Tailored biochar for effective cadmium immobilization in soil and reduced accumulation in plants: a meta-analysis and experimental validation study

Abstract

Soil available cadmium (Cd) governs its phytoavailability, thereby threatening food and medicinal plant safety. While biochar offers a promising remediation approach due to its high adsorption capacity and cost-effectiveness, its efficacy for Cd passivation requires a customized design. Here, a meta-analysis was conducted to examine how biochar preparation factors influence soil available Cd. The results indicate that biochar derived from herbaceous single Chinese medicine residues (SCMR), prepared at moderate-to-low pyrolysis temperatures (< 500 °C) with extended duration (> 3 h), achieved the highest Cd passivation efficiency. Adsorption kinetics experiments confirmed that biochar prepared from the decoction residue of Houttuynia cordata (i.e., a typical herbaceous SCMR) at 450 °C and 3.5 h exhibited optimal Cd adsorption capacity, verifying the meta-analysis. Pot experiments with lettuce (Lactuca sativa L.) further validated the findings of the meta-analysis: the 2% H. cordata biochar application led to the greatest reductions in soil available Cd and plant Cd accumulation by 17.6% and 52.3%, respectively. In heavy metal-accumulating medicinal plants (Taraxacum officinale F.H.Wigg. and Lilium davidii var. willmottiae), this biochar decreased soil available Cd by 18.0%–55.5% and plant Cd accumulation by 42.9%–68.6%. These results indicate the promising cross‑species potential of the tailored biochar in mitigating Cd uptake in plants. In summary, this study establishes a meta‑analysis‑guided framework for tailoring biochar production, offers an evidence‑based strategy for soil Cd remediation, and proposes a practical pathway for the valorization of Chinese medicine residues. A comprehensive study guides biochar customization for soil cadmium passivation. Optimal biochar reduces soil available Cd by 55.5% and dandelion Cd by 68.6%. Our customized biochar is applicable for Cd uptake reduction in various plants. A promising yet underexplored route for valorization of Chinese medicine residues. A comprehensive study guides biochar customization for soil cadmium passivation. Optimal biochar reduces soil available Cd by 55.5% and dandelion Cd by 68.6%. Our customized biochar is applicable for Cd uptake reduction in various plants. A promising yet underexplored route for valorization of Chinese medicine residues.