Desktop version

Home arrow Environment

  • Increase font
  • Decrease font


<<   CONTENTS   >>

Bioremediation methods of heavy metal contaminated soils

It is estimated that nearly 20 million hectares of soils are contaminated with different heavy metals, both originating from natural sources as well as anthropogenic activities (Liu et al. 2018). Many approaches are employed to reduce heavy metal pollution in soils which include physical, chemical, biological techniques and integrated approaches. Physical approaches of remediation rely mainly on removal of contaminated soil, applying electro-kinetic approaches, and verification while chemical methods include soil washing, immobilization and encapsulation; in biological methods, different organisms (plants and microbes) are used to extract, stabilize, volatilize and remove heavy metals from polluted soils (Klialid et al. 2017). In integrated methods, physical, chemical, or biological approaches are implied in combination. Particularly employed teclmiques in the remediation processes have their own merits and demerits. Liu et al. (2018) advocated in situ and landfilling approaches as more effective than the other methods. Araliah et al. (2019) asseited that an integrated approach using chemical and biological techniques is more effective and environmentally sound. A combination of nanotechnology with the use of microorganisms is also considered as a promising method to reclaim contaminated soils (Cao et al. 2019). In many recent reviews, employment of bioremediation techniques has been favored for reclamation of heavy metal contaminated soils because of their cost-effectiveness, feasibility and eco-friendliness (Ashraf et al. 2019, Fu et al. 2019, Yang et al. 2019, Muthusaravanan et al. 2020).

Table 1. Heavy metals and their consequences on germination, growth, physiological, metabolical and yield attributes of

different plants.

Plants under heavy metal stress

Heavy

metals

Nature of heavy metals

Effects on plants

References

Phaseohis vulgaris

As

Non-essential,

toxic

At concentration 5 mg dm"5, As stress significantly reduced growth, physicochemical activities and protein contents

Stoeva et al. (2005)

Hordeum vulgare

Ni

Essential

100 pM concentration of Ni caused necrosis, chlorosis and reduced growth and mineral distribution

Rahman et al. (2005)

Sesbania drummondii

Pb

Non-essential,

toxic

Poor seedling growth, photosynthesis and anti-oxidative responses

Israr et al. (2006)

Brassica pekinensis

Cu

Essential

At higher concentration, growth and nitrogen metabolism reduced

Xiong et al. (2006)

Hordeum vulgare

Cu, Al, Cd

Essential and non-essential

Poor growth and metabolic activities at higher concentrations

Guo et al. (2007)

Elsholtzia atg)n

Pb

Non-essential,

toxic

Photosynthesis, leaf growth and membranes’ abnormalities at 200 pM

Islam et al. (2008)

Leucaena

leucocephala

Cd, Pb

Non-essential

75 ppm concentration of Pb while 50 ppm of Cd reduced seedlmg root and shoot growth and dry weight

Shafiq et al. (200S)

Vetiveria zizanioides

Cd

Non-essential,

toxic

Protem, chlorophyll contents, reduced water uptake and poor root activity

Aibibu et al. (2010)

pakchoi and mustard

Cd

Non-essential

Reduced growth and photosynthesis, shoot and root w'eight decreased

Chen et al. (2011)

Liman usitatissimum

Cd, Cr

Non-essential

Decreased photosynthesis and plant growth attributes

All et al, (2015)

Eichhornia crassipes

Pb

Non-essential

Plant growth and chlorophyll content drastically decreased

Malar et al. (2016)

Entca sativa

Cu, Ni, Zn, Hg, Cr, Pb

Essential/non-

essential

Decreased germination and seedling growth

Zhiet al. (2015)

Brassica juncea

Cr, Cd, Pb, Hg

Non-essential

Increased level of heavy metals decreased photosynthesis, biomass and chlorophyll content

Sheetal et al. (2016)

Zea mays

Ni

Essential

At higher concentrations, Ni stress induced low mineral contents, photosynthesis, growth and biomass

Rehman et al. (2016)

Pisum sativum

Co, Pb, Cd

Essential/

Non-essential

Abnormal growth and biomass at concentration 750-1250 ppm

Majeed et al. (2019)

Spinacia oleracea

As, Hg

Non-essential

Abnormal and reduced plant growth, and metal distribution

Zubair et al. (2019)

Triticum aestivum

Zn, Cu

Essential

Germination parameters and seedlmg growth attributes responded negatively to higher concentration of metals

Wang et al. (2019)

T. aestivum

Cu, Pb

Essential non- essential

Reduced plant growth and enzymatic activities

Jiang et al. (2019)

Desmodesmus sp.

Cu

Essential

Negative effect on growth and filament structure

Buayam et al. (2019)

Zea mays

Cu

Essential

At higher concentrations, plant height and weight reduced u'hile mineral uptake w'as disturbed

Reckova et al. (2019)

Table 1 Contd. ...

Heay Metal Pollution in Agricultural Soils: Consequences and Bioremediation Approaches 231

...Table 1 Contd.

Plants under heavy metal stress

Heavy

metals

Nature of heavy metals

Effects on plants

References

Petunia hybrid

Cd, Cr, Cu, Ni and Pb

Essential/non-

essential

Morphological and biochemical abnormalities

Khan et al. (2019)

Uvginea maritime

Al. Cr, Cd, Pb

Essential/non-

essential

Decline in photosynthesis and chlorophyll pigments

Houri et al. (2020)

Nicotiana alata

Cd, Cr, Co, Ni, Pb

Essential/non-

essential

Stress imposition, negative effects on physiology' and photosynthesis

Khan et al. (2020)

Bioreinediation in wider terms implies the use of living organisms for minimizing the concentration and adverse effects of heavy metals in contaminated soils. Generally, plants (herbs, shrubs, trees and even algae) are used as remediating agents in most of the polluted sites and the technique is referred to as “phytoremediation”. Microorganisms such as bacteria and some fungi may also be used in remediation processes and this approach is termed as “microbial remediation”. Phytoremediation coupled with the microbial application (bacteria, microfungi, and microalgae) is termed as “microbial assisted phytoremediation” (Dotaniya et al. 2018). Plants used wither alone or in combination with microbes, and employ different strategies such as chelation, accumulation, extraction, volatilization and stabilization of heavy metals (Figure 1).

An illustration of the heavy metal input mto soils and bioremediation strategies employed by plants and microbes

Figure 1. An illustration of the heavy metal input mto soils and bioremediation strategies employed by plants and microbes.

 
<<   CONTENTS   >>

Related topics