Efficacy of Ca-modified cypress biochar in immobilization of heavy metals in contaminated soils.

Heavy metal (HM) pollution remains a pressing global concern, affecting soil regarding food safety, and negatively influencing the UN Sustainable Development Goals (SDGs). We investigated the efficacy of untreated cypress biochar (UCB) and Ca-modified cypress biochar (MCB) in mitigating HM contamination and enhancing growth across native and contaminated soils (40 mg/kg) in carrot pot experiments. Both biochar types were pyrolyzed at 900 °C and applied at rates of 3 %, 6 %, and 9 %. We found that carrot growth parameters significantly improved, particularly with 6 % UCB also for the contaminated soil. X-ray fluorescence (XRF) analysis showed that both UCB and MCB reduced HM concentrations in the edible part of carrots grown in native and contaminated soils. Pb concentration declined from 1.3 mg/kg to below the detection limit (< 0.3 mg/kg), Zn concentrations decreased from 50.3 mg/kg to 39.8 mg/kg (9 % UCB) and to 36.8 mg/kg (9 % MCB), while Cu concentrations reduced from 35.3 mg/kg to 25.9 mg/kg (9 % UCB) and to 22.6 mg/kg (9 % MCB). MCB, characterized by high pH (9.7) and active nano-sized CaCO 3 particles, demonstrated superior HM immobilization compared to UCB. Statistical analysis supported the superior efficacy of MCB in reducing HM bioavailability and uptake. Understanding the specific responses of different plant species to biochar amendments is essential for recommending broader applications of MCB for soil remediation and sustainable agriculture. [Display omitted] • Ca-impregnated cypress biochar (MCB) was used to immobilize Pb, Zn, and Cu in contaminated soil. • XRF analyzer was used to determine heavy metals in soil, biochar and carrot parts. • MCB enhanced immobilization through elevated pH and highly active nano sized CaCO 3 particles. • MCB decline the BF, TF and HRI values associated with HM exposure. • Statistical analysis revealed MCB showed superior performance compared to UCB. [ABSTRACT FROM AUTHOR]