Wang et al. 2023 — Heavy metal(loid)s in Chinese grain-production agricultural soils: bioaccessibility and health risks
This is a systematic meta-analysis of 509 agricultural soil datasets from 13 Chinese grain-producing provinces (Heilongjiang, Henan, Shandong, Anhui, Jilin, Hebei, Jiangsu, Inner Mongolia, Sichuan, Hunan, Hubei, Liaoning, and Jiangxi), integrating published data from 2000–2022. The paper’s primary contribution is applying bioaccessibility correction factors to soil metal concentrations to derive more accurate human health risk estimates for incidental soil ingestion — the dominant non-dietary exposure pathway for Chinese grain-region agricultural workers and children. Cadmium emerged as the priority pollutant: mean soil Cd was 0.47 mg/kg (versus Chinese background of 0.097 mg/kg), with a geo-accumulation index up to 5.24, and children faced higher carcinogenic risk than adults from Cd ingestion across all regions.
Key numbers
Summary statistics across 269 compiled farmland soil samples (Table 2, mg/kg):
- As: median 8.83, mean 9.68, max 38.70 (Chinese background 11.20)
- Cd: median 0.18, mean 0.47, max 10.50 (Chinese background 0.097)
- Cr: median 61.20, mean 56.82, max 135.00 (background 61.00)
- Cu: median 24.71, mean 26.99, max 75.72 (background 22.60)
- Ni: median 29.00, mean 29.87, max 74.30 (background 26.90)
- Pb: median 25.84, mean 30.60, max 145.99 (background 26.00)
- Zn: median 78.40, mean 88.18, max 295.30 (background 74.20)
- Hg: median 0.08, mean 0.13, max 1.60 (background 0.065)
Bioaccessibility (SBRC gastric phase): Cd 57.37% (highest), Cr 17.51% (lowest), Pb and Cu intermediate 29.2% of soils exceeded GB 15618-2018 Soil Environmental Quality Control Standard for Cd Cd geo-accumulation index range: 0 to 5.24 (indicating unpolluted to extremely polluted across sites)
Methods (brief)
Literature meta-analysis; data extracted from Web of Science, China National Knowledge Internet, and PubMed (2000–2022 search). Bioaccessibility data from PBET, SBRC, UBM, and IVG in vitro assays, selecting SBRC gastric phase (SBRC-GP) for As and PBET for Cd, Cr, Cu, Ni, Zn, Pb. Monte Carlo simulation (Oracle Crystal Ball, 10,000 iterations) for uncertainty quantification of health risk.
Limitations
Soil data, not food grain data; dietary exposure via grain ingestion is a separate pathway. Bioaccessibility estimates span multiple in vitro methods with known inter-method variability (CVs 33.3–213% cited). Data density is highest in Jiangsu province (54 samples) and lower in other regions. This paper does not report metal concentrations in grain itself.
Implications
- Certification: Establishes the soil baseline for Chinese grain-producing provinces. Cadmium soil contamination is severe (mean 0.47 mg/kg vs. background 0.097 mg/kg) across these provinces, which produce 75% of China’s grain output. This is the upstream driver of Cd in Chinese-origin rice, wheat, and maize.
- Courses: Key reference for soil-to-crop transfer pathway discussion; illustrates why bioaccessibility-based risk assessment produces different results than total-concentration models.
- App: Contextualises elevated Cd risk in Chinese-origin rice and grain ingredients. Soil data does not directly translate to grain ppb values; use in conjunction with grain-level studies.