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5 Bioremediation of Heavy Metals

Table 5.5

Glimpses of different categories of phytoremediation strategies to decontaminate

environmental heavy metal pollution.

Techniques

Description

Heavy metals

References

Phytoextraction

●Accumulation of organic and inorganic

pollutants in harvestable biomass i.e.

shoots

●Plants able to absorb metals are chosen

to remove contaminants from soil with

the harvesting or removal of the plant

●Time consuming

Gold and

nickel

[31]

Phytodegradation

(vegetal degradation)

●Degradation of organic xenobiotics by

plant enzymes through metabolic

processes within plant tissues

●Applied to soil, clay, sediment, and

underground waters

●Reduction and degradation occur inside

the plant as a physiological process and

do not depend on microorganisms

Mercury and

lead

[32]

Phytostabilization

(root stabilization)

●Stabilizing the mobility and

bioavailability of pollutants in soil by

plant roots

●Phytostabilization plants are able to

tolerate heavy metal levels and

immobilize the metals through sorption,

sedimentation, complexation, or

reduction of metal valences

Copper

[32]

Phytovolatilization

(vegetal evaporation)

●Conversion of heavy metals to volatile

form and their subsequent release to the

atmosphere

●The most important aspect of this

method is transformation of the excessive

toxic compounds into less toxic forms

●The contaminants can be removed from

the plant by transpiration or evaporation

Selenium

[33]

Rhizodegradation (the

use of roots for

degradation)

●Degradation of organic contaminants in

rhizosphere by microorganisms in soil

●The most important benefit is the

dissolution of the contaminants in their

natural environment

Cadmium

[32]

Source: Based on Ali et al. [34].

effective strategy for successful phytoremediation of heavy metals. Recently, myriad

plant species have been reported as metal hyperaccumulators for effective phytore-

mediation. It has been earlier reported that phytoremediation can cost as less as 5%

of alternative clean-up methods. The establishment of vegetation on polluted soils

also helps prevent erosion and metal leaching.

An improved understanding of heavy metal uptake by plants from soil will also

help in promoting phytomining – a plant-based eco-friendly mining of metals,

which can be used for the extraction of metals even from low-grade ores. High

biomass-producing crops, such as Helianthus annuus, Cannabis sativa, Nicotiana