Chitosan-Based Biostimulation: A Novel Approach for Simultaneous Remediation of Co-Existing Cadmium and Arsenic Contamination in Soil

Cadmium (Cd) and arsenic (As) are both potentially toxic heavy metals (HMs) found ubiquitously in the environment. These HMs are prevalent in soil due to natural occurrences or anthropogenic activities. Co-contamination of Cd and As in soil is a major concern for plant and human health as well as ecosystem sustainability due to their hazardous properties. Therefore, a global imperative is developing improved technologies for managing and remediating soil co-contaminated with Cd and As. One effective solution for remediating Cd/As co-contaminated soil involves the utilization of natural biopolymers and biostimulants, such as chitosan (CS). CS offers distinct advantages, including its ready availability, biodegradability, biocompatibility, environmental friendliness, and cost-effectiveness when compared to alternative adsorbents. The adsorption mechanism of CS and CS-based adsorbents for Cd and As primarily relies on electrostatic attraction, complexation, and ion exchange. This review article provides a comprehensive overview of Cd and As co-contamination in soil, elucidating their sources, distribution patterns, exposure pathways, and the prospective remediation approaches employing CS biostimulants and CS-based adsorbents. Furthermore, it summarizes recent studies investigating the adsorption of Cd/As by CS, the factors influencing the adsorption efficiency and the challenges associated with the utilization of CS and CS-based adsorbents. In conclusion, the review underscores the need for further research to concurrently remediate Cd and As co-contaminated soil, enhance the adsorption efficiency of CS and CS-based composites, and broaden their practical applicability for remediating co-contaminated soils.