Exploring the role of ligands in metal phytoremediation and its influence on metal availability and toxicity

Heavy metal pollution is a global issue of concern. Most heavy metals are non-biodegradable which as a result accumulate in the environment and affect the soil ecosystem adversely. Thus, remediation of heavy metal pollution is decisive for a cleaner environment. Various traditional and emerging remediation techniques are being adopted to overcome this pollution. Conventional remediation techniques have several limitations like high cost, intensive labor, alteration of soil properties as well as disturbance of soil microbes. In recent years, phytoremediation has taken over traditional soil washing and soil burning processes due to its cost-effectiveness, sustainability, and environmental safety. Ligands have a progressive role in enhancing the phytoremediation of heavy metals. This review explores the type of ligands and their role in enhancing metal availability, decreasing metal toxicity, metal transport, and the sequestration of metals into the vacuole. Some contradictory effects of ligands are also discussed systematically, such as the mobilization and immobilization of metals under the influence of ligands. Moreover, this review article widely discusses the background, concepts, and future trends in the phytoremediation of heavy metals under the influence of ligands.