Introduction heavy metal pollution

INTRODUCTION
Fast growing population, industrialization, mineral mining, oil exploration, modern agricultural practices and related anthropogenic activities in the world has resulted elevated levels of toxic metal and xenobiotic pollutants in the environment (Bernhoft, 2012). Mineral mining, oil exploration and various metal processing industries has led to the dramatic increase in concentration of toxic heavy metals and metalloids such as iron, chromium, Nickel, cadmium mercury, lead, zinc, arsenic etc (Giri et al. 2014); petroleum hydrocarbons (PHC), and polycyclic aromatic hydrocarbons (PAHs). However, intensive agriculture, and crop protection strategies led to the build up of variety of persistent organic pollutants such as insecticides, fungicides, herbicides, rodenticides, nematicides and other toxic organic compounds in the air, water and soil. In order to cater the demands of fast growing population, the rapid expansion of industries, food, health care, vehicles, etc. is necessary, but it is very difficult to maintain the quality of environment with all these new developments, which are unfavourable to the environment. The adverse effects of metals and pesticide toxicity have been well documented. These pollutants impose hazardous impacts on living organisms and ecosystem health (Bernhoft, 2012; Godt et al. 2006; Jomova et al. 2011; Patrick, 2006; Auger et al. 2013).

Therefore, remediation of these contaminants is becoming one of the serious environmental issues in the world (Chaudhry et al. 2005; Euliss et al. 2008). The common remedial measures for restoration of contaminated environment include various Conventional physico-chemical methods. These remediation technologies required high energy or large input of chemicals causing pollution (Yang et al. 2009); and all these methods are not cost-effective because of secondary waste generation (Rawat et al. 2014). Phytoremediation has now emerged as a promising strategy for in-situ removal of many organic and inorganic contaminants (Susarla, et al. 2002; Macek et al. 2000; Pulford, & Watson, 2003; Pilon-Smits, 2005; Greenberg, 2010). Microbe-assisted phytoremediation, including rhizoremediation, appears to be effective for removal and/or degradation of contaminants from contaminated environment, particularly when used in conjunction with appropriate agronomic techniques (Kuiper et al. 2004; Singer et al. 2004; Chaudhary et al. 2005; Hauang et al. 2005 & Zhuang et al. 2007). However, restoration of mine degraded and jhom land represents an indefinitely long-term commitment of ecosystem restoration process. Natural recovery in mine spoils/jhom land is a very slow process which may take many years of natural succession on a mine degraded land for the total nutrient pool recovery to the level of native forest soil. The first step in any restoration program is to protect the disturbed habitat and communities from being further wasted followed by to accelerate re-vegetation process for increasing biodiversity and stabilizing nutrient cycling. As a result of natural succession by planting desirable plant species on mine degraded ecosystems/jhom lands a self-sustaining ecosystem may be developed in a short period of time (Bhattacharya, 20005; Giri et al. 2014). This chapter provides an overview of plant microbe interaction for restoration of degraded environment (Anderson et al. 1993; Siciliano and Germida, 1998).