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Heavy metals are serious environmental pollutants especially in areas of high anthropogenic pressure. Unlike organicals that can be mineralized, heavy metals must be either physically removed or converted to a biologically inert form. Phytoremediation - the use of plants for pollution abatement - offers an innovative green clean technology. Aquatic Macrophyte-based water Treatment Systems (AMS) offer a low-energy consuming and low-cost method for removing the contaminants from polluted waters. Eichhornia crassipes (Mart.) Solms is well-known for its amazing ability to absorb and concentrate heavy metals such as cadmium, copper, lead, mercury, europium etc. in aquatic systems. The present paper reviews the phytoremediating potential of E. crassipes.
Heavy metals such as Cd, Cu, Pb, Cr and Hg pose a major occupational and environmental hazard as they are non-biodegradable with a very long biological half-life (Barbier et al., 2005). They are toxic to living organisms when taken in excess. However, a subset of these at low concentrations are essential micronutrients. It is exceedingly difficult to make a clear distinction between essential and toxic metallic elements, as all metals are probably toxic if ingested in sufficiently large doses. Non-essential heavy metals, such as arsenic, antimony, cadmium, chromium, mercury, lead, etc., are of particular concern to surface water and soil pollution (Ghosh and Singh, 2005).
Heavy metals are difficult to remove from the environment and, unlike many other pollutants, cannot be chemically or biologically degraded and are ultimately indestructible. Hence, a clean up of these metals requires their complete removal from the medium (Mejare and Bulow, 2001). The vegetation acts as a buffer for heavy metals. It absorbs heavy metals to reduce their impact on soil and water. Phytoremediation, the use of vegetation for the in situ treatment of contaminated soils and sediments, is an emerging technology that promises effective and inexpensive clean up of certain hazardous waste sites (Solis-Dominguez et al., 2007).
The fact that the aquatic plants improve water quality must have been realized several centuries ago, with the observation that wastewaters flowing out of channels infested with vascular plants such as water hyacinth, seemed to be clearer than the wastewaters entering such channels. However, scientific studies to employ aquatic plants as bioagents in water purification began only in the 1970s. |
