phytoremediation potential of eichhornia crassipes (mart.) solms

Phytoremediation Potential of Eichhornia crassipes (Mart.)

SolmsUpma Narang*, Renu Bhardwaj*, S.K.Garg**, A.K.Thukral*

([email protected];[email protected];[email protected])

*Department of Botanical & Environmental Sciences**Department of Molecular Biology & BiochemistryGuru Nanak Dev University, Amritsar- 143005, India

ABSTRACTThe heavy metals are serious environmental pollutants especially in areas of high

anthropogenic pressure. Unlike organicals that can be mineralized, heavy metals must

either be physically removed or converted to a biologically inert form.

Phytoremediation – the use of plants for pollution abatement offers an innovative

green clean technology. Aquatic macrophyte based water treatment systems (AMS)

offer a low energy consuming and low-cost method for removing contaminants from

polluted waters. Eichhornia crassipes (Mart.) Solms is well known for its amazing

ability to absorb and concentrate heavy metals such as cadmium, copper, lead,

mercury and europium etc. in aquatic systems. The present paper reviews the

phytoremediating potential of E. crassipes.

Key words – E. crassipes, heavy metals, phytoremediation, wastewater treatment,

metal detoxification.

IntroductionHeavy metals like Cd, Cu, Pb, Cr and Hg pose a major occupational and

environmental hazard as they are non-biodegradable with a very long biological half-

life (Barbier et al., 2005). Heavy metals are toxic to living organisms when taken in

excess. However, a subset of these at low concentrations, are essential micronutrients.

It is exceedingly difficult to make a clear distinction between essential and toxic

metallic elements, as all metals are probably toxic if ingested in sufficiently large

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doses. Non-essential heavy metals such as arsenic, antimony, cadmium, chromium,

mercury and lead etc. are of particular concern to surface water and soil pollution

(Ghosh and Singh, 2005).

Heavy metals are difficult to remove from the environment, and unlike many

other pollutants cannot be chemically or biologically degraded and are ultimately

indestructible (Mejare and Bulow, 2001), hence a clean up of these metals requires

their complete removal from the medium. The vegetation acts as a buffer for heavy

metals. It absorbs heavy metals to reduce their impacts in soil and water.

Phytoremediation, the use of vegetation for the in situ treatment of contaminated soils

and sediments, is an emerging technology that promises effective and inexpensive

clean up of certain hazardous waste sites (Solis-Dominguez et al., 2007).

Macrophyte based Water Treatment Systems (AMS)That the aquatic plants can improve water quality must have been realised

several centuries ago, with the observation that wastewaters flowing out of channels

infested with vascular plants such as water hyacinth, seemed to be clearer than the

wastewaters entering such channels. However, scientific studies to employ aquatic

plants as bioagents in water purification began only in 1970s. There were occasional

publications on the subject earlier, including a pioneering report from India (Sinha

and Sinha, 1969), which caught the attention of environmental engineers to give a

major spurt to research and development on macrophyte based water treatment

systems in various countries viz., The Netherlands (De Jong et al., 1976), USA

(Wolverton and Mc Donald, 1975a and b; Dinges, 1976) and Germany (Kickuth,

1975; Seidel, 1976; Siedel et al., 1978) etc. Among the various types of AMS, pond

systems containing floating macrophytes, such as, water hyacinth were most

commonly used.

Aquatic plants based wastewater treatment systems are becoming popular in

India. Performance for two constructed water hyacinth systems was studied by

Trivedy and Nakate (1999) for one year. The systems effected a high degree of

reduction in suspended solids, BOD, COD, nitrogen, phosphorus, oil and grease.

These systems were constructed at extremely low cost. Wolverton, Mc Donald and

coworkers brought out the amazing capability of water hyacinth in treating sewage

and industrial effluents (Wolverton and Mc Donald, 1975a; 1975b; Wolverton et al.,

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1976; Wolverton and Mc Donald, 1977; 1979; Wolverton, 1979; Wolverton and Mc

Donald, 1980a; 1980b; 1980c; 1980d).

Eichhornia crassipes (Mart.) SolmsEichhornia crassipes (Mart.) Solms (Fig. 1) belongs to family Pontederiaceae.

