Page 15 - Plant-Based Remediation Processes

2 S. Chatterjee et al.

inorganic molecules at contaminated sites to achieve site-specific remedial goals.”
Cleaning up of the environment through plants are rendered by direct uptake of the
toxic chemical, followed by subsequent transformation, transport, and their accumu-
lation in less toxic forms (Schnoor et al. 1995). In addition, plants support remediation
process by releasing exudates and enzymes that induce microbial diversity at rhizo-
sphereand biochemical activityinthebulksoiland mineralization(Maceketal. 2000).
Phytoremediation techniques are developing great interest because the method
became an alternative to the conventional energy intensive, instrument, and
chemical-based expensive restoration technologies of vast polluted areas of land
and water (Azadpour and Matthews 1996; Garbisu et al. 2002; Vassilev et al.
2004; Padmavathiamma and Li 2007; Lone et al. 2008) and thus decontaminating
the polluted environment by improving the utility, even of the marginal lands
(Meagher 2000). The concept of cleaning pollutants using green living systems for
environmental remediation is quite old. Nickel accumulation by the plant Alyssum
bertolonii was first reported in 1948; however, the concept received momentum
after the reports from the researcher Robert Brooks, of Massey University in
New Zealand in 1977. Thereafter, widespread researches on the use of wetland
plants, for treating heavy metals, radionuclide contaminated waters were initiated.
After the nuclear disaster at Chernobyl, Ukraine, in 1986 Phytotech began using
plants to decontaminate water and soil. This was to be proving ground for new
technology. Iowa City used tree farms to clean landfills in 1989, after the results
published from Phytotech experiments. In 1990, nitrogen-rich aquifer in New
Jersey was managed by phytoremediation technology. The first Living Machine
was designed and constructed in Europe during 1995, which lead to researching
genetic engineering applications. Research proved that specific plants were capa-
ble of removing toxins and certain metals. The Department of Defense and EPA
joined forces to develop plant-based cleanup approaches to large-scale cleanup
projects (Rai and Pal 1999).
Phytoremediation of toxic elements like mercury (Hg), arsenic (As), cadmium (Cd),
chromium (Cr), lead (Pb), cesium (Cs), and strontium (Sr) involves extraction and
translocation of toxic cation or oxyanion to above ground tissues by plants for later
harvest, converting the element to a less toxic chemical species (Meagher 2000). On the
other hand, for organic pollutants, such as polychlorinated biphenyl (PCBs), dioxin,
polycyclic aromatic hydrocarbons (PAH), trichloroethylene, the target of phyto-
remediation is to completely mineralize them into relatively nontoxic constituents,
such as CO 2 , nitrate, chlorine, and ammonia (Cunningham et al. 1996). Plants have
several strategies (Fig. 1.1) for dealing with xenobiotics: phytostabilization,
phytoextraction, phytovolatilization, rhizofiltration, phytodegradation, and phytosti-
mulation (Saltetal. 1998; Fulekar et al. 2009;Marquesetal. 2009). For soil
phytoremediation, phytostabilization and phytoextraction are preferred (Salt et al.
1998).