Phytoremediation of Heavy Metals/Metalloids by Native Herbaceous Macrophytes of Wetlands: Current Research and Perspectives

Abstract

This chapter focuses on heavy metal/metalloid phytoremediation potential of some native herbaceous wetland macrophytes with special reference to macrophytes found in wetlands of Assam, India. Depending on the plant type, site condition and contaminants, seven different plant-based phytoremediation techniques can be used. Aquatic macrophytes are usually found to follow phytofiltration (rhizofiltration) technique for cleanup of inorganic as well as organic contaminants in aquatic environment. Physiological, biochemical and molecular mechanisms of the plants are being studied for better understanding of metal uptake, translocation, localization and tolerance capacity. Accumulation of toxic metals/metalloids in plant cells cause deactivation of cell enzymes, consequently affects plant growth. Detoxification mechanisms of plant to survive and grow in metal contaminated environments include chelation of metal cations by ligands and sequestered away these toxic metal complexes into less metabolically active sites such as vacuoles and cell wall where metal cannot readily dissociate. Different techniques such as electron energy loss spectroscopy (EELS), particle-induced X-ray emission (micro-PIXE), transmission electron microscopy (TEM), nuclear micro-probe technique (NMP) are applied to assess the distribution of metals/metalloids in plant tissues at subcellular level. However, physicochemical parameters such as pH, salinity, light, temperature and, presence of other cations and anions also play important roles in metal/metalloids uptake by macrophyte. Some of the macrophytes are reported as hyperaccumulator of one or more metals/metalloids. Many of the native macrophytes found in Indian wetlands also have worldwide distribution which indicates their global interest in the research area of phytoremediation. This chapter also presents an appraisal of the current research and practical applicability of these macrophytes in an effort to elucidate their significance in environmental pollution research. A multidisciplinary as well as integrated approach towards this phytoremediation technology is necessary to make it as the most promising solution to combat heavy metal contamination in aquatic environment.