E. crassipes is found in many tropical, warm and temperate freshwater habitats

worldwide. It occurs in estuaries, lakes, watercourses, wetlands, shallow temporary

ponds, sluggish flowing waters, reservoirs and rivers (Fig. 2). It is an erect, free-

floating aquatic macrophyte growing generally to 0.5 m in height. It forms a shoot

consisting of a branched, stoloniferous rhizome. The roots are feathery, hang

submersed beneath floating leaves and have tips with long root caps. Leaves are

petiolate and appear to be in a rosette due to spiral arrangement of petioles. It bears

showy lavender flowers.

Metal Accumulation by E. crassipesWater hyacinth’s quest for nutrients has been effectively used to clean up

wastewaters in small-scale sewage treatment plants. Studies carried out on the uptake

of heavy metals by Eichhornia are presented in table 1.

Jamil et al. (1985) revealed the remarkable ability of Eichhornia to uptake the

heavy metals to the maximum within 5 minutes of the exposure. About 80% of

cadmium, 35% of zinc and 28% of iron were absorbed by water hyacinth in the same

time. The remaining quantity of the metal was gradually absorbed over a period of 24

hours. It was found that within 24 hours, 92% of copper, 82% of cadmium, 66% of

zinc and 78% of iron were absorbed by these plants

The plants of E. crassipes growing along the effluent channel of an electronic

component manufacturing unit were observed to accumulate high levels of heavy

metals, particularly copper (Barman et al., 2001). Effect of sequential exposure of

copper on water hyacinth and effect of zinc on the uptake of copper by E. crassipes

was studied by Rai et al. (1993). It was observed that at each stage of exposure the

plant placed in fresh copper solution continued to remove the metal from the solution

in direct proportion to the increase in the copper concentration of the solution.

However, during each subsequent exposure, the amount of copper taken up was

decreased.

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Fig. 1: E. crassipes

Fig. 2: E. crassipes growing in a pond at Amritsar

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Table 1: Metal Uptake by E. crassipes

Metal

Mode of treatment Accumulation Reference

Arsenic

Cadmium

Cadmium

Chromium

Iron

Iron

Lead

Treatment with six different concentrations ranging from 5 mg l-1 to 50 mg l-1.

a) Treatment with 1.0, 4.0 and 8.0 mg l-1 for 16 days.

b) Cd (1 mg l-1) + Pb (1 mg l-1) + Hg (0.5 mg l-1); Cd (4 mg l-1) + Pb (4 mg l-1) + Hg (1 mg l-1); Cd (8 mg l-1) + Pb (8 mg l-1) + Hg (2 mg l-1) for 16 days.

0.5, 1, 2 and 4 mg l-1 for 12 days.


0.001M and 0.01M for 4 days.

Exposed to 9.27 mg l-1 for 15 weeks.


Maximum uptake observed to be 26 mg kg-1 dry wt at 5 mg l-1. Plants started wilting at 10 mg l-1

and higher concentrations.

Maximum Cd content was observed on 16th day for 8.0 mg l-

1 as 2,326 mg kg-1 dry wt for tops and 10,600 mg kg-1 dry wt for roots.

Maximum accumulation was observed on 16th day for Cd (8 mg l-1) + Pb (8 mg l-1) + Hg (2 mg l-1) as 5,455 mg kg-1 dry wt in tops and 9,030 mg kg-1 dry wt in roots.

Maximum accumulation was observed for 4 mg l-1 on 8th day as 2,044 mg kg-1 in roots and 113.2 mg kg-1 in shoots.

Maximum uptake observed to be 108 mg kg-1 dry wt at 5 mg l-1. Plants started wilting at 10 mg l-1

and higher concentrations.

Maximum accumulation in roots as 115.21 mg kg-1 on day 4 for 0.001M and 334.74 mg kg-1 on day 3 for 0.01M.

Highest accumulation of 6,707 mg kg-1 dry weight at the 6th

week.

Maximum Pb content was observed on 16th day for 8.0 mg l-

1 as 1,810 mg kg-1 dry wt for tops and 25,790 mg kg-1 dry wt for roots.

