Phytoremediation Technologies for Heavy Metal Contaminated Soils

Abstract

Soil contamination by heavy metals (e.g., Cd, Pb, Cr, As, Hg, Ni, Zn, Cu) poses a severe threat to global ecosystems, food security, and human health. Traditional physical and chemical remediation methods are often prohibitively expensive, destructive to soil ecology, and unsuitable for large-scale applications. Phytoremediation, the use of plants and their associated microbiota to stabilize, extract, degrade, or volatilize contaminants, has emerged as a promising, cost-effective, solar-driven, and ecologically sustainable alternative. This comprehensive review synthesizes the state-of-the-art in phytoremediation technologies specifically designed for heavy metal-contaminated soils. We detail the core mechanisms: phytoextraction (uptake and accumulation in harvestable biomass), phytostabilization (immobilization and reduction of bioavailability), phytovolatilization (conversion and release to the atmosphere), and phytodegradation/rhizodegradation (microbial degradation in the root zone). A critical analysis of hyperaccumulator species-their discovery, physiology, and genetic basis for metal tolerance and accumulation-is provided. The review further examines the pivotal role of soil amendments (chelators, biochar, fertilizers) and plant growth-promoting rhizobacteria (PGPR) in enhancing remediation efficiency. We evaluate the agronomic management practices for field-scale application and present a series of global case studies showcasing successful implementation. However, significant challenges remain, including slow remediation rates, biomass disposal, potential for food chain contamination, and climate dependencies. This article explores cutting-edge strategies to overcome these limitations, such as genetic engineering for enhanced metal uptake and tolerance, intercropping systems, and the integration of phytoremediation with bioenergy production (phytomining). Finally, we propose a multi-criteria framework for technology selection and outline future research directions aimed at optimizing phytoremediation for wider commercial and environmental adoption, positioning it as a cornerstone of the circular economy and sustainable land management.