ABSTRACT
Human evolution has led to immense scienti c and technological progress. Global development, however, poses new challenges, especially in the eld of environmental protection, pollution prevention and control, and ecosystem conservation. Technological ingenuity has enhanced the potential for improving industrial development and rapid progress has been made not only in the eld of electronics but also in engineering, biological, medical, and pharmaceutical applications. In recent decades, increasingly precise knowledge of basic biological structures and functions has brought about biotechnological advances (Barceló and Poschenrieder, 2003). The possibility to produce transgenic organisms has opened up new elds of experimentation and perspectives for scienti c and technological development,
6.1 Introduction .................................................................................................. 127 6.2 Principles of Phytoremediation .................................................................... 128
6.2.1 Plant and Microbial Interactions in Phytoremediation ..................... 130 6.3 Remediation of As Pollution-A Worldwide Challenge .............................. 131 6.4 As Removal Processes .................................................................................. 133
6.4.1 General Properties of As .................................................................. 133 6.4.2 As Speciation and Toxicity ............................................................... 133 6.4.3 As Hyperaccumulators ..................................................................... 134 6.4.4 As Hyperaccumulation Mechanisms ................................................ 135 6.4.5 Phytoextraction of As by Other Plant Species .................................. 137
6.5 Chelating Agents in As Phytoremediation ................................................... 139 6.6 As Phytoremediation with Transgenics ........................................................ 140 6.7 Concluding Remarks .................................................................................... 142 References .............................................................................................................. 143
which go beyond the limits of natural evolution. Metal and metalloids [such as lead, arsenic (As), cadmium, copper, zinc, nickel, and mercury] are continuously being discharged in the soil through agricultural activities (such as agrochemicals usage and long-term application of biosolids in agricultural soils) and from industrial sources (such as waste disposal, waste incineration, and vehicle exhausts). Many of the metal pollutants are also known carcinogens (Ensley, 2000). All these sources cause accumulation of metals and metalloids in our soils and water bodies, and pose a serious threat to food safety and public health due to As accumulation and transformation in food chains (Khan, 2005). Pollutants in both organic and inorganic forms severely impact human health, productivity of agricultural lands, and sustainability of natural ecosystems (Bridge, 2004). Widespread contamination of agricultural lands has signi cantly decreased the extent of arable land available for cultivation worldwide (Grêman et al., 2003). Unlike some organic pollutants, most inorganic pollutants, such as heavy metals and radionuclides, cannot be eliminated by chemical or biological transformation. Although it is possible to reduce their toxicity by in uencing their chemical speciation, heavy metals do not degrade and are generally persistent in the environment. The costs associated with the cleanup of organic and inorganic pollutants can be overwhelming, even for developed countries. Given the nature and extent of contamination worldwide and the costs involved in remediation, there has been a strong drive in recent years in developing alternative yet effective remediation technologies for the cleanup of polluted sites, including microbe-based bioremediation and plant-based phytoremediation (Mrak et al., 2008). Phytoremediation technologies have generated much interest as cost-effective and environmental-friendly technologies for the cleanup of a broad spectrum of hazardous organic and inorganic pollutants (Pilon-Smits, 2005). Plant-based environmental remediation has been widely pursued by academic and industrial scientists as a sustainable cleanup technology applicable in both developed and developing nations (Raskin and Ensley, 2000; Robinson et al., 2003).