Ingole and Bhole (2003)

Muramoto and Oki (1983)

Lu et al. (2004)


Win et al. (2002)

Jayaweera et al. (2007)


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Lead

Mercury

Mercury

Mercury

Mercury

Mercury

Zinc


0.001M and 0.01M for 4 days.



1 mg l-1 HgCl2 for 96 h.

1 mg l-1 treatment for 16 days.


Plants growing in aquatic habitats with mercury in the range of 3.1 g l-1 to 18.0 gl-1.

5, 10, 20 and 40 mg l-1 for 12 days.

Maximum accumulation was observed on 16th day for Cd (mg l-1) + Pb (8 mg l-1) + Hg (2 mg l-1) as 1,205 mg kg-1 dry wt in tops and 20,100 mg kg-1 dry wt in roots.

Maximum accumulation in roots on day 4 for 0.001M as 438 ppm.

Maximum Hg content was observed on 16th day for 2.0 mg l-

1 as 680 mg kg-1 fresh wt for roots. Accumulation in tops was observed to be negligible.

Maximum accumulation was observed for Cd (8 mg l-1) + Pb (8 mg l-1) + Hg (2 mg l-1) as 1,241 mg kg-1 fresh wt on 4th day.

0.700 mg kg-1 dry wt of plant.

Maximum accumulation was observed on 16th day as 0.20 mg kg-1 in shoots and 16.0 mg kg-1 in roots.

Maximum uptake was observed to be 327 mg kg-1 dry wt at 5 mg l-1. Plants started wilting at 10 mg l-1 and higher concentrations.

Mercury content observed in the range of 0.21 to 0.28 g g-1 dry wt in roots, 0.12 to 0.60 g g-1

dry wt in petioles and 0.14 to 0.64 g g-1 dry wt in leaf laminae.

Maximum accumulation was found to be 9652.1 mg kg-1

(roots) and 1926.7 mg kg-1

(shoots) on 4th day for 40 mg l-1.

Win et al. (2003)


Srivastava and Rao (1997)

Riddle et al. (2002)


Narang et al. (2003)

Lu et al. (2004)

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E. crassipes grown at different concentrations of nickel and zinc ranging from

5 to 100 ppm showed the accumulation of nickel up to 5.32 mg g -1 of dry plant tissue.

The plants showed higher absorption capacity for zinc showing an accumulation of

14.42 mg g-1 of dry weight (Panda, 1996). E. crassipes plants growing in a river being

polluted by a cocoa production plant have been found to contain elevated levels of

copper, aluminium and chromium (Klump et al., 2002).

Win et al. (2002) studied iron uptake by water hyacinth. It was observed that

the absorption of iron occurred predominantly in the roots. However, the petiole iron

content was much lower than that of leaves at 0.001 M Fe, whereas, it was higher than

leaf iron at 0.01 M Fe, suggesting the preferential transportation of Fe to leaves

initially. Accumulation of iron in the petioles occurred only when the leaves became

saturated. Jayaweera et al. (2007) while working on the uptake of iron by water

hyacinth showed that the plants grown under nutrient poor conditions were best suited

for iron removal from wastewaters. Also, the iron removal was found to occur mainly

through rhizofiltration and chemical precipitation of Fe2O3 and Fe(OH)3 followed by

flocculation and sedimentation.

Biosorption by E. crassipesBhainsa and D’Souza (2001) reported that uranium uptake by dried roots of

Eichhornia crassipes was rapid and the biomass could remove 54% of the initial

uranium present within 4 minutes of contact time. The process was favored at pH 5-6

and was least influenced by temperature. The maximum loading capacity obtained

was 371 mg g-1 dry biomass. The specific metal ion uptake decreased with increasing

initial uranium concentration.

