Assistant Professor

Chemistry

Ramabai Ambedkar Government Degree College

 Gajraula, Amroha, U.P., India 

Phyto word stand for plants and remediation mean treatment. Phytoremediation is a technique, in which organic and inorganic pollutants are removed from contaminated water or soil bodies by suitable plants. The plants which accumulate organic/inorganic pollutants such as pesticides, insecticides and heavy metals in more amount are known as hyperaccumulator. Hyperaccumulating plants are those plants which accumulate a specific pollutants or heavy metals in more amount than other plants, they have good tolerance for specific pollutants so used to Phyto remediate those pollutants.  In phytoremediation process, good tolerance for pollutant of hyperaccumulating plants is more important than high biomass [1].

Key Words: Phytoremediation, Hyperaccumulator, Contaminants, Heavy metals, Pollution.

Introduction:  Heavy metal contamination of soil and water bodies is very leading source of pollution and serious menace for human health, animal health and aquatic ecosystem. Other technologies like soil treatment by heating, chemical treatment, electrolysis method, osmosis method, etc used to remove heavy metals pollutants from water body or from soil are time consuming, very costly, harmful to environment and not feasible. In spite of this, it creates secondary pollution also. While phytoremediation techniques are used to remove inorganic and organic pollutants. Phytoremediation techniques are of low cost, time saving, eco- friendly, environment friendly and easy to perform experimentally. Already there is very scarcity of drinkable water in the world as well in India, then heavy metal pollution in water sources like ponds, underground water, river, drains increase the level up to dangerous situation for fauna, flora and human being.

Various metals are needed in our daily developmental activities like growing food requirement, growing number of small and big industries, growing population, growing consumption, fast urbanization, growing use of pesticides, insecticides, fertilizers in agriculture which cause growing household and industrial wastes. Thus, it leads soil and water contamination/pollution.

Industries like – geothermal energy plants, sugar industry, paint industry, colour- paper industry, (Cr, Hg, Pb, As, Sb, Sn, Ni etc) metal extraction industry,  metal related industry, pesticide industry, herbicide industry, soap industry,  Dyeing industries, automobile industry,  tanning industry, mining,  plastic industries, rubber industry, battery,  cell/battery manufacturing industry, hazardous chemical industries etc create point sources for water and soil  pollution. To fulfil the increasing demand of above industries and our society, reclamation of contaminated water and soil is the only option and solution. Heavy metals in soil and water are nonbiodegradable and exist in the soil and water bodies for hundreds of years. Toxic heavy metals come in water and soil from different industries and from domestic/ household wastes.

These contaminants from water go in food products from soils through water. Heavy metals accumulate with time and do not corrode. Heavy metal removal is very complicated because they exist in various oxidation states. There are several techniques which are used in to remove heavy metals from contaminated water. These techniques are chemical precipitation, extraction by solvents, ion exchange method, reverse osmosis, adsorption and evaporation of water and heating of soil etc. But these techniques involve high number of operations, time consuming and very high cost of each project thus these techniques become practically impossible. Thus, phytoremediation is very versatile techniques which purify contaminated water and soil comparatively fast and in economically way. Aquatic plants and some other plants have high potential to remove heavy metals from contaminated water and plant like Brassica juncea (Indian mustard) is used to remove heavy metals,

Many researches have shown that a number of plants can increase biological degradation of harmful organic molecules in soil. Toxic heavy metals naturally present in the soil and water, but when they accumulate in more than prescribed limit these heavy metals become destructive pollutants [1,2,3,4,5,6].

Plants used in phytoremediation
 Different water and soil plants which are used to remove specific heavy metals and other pollutants from contaminated water and soil are shown in following table. Plants used in phytoremediation may be different from list given belove. (2,3,4) 

S. No.	Aquatic and soil plants	Common Name	Metals/Metalloids
1	Eichhornia crassipes	Water hyacinth	Pb, Hg, Cu Cr, Ni, Zn
2	Pistia stratiotes	Water lettuce	Cr, Zn Fe, Mn, Cu
3	Salvinia minima	Water spangles	As, Ni Cr, Cd
4	Salvinia herzoggii	Water fern	Cd, Cr
5	Lemna minor	Duckweed	Cr, As, Ni, Cu, Pb
6	Spirodela intermedia	Duckweed	Fe, Zn, Mn, Cu, Cr, Pb
7	Nasturtium  officinale	Water cress	Cr, Ni Zn, Cu
8	Myriophyllum spicatum	Parrot feathers	Pb, Cd, Fe Cu
9	Ceratophyllum demersum	Hornwort	As, Cd, Cr,Pb
10	Potamogeton crispus	Pondweed	Cu, Fe, Ni, Zn, Mn
11	Potamogeton  pectinatus	American pondweed	Cd, Pb, Cu Zn
12	Typha latifolia	Common cattail	Zn, Mn, Ni, Fe, Pb, Cu
13	Mentha aquatica	Water mint	Pb, Cd, Fe, Cu
14	Vallisneria spiralis	Tape grass	As
15	Spartina alterniflora	Cordgrass	Cu, Cr, Zn, Ni, Mn, Cd Pb, As
16	Phragmites australis	Common reed	Fe, Cu, Cd, Pb, Zn
17	Scirpus	Bulrush	Cd, Fe, Al
18	Polygonum hydropiperoides	Smartweed	Cu, Pb, Zn
19	Brassica juncea	Indian mustard	Pb, Cd, Zn

