Abstract
Rapidly increasing human population, urbanization, industrialization, and mining activities have become the serious environmental issue of today's world. Conventional physico-chemical remediation methods are highly expensive and generate secondary waste. However, bioremediation of contaminated ecosystems using indigenous microbes and plants or amalgamation of both has been recognized as a cost effective and eco-friendly method for remediation as well as restoration of polluted or degraded ecosystems. Further, variety of pollutant attenuation mechanisms possessed by microbes and plants makes them more feasible for remediation of contaminated land and water over physico-chemical methods. Plants and microbes act cooperatively to improve the rates of biodegradation and biostabilization of environmental contaminants. This chapter aims to emphasize on potential application of microbes and plants to attenuate the organic and inorganic pollutants from the contaminated sites as well as eco-restoration of mine degraded and jhum lands by way of biodegradation and phytoremediation technologies.
TopIntroduction
Fast growing human civilization, 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 (pesticides, pharmaceuticals petroleum hydrocarbons etc) 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., 2014a); 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, Blom-Zandstra, Gupta, & Joner, 2005). The common remedial measures for restoration of contaminated environment include various Conventional physico-chemical methods. These technologies have several disadvantages such as high energy requirement or large chemical input that may cause generation of secondary wastes ; and all these disadvantages make a conventional treatment process very costly (Yang, He, & Wang, 2009). Phytoremediation has now emerged as a promising strategy for in-situ removal of many organic and inorganic contaminants (Macek, Mackova, & Kas, 2000; 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 (Singer, Thompson, & Bailey, 2004; Chaudhry et al., 2005; Huang, El-Alawi, Gurska, Glick, & Greenberg, 2005 ; Zhuang, Chen, Shim, & Bai, 2007). However, restoration of mine degraded and jhum land represents an indefinitely long-term commitment of ecosystem restoration process. Natural recovery in mine spoils/jhum 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/jhum lands a self-sustaining ecosystem may be developed in a short period of time (Giri et al., 2014a). This chapter provides an overview of plant microbe interaction for restoration of degraded environment.
Key Terms in this Chapter
Bioremediation: Bioremediation is the use of living organisms such as microbes and plants for mitigation and wherever possible, complete elimination of the noxious effects caused by environmental pollutants.
Biodegradation: Biodegradation is a natural process, where the degradation of a xenobiotic chemical or pesticide by an organism is primarily a strategy for their own survival.
Upper Metabolic Pathway: The organic pollutant degradation pathway leading to formation of some key intermediates/secondary product is called upper metabolic pathway.
Phytostabilization: Plants are used to reduce the mobility and bioavailability of environmental pollutants.
Environmental Pollution: Introduction of contaminants into the natural environment that cause adverse effects on living organisms and ecosystems.
Lower Metabolic Pathway: The organic pollutant degradation pathway involving cleavage of the aromatic ring structure is called lower metabolic pathway.
Co-Metabolism: The co-metabolic degradation corresponds to the non specific degradation of xenobiotic molecule by microorganisms.
Xenobiotics: A synthetic organic compound such as drug, pesticide, or carcinogen that is foreign to a living organism is called xenobiotic compounds.
Biosorption: Biosorption is a physiochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure.
Ecological Restoration: Ecological restoration is the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.
Heavy: Metals: A heavy metal is a metallic element which has high density, specific gravity or atomic weight and usually toxic in nature.
Phytoextraction: Plant roots take up contaminants and store them in stems and leaves.
Bioavailability: The fraction of contaminant actually available to microorganisms is said to be bioavailable.
Phytoremediation: Phytoremediation is the process of removing/eliminating inorganic toxic metals and organic compounds using plants and trees from contaminated environment.
Metabolic Degradation: Metabolic biodegradation of the organic pollutants is carried out by the soil microbial populations harbouring specific catabolic enzymes leading to the complete mineralization of target compound.
Phytovolatilization: Contaminants taken up by the roots pass through the plants to the leaves and are volatized through stomata, where gas exchange occurs.