Phytoremediation of Heavy Metals by E. crassipesWetland plants are being used successfully for the phytoremediation of trace

elements in natural and constructed wetlands. Roots and shoots of water hyacinth

have been shown to accumulate Cd and Zn in a concentration- and time-dependent

manner by Lu et al. (2004). Plants treated with 4 mg l-1 of Cd (highest conc.)

accumulated the highest concentration of metal in roots (2044 mg kg-1) and shoots

(113.2 mg kg-1) after 8 days, while those treated with 40 mg l-1 of Zn (highest conc.)

accumulated the highest concentration of metal in roots (9652.1 mg kg-1) and shoots

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(1926.7 mg kg-1) after 4 days. The maximum values of bioconcentration factors (BCF)

for Cd and Zn were 622.3 and 788.9 respectively, suggesting water hyacinth to be a

moderate accumulator of Cd and Zn. Hasan et al. (2007) have also reported E.

crassipes to be accumulator of Zn and Cd with more Zn being accumulated in the

roots compared to Cd. They further revealed that the accumulation factors for tops

and roots were higher for solutions containing either Zn or Cd compared to the

solution containing the mixture of Cd and Zn.

Muramoto and Oki (1983) while examining the ability of water hyacinth to

remove some toxic heavy metals (Cd, Pb and Hg) from metal containing solutions,

reported the concentration factors to be higher in roots of E. crassipes plants as

compared to tops. They further reported that Cd and Pb concentrations in both tops

and roots tended to increase with increasing concentration and with passage of time.

However, Hg concentration was reported to be markedly lower in tops, but increased

exponentially with passage of time in roots.

Win et al. (2003) reported the accumulation of lead by roots of water hyacinth,

more accumulation being observed for lower concentration i.e., 0.001 M Pb compared

to the higher concentration (0.01 M Pb). Moreover, the lead accumulation was found

to be higher in leaves as compared to petioles at 0.001 M Pb, whereas, the lead

content of petioles increased to a level higher than that of leaves at 0.01 M Pb. Water

hyacinth has also been shown to readily absorb the heavy metals like Cu, Pb, Zn, Hg,

Cd and Ni when placed in non-biodegradable effluents containing heavy metals

(Tatsuyama et al., 1977; Cooley et al., 1979).

The uptake and growth effects of mercury on E. crassipes under field

conditions and with lakewater as culture medium were investigated by Tabbada et al.

(1990). Absorption of the heavy metal increased with higher levels of Hg in the

culture solution. Roots accumulated much more of the heavy metal than the leaves.

The results suggested a beneficial role of the plant long considered as a noxious weed,

as a bioaccumulator of Hg on polluted lakes.

Bioconcentration and genotoxicity of aquatic mercury was assessed by Lenka

et al. (1990) by exposing the water hyacinth plants to water contaminated with

mercuric chloride and phenyl mercuric acetate at 0.001 to 1.0 mg l -1, or mercury

contaminated effluent from a chloralkali plant for various periods of 4 to 96 h. The

results indicated that bioconcentration of mercury in root tissue was both time- and

concentration-dependent, providing evidence for water hyacinth to be a good

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absorbant of aquatic mercury. The genotoxicity tests revealed that frequency of root

meristematic cells with micronuclei followed a concentration-response. The findings

indicated the potential of water hyacinth plants for in situ monitoring and for

mitigation of aquatic mercury pollution.

Srivastava and Rao (1997) while evaluating the relative efficiencies of five

selected weeds for mercury detoxification found Eichhornia to have the highest

capacity of mercury removal compared to Salvinia, Chara, Hydrilla and Vallisneria.

E. crassipes along with Pistia stratioites has also been reported to be better

accumulator of mercury compared to Colocasia esculenta and Scirpus

tabernaemontani by Skinner et al. (2007).

Metal Detoxification by E. crassipesReduction of heavy metals in situ by plants or binding of metals to some

chelating agents might be a useful detoxification mechanism for phytoremediation.

Using X-ray spectroscopy, Lytle et al. (1998) showed that E. crassipes, supplied with

Cr (VI) in nutrient culture, accumulated nontoxic Cr (III) in root and shoot tissues.

The reduction of Cr (VI) to Cr (III) appeared to occur in the fine lateral roots, which

was subsequently translocated to leaf tissues. In roots, Cr (III) was hydrated by water,

but in petioles and more so in leaves, a portion of the Cr (III) might be bound to

oxalate ligands. This suggested that E. crassipes detoxified Cr (VI) to Cr (III) in the

root tissues and transported a portion of Cr (III) to leaf tissues.

