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The dissolved organic matter from the co-decomposition of Chinese milk vetch and rice straw induces the strengthening of cadmium (Cd) remediation by Fe-modified biochar

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Overview

Liang and colleagues tested whether dissolved organic matter from co-decomposed Chinese milk vetch and rice straw strengthens Fe-modified biochar immobilization of cadmium in a paddy-rice pot experiment. The food-matrix endpoint is brown-rice cadmium (Cd), not rice milk: the combined Fe-modified biochar plus milk-vetch/rice-straw treatment lowered brown-rice Cd by 86.2% versus untreated soil, 82.5% versus the organic-residue mixture alone, and 34.7% versus Fe-modified biochar alone. The source is useful for agronomic mitigation and rice-grain Cd routing, but it is not a market-occurrence survey and should not be pooled as a consumer-market benchmark distribution.

Key numbers

  • Pot experiment: October 2021 to July 2022, Changsha City, Hunan Province, China.
  • Treatments: untreated paddy soil (CK-S), Chinese milk vetch (MV-S), rice straw (RS-S), milk vetch plus rice straw (MR-S), Fe-modified biochar (FB-S), and Fe-modified biochar plus milk vetch/rice straw (MRFB-S).
  • Replication: each of the six treatments was replicated four times, for 24 experimental pots.
  • MRFB-S reduced available soil Cd by 81.4% versus CK-S, 76.3% versus MR-S, and 23.1% versus FB-S.
  • MRFB-S increased DCB-extractable Fe in rice root iron plaque by 11.8% versus FB-S, and increased DCB-Fe and DCB-Cd by 37.2% and 35.9% versus MR-S.
  • MRFB-S lowered brown-rice Cd by 86.2% versus CK-S, 82.5% versus MR-S, and 34.7% versus FB-S.
  • The authors report that brown-rice Cd under MRFB-S did not exceed the cited Cd safety threshold of 0.2 mg/kg.
  • MRFB-S lowered shoot and root Cd by 77.7% and 58.8% versus MR-S, respectively.
  • Adsorption experiment: Fe-modified biochar after addition of DOM-MR had a maximum Cd(II) adsorption capacity of 634 mg/g, 1.30 times the capacity without DOM-MR.

Methods (brief)

The pot trial used Cd-polluted paddy soil with six amendment treatments and four replicates per treatment. Rice was transplanted after in situ incorporation of milk vetch, rice straw, and/or Fe-modified biochar. The paper paired plant-tissue Cd measurements with soil Cd fractions, available Cd, root iron-plaque measurements, and adsorption studies. DOM was characterized by EEM-PARAFAC and FT-ICR MS; biochar/adsorption mechanisms were assessed with FT-IR, XRD, XPS, BET surface analysis, and adsorption kinetic and thermodynamic modeling. Cd in brown rice is reported as a total Cd concentration; the extractable text gives percent reductions and the 0.2 mg/kg threshold comparison, while the absolute brown-rice bar-chart values are not printed in the text layer.

Implications

  • Rice and rice products: supports agronomic mitigation context for Cd uptake into brown rice under Cd-polluted paddy-soil conditions.
  • Product routing: route as rice-grain/brown-rice evidence, not rice-milk evidence despite the wishlist query term.
  • Standards workbench: not a market-occurrence distribution; use as mitigation evidence rather than a benchmark-pool row.
  • Testing and methods: Cd species are not speciated; this is total Cd in rice tissues and soil fractions.

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