A novel calcium-based magnetic biochar reduces the accumulation of As in grains of rice (Oryza sativa L.) in As-contaminated paddy soils.

The present study used calcium-based magnetic biochar (Ca-MBC), a novel material made through pyrolyzing rice straw impregnated with iron oxide (Fe ₃ O ₄ ) and calcium carbonate (CaCO ₃ ) under oxygen-limited conditions, to reduce arsenic (As) accumulation in rice plants (Oryza sativa L.) through a 130-day pot experiment. The BCR (European Community Bureau of Reference) sequential extraction confirmed that Ca-MBC decreased the unstable fraction of As through transforming to the stable fraction at both tillering stage and maturity. The addition of Ca-MBC decreased while the pristine biochar increased the concentrations of NH ₄ H ₂ PO ₄ - and BCR-extracted As. The μ-XRF test revealed that iron oxide on the Ca-MBC played an important role in decreasing As bioavailability. The addition of Ca-MBC greatly decreased As concentration in rice grains, mainly due to (1) the decreases in bioavailability of As in soil and (2) adsorption of As in pore water by Ca-MBC; and (3) the enhanced formation of iron plaque that acted as a barrier for plant As uptake. Furthermore, the addition of Ca-MBC at 1% but not 2% promoted plant growth. The results suggest that Ca-MBC can be used as an efficient material to lower As accumulation in grains and promote plant growth in rice paddy fields.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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