Kelley et al. (1999) have demonstrated that water hyacinth accumulated

europium- Eu (III) from water, and that it occurred predominantly in the root material.

Further studies using NMR and IR spectroscopy revealed that the extractable root Eu

(III), which most likely corresponds to intracellular Eu (III), was complexed to

organic acids (Kelley et al., 2000).

The X-ray absorption spectroscopic analysis of Hg compounds and water

hyacinth roots and shoots done by Riddle et al. (2002) revealed that Hg was initially

bound ionically to oxygen ligands in roots, most likely to carboxylate groups, and was

bound covalently to sulphur groups in shoots.

Humic acids (HAs) are animal and plant decay products that confer water

retention, metal and organic solute binding functions and texture/workability in soils.

HAs assist plant nutrition with minimal run-off pollution. Ghabbour et al. (2004)

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isolated HAs from the leaves, stems and roots of live water hyacinth plants. Similar

carbohydrate and amino acid distributions and tight metal binding capacities of the

HAs and their respective plant components suggested that the presence of HAs in

plants is related to their metal binding properties.

Constraints in using E. crassipesIn spite of well documented capability of water hyacinth, salvinia, duckweed

and other aquatic plants to absorb heavy metals from polluted waters (Abbasi and

Nipaney, 1993; 1994; Garg and Chandra, 1994; Zaranyika et al., 1994), attention is

generally directed for their elimination from water bodies, since dense strands of these

plants harm water resources in terms of quality as well as quantity (Abbasi and

Nipaney, 1989; 1993; Abbasi and Abbasi, 1995). They also adversely affect fisheries,

impede navigation, hasten water loss, encourage insects and pests and disturb fragile

O2 balance of water bodies through decay. Volumes of literature have been generated

on methods to control the growth of aquatic plants. As many as 90% of the

approximately 2500 literature citations available on water hyacinth are related to its

control.

E. crassipes as a Resource The distinctive characteristics of these weeds – hardiness, ability to survive

under adverse environmental conditions and high productivity can be harnessed to

make them efficient bioagents for treating wastewaters. Till recently, the exploitation

of aquatic plants in this respect had been constrained by the lack of economically

viable methods of post-harvest utilization of the “spent” plants. But now it has been

demonstrated that it is feasible to use such plants as energy feedstock (Lakshman,

1987; Abbasi et al., 1991a; 1991b; 1992a; 1992b; Abbasi and Nipaney, 1991; 1992;

1993), animal fodder (Virabalin et al., 1993; Haustein et al., 1994), fertilizers

(Polprasert et al., 1994) and a source of commercially important organics

(Krishnakumari, 1995). Singhal and Rai (2003) reported the biogas production from

water hyacinth employed for phytoremediation of lignin and metal-rich pulp and

paper mill and highly acidic distillery effluents. These plants eventually grew well in

diluted effluent up to 40% (i.e., 2.5 times dilution with deionized water) and often

took up metals and toxic materials from wastewater for their metabolic use. Slurry of

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the plants used for phytoremediation produced significantly more biogas than

produced by the plants grown in deionized water, the effect being more marked with

plants used for phytoremediation of 20% pulp and paper mill effluent.

ConclusionsPhytoremediation has emerged as an environment friendly technology for the

reclamation of habitats inundated with heavy metals. Eichhornia crassipes well

known for its capacity to accumulate heavy metals viz. Cd, Cu, Mn, Ni, Pb, Eu(III)

and Hg has a good phytoremediation potential and can be utilized for the reclamation

of aquatic habitats polluted with moderate levels of heavy metals by harvesting the

spent plants at regular intervals. The biomass thus generated during the course of

phytoremediation may be regularly harvested and utilized for the production of

biogas, organicals, paper or other products. Better uses of E. crassipes are required to

be worked out depending upon the local needs. Further studies in this direction might

provide a strategy to enhance the phytoremediation and economic potential of this

plant, otherwise considered a noxious weed.

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phytoremediation potential of eichhornia crassipes (mart.) solms

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