Asadi Touranlou et al. 2025 — Heavy metals in bread and wheat flour, Mashhad, Iran
This study provides the first health risk assessment of heavy metal exposure from bread consumption in Mashhad, Iran’s second-largest metropolitan area and a city with some of the world’s highest per capita bread consumption (approximately 420 g/person/day). The authors collected 270 samples — flour, dough, and bread in matched triplets from 90 bakeries spanning five city regions — and measured 12 elements by ICP-OES against certified reference material NIST 1567a (Wheat Flour). The principal finding is that arsenic dominates non-carcinogenic and carcinogenic risk, with hazard quotients for As exceeding 1 in every region for both children and adults, and carcinogenic risk estimates ranging from 3.56×10⁻³ to 6.11×10⁻³ — one to two orders of magnitude above the EPA’s 10⁻⁴ threshold. Lead and mercury were below detection limits in all 270 samples.
Key numbers
Analytical method: ICP-OES (Spectro Arcos model 76004555). Acid digestion by EPA 3050B using HNO₃/HCl 1:1. Reported on a dry-weight basis. Recovery 80.56%–100.47% against NIST 1567a.
Detection limits (mg/kg dry weight): Fe 0.06, Zn 0.10, Cu 0.10, Co 0.02, Cr 0.06, V 0.06, Al 0.18, Ni 0.012, As 0.02, Hg 0.01, Pb 0.01, Cd 0.01.
Pb and Hg: Below detection limits in all 270 samples.
Elements exceeding WHO/FAO thresholds: Al, As, Cr, and Fe exceeded permissible limits in all five regions. Cd exceeded Iranian national standards across all sampling stations.
Hazard index (non-carcinogenic, all regions):
| Region | Adult HI | Child HI |
|---|---|---|
| South | 7.64 | 8.77 |
| East | 6.85 | 8.57 |
| North | 5.23 | 6.53 |
| West | 6.14 | 7.68 |
| Center | 6.97 | 8.69 |
Arsenic drove 69.0%–69.3% of HI variance; As HQ alone ranged from 3.96 to 5.36 (adult) and 4.94 to 6.70 (child) across regions.
Carcinogenic risk (CR) from bread consumption:
| Region | Adult Total CR | Child Total CR |
|---|---|---|
| South | 4.76×10⁻³ | 5.94×10⁻³ |
| East | 4.62×10⁻³ | 5.77×10⁻³ |
| North | 3.61×10⁻³ | 4.50×10⁻³ |
| West | 4.23×10⁻³ | 5.28×10⁻³ |
| Center | 4.90×10⁻³ | 6.11×10⁻³ |
Arsenic contributed 84.5%–84.6% of CR variance. Cadmium contributed a second, much smaller carcinogenic component (OSF 0.38 per mg/kg/day), with Cd CR values in the range of ~4.6–8.0×10⁻⁵.
Monte Carlo 95th-percentile estimates (10,000 iterations): HI ranged 1.50–8.94 (children) and 1.20–7.14 (adults); CR ranged 1.21×10⁻³–3.10×10⁻³ (children) and 9.67×10⁻⁴–2.48×10⁻³ (adults).
Exposure parameters used: Ingestion rate adult 420 g/day, child 210 g/day; body weight adult 70 kg, child 20 kg; exposure duration adult 70 yr, child 6 yr.
Contamination pathway attribution: 83% of heavy metal content entered bread through flour, 14.5% through dough preparation, and 2.5% from baking ovens. No significant differences were observed across the four traditional bread types (Barbari, Sangak, Taftoon, Lavash).
Methods (brief)
ICP-OES; total element analysis (not speciated). All values reported as total arsenic (tAs), not inorganic arsenic (iAs); no HPLC-ICP-MS speciation was performed. Dry-weight basis throughout. Microwave-assisted acid digestion (EPA 3050B); samples dried at 100°C, sieved at 2 mm. Triplicate measurement of each sample. Five-region stratified sampling (90 bakeries, 3 sample types per bakery = 270 samples total). Sampling period June–December 2020 (one season).
Key limitations: single city, single sampling season (2020), no speciation of arsenic (total As only), no speciation of Cr (total Cr only, not Cr-VI), ICP-OES rather than ICP-MS (higher LODs for some elements), and n=270 across 5 regions (54 per region) is adequate but not large.
Implications
Certification: As concentrations in Iranian bread exceed any plausible HMT&C limit for this matrix; this paper documents a high-arsenic-exposure food context. Primary value for the wiki is establishing that wheat/flour is an arsenic accumulation pathway via contaminated groundwater irrigation in high-risk geographies. The Pb-BDL finding and Hg-BDL finding are directly useful as a contrast point to regions where these metals have been detected.
Courses: Illustrates the importance of irrigation-water arsenic as an upstream driver of cereal arsenic contamination; contextualizes why Iranian bread arsenic risk differs from US or EU contexts.
App: Supports flagging wheat flour and wheat-based products as tAs-positive ingredients in high-arsenic-irrigation geographies (Iran, parts of South Asia, Bangladesh), while the BDL Pb/Hg results suggest these are not primary concerns for this matrix in this geography.