The journal Frontiers in Environmental Science recently published a study by Zhaoqin Huang, Buyun Du, Ting Sun, and Dongliang Ji investigating how different modes of heavy metal deposition affect rice crops. The researchers found that metals entering the ecosystem via dust and rainfall are far more mobile and bioavailable than those found in smelting slag. This high mobility means these metals are more likely to enter the soluble and exchangeable fractions of the soil solution, where they are easily accessed by plant roots. Because newly deposited metals often accumulate on the surface of soil aggregates rather than being locked deep within the core, they pose an immediate and high risk for biological uptake.

One of the most critical findings is that rice plants utilize a dual pathway for metal accumulation, absorbing contaminants through both foliar and root pathways. While the overall efficiency of root uptake from the soil is higher for the total mass of metals, foliar-absorbed metals enter the plant’s phloem system. This allows foliar-deposited contaminants to be translocated downward to the developing grains with high internal efficiency. Interestingly, the transport direction differs by source: root exposure results in a bottom-up increase in metal concentrations through the stem nodes, whereas leaf exposure creates a top-down concentration pattern. Cadmium was identified as the most bioavailable metal in these systems, appearing most readily in rice grains compared to copper, zinc, or lead.

To combat this contamination, the study highlights the effectiveness of soil biochar applications. Biochar, a carbon-rich material produced from the pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More of organic waste like rice husks, works by immobilizing metals in the soil and shifting them from mobile fractions to more stable, unavailable forms. In experimental simulations, biochar significantly reduced the concentration of copper, zinc, cadmium, and lead in rice grains, with reductions for lead reaching as high as seventy-four percent in rainfall-affected soils. This immobilization is largely due to biochar’s ability to increase soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More and provide functional groups that bind with metal ions. However, biochar proved less effective for arsenic, likely because arsenic forms negatively charged species in alkaline environments that do not bind easily to biochar surfaces.

Ultimately, the researchers suggest that reducing atmospheric emissions and implementing soil remediation are both necessary to mitigate ecological risks. While biochar provides a promising strategy for stabilizing metals already in the soil, the continuous nature of atmospheric deposition in the real world presents ongoing challenges. Future research is expected to focus on long-term field studies to determine how the effectiveness of biochar might change as it ages in the environment. By understanding these complex interactions between the atmosphere, soil, and plant transport systems, scientists can better protect food safety and promote sustainable agricultural practices in areas with high heavy metal loads.

Source: Huang, Z., Du, B., Sun, T., & Ji, D. (2025). Biochar mitigates soil-rice accumulation of highly bioavailable heavy metals from atmospheric deposition. Frontiers in Environmental Science, 13:1734892. .