Modified Biochar for Arsenic Immobilization in Soil: A Critical Review

Arsenic (As) is a potentially toxic element (PTE) that causes adverse effects on human health through contamination of soil and groundwater worldwide. Biochar has captured great interest as an amendment for improving soil fertility, immobilizing PTEs, and being a carbon stabilizer. However, unlike other cationic PTEs, pristine biochar has shown unsatisfactory results for soil As immobilization, owing to increased soil pH and accompanying electrostatic repulsion between the biochar surface and As anions. Complex soil conditions due to dynamically variable dissolved organic matter concentration, redox potential, and pH significantly influence the As immobilization capacity of biochar. To overcome the above drawbacks and improve As immobilization performance, recent studies have proposed biochar modification in various ways. This review summarizes the latest studies on modified biochar for As immobilization in soil, focusing on modification methods and performance evaluation. Limitations and perspectives of key biochar modification methods are critically discussed, advancing our understanding of the underpinned science for designing biochar to achieve increased stability for long-term application. The collated information will help environmental policymakers and stakeholders in predicting the benefits and future directions of modified biochar research for the immobilization of As and other PTEs.