Effect of Coconut Shell and Zinc-Modified Biochar Composite Applications on Phthalate Ester (PAE) Accumulation, Growth Performance, and Soil Health in Wheat (Triticum aestivum L.)

Soil contamination with phthalate esters (PAEs), particularly in e-waste-impacted regions, poses serious threats to crop productivity, soil health, and environmental sustainability. This study investigates the effectiveness of coconut shell biochar (BC) and zinc-modified biochar (Zn-BC) in mitigating PAE accumulation, improving wheat (Triticum aestivum L.) growth, and restoring soil fertility in contaminated soils. Characterization analyses revealed that Zn-BC possessed enhanced surface functionality, crystallinity, and elemental composition, favoring greater adsorption potential. Batch adsorption experiments demonstrated that Zn-BC exhibited higher equilibrium adsorption capacities for DMP (23.9 mg/g) and DBP (26.6 mg/g), following pseudo-second-order kinetics. Zn-BC significantly improved plant growth parameters including shoot height, root length, and biomass compared to unamended soil in a pot experiment. Post-harvest soil analysis showed increased pH (6.6), CEC (18.3 cmolc/kg), TOC (1.85%), and microbial biomass carbon (320 mg/kg) under Zn-BC treatment. Enzymatic activities such as dehydrogenase (45.2 µg TPF/g/d) and phosphatase (58.6 µg PNP/g/h) also improved markedly, indicating restored biological activity. These findings highlight the potential of Zn-BC as a sustainable amendment for remediating phthalate-contaminated soils and improving crop health under environmental stress conditions.