This field study sampled root-zone soil and whole rice plants at 15 paddy sites beside the Xihuashan, Dangping and Piaotang tungsten mines in Dayu county, southern Jiangxi. Soil tungsten was well above provincial, national and world background values, but more than 89% of it sat in the residual (least mobile) fraction. Rice accumulated tungsten mainly in roots and leaves, with grain carrying the lowest concentrations and enrichment factors.
Key numbers
- Soil total tungsten: 3.99 to 43.65 mg/kg (mean 16.57, median 15.20), n = 15 air-dried root-zone soils (Table 1, p. 3).
- Soil pH 4.95 to 5.92 (mean 5.38) (Table 1, p. 3).
- Residual fraction: 89.26% to 97.01% of soil tungsten (mean 93.24%); organic-matter-bound fraction 2.87% to 10.25% (Table 2, p. 3).
- Rice grain without husk: 0.02 to 0.57 mg/kg dry weight (mean 0.17, median 0.09), n = 15 (Table 3, p. 4).
- Rice root mean 7.06 mg/kg (1.57 to 25.76); stem mean 2.34 (0.23 to 7.50); leaf mean 4.76 (0.59 to 16.66), dry weight (Table 3, p. 4).
- Enrichment factor (tissue divided by soil): root 0.221 to 0.590, stem 0.055 to 0.212, leaf 0.086 to 0.594, grain 0.005 to 0.020 (Table 3, p. 4).
- Linear fits of tissue tungsten on soil tungsten had determination coefficients of 0.7178 to 0.9496 (Table 4, p. 5; text p. 6).
- Authors’ screening estimate: up to 0.23 mg tungsten per person per day from rice at the highest grain value, assuming 0.4 kg rice per day; 0.002 mg per day from incidental soil intake at 50 mg soil per day (p. 6).
- Values the authors cite from other work, not measured here: a workplace air limit of 5 mg/m3 in the USA and a former USSR drinking-water limit of 0.05 mg/L; the authors state no tungsten threshold for plants has been set for food safety (p. 6).
Methods (brief)
Rice plants were pulled at harvest with root-attached soil. Soils were air-dried, sieved to 0.149 mm and digested with HNO3, HF and HClO4; plant parts were oven-dried at 70 C, separated into root, stem, leaf and husked grain, and digested with HNO3 and H2O2. Tungsten was measured by ICP-MS. Soil chemical forms were split into five operational fractions with a Tessier sequential extraction, with the residual fraction taken by difference. A reference soil (GSD7a) was run in triplicate for quality control.
Evidence fitness
Supports site-specific statements about tungsten in paddy soil and rice near a long-operating tungsten mining district, and about transfer from soil to rice tissues. The daily-intake figure is a simple screening calculation from one assumed rice intake, not a dietary survey. The paper does not support national or market-level rice occurrence, product-level claims, or health-based limits.
Limitations
Single sampling campaign at 15 sites with one composite plant and soil sample each. No detection limit is reported for plant tungsten, and the printed reference-soil recovery for tungsten is not clearly legible in the source text. Grain was analyzed without husk, so values may differ from polished rice as eaten. Comparisons with other regions rely on values the authors cite from earlier literature. The abstract describes tissue tungsten as linearly independent of soil tungsten, while the results text and Table 4 report linear increases with soil tungsten, an internal inconsistency in the paper.
Related evidence
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