Asadi Touranlou et al. 2025 — Health risk from heavy metals in Iranian bread, Monte Carlo analysis
This study quantifies heavy metal contamination in 248 Iranian bread samples spanning four traditional bread types (lavash, taftoon, barbari, sangak) across 11 provinces, then applies Monte Carlo simulation (10,000 iterations, Crystal Ball software) to characterize non-carcinogenic and carcinogenic health risks for children and adults. The principal findings are that chromium (Cr) and iron (Fe) drive non-carcinogenic risk, with hazard indices (HI) exceeding 1 for both children and adults even at the 95th percentile, and that lead (Pb) and cadmium (Cd) — detectable in only four provinces — present moderate carcinogenic risk (10^-6 to 10^-4 range). Pb and Cr mean concentrations exceeded WHO/FAO and Iranian national standards. This paper should not be conflated with the companion Asadi Touranlou et al. (2025) PLoS ONE study of Mashhad bakeries (cite-key: asaditouranlou2025-bread-wheat-mashhad), which used a different sampling frame (Mashhad only, n=270, flour-dough-bread triplets with As speciation).
Key numbers
All concentrations in mg/kg dry weight.
Mean concentrations (n=248 total samples): Cu 3.08 ± 1.24; Zn 13.6 ± 44.94; Fe 59.24 ± 30.62; Cd 0.004 ± 0.02; Al 4.98 ± 2.85; Co 0.01 ± 0.03; Pb 0.65 ± 1.71; Cr 1 ± 1.42; Ni 0.05 ± 0.23; Hg 0.03 ± 0.12.
Converting to ppb (µg/kg): Cd mean 4 ppb; Pb mean 650 ppb; Cr mean 1,000 ppb; Hg mean 30 ppb; Ni mean 50 ppb; Al mean 4,980 ppb; Fe mean 59,240 ppb; Zn mean 13,600 ppb; Cu mean 3,080 ppb.
Detection rates: Fe 100%, Zn 99.59%, Al 96%, Cu 91.53%, Cr 63.30%, Pb 29% (72/248), Co 18.54%, Ni 12.50%, Hg 9.67%, Cd 8.87%.
Comparison with WHO/FAO and INSO (Iranian national) limits: Pb mean (0.65 mg/kg) exceeds WHO/FAO limit (0.3 mg/kg) and INSO limit (0.05 mg/kg). Cr mean (1 mg/kg) exceeds WHO/FAO limit (0.1 mg/kg). Hg mean (0.03 mg/kg) exceeds WHO/FAO limit (0.005 mg/kg). Fe mean (59.24 mg/kg) exceeds WHO/FAO limit (20 mg/kg). Al mean (4.98 mg/kg) exceeds WHO/FAO limit (0.237 mg/kg). Cd, Co, Ni, Zn, Cu were within or below WHO/FAO limits.
By bread type, Pb means (mg/kg): lavash 0.70 ± 1.90; taftoon 0.96 ± 2.20; barbari 0.57 ± 1.39; sangak 0.46 ± 1.40. Sangak had the highest Zn (14.64 mg/kg), likely from Zn transfer from the hot pebble baking surface. Taftoon had the highest Fe (67.41 mg/kg).
Non-carcinogenic risk (hazard index, Monte Carlo 95th percentile): HI for children 3.37-8.53 (exceeds threshold of 1); for adults 1.52-3.78 (exceeds threshold of 1). THQ for Cr exceeded safe threshold (>1) in adults; THQ for Cr and Fe both exceeded threshold in children.
Carcinogenic risk (Cd and Pb only, four provinces where both were detectable): average CR for children 8.67×10^-6 ± 2.11×10^-5; for adults 2.05×10^-5 ± 5×10^-5. Moderate risk category (10^-6 < CR ≤ 10^-4).
Sensitivity analysis: Cr concentration drove 45.8% of HI variance in children and 44.7% in adults. Fe was second (17.6% children, 17.4% adults). For carcinogenic risk: Pb concentration dominated (32.2% children, 36.8% adults), followed by Cd (29.3% children, 31.8% adults).
Methods (brief)
ICP-OES (Spectro Arcos, model 76004555, Germany) following EPA 3050B method. Samples dried at 100°C to constant weight, homogenized, passed through 2 mm sieve. LODs reported in Table S1 (supplemental). Recovery rates 80.5%-100.6% (acceptable range 80%-120%). Calibration curve R² > 0.99 for each element. Each sample measured in triplicate. Concentrations reported in mg/kg dry weight. Monte Carlo modeling: Crystal Ball v11.1.34190, 10,000 iterations at 95% confidence. Heavy metal concentrations modeled as lognormal distributions; bread consumption rate as lognormal; EF and ED as uniform; BW as normal. The study measures total metals throughout; speciation into iAs/tAs or MeHg/tHg was not performed. The Cr measurement is total Cr; Cr-VI was not speciated. Note: As (arsenic) was not included in the analyte panel despite being listed in the title abstract reference list as a PTE of concern; all arsenic measurements come from the companion Mashhad study.
Implications
Certification: Provides population-scale baseline data on Pb, Cr, Cd, and Hg in Iranian bread. Pb exceedances relative to WHO/FAO limits in 29% of samples, combined with high carcinogenic risk from Pb in four provinces, support strict Pb limits in wheat-derived products. Cr concentrations (mean 1,000 ppb) substantially exceeding WHO/FAO limits (100 ppb) are notable, though total Cr rather than Cr-VI was measured; HMT&C certifies on Cr-VI per the analyte vocabulary in CLAUDE.md Part 14, and total-Cr data cannot substitute. The very high Pb mean (650 ppb) relative to the INSO standard (50 ppb) is striking and suggests significant contamination from milling equipment or flour additives, consistent with findings from the companion Mashhad study.
Courses: Useful case study for Monte Carlo vs. deterministic risk assessment methodology. Also illustrates how traditional baking method (pebble-bed sangak) can transfer trace metals from environmental surfaces to food. Detection-rate-based exclusion of some elements from HI calculations (Hg, Cd, Co, Pb, Ni excluded due to <30% detection) is a methodological choice that understates risk and is worth discussing.
App: Iranian bread is not currently in the app ingredient-mapping scope (US/EU focus), but the total-Cr data and Pb data are relevant to the wheat ingredient page’s geographic-breakdown sub-field for Middle Eastern wheat products.