Role of biochar-based free radicals in immobilization and speciation of metals in the contaminated soil-plant environment

The structure of biochar produced at various pyrolysis temperatures influences metal geochemical behavior. Here, the impact of wheat straw-derived biochar (300, 500, and 700 degrees C) on the immobilization and trans-formation of metals in the contaminated soil-plant system was assessed. The findings of the sequential extraction revealed that biochar additives had a substantial influence on the speciation of Cr, Ni, Pb, and Zn in the contaminated soil. The lowest F1 (exchangeable and soluble fraction) + F2 (carbonate fraction) accounted for Cr (44%) in WB-300, Ni (43.87%) in WB-500, Pb (43.79%), and Zn (49.78%) in WB-700 with applied amendments of their total amounts. The characterization results indicated that high pyrolysis temperatures (300-700 degrees C) increased the carbon-containing groups with the potential to adsorb metals from the soil-plant environment. The bioconcentration and translocation factors (BCF and TF) were less than 1, indicating that metal concentration was restricted to maize roots and translocation to shoots. Reactive oxygen species (ROS) intracellularly influence metal interactions with plants. Electron paramagnetic resonance (EPR) was performed to determine hydroxyl radical generation (center dot OH) in plant segments to assess the dominance of free radicals (FRs). Consequently, the formation of center dot OH significantly depends on the pyrolysis temperature and the interaction with a contaminated soil-plant environment. Thus, metal transformation can be effectively decreased in the soil-plant environment by applying WB amendments.

Automated summary

The structure of biochar produced at various pyrolysis temperatures has a significant impact on the behavior of metals in the soil-plant system. High pyrolysis temperatures increase the carbon-containing groups in biochar, which can adsorb metals from the soil-plant environment. Applying biochar amendments effectively decreases metal transformation in the soil-plant environment.