International Journal of Environmental Research University of Tehran ISSN: 1735-6865 EISSN: 2008-2304 Vol. 4, Num. 3, 2010, pp. 525-532

International Journal of Environmental Research, Vol. 4, No. 3, July-September, 2010, pp. 525-532

Article

Study of the enhanced phytoextraction of cadmium in a calcareous soil

Motesharezadeh, B. * , Savaghebi-Firoozabadi Gh. R., Mirseyed Hosseini, H. and Alikhani, H. A.

Department of Soil Science Eng., University College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran

Correspondence Address: *Department of Soil Science Eng., University College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran
moteshare@ut.ac.ir

Date of Submission: 25-Jun-2009
Date of Decision: 05-Feb-2010
Date of Acceptance: 15-Mar-2010

Code Number: er10059

Abstract

Keywords: Phytoextraction, Cadmium, Soil pollution, Inoculants, Translocation factor

Introduction

In recent years, heavy metal contamination in soil has become a major problem which their accumulation in plants can directly or indirectly influence animals and humans (Pal et al., 2006). The highest amount of cadmium enter into the soil through application of sew-age sludge and waste in agricultural soils and also as a result of industrial activities such as dye making, rub-ber making, production of fertilizer from phosphate rock , automobile fuel and metal melting industry (Ansari & Malik, 2007; pal et al., 2006). Phytoextraction serves as one of the phytoremediation technologies and it is the technique of using plants for decontamination of the environment. Soil remediation by phytoextraction method has many advantages and disadvantages (Erakhrumen, 2007; Ghosh & Singh, 2005). Low biom-ass production in hyper-accumulator plants and sus-ceptibility of other plant' root to high metal concentra-tion lead to extension of researches on use of microor-ganisms in order to develop application of phytoextraction and to make this method economical (Glick, 2003; Ansari & Malik, 2007).

In the present study, effect of the application of inoculants of two strains, resistant to heavy metals was tested on cadmium absorption in greenhouse ex-periment with amaranthus, sunflower and alfalfa. The objective was to provide a practical solution for de-creasing and diminishing of heavy metal contamina-tion from different sources such as fertilizers, indus-tries and mines to agricultural lands using native plant growth promoting rhizobacteria (PGPR) separated from soil around lead and zinc mines in Haft Emarat, Arak, at central province of Iran.

Materials and Methods

First, composite soil sample was collected from depth of 0-30 cm from the Campus of Agriculture and Natural Resources of University of Tehran located in Karaj with coordinates of latitude of northern 35 ⁰ 48 ^' 35 ^'' and longitude of eastern 50 ⁰ 58 ^' 18 ^'' and 1315.5 meters above sea level.The soil was classified as Xeric Haplocambids, Fine Loamy, Mixed, Super Active ther-mic. Samples were air dried and passed through 2-mm sieve and mixed uniformly. Physical and chemical prop-erties and concentrations of elements in samples were measured: Measurements of the soil N was done by Kjeldal method, (Bremner, 1996), available phospho-rus by Olsen Method (Kuo, 1996), available Potas-sium by normal acetate ammonium method (Hemke and Sparks, 1996). Measurements of the soil pH was done on saturated extract (Thomas, 1996) and electri-cal conductivity by Rhoades method (1996), Equal Calcium Carbonate by Bouyoucos method (Bouyoucos, 1962), organic carbon percentage by Walkly Black (Nelson and Sommers, 1982) and texture of the soil by hydrometric method (Bouyoucos, 1962) and cation exchange capacity by Bower method (Sumner and Miller, 1996). Available concentration of cadmium, lead and zinc were extracted by DTPA method (Linsay and Norvell, 1978) and measured by Atomic Absorption Spectrometery (AAS). Results are given in [Table - 1]. The methods for bacteria isolation and purification and their PGPR characteristics have been reported previ-ous in Moteshare Zadeh et al. (2008). The effects of three levels of inoculants [control (B0), Bacillus mycoides M1 (B1), Micrococcus roseus M2 (B2)] and four levels of Cd [control (Cd0), Cd50, Cd100 and Cd200 mg/kg CdCl ₂ .H ₂ O ] on three plant cultivars (Amaranthus retroflexus , Helianthus annus and Medicago sativa), were studied under controlled con-ditions in a factorial experiment with randomized com-plete block design (RCBD) with three replicates of each treatment. After 70 days, at the beginning of repro-ductive period, shoot and root of sunflower and aramanthus and after three cuts of alfalfa (mean of three cuts in calculations and comparing it with other plants) in alfalfa, plant material was washed with distilled wa-ter and fresh weight determined, then dried in oven at 70ºc and dry weight was recorded. Then, samples were milled and extract was prepared by dry ash, and con-centration of cadmium, iron, copper, zinc, and manga-nese were measured using ICP- OES, CAP-6500 model. (Madejon et al., 2003). In order to assess amount of metal transfer from root to shoot, translocation factor was determined by dividing metal concentration at shoot by its concentration at root (Marchiol et al., 2004). The analysis of variance of the data was done in a factorial design with random blocks basic design with three replications by means of SAS software. The com-parison of means was done with LSD test at 1% level and also figures were drawn by Excel software.

