Overview
This study assessed arsenic and potentially toxic elements in flour, dough, and finished bread from 90 bakeries in Mashhad, Iran. The authors collected matched flour-dough-bread triplets across five city regions between June and December 2020, then measured 12 elements by ICP-OES against certified reference material NIST 1567a (Wheat Flour). The principal source finding is that total arsenic dominates both the non-carcinogenic and carcinogenic risk models for bread consumption in Mashhad. 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, chromium (Cr) 0.06, V 0.06, aluminum (Al) 0.18, nickel (Ni) 0.012, arsenic (As) 0.02, mercury (Hg) 0.01, lead (Pb) 0.01, cadmium (Cd) 0.01.
Pb and Hg: Below detection limits in all 270 samples.
Elements exceeding source-cited comparators: Al, As, Cr, and Fe exceeded the WHO/FAO thresholds cited by the authors in all five regions. Cd exceeded the Iranian national standards cited by the authors across all sampling stations. In the discussion, the paper also states that Cu, Ni, Zn, Cd, Co, and V remained within permissible thresholds; this page preserves the Results-section statement for Cd and flags the source-side tension below.
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 approximately 4.6-8.0 x 10^-5.
Monte Carlo 5th-to-95th percentile bounds (10,000 iterations): HI 1.50-8.94 (children) and 1.20-7.14 (adults); CR 1.21 x 10^-3 to 3.10 x 10^-3 (children) and 9.67 x 10^-4 to 2.48 x 10^-3 (adults). Fig 3 of the source labels each distribution with the 5th- and 95th-percentile pair; the source text on p.9 paraphrases this as “95th percentile values … ranged from 1.50 to 8.94,” which this page corrects to the underlying figure’s framing.
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 years, child 6 years.
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)
The study used five-region stratified sampling in Mashhad: 90 bakeries, 3 sample types per bakery, and 270 total flour, dough, and bread samples. The sampled bread types included Barbari, Sangak, Taftoon, and Lavash, and sampling occurred from June to December 2020.
Samples were transported cool and dark, stored at 4 deg C, dried as 10 g portions at 100 deg C, blended, and passed through a 2 mm sieve. Approximately 1 g of each dried sample was digested with HNO3/HCl at 1:1 and 90 deg C until clear, filtered through 0.22 micrometer filters, diluted to 20 mL, and analyzed by ICP-OES. Reagents and standard solutions were from Merck; the source also names Whatman filters, Spectro Arcos ICP-OES, Crystal Ball v11.1.34190, and SPSS in the analytical/statistical workflow.
Quality-control details include calibration blanks and standards, calibration-curve correlation coefficients above 0.99, triplicate measurements, control-sample checks after each batch of 10 samples, and NIST 1567a Wheat Flour CRM/spike recoveries of 80.56%-100.47%. The statistical workflow used Kolmogorov-Smirnov testing, one-way ANOVA for normally distributed data, Kruskal-Wallis testing for non-normal data, and Monte Carlo risk modeling with 10,000 iterations at 95% confidence.
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, and several concentration tables are supplied as supporting-information tables rather than reproduced in the main PDF text.
Speciation and methods caveats
- Arsenic is total arsenic (tAs), not inorganic arsenic (iAs); no HPLC-ICP-MS speciation was performed.
- Chromium is total chromium, not hexavalent chromium (Cr-VI).
- Mercury is total mercury; methylmercury was not measured.
- The paper contains a source-side tension on Cd: the Results section says Cd exceeded Iranian national standards in all sampling stations, while the Discussion says Cd remained within permissible thresholds.
Implications
Standards work: This source contributes Mashhad-specific evidence that total arsenic can dominate bread-consumption risk when flour, dough, and baking pathways are assessed together. It is most useful for source-route reasoning around wheat, flour, and bread in high-arsenic geographies, with Pb and total Hg below detection in this dataset.
Courses: The paper is useful for teaching how a staple-food exposure model can combine measured occurrence, local consumption rates, non-cancer HI/HQ, cancer-risk calculations, and Monte Carlo sensitivity analysis. It also illustrates why total-arsenic results cannot be read as inorganic arsenic without speciation.
App: The source can support dry-weight occurrence and risk-context displays for Iranian bread and wheat-flour routes, with clear labels for total arsenic, total chromium, total mercury, and single-city sampling.
Related evidence
- Arsenic
- Arsenic, Total
- Aluminum
- Cadmium
- Chromium
- Cobalt
- Copper
- Iron
- Lead
- Mercury, Total
- Nickel
- Vanadium
- Zinc
- Wheat
- Non Rice Grains
- Bread
- Bread and baked goods
- Flour (wheat, corn, other)
Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git.
| Commit | Date | Change | Description |
|---|---|---|---|
| 798aec225d | 2026-11-06 | major | 7 sections added; narrative text revised |
| db716d13d5 | 2026-11-04 | major | 7 sections added; narrative text revised |
| 49384c8e11 | 2026-11-04 | major | 7 sections added; narrative text revised |
| 59239f2c06 | 2026-11-04 | major | 7 sections added; narrative text revised |