Heavy Metal Phytoremediation from Aquatic Ecosystems with Special Reference to Macrophytes

Abstract

The rapid pace of industrialization and urbanization has given birth to heavy metal pollution. Heavy metals are one of the most hazardous contaminants that may be present in the aquatic environment. It derives its origin from both natural and anthropogenic sources. Heavy metal pollution in aquatic ecosystem poses a serious threat to aquatic biodiversity, and drinking contaminated water poses severe health hazards in humans. The economic aspects and side effects of conventional treatment technologies in aquatic ecosystems paved the way to phytoremediation technology. In phytoremediation, plants are used to ameliorate the environment from various hazardous pollutants. It is cost-effective and eco-friendly technology for environmental cleanup. The characteristics, general mechanism, and ecology of metal hyper-accumulation have been discussed previously. The present review examines the role of aquatic macrophytes in phytoremediation studies. Macrophytes are potent tools in the abatement of heavy metal pollution in aquatic ecosystems receiving industrial effluents and municipal wastewater. They are preferred over other bio-agents due to low cost, frequent abundance in aquatic ecosystems, and easy handling. Aquatic macrophytes usually follow the mechanism of rhizo-filtration for metal removal. The efficiency and selection of potent aquatic plants is done through microcosm investigation, and an overview of significant works is given here. Aquatic macrophytes in natural and constructed wetlands proved to be a potent tool for the treatment of heavy metals from industrial effluents. Physico-chemical factors like temperature, pH, light, salinity, and presence of other heavy metal may affect the metal uptake. Both live and dead biomass of macrophytes may be used in phytoremediation, though dead biomass is generally preferred in the treatment of industrial effluents due to reduced cost, easy disposal, and lack of active biochemical machinery leading to metal toxicity and death of plants. Biomass disposal problem and seasonal growth of aquatic macrophytes are some of the limitations in the transfer of phytoremediation technology from the lab to the field. However, an eco-sustainable model has been developed through our various works that may curb some of the limitations. Disposed biomass of macrophytes may be used for many fruitful applications. Genetic engineering, biodiversity prospecting, and X-ray diffraction spectroscopy are promising future prospects regarding the use of macrophytes in phytoremediation studies. A multidisciplinary and integrated approach may enable this embryonic technology to become the new frontier in environmental science and technology.

KEY WORDS:

• heavy metals
• aquatic macrophytes
• rhizofiltration
• phytoremediation
• biodiversity prospecting
• genetic engineering

ACKNOWLEDGMENT

The author is extremely thankful to J.N.B. Bell, Professor of Environmental Pollution and Director of MSc in Environmental Technology affliated with Centre for Environmental Policy, Imperial College London, for English editing as well as valuable suggestions for the improvement of the manuscript. Professor Bell has shown a keen interest for the enhancement of the quality of the manuscript, in spite of his busy schedule. The author is also thankful to the Council of Scientific and Industrial Research, New Delhi, India, for the financial assistance to Prabhat Kumar Rai in the form of Junior Research Fellowship and Senior Research Fellowship. The author also extends his regard to Professor A.N. Rai, Vice Chancellor Mizoram University, for his kind co-operation and support.