Phytoremediation Techniques 

Mechanism of detoxification in Phytoremediation

Detoxification is requirement in phytoremediation process. Plants use two defence mechanism to cope with the toxicity of heavy metals. These defence mechanisms are tolerance and avoidance [5].

[a] Avoidance:   In this mechanism, plants restrict the heavy metal uptake.                                 

Plants first immobilize ions as root sorption, modifying ions and by making chelate complexes in rhizosphere area. Various root exudates may change pH of rhizosphere thus making heavy metal ions to precipitate/immobilize. These processes limit the bioavailability of heavy metal ions to the plants [5].

Citrate mediates chelation with Ni in T. goesingense leaves. Citric/acetic acids make chelate with Cd in solanum nigrum leaves. Malate makes chelate with Zn in A. halleri. Excess Ni induce histidine accumulation while excess Zn, Pb, Cu and  Cd induce proline. Heavy metals are immobilized  and detoxified  by making chelates with amino acids in cells and in xylem sap. These complexes are transported from cytosol to inactive vacuole after chelation [5].

Conclusion

Phytoremediation technique is very useful, effective and feasible on very large contaminated water body or soil body. Phytoremediation is specific class of bioremediation. It is a natural biological process of removing pollutants from soil or water bodies. Mechanism of phytoremediation is same as mechanism of bioremediation. Microbes may be used to remove or destroy the toxic compounds like-herbicides, insecticides, thiocarbamates, chlorinated aromatic and aliphatic compounds, sulphonates, amines and heavy metals. This method does not require any outside help to do its remediation works. This method is very cheap/low cost, feasible, easy to perform and produce no secondary pollution. It not only removes pollutants from contaminated bodies but also inhibits the spreading of pollutants from one place to other. In this technique, a localized pollutants are removed locally. Roots play main function in this technique. Roots may absorb or adsorb the pollutants from contaminated bodies and send it to stem, leaves, fruits and other parts of the plants.

1-It is promising approach in the revegetation of heavy metal polluted land: Heavy metals come in soil or water bodies by natural and anthropogenic activities. These metals persist in environment because these are non-biodegradable in nature. Above the WHO’s prescribed limits of these heavy metals in soil or water bodies, these heavy metals are very toxic for plants, human and animals. It is eco-friendly approach and very successful mitigation measure to revegetate the polluted land. To increase the efficiency of the phytoremediation, one must understand the mechanism of it. In mechanism, plant absorb or adsorb pollutants first, translocate these by various enzymes and detoxify them in a limited portion of the plants [5].  

References

1.https: //iwaponline.com/wpt/article/12/4/894/38660/Phytoremediation-of-chromium-from-tannery-.  Phytoremediation of chromium from tannery wastewater using local plant species . By Gemechu Kassaye, Nigus Gabbive, Agegnehu Alemu. Water Practice and Technology (2017) 12 (4): 894–901.

https://doi.org/10.2166/wpt.2017.094.

2. Application of Floating Aquatic Plants in Phytoremediation of Heavy Metals Polluted Water: A Review, Sustainaqbility [ MDPI] , Received: 11 February 2020; Accepted: 24 February 2020; Published: 3 March 2020.

3. Abhijit mitra , University of Calcutta, India, Phytoremediation by mustard plant, sept-2017

4. P.K.Gautam, R.K.Gautam, S. Banerjeet, M.C.Chattopadhyaya, J.D.Pandey, Chemistry department, University of Allahabad, India. Heavy metals in the environment: fate, transport, toxicity and remediation technologies. Nova science publishers, capter-4, p101-130,  ResearchGate-February 2016.

5. Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land,  An Yan, yamin Wang, Swee Ngin Tan, Mohmed Lokman, Mohd Yusof, Subhadip Ghosh and Zhong Chen.1-1Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, Singapore, Singapore, 2-2Centre for Urban Greenery and Ecology, National Parks Board, Singapore, Singapore3-3School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia. 4-4M Grass International Institute of Smart Urban Greenology, Singapore, Singapor.

6. Sonali Bhawsar, Importance of phytoremediation. Date-29/01/2011. https://www.biotecharticles.com/Applications-Article/Importance-of-Phytoremediation-613.html