Overview
This study measured Cr, Ni, As, Pb, Cd, and F concentrations in 149 wheat grain samples from Bijie City, Guizhou Province, China, a karst region with naturally elevated geological background values for several heavy metals including Cd (background soil Cd 0.659 mg/kg, far above China’s national standard of 0.097 mg/kg) and extensive industrial activity including lead and phosphate mining. Mean concentrations of As, Ni, Cd, and Pb met FAO standard limits, but mean Cr exceeded the standard limit by 3.25-fold (3.250 mg/kg vs. 1.000 mg/kg standard), with 58.4% of samples exceeding the Cr limit. Probabilistic Monte Carlo risk assessment found cumulative hazard indices exceeding 1 for all population groups (children 2.57, adult females 1.29, adult males 1.12), with As being the primary driver of hazard for children (HQ = 1.03). Carcinogenic risk was unacceptable (>1×10−4) for all three populations.
Key numbers
PTE concentrations in wheat grains (mg/kg; equivalent to ppm wet weight):
| Metal | Mean | Median | Range (min–max) | FAO limit | Exceedance rate |
|---|---|---|---|---|---|
| Cr | 3.250 | 1.488 | nd – 8.546 | 1.000 | 58.4% |
| Ni | 0.684 | 0.468 | nd – 5.034 | 1.000 | 20.1% |
| As | 0.055 | 0.054 | 0.036 – 0.132 | 0.500 | 0.0% |
| Cd | 0.149 | 0.124 | 0.012 – 0.538 | 0.200 | 28.9% |
| Pb | 0.039 | 0.029 | 0.001 – 0.311 | 0.200 | 1.3% |
| F | 4.539 | 4.243 | 0.272 – 9.730 | — | — |
Converting to ppb (µg/kg): Cr mean 3,250 µg/kg; Ni mean 684 µg/kg; As mean 55 µg/kg; Cd mean 149 µg/kg; Pb mean 39 µg/kg.
Probabilistic hazard indices (Monte Carlo, 10,000 simulations):
- Children HI: 2.57 (exceeds safe limit of 1.0)
- Adult females HI: 1.29
- Adult males HI: 1.12
- As HQ for children: 1.03 (sole analyte exceeding HQ=1 on its own)
Threshold carcinogenic risk (TCR) values (all unacceptable >1×10−4):
- Children TCR: 1.32×10−2
- Adult females TCR: 6.61×10−3
- Adult males TCR: 5.81×10−3
- Sensitivity analysis identified PTE concentration (CW) as the dominant parameter affecting human health risk outcomes.
Source attribution by PCA:
- PC1 (29.2% variance): Cr and Pb — industrial activities
- PC2 (21.0% variance): Ni, As, Cd — mixed sources (geogenic background + agricultural inputs)
- F — high geological background value
Methods (brief)
149 wheat grain samples collected at maturity in 2021 using systematic composite grid sampling (5 sub-samples per composite), Bijie City, Guizhou. Samples oven-dried at 60°C for 72 h. Digestion with HNO3:HClO4 (5:1) at 110–130°C; filtered through 0.45 µm. Cr, Ni, Pb, Cd, As measured by ICP-MS (NexION 2000, PerkinElmer). Fluoride measured by fluoride-ion electrode (GB/T5009.18-2003 method). Duplicates run for QA; recoveries 85–90%. Total arsenic only — no iAs speciation. No LOD/LOQ explicitly reported in the accessible section; As range starts at 0.036 mg/kg suggesting a detection level around that value. Probabilistic health risk assessment used Crystal Ball software (Monte Carlo simulation, 10,000 iterations) with Chinese population-specific body weight and dietary intake parameters.
Implications
Certification: Wheat and wheat-derived ingredients (flour, wheat starch, wheat bran) are widely used in certified products. Cr is the primary concern in this dataset, driven by geological background in karst regions; concentration of 3,250 µg/kg mean and up to 8,546 µg/kg max for wheat grown in high-background soil zones is substantially above the 1,000 µg/kg FAO limit. Cd at mean 149 µg/kg and up to 538 µg/kg is relevant for certification thresholds. Supply chain sourcing from karst regions of southwestern China (Guizhou, Guangxi, Yunnan) warrants special scrutiny for Cr, Ni, and Cd in wheat-based ingredients.
Courses: Strong case study for geogenic contamination pathways: naturally elevated soil Cd and F from karst geology transfers into wheat grain without any anthropogenic input. Contrasts with Cr and Pb contamination from industrial activities in same region. Demonstrates why origin region is a critical sourcing variable for grain ingredients.
App: Wheat grain contamination profile: Cr and Cd are the primary analytes of concern when wheat is sourced from southwestern China karst regions; values substantially higher than European or North American wheat norms. App should flag wheat-containing products sourcing from Guizhou, Guangxi, or Yunnan provinces as elevated risk for Cr and Cd.
Microbiome: Not applicable; no microbiome measurements in this study.
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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. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Change | Description |
|---|---|---|---|
| e317189 | 2026-08-11 | correction | 6 sections added; narrative text revised |