1. Phytoremediation

2. Phytoremediation:
Plant mediated processes for decontamination/detoxification of soil water or air are commonly referred to as phytoremediation. It has been proposed as an alternative method to remove pollutants from air, soil, and water or to render pollutants harmless and does not affect soil biological activity, structure and fertility (Prasad, 2003, 2004). There are several types of phytoremediation technologies currently adopted as successful clean up process, both in contaminated soils and water. (Schulz, and Beck, 2002; Prasad et al 2010).

3. Overview

4. Mechanisms

5. Phytoextraction – Reduction of metal concentration in the soil by cultivating plants with a high capacity for metal accumulation in the shoots;
Rhizofiltration – Adsorption or precipitation of metals onto roots or absorption by the roots of metal tolerant aquatic plants;
Phytostabilization – Immobilization of metals in soils by adsorption onto roots or precipitation in the rhizosphere;
Hydraulic control – Absorption of large amounts of water by fast growing plants and thus prevent expansion of contaminants into adjacent uncontaminated areas;
Rhizodegradation – Decomposition of organic pollutants or biotransformation of metals by rhizospheric organisms.
Phyto volatilization – Detoxify soil metal contaminant by bio-methylation processes.
Phyto degradation – Uptake of contaminants and the subsequent transformation, mineralization or metabilisation by the plant itself through various internal enzymatic reactions and metabolic processes (Prasad et al 2010).

6. Phytosequestration – Phytochemical complexation in the root zone, leading to the precipitation or immobilization of target contaminants in the root, such complexes and there by stored in the vacuolar space of root cells. Transport proteins are also present that facilitate transfer of contaminants between cells (Prasad, 2011).
Phytoattenuation – Production of plant biomass as sink of toxic metals at contaminated sites, where conventional agriculture is affected by the presence of elevated amounts of plant available trace elements, causing economic losses and endanger or diminish food and feed quality and safety (Meers et al 2005, 2010).
Biofortification of phytofortification – It is the process of increasing the bioavailable concentrations of essential nutrients in edible portions of food crops through agronomic intervention or genetic selection; essential nutrients like trace elements, vitamins and metabolites which are accumulated or synthesized during the growth and development of selected plants can be used as food or feed (healthy diet) in many areas (Kralova & Masarovicova, 2006).
Metal Nanoparticles – The natural production of metal nanoparticles viz. TiO2, ZNo, Al2O3, AgNO3 etc. in plants of contaminated sites are often offered resistance to plants against invasion of disease and pests or render better stress adaptability to salt or water (li & Xing, 2007; Havenkamp & Karshall, 2009).

7. Cadmium phytoremediation:
The main anthropogenic pathway through which Cd enters the water bodies is via wastes and waste waters from industrial processes such as electroplating, plastic manufacturing, metallurgical processes and industries of pigments and Cd/Ni batteries Cadmium exists in wastewaters in many forms including soluble, insoluble, inorganic, metal organic, reduced, oxidized, free metal, precipitated adsorbed and complexed forms. Watanabe et al. (2009) grew selected species of family Amaranthaceae viz. Amaranthus tricolor, and observed the higher Cd-accumulating properties in plants. Later similar hyper accumulation properties of Cd were reported in Brassica juncea (Family Cruciferae), Chrysanthemum indicum (Family Asteraceae) and some other plants, using EDTA chelator, the hyper accumulation of Cd – can be enhanced many fold n vitro & in vivo.

8. Arsenic phytoremediation:
In lower part of gangetic delta & Brahmaputra basin, groundwater arsenic contamination is a natural geogenic processes. However, in many parts of Asia, arsenical products have been widely used in agriculture and industrial practices viz. pesticides, fertilizers, wood preservatives, smelter wastes and coal fly ash, which are of great environmental concern.
The Chinese brake fern Pteris vittata is a major arsenic hyperaccumulating plants which can accumulate 23 g kg-1 of arsenic in its fronds. Similarlarly, other species Pteris longifolia, Pteris umbrosa and Pityrogramma calomelanos are also known to be hyperaccumualtors. In presence of available phosphate, the uptake of As- by the plants appears to be higher. The root associated VAM fungi in ferns also helps in hyperaccumulation of arsenic.

11. Mercury phytoremediation:
The mercury contamination in environment is primarily anthropogenic, more precisely, industrial sources viz. coal thermal plant, iron and steel industry, chloralkali plants, battery industry and so on being the mail sources. Bioremediation by microbes in mercury contaminated site detoxification is quite established. Bacteria and several higher plants have properties to make phytovolatilization of mercury at contaminated sites.

13. Chromium phytoremediation:
Chromium is the chief heavy metal contaminant found in the tannery effluent and chromite mine areas. Phytoremediation appears to be one of the major thrust areas in chromium contaminated land detoxification. Selected chromium tolerant plants root zone in association with VAM fungi, helps in hyperaccumulation of chromium on site.
A number of tree species helps in phytoextraction of chromium at contaminated sites.

14. Cyanide phytoremediation:
Cyanide primarily found in waste water of steel plants, gold mine areas. Selected water plants like water hyacinth (Eichhornia crassipes) and bacteria are often used for phytoremediation/ bioremediation purpose.

