Phytoremediation of Heavy Metal Contaminated Soils: Mechanisms, Applications and Enhancement Strategies Using Brassica Species

Abstract

Environmental pollution continues to escalate at an alarming rate due to anthropogenic activities including urbanization, technological advancement, unsafe agricultural practices, and rapid industrialization. Heavy metals such as nickel (Ni) represent particularly persistent environmental contaminants that pose severe threats to ecosystems and human health through their toxicity, bioaccumulation potential, and capacity to induce oxidative stress via reactive oxygen species (ROS) generation. Bioremediation has emerged as an eco-friendly and cost-effective alternative to conventional remediation methods for heavy metal contamination. This comprehensive review examines phytoremediation as a promising bioremediation strategy, focusing particularly on the mechanisms of phytoextraction and the potential of Brassica species as effective hyperaccumulators. The analysis covers nickel toxicity in plants, including its detrimental effects on growth, physiology, photosynthesis, and antioxidant systems. Various enhancement strategies for phytoremediation are evaluated, including the application of organic amendments (compost, biochar), chelating agents (EDTA, citric acid), and microbial inoculants to improve metal uptake and plant tolerance. The review synthesizes current knowledge on the use of Brassica species—notably B. juncea, B. napus, and B. oleracea—for heavy metal remediation, highlighting their accumulation capacities, tolerance mechanisms, and the factors influencing their remediation efficiency. The integration of multiple approaches, including combined amendments and microbial-assisted phytoremediation, presents a viable path forward for effective and sustainable remediation of heavy metal-contaminated environments.