Introduction to Phytoremediation

Introduction

Phytoremediation is a technology that uses plants for remediating soils and ground water. The processes of phytoremediation include number of techniques (phytodegradation, phytoextraction, phytostabilization, phytovolatilization and phytostimulation) showed in (figure 1). It is currently an exciting area of active research now to clean up the environment. A promising approach to low cost remediation technologies is phytoextraction, the use of plants to clean up polluted soils. Heavy metals are the most important inorganic pollutants, which are not degraded and progressively accumulate in the environment. Heavy metal pollutants are mostly resulting from industries such as; chemical fertilizers, chemical reagents, industry wastes and most important used in agriculture field herbicides and pesticids.

Pollution also comes from long sewage sludge, vehicle exhaust and several sources of waste water and it causes severly effects on plants, animal, soil, human beings and also on beneficial microbes which use for improvement of crops. These contaminants accumulate in soils and after that crop uptake their contaminants and move into the food chain of humang being and also living organisms (Tak et al., 2013). The mainly general heavy metals (Cd, Cr, Hg, Se, Mn, Ni, Cu, Mg, Pb) significantly effect on environment and ecological evolutionary (Allen, 2014; Orisakwe, 2012). So, plants have the ability to translocate and accumulate metals in their organs and cells; i.e phytoextraction processs. There are different steps that involve in phytoextraction process (i) uptake and bioavalibity (ii) translocate of heavy metals (iii) sequestration of metals in leaves and vacuoles. High amount of heavy metals concentration accumulate in plant organs is not usually a naturally process for favoured reaction some how it’s the plant capability to uptake more than other plants. Under conditions dependent mechanism are favoured reactions in specific plants to uptake the nutrients more than limits. In this condition plant defence system mechanism play a role for metabolic, physiological and expressional changes under stressful conditions caused by different pollutants. Studies can be required in details for known hyperaccumulators plants to enhance its phytoremdiation process.

Figure 1.

Different kinds of phytoremediation used for cleaning polluted soil and water

Phytoremediation Types

• 1.

  Phytoextraction: absorbed contaminates and store in above shoots and parts of roots.

• 2.

  Phytostabilization: immobilize contaminates through adsorption and preventing the spreading of contaminants in plants

• 3.

  Phytodegredation: enzymatic degradation of organic contaminates through the secreted enzymes

• 4.

  Phytostimulation: soil microbial communities break down the contaminants

• 5.

  Phytovolatilization: volatile through the stomata when gas exchange occurs

Hyperaccumulator Plants

Hyperaccumulator term was proposed first time by Brooks et al. (1977) in reverence to those plants that can accumulate more than their natural favoured condition approximately 1000 mg kg^-1 of heavy metals. Plants accumulate more and more contaminants and tolerate without showing any symptoms (Memon and Schroder, 2009). According to Baker and Brooks suggested that the minimum threshold tissue concentration for plants as 0.1% considered Ni, Cr, Cu, Co, and Pb hyperaccumulators but same as above the experiment was done in case of Mn, and Zn threshold value for plants established 1% (Baker and Brooks, 1989; Baker et al., 2000). Plants accumulate heavy metals in root to shoots which favoured that can allow translocation of minerals and sugars as they required a proper ratio maintained between the amounts of heavy metals specific in roots to shoots. These process names as translocation factor (TF). Hyperaccumulator plant need more than the TF value 1 (Tangahu et al., 2011). Same as above another factor discussed here about bioaccumulation factor (BF) value also is required more than 1 for hyperaccumulation (Ahmadpour et al., 2014).