Page 16 - Plant-Based Remediation Processes

1 Phytoremediation Protocols: An Overview 3

Fig. 1.1 Major processes of phytoremediation where root zone (rhizosphere) plays an important
role in contaminant uptake and stabilization

1.2 Phytostabilization: Mobility Reduction of Contaminants

Phytostabilization is the process to reduce the mobility of contaminants in soil
through adsorption onto roots, adsorption and accumulation by roots, or precipita-
tion within the root zone. Vegetation are used to provide stabilization of migration
of contaminants by leaching, erosion, or dispersion along with soil, water, or air to
prevent pollution to ground water and surrounding environments (Ernst 2005).
Plants suitable for phytostabilization should develop an extensive root system that
provide good soil colonization, possess tolerance to the contaminant metals, ideally
immobilize the contaminants in the rhizosphere (Kramer 2005), and endure drought
and high temperature as well (Ernst 2005). This technique generally employs metal-
tolerant varieties of grass species such as Agrostis capillaris and Festuca rubra
(Kidd et al. 2009) but the leguminous species Lupinus albus also has been
suggested as a good candidate for remediation of Cd and As-contaminated soil
(Vazquez et al. 2006).
In addition, soil amendments are indispensable to achieve a long-term
phytostabilization such as (1) increasing soil pH to more than 5 by liming with
CaCO 3 and/or Ca(OH) 2 (Mench et al. 1994), (2) immobilization of heavy metals by
the application of soil additives such as compost (Vangronsveld et al. 1995), and (3)
improving soil quality by fertilization (Li and Chaney 1998). The toxic elements,
chiefly chromium and lead can be promisingly phytostabilized. Deep-rooted plants