Health risk assessment of heavy metals via dietary intake of wheat in Golestan Province, Iran

Overview

This Iranian post-harvest survey quantifies total lead (Pb), cadmium (Cd), Cu, Fe, and Zn in bulk wheat grain drawn from 35 storage silos in Golestan province, northern Iran. Wheat from each silo was sampled per Iranian National Standardization Organization (INSO) protocol No. 13535, dried at 100 °C for 24 h, ground, dry-ashed at 450 °C, dissolved in 6 M HCl on a water bath, and re-suspended in 1 % HNO₃ for atomic absorption spectrometry per Jorhem (NMKL1; J. AOAC Int. 2000). Pb and Cd were quantified by graphite-furnace AAS (Perkin-Elmer AAnalyst 800 with Zeeman background correction, AS 800 auto-sampler, L’vov platform, pyrolytic-coated graphite tubes, 99.996 % Argon); Cu, Fe, and Zn by flame AAS (air-acetylene burner, deuterium background correction). Recovery across the five analytes was 70–110 % with RSD < 20 %; LODs (mg/kg) were Cd 0.0007, Pb 0.002, Cu 0.057, Fe 1.4, and Zn 0.56. Mean ± SD concentrations across the 35 silos were Pb 0.057 ± 0.003, Cd 0.016 ± 0.005, Cu 2.7 ± 0.17, Fe 111.2 ± 21, and Zn 5.7 ± 0.22 mg/kg dry weight (ranges Pb 0.013–0.14, Cd 0.008–0.031, Cu 0.48–6.2, Fe 58.50–406.9, Zn 3.41–32.75 mg/kg). The concentration rank was Fe > Zn > Cu > Pb > Cd. All five mean values sat below the FAO/WHO maximum permissible limits cited by the authors (Cd 0.2, Pb 0.3, Cu 73.3, Fe 425.5, Zn 99.4 mg/kg) and below the INSO 2013 limits where applicable (Cd 0.03, Pb 0.15 mg/kg). Estimated daily intakes for an Iranian adult (70 kg body weight, 334 g wheat/person/day) were Pb 0.2679, Cd 0.0752, Cu 12.69, Fe 522.64, and Zn 26.79 µg/kg bw/day — all below the JECFA-derived TDIs the paper cites (Pb 3.5, Cd 0.8, Cu 50, Fe 800, Zn 30–100 µg/kg bw/day). The paper concludes wheat from Golestan does not pose a measurable non-carcinogenic health risk via the cereal pathway alone.

Key numbers

Table 1 — Mean ± SD, recovery, LOD, LOQ, and reference safe limits for the five heavy metals across 35 Golestan wheat-grain silos (page 17)

“NSO” = Iranian National Standardization Organization (INSO 2013, Food and Feed — Maximum Limit of Heavy Metal, Amendment No. 1). The Cu, Fe, and Zn rows show ”—” under NSO because the Iranian standard does not set permissible limits for those essential metals in wheat in the amendment the authors cite. All concentrations are dry weight (samples were oven-dried at 100 °C for 24 h before digestion).

Per-analyte ranges across the 35 silos (text, pages 1–2 abstract and pages 8–9 §“Results”):

• Cd: 0.008 – 0.031 mg/kg dry weight.
• Pb: 0.013 – 0.14 mg/kg dry weight.
• Cu: 0.48 – 6.2 mg/kg dry weight.
• Fe: 58.50 – 406.9 mg/kg dry weight.
• Zn: 3.41 – 32.75 mg/kg dry weight.

Calibration-curve correlation coefficients (text, page 8): Cd 0.9981, Pb 0.9973, Cu 0.9978, Zn 0.9989. Fe correlation coefficient not stated.

