Li et al. 2022 — Co-exposure of PTEs in wheat grains in Guizhou karst region with probabilistic health risk assessment
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.