16. Constructed Wetland for Removal of Metal in Aquatic Environment

17. Processes Occurring in a Wetland

18. BIOTIC MECHANISMS TREATING ORGANIC COMPOUNDS IN WETLAND

19. BIOTIC MECHANISMS TREATING INORGANIC COMPOUNDS IN WETLAND

20. Abiotic Mechanisms Treating Organic Compounds in Wetland

21. Organic Compound Removal in Wetland

22. BOD/ Carbon Pathways Legend DM Dissolved Matter PM Particular Matter
# Denotes dissolved
or in solution
Se Sedimentation Re Resuspension of bed particulates
Bu Biofilm Uptake Rs Respiration by algal biofilm and
Ao Aerobic decomposition phytoplankton
An Anaerobic decomposition
Fb Bio film fall and deposition
Fm Microphyte litter
Di Dilution of O at water/air interface

23. Plants recommended for phytoremediation purpose
Sl. No.
Plant’s name
Common name
Phytoremediation function
Agropyron repens
Wheat grass
Stabilization of lead in soil
Agropyron smithii
Metal extraction (phyto extraction)
Agrostis castellana
Beat grass
Agrostis tenuis
Alyssum bertoloni --
Hyperaccumulation of metal (phyto extraction)
Asabidopsis halleri
Metal tolerance (phytoextraction)
Azolla pinnata
Water fern
Bioabsorption of toxic metals (Rhizofiltration)
Azolla filculoides
Bacopa monnieri
Water hyssop
Metals accumulation
Brassica oleracea
cauliflower
Metals accumulation (Phytoextraction)
Brasica napus
Indian mustard
Brassica juncea
Rape

24. contd… Sl. No. Plant’s name Common name Phytoremediation function
Brassica campestris
Cabbage
Metals accumulation (Phytoextraction)
Carex praegractlis
Sedge
Phytoirrigation
Elchhornia crussipes
Water hyacinth
Metal accumulation (Biosorption)
Hordeum brachyantherum --
Phytoiirrigation metal hyper accumulation
Hydrocotyle umbellate
Pannywort
Biosorption of toxic metals
Hygrophila corymbosa
Cadmium accumulation
Macademia neurophylla
Metal hyperaccumulation
Pistia stratoites
Water lettuce
Pteris vittata / P. longifolia
Brake fern
As-hyperaccumulation
Salvinia molesta
Kariba weed
Metal accumulation (Rhizofiltration)
Silene vulgaris
Bladder champion
Phytostabilization
Solidago hispida
Hairy golden rod
Streptanthus polygaloides
Nickelhyperaccumulation
Vallisnaria spiralis
Eel grass
Vetiveria zizanordes
Vetiver grass
Source: Glass 1988, McGutcheon and Schnoor 2003, Prasad 2004, 2007, 2012, Prasad and Strzalka,

25. Phytoremediation and Genetic Engineering:
Understanding the physiology and biochemistry of metal accumulation in plants is important for several reasons. The main implications are that this knowledge allows the identification of agronomic practices capable of optimizing the potential for phytoremediation and permits the identification and isolation of gene responsible for the expression of the hyperaccumulating phenotypes. Thus ideal plant for the phytoremediation of any metal must have a substantial capacity for metal uptake, bioaccumulation and stability as well as durability to reduce the length of treatment as for as possible and practicable. It then follows that there is a promising alternative in the development of transgenic plants with enhanced properties of metal uptake and translocation, bioaccumulation potential and higher tolerance to toxicity. Such heightened metal bioaccumulation and tolerance could be mainly achieved by normally over expression the natural or modified genes encoding antioxidant enzymes. Several researchers have reported to date rather encouraging results using plants genetically engineered with increased cadmium tolerance and uptake for phytoremediation purposes. However, a majority of these genetically manipulated plants for phytoremediation have only been tested under strict laboratory conditions and a very scanty few have been analysed for their phytoremediation potential at field scale. Metal hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate and detoxify metals, including cadmium and other metal or metalloids hence constitute an essential pool of material for genetic modification for targeted enhancements in phytoremediation potential (Fulekar et al 2009).

26. Fig. : Possibilities for genetic engineering in phytoremediation
Genetic engineering modifications of the physiological and molecular mechanism of plants, cadmium uptake and tolerance have also been successfully achieved and these show promose in opening new avenues for enhancing the overall efficiency of cadmium phytoremediation (Eapen and D’souza, 2005). The possibilities for genetic engineering plants for phytoremediation is shown in the Fig.
Fig. : Possibilities for genetic engineering in phytoremediation

27. A number of genetically modified (transgenic) plants have been generated and tested in recent studies and they have demonstrated the merits of genetic engineering in enhancing the tolerance, uptake and /or bioaccumulation of Cadmium. Wojas et al. (2009) have demonstrated in a study first of its kind that the hetergenous expression of Arabidopsis MRP7 in tobacco (Nicotiana tabacum var. xanthi L.) could modify cadmium accumulation, distribution and tolerance.

28. UNUSUAL ACCUMULATION OF METALIC ELEMENTS /METALLOID BY PLANTS
Club moss; Hydrangea sp., tea plants As
Brown algae, fern like Pteris vittata B
Brown algae, Plumbaginaceae Ba
Rhizopods, Brazil nut Cu
Caryophyllaceae F
Dichopetalum cymosum Li
Thallictrum sp., Cissium Sp. Mn
Ferns, Digitalis purpurea Mo
Papilionaceae Ni
Alyssium sp., Hybanthus floridundus Se
Cruciferae, Astragalus racemosus Sr
Brown algae V
Amonita sp. Brown algae Zn
Thlaspi calaminare
Sources: Brown H.J.M. (1966), H eevit E.J. and Smith, T.A. (1975)

29. Thank You