Efficacy of rice husk biochar and compost amendments on the translocation, bioavailability, and heavy metals speciation in contaminated soil: Role of free radical production in maize (Zea mays L.)

Abstract The present study investigated the effectiveness of rice husk biochar (RHB) and chicken manure compost (CMC) amendments (T1: Control, T2: 2% RHB, T3: 2% CMC, T4: 1% RHB + 1% CMC) on the potential mobility of heavy metals (HMs) and the growth of maize plants in contaminated soil. Results indicated that the potential mobile fraction of Cr (44.43%), Ni (29.93%), and Zn (44.68%) accounted for T2, whereas Cu (69.33%) and Pb (34.38%) for T4 of their total amount. Amending the soil resulted in a significant increase in maize growth and biomass production, whereas T4 showed an increment of 156% in fresh maize weight. While root biomass was highest with T2 treatment, which increased fresh and dry weight by 35% and 90%. The bioaccumulation factor (BF) and Translocation factor (TF) were less than one indicating that the low content of HMs accumulation in roots from soil and slight transferred to shoot (edible tissues). The results of electron paramagnetic resonance (EPR) revealed the generation of hydroxyl radical (•OH) as reactive oxygen species (ROS) in root and shoot of maize seedling. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrum confirmed the complexation and the adsorption of HMs as prominent mechanisms owing to their complexation with hydroxyl, carbonyl and carboxyl groups. The results indicate that the RHB and CMC, especially their combination can be used effectively for the remediation of HMs by reducing their toxicity and bioavailability in food matrices and soils.