Soybean was grown for six weeks on two acidic soils that were either left at natural pH or limed, after aging the soils for 11 months with metallic tungsten powder. Liming sharply raised soluble tungsten and plant uptake, and at the highest addition the limed-soil plants died within about three weeks. In acidic soils with high tungsten, a large share of soluble tungsten was polymeric, which coincided with lower uptake but poorer growth and nutrient status.
Key numbers
- Soil solution tungsten, mean +/- SE (n = 3): acidic 5000 mg/kg treatment 24.8 (clay) and 9.74 (sand) mg/L; limed 500 mg/kg 2.43 (clay) and 3.34 (sand) mg/L; limed 5000 mg/kg 126.1 (clay) and 113.7 (sand) mg/L; controls below LOQ (Table 2, p. 6149).
- Seedling death after 3 weeks in limed 5000 mg/kg soils at tissue tungsten of at least 211 mg/kg (shoot) and 747 mg/kg (root) (p. 6149).
- No biomass effect at shoot 135 +/- 10 and root 398 +/- 76 mg/kg (mean +/- SE, limed sand, 500 mg/kg) (p. 6149).
- Liming raised root and shoot tungsten by average factors of 4 +/- 2 and 15 +/- 9 (mean +/- SD); at 500 mg/kg, shoot tungsten rose 18 to 24 times with liming (pp. 6149 to 6150).
- Nodule tungsten 310 +/- 11 mg/kg in limed 500 mg/kg soils; 581 +/- 103 mg/kg nodules versus 318 +/- 63 mg/kg roots in acidic 5000 mg/kg sand (p. 6149).
- Polymeric tungsten (above 10 kDa) made up 46% to 68% of soluble tungsten in acidic 5000 mg/kg soils versus 15% to 17% in limed soils (Table 4; text p. 6152).
Methods (brief)
Two Cambisols from Lower Austria (silt clay loam and sandy loam) were kept at natural pH (about 4.5 to 5) or limed with 2.5% calcium carbonate, spiked with metallic tungsten powder (under 2 micrometers) at 0, 500 and 5000 mg/kg dry weight, and aged for 11 months. Inoculated soybean grew in 2 kg pots (four per treatment) in a greenhouse. Tissue and soil-solution tungsten were measured by ICP-MS; polymer size classes were separated by ultrafiltration (under 10 kDa, 10 to 30 kDa, 30 kDa to 0.45 micrometers). Nitrate reductase and nitrogen fixation were also measured.
Evidence fitness
Supports mechanistic statements that soil pH governs tungsten solubility, speciation and plant uptake, and gives plant tissue concentrations associated with no effect and with seedling death. It is a spiked pot experiment with vegetative tissues, so it does not support statements about tungsten in soybeans as food, about field contamination levels, or about human exposure.
Limitations
Spiking with metallic powder at 500 and 5000 mg/kg represents heavily contaminated scenarios. Plants grew six weeks and seeds were not analyzed. The authors note that soil-solution speciation analysis is difficult and may have been altered by the plants. ICP-MS measurements received instrument-vendor support, as acknowledged by the authors.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.