Table 2 — Estimated daily intake (EDI) vs. tolerable daily intake (TDI) for the Iranian adult population via wheat consumption (page 18)

EDIs computed per the standard formula EDI = (EF × ED × FIR × C) / (W_AB × T_A) with EF = 365 d/year, ED = 70 years, FIR = 334 g/person/day, W_AB = 70 kg, T_A = 365 × 70 days, and C = the mean wheat concentration in µg/g (Qian et al. 2010 formulation; text page 7). EF × ED cancels with T_A in the EDI ratio for non-carcinogens, leaving EDI = C × FIR / W_AB; the wiki-side recalculation using the Table 1 means is Pb 0.272, Cd 0.0763, Cu 12.88, Fe 530.6, Zn 27.20 µg/kg bw/day, which match the Table 2 figures within rounding (the small offsets are consistent with the paper using higher-precision unrounded means before the final EDI computation). The TDI rank-order matches the EDI rank-order across all five metals: Fe > Zn > Cu > Pb > Cd. The text abstract figure “0.27, 0.075, 12.69, 522.64 and 26.79 µg/kg bw/per day” is a rounded restatement of the Table 2 row.

EDI relative to TDI (calculated from Table 2):

• Pb: 0.2679 / 3.5 = 7.65 % of TDI.
• Cd: 0.0752 / 0.8 = 9.40 % of TDI.
• Cu: 12.69 / 50 = 25.38 % of TDI.
• Fe: 522.64 / 800 = 65.33 % of TDI.
• Zn: 26.79 / 30 = 89.30 % at the lower TDI bound; 26.79 / 100 = 26.79 % at the upper TDI bound.

The paper does not tabulate the percentage-of-TDI values; the wiki-side calculation is included for downstream synthesis.

Methods (brief)

Study design. Cross-sectional post-harvest survey of 35 bulk-wheat-grain composites drawn from 35 storage silos in Golestan province, northern Iran. Each composite was mixed from different parts of a single silo to give a homogeneous sample (text, page 4). Samples were stored in polythene bags and transported to the laboratory for preparation and analysis. The paper does not state the sampling year, the geographic distribution of the 35 silos within Golestan, the wheat cultivar(s), the harvest season, or the upstream agronomic context (irrigation source, fertilizer regimen, soil type). The cited Iranian-population consumption rate (334 g wheat/person/day) and demographic anchor (70-kg adult) describe the exposure population, not the wheat-source population.

Sample preparation. Wheat samples were oven-dried at 100 °C for 24 h to remove flour humidity, then ground to a fine powder using an acid-washed pestle. Per AOAC method, 10 g of ground sample was weighed into a porcelain capsule, gradually heated to 450 °C (50 °C/hour) in a muffle furnace, then left to stand overnight; the resultant ash was wetted with drops of 65 % HNO₃, evaporated on a hot plate, returned to the muffle furnace at 450 °C for 1–2 h until a white/grey/slightly coloured product was obtained, then exposed to 5 mL 6 M HCl on a water bath. The residue was dissolved in 10 mL 1 % HNO₃ and brought up to a final volume of 50 mL. A sample blank was prepared in parallel.

Instrumentation. Pb and Cd determined by graphite-furnace AAS on a Perkin-Elmer AAnalyst 800 with Zeeman background correction, AS 800 auto-sampler, L’vov platform, pyrolytic-coated graphite tubes, and 99.996 % Argon as inert gas. Hollow-cathode lamps operated at 217 nm / 10 mA (Pb) and 228 nm / 4 mA (Cd) with a 0.7 nm spectral band pass. Cu, Fe, and Zn determined by flame AAS with a 100 mm air-acetylene burner head and deuterium background correction at 324.8 nm (Cu), 248 nm (Fe), and 213.9 nm (Zn).

Reagents and calibration. Stock standard solutions of each metal ion at 1000 mg/mL were diluted to working solutions with deionized water (per source page 5, “deionized water was used in all dilution procedures”). All glassware was washed with liquid soap, soaked overnight in 10 % (v/v) HNO₃, and rinsed with double-distilled water before use. All reagents were analytical grade.

Method validation. Recovery determined by spiked-sample analysis; achieved recovery across the five analytes was 70–110 % with RSD < 20 %. LOD computed as 3 × standard deviation of 10 blank-matrix measurements. LOQs reported in Table 1 alongside LODs. The paper does not name a certified reference material (CRM); accuracy is anchored on spike recovery alone. Linearity confirmed by calibration-curve correlation coefficients > 0.997 for the four metals reported (Cd, Pb, Cu, Zn).

