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Effects of soil properties on heavy metal bioavailability and accumulation in crop grains under different farmland use patterns

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Overview

Xu and colleagues collected 81 crop-grain samples and 81 paired agricultural-soil samples from rape, wheat, and paddy fields in Tongling, China, and measured Cu, Zn, lead (Pb), cadmium (Cd), Fe, and Mn. The food endpoints are rape grain, wheat grain, and rice grain; the auto-fetch target of salt Cd is a false row fit. Cd and Pb were the most important food-safety findings: 96% of wheat grain and 60% of rice grain samples exceeded the cited Chinese Cd maximum levels, 70% of rice grain samples exceeded the cited Pb maximum level, and about 10% of rice grain samples exceeded 1.0 mg/kg Cd.

Key numbers

  • Samples: 81 paired soil and crop-grain sites, including rape, wheat, and paddy fields; the paper identifies 36 rape-field, 25 wheat-field, and 20 paddy-field soil samples.
  • Soil total Cd: 0.1-24.8 mg/kg; more than 86% of soil samples exceeded the GB 15618-2018 soil pollution risk screening value.
  • Soil Cd over-background rate: 98%, the highest over-standard rate among the measured metals.
  • Grain exceedance findings:
    • Cd exceeded the cited maximum allowable levels in 96% of wheat grain samples and 60% of rice grain samples.
    • About 10% of rice grain samples exceeded 1.0 mg/kg Cd.
    • Pb exceeded the cited 0.2 mg/kg food maximum level in 70% of rice grain samples.
    • Only four rape grain samples and two wheat grain samples exceeded the cited Pb threshold.
    • Only 14% of rape grain samples exceeded the cited 0.1 mg/kg Cd level for rape; the maximum Cd concentration in rape grains was 0.18 mg/kg.
  • Cited Chinese food maximum levels used by the authors: Cd 0.1 mg/kg for wheat, Cd 0.2 mg/kg for rice, Cd 0.1 mg/kg for rape, and Pb 0.2 mg/kg under GB 2762-2005.
  • Soil extractable-metal table examples, mg/kg ranges:
    • Rape-field DTPA extractable Cd: 0.05-5.2, median 0.27.
    • Wheat-field DTPA extractable Cd: 0.06-1.1, median 0.2.
    • Paddy-field DTPA extractable Cd: 0.07-11, median 0.33.

Methods (brief)

Soil samples were collected from 0-20 cm depth at 81 sites, with crop grains collected at corresponding sites. The study measured total and extractable metals in soils and metals in rape, wheat, and rice grains using inductively coupled plasma atomic emission spectroscopy. Soil extractants included DTPA, EDTA, ammonium acetate, ammonium nitrate, and HCl. Crop-grain values are total metal concentrations; no arsenic, mercury, chromium speciation, or cadmium speciation is reported.

Implications

  • Rice and wheat: high relevance for mining-affected farmland context and crop-specific Cd/Pb accumulation.
  • Rape grain: despite high soil Cd, rape grain accumulated less Cd than wheat or rice in this study.
  • Standards workbench: not a salt source. Use only crop-grain rows and preserve China/Tongling mining-adjacent geography.
  • Methods: total metals only; no analyte speciation beyond elemental totals.

Update history

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