Remediation of nickel-contaminated wastewater-irrigated soil using agricultural waste: a sustainable approach

A study was conducted to evaluate the efficacy of rice husk (RH), rice straw (RS), and sawdust (SD) at application rates of 0.25% and 0.5% w/w to mitigate nickel (Ni) contamination in soil irrigated with Ni-spiked wastewater (1 ppm and 2 ppm). The study aimed to reduce Ni bioavailability in soil using these amendments while also evaluating their effects on soil nutrients, Ni content, physiology and yield of spinach. The application of 0.5% rice husk significantly enhanced spinach growth and physiological parameters, with total dry matter production of 4.1 t ha^-1, and led to higher nickel accumulation in spinach compared to its 0.25% rate. RH (0.5%) incorporation significantly (p < 0.05) reduced Ni concentration in shoot (50 and 47%) and root tissues (50 and 37%) of spinach compared to SD and RS amendments. Soil organic carbon and nitrogen levels significantly increased with the amendments, while DTPA-extractable nickel -Ni was minimized in plots treated with 0.5% RH, indicating effective nickel immobilization. Amendments with RH (0.5%) demonstrated the lowest bioconcentration factor(0.107) and hazard quotient (2.2 × 10^-4), underscoring its superior potential for Ni remediation in soil compared to RS and SD. The study demonstrates RH's effectiveness in mitigating nickel contamination and enhancing soil health and crop productivity.