Speciation. Total Pb, total Cd, total Cu, total Fe, total Zn — no inorganic vs. organic fractionation; no arsenic (As)/mercury (Hg) panel.

Reporting basis. Concentrations on a dry-weight basis (samples were oven-dried for 24 h at 100 °C prior to digestion; the Table 1 column header reports mg/kg without explicit “dw” annotation, but the §“Zinc” results paragraph explicitly states “dry weight” and the methods §“Sample preparation” describes the 100 °C / 24 h drying step before ashing). The EDI calculation uses µg/g wheat × g/day consumption ÷ kg body weight, treating the Iranian adult consumption (334 g/day) as a dry-equivalent intake without an explicit wet-to-dry conversion — this is the standard approach in bulk-grain dietary-exposure studies (wheat moisture at harvest is ≈ 12–14 %, so the as-consumed conversion would lower the EDIs by roughly that factor for water-bearing intermediate flour or bread products).

Statistics. Results reported as mean ± standard deviation. ANOVA in SPSS (version not stated).

Exposure-model parameters. EF 365 d/year; ED 70 years; FIR 334 g wheat/person/day; W_AB 70 kg adult; T_A 365 × 70 d (non-carcinogenic averaging). Parameters attributed to Qian et al. 2010 (Food Control 21:1757–1763). The 334 g/day Iranian per-capita wheat consumption is not separately referenced inside the methods text but is the canonical figure for Iranian adult wheat/bread intake from this period; the paper attributes the broader formula and parameter scaffolding to Qian et al. 2010.

Tolerable daily intakes. JECFA-derived TDIs as reported in Table 2: Pb 3.5, Cd 0.8, Cu 50, Fe 800, Zn 30–100 µg/kg bw/day. The Pb TDI of 3.5 µg/kg bw/day is the daily-equivalent of the JECFA 1972 PTWI of 25 µg/kg bw/week (25/7 ≈ 3.57); JECFA withdrew this PTWI in 2010, judging that no PTWI for lead could be established that would be considered health-protective. The Cd TDI of 0.8 µg/kg bw/day is the daily-equivalent of the JECFA 2010 PTMI of 25 µg/kg bw/month (25/30.4 ≈ 0.82). The paper does not flag the JECFA-2010 Pb-PTWI withdrawal; the comparison should be read as the authors’ chosen reference TDI, not as the current JECFA position. See Verification notes.

Implications

This source contributes Iranian post-harvest bulk-wheat-grain occurrence data for total Pb, Cd, Cu, Fe, and Zn from 35 storage silos in Golestan province. Its principal contributions to the wiki evidence pool:

