds the 10 µg/L irrigation guideline by ~49-fold. Useful as upper-end pooling data for Iranian-industrial-context leafy-vegetable Pb occurrence.
• Bulk leafy-vegetable and herb tHg occurrence (µg/kg dw): range 36 (S. oleracea) to 56 (A. dracunculus) across species means; soil tHg 52 µg/kg dw; irrigation water tHg 67 µg/L. Four of ten species exceed the 50 µg/kg threshold the authors invoke; the rest fall below. Useful as low-to-moderate-end occurrence data for a non-fish vegetable matrix in an industrial setting.
• Pathway evidence. Soil-to-plant TF for Pb is uniformly <1 (0.19–0.34) while TF for Hg is >1 for four species (1.02–1.07), suggesting that for these vegetables in this region, Pb accumulation is limited by root barriers despite high soil burden while Hg uptake may be supplemented by atmospheric deposition onto leaf surfaces (Cao et al. 2010). The paper does not measure atmospheric Hg directly, so the deposition pathway remains inferential.
• Risk-assessment parameter set. Documents a complete Iranian-context THQ/HI parameterization (Asgari et al. 2009 urban/rural body-weight surveillance values across five 10-year age cohorts; FAO 2015 250 kg/person/year vegetable consumption; USEPA 2000 RfDs). The 684 g/day FIR is a high-end staple-vegetable consumption value typical of Iranian dietary surveys and is not directly transferable to settings where leafy vegetables and herbs are non-staple commodities.
• Speciation limitation. Total Pb and total Hg only; no MeHg analysis. The 50 µg/kg Hg threshold the authors apply is a drinking-water-context value (WHO 2007 via Fawell et al. 2005), not a vegetable-matrix regulatory ceiling; the cross-matrix transfer should not be treated as a regulatory exceedance for downstream synthesis. source metadata metals: reflects this ([Pb, tHg]).

Sample size is moderate (n=100 vegetable composites across 10 species × 5 sites × 2 replicate samples per site; n=30 each for soil and water). The single-province sampling footprint, single-year window (May–August 2014), and absence of certified-reference-material validation limit standalone authority; the paper supports B-tier generalization to Iranian-industrial leafy-vegetable Pb burden but not to non-industrial Iranian agriculture or to other commodity classes. The 1.07 Hg TF in Artemisia dracunculus is notable but the underlying mechanism (foliar deposition vs. true root uptake) is not isolated by the study design.

Related evidence

• Lead
• Mercury, Total
• Mercury
• Spinach
• Parsley
• Leafy Vegetables
• Vegetables
• Fresh Herbs
• Herbs And Spices
• Water
• Leafy / Green Vegetables, Other
• Spinach

Update history

No substantive edit history is available in this build. The full commit record is available in git.