• Bulk wheat-grain Pb occurrence in northern Iran (Golestan): mean 0.057 ± 0.003 mg/kg dw, range 0.013–0.14 mg/kg dw. Below the Codex Alimentarius 2001 cereal Pb MPC of 0.2 mg/kg (FAO/WHO 2001) and below the INSO 2013 wheat-Pb limit of 0.15 mg/kg. Sits at the low end of the global wheat-grain Pb occurrence distribution and substantially below the industrial-region Iranian wheat-grain Pb values reported in moradi2015 (Zarrinshahr 2.00, Mobarakeh 2.10 mg/kg dw) and the upper-tail Serbian and Chinese values cited in the paper’s discussion (Škrbić & Čupić 2005 Serbia mean 0.137 mg/kg; Huang & Zhou 2008 Kunshan range 0.017–1.158 mg/kg).
• Bulk wheat-grain Cd occurrence in northern Iran: mean 0.016 ± 0.005 mg/kg dw, range 0.008–0.031 mg/kg dw. Below both the FAO/WHO 2001 wheat-Cd permissible limit of 0.2 mg/kg cited by the authors (the contemporary Codex CXS 193 cereal-grain Cd ML is 0.1 mg/kg, lower than the 0.2 the paper cites) and the INSO 2013 wheat-Cd limit of 0.03 mg/kg, though the upper end of the range (0.031 mg/kg) sits just above the INSO limit, suggesting some individual silos approach the Iranian threshold. The mean is substantially below the industrial-region Iranian wheat-grain Cd values in moradi2015 (Zarrinshahr 0.31, Mobarakeh 0.28 mg/kg dw) and below the Swedish long-term soil-fertility experiment range (Kirchmann & Mattsson 2009: Cd 0.007–0.229 mg/kg) the discussion cites.
• Bulk wheat-grain Cu, Fe, Zn occurrence: Cu mean 2.7 mg/kg dw (range 0.48–6.2); Fe mean 111.2 mg/kg dw (range 58.50–406.9); Zn mean 5.7 mg/kg dw (range 3.41–32.75). All well below the FAO/WHO essential-metal reference limits the authors cite (Cu 73.3, Fe 425.5, Zn 99.4 mg/kg). The Fe upper-range value (406.9 mg/kg dw) approaches but does not exceed the 425.5 mg/kg FAO/WHO limit. These essential-metal values are useful as occurrence benchmarks for the cereal-pathway nutritional baseline alongside the toxic-metal data.
• Adult Iranian exposure burden via wheat: EDIs 0.2679 (Pb), 0.0752 (Cd), 12.69 (Cu), 522.64 (Fe), 26.79 (Zn) µg/kg bw/day. All below the authors’ TDIs (Pb 3.5, Cd 0.8, Cu 50, Fe 800, Zn 30–100). Fe EDI is the closest to its TDI at 65 % of the FAO/WHO 2007 Fe PMTDI; Zn EDI is at 89 % of the lower 30 µg/kg bw/day TDI bound. Pb and Cd EDIs sit well below the JECFA-1972/2010 reference points (7.7 % and 9.4 % respectively). These exposure figures apply to the wheat pathway alone; the paper notes that “intake through other dietaries would probably increase the EDI values” (page 12).
• Methodological reference point: GF-AAS for Pb/Cd on Perkin-Elmer AAnalyst 800 with Zeeman background correction; flame AAS for Cu/Fe/Zn; dry-ashing digestion at 450 °C per Jorhem (NMKL1, J. AOAC Int. 2000). Spike-recovery validation across 70–110 %; no CRM-anchored accuracy validation. This is the principal reason for the B-tier (rather than A-tier) evidence grading: no certified reference material was used to anchor analytical accuracy, and the paper does not report inter-laboratory cross-validation.
• Bulk-grain post-harvest occurrence (vs. soil-to-plant): this paper samples wheat at the silo (post-harvest, pre-milling) stage and reports five-analyte concentrations in the bulk-grain form before processing into flour or bread. The matrix is therefore comparable to moradi2015 wheat-grain values and to the Tejera et al. 2013 Canary-Islands and Bermudez et al. 2011 Argentinian wheat-grain surveys the discussion cites — and one level upstream of wheat-flour and finished-bread occurrence surveys (Doe et al. 2013 Ghana wheat flour; Edem Christopher et al. 2009 Calabar-Nigeria wheat flour; Tejera et al. 2013 Canary Islands wheat flour; Jorhem & Sundström 2013 Swedish wheat and rye flours).

The contribution is bounded by several limitations: the 35 silos are not broken out by sub-region within Golestan; the sampling year is not stated; cultivar, harvest season, and upstream agronomic context (irrigation source, fertilizer regimen, soil-Cd background) are not reported; the demographic anchor is a single 70-kg adult cohort with no infant, child, or elderly stratification; the analytical accuracy is anchored on spike recovery alone without a CRM; and the As/Hg panel is absent. Pools with other Iranian and global wheat-grain surveys to characterise typical and tail occurrence of toxic Pb/Cd and essential Cu/Fe/Zn in post-harvest bulk wheat in northern Iran; does not anchor any standalone characterisation. The principal usable result is the low-mean / narrow-range occurrence signature of bulk Golestan wheat against the higher industrial-region Iranian values in moradi2015 and the upper-tail Chinese/Serbian values cited in the discussion.

Related evidence

• Lead
• Cadmium
• Copper
• Iron
• Zinc
• Wheat
• Other grain products (oat, millet, quinoa, barley)
• Codex Alimentarius — Maximum Levels for Cadmium in Food
• JECFA — Provisional Tolerable Monthly Intake for Cadmium, 25 µg/kg b.w./month
• JECFA — Lead Provisional Tolerable Weekly Intake (Withdrawn 2010)

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