Results and Discussion

The soil used in greenhouse test [Table - 1] was selected based on metal toxicity limits and study of sources and doubling concentration of each treatment in comparison with the previous treatment, contami-nated with cadmium at rates (0, 50, 100 and 200 mg Cd /kg) (Alloway, 1990; Purohit and Agrrawal, 2006). Re-sults of the analysis showed that the intended soil has suitable physical and chemical properties for green-house culture and no heavy metal contamination was induced due to the treatments. Results of cadmium test for three plants: amaranthus, sunflower and alfalfa: The results of triplet effects of bacterium, cadmium level and plant in root and shoot are illustrated in [Figure - 1],[Figure - 2],[Figure - 3],[Figure - 4],[Figure - 5],[Figure - 6],[Figure - 7],[Figure - 8],[Figure - 9],[Figure - 10],[Figure - 11],[Figure - 12],[Figure - 13],[Figure - 14].

Strains of bacillus mycoides M1 (B1), among two strains used at this study, was individually indentified resistant to four metals: lead, zinc, cadmium and nickel (Moteshare Zadeh et al., 2008). According to Yan- de et al., (2007), multiple metal resistance (MMR) have more effects in bacteria than the resistance to one metal, thereby it is possible that in treatments with applica-tion of this inoculants, better results will be achieved in terms of plant growth and phytoextraction. In a simi-lar study at India (Malik & Jaiswal, 2000), 45 Pseudomonas strains were separated from soils of con-taminated lands with industrial sewage and also non-contaminated lands, and their biochemical and mor-phological characteristics were determined. The research's results of these researchers showed that 80% of strains were resistant to copper, %73 resistant to cadmium, 71% to zinc and % 48.8 to mercury. The applied concentration in the study were 3.12 to 3200 mg/ml. Aleem et al., (2003), in the study on non-con-taminated soils and soils of grain fields which were irrigated by industrial sewage for a long time, 57 strains of Azotobacter chroococcum isolated from rhizospheric soil and assessed their chemical and superficial characteristics. Among 36 identified strains from rhizosphere of wheat and %94.4 strains were re-sistant to lead and mercury and %63.8, %77.5 and %86.1 resistant to zinc, Cr ⁺⁶ , Cr ⁺³ . According to obtained re-sults, this researchers declared that identified bacteria from soil irrigated by industrial sewage had significant difference in terms of resistance to metal, with non-contaminated soil. According to the report of Hada and Sizemone (1981), although bacterium in non-con-taminated area may be compatible to high concentra-tion of metal, but evidences indicated that there were more resistant strains in contaminated area than in non-contaminated area. Also, it was reported that amount of metal in soil was associated with the rate of bacte-rium resistance to metal. The gram positive and nega-tive bacteria could be resistant to heavy metals (Siler &Misra, 1998).

With regard to results provided in [Figure - 2]. applica-tion of inoculants led to cadmium concentration in-crease in roots of three plants also, iron concentration have increased in similar treatments [Figure - 3]. Glick (2003) declared that growth stimuli bacterium can ef-fect on plant growth both directly and indirectly. In the direct effect, plant growth and consequently ab-sorption and nutrition synthesis improvement will in-crease. Growth stimuli bacterium may stabilize nitro-gen of atmosphere and increase availability of this el-ement for plants or by siderosphore production, in-crease the solubility of iron in soil and facilitate iron absorption by plants. The synthesis of different plant hormone such as axing, considered as one method for stimulation and influence on plant growth by growth stimuli bacterium. By synthesis of ACC Deaminase enzyme, tension ethylene decrease and plant growth will stimulate. Moreover, in the indirect stimulation, useful bacteria prevent the influence of phyto-patho-gens (Glick, 2003). This researcher expressed that high heavy metal concentration have negative influence on plant growth by generating two problems: tension eth-ylene and limited iron concentration. The growth stimuli bacteria have useful characteristics such as ability of ACC deaminase enzyme production and siderophore production which can help to hind's plant growth in confronting with high heavy metal concentration. The close identification and analysis of these characteris-tics can be useful for understanding of heavy metal phytoextraction and phytoremediation mechanisms. Kuffnet et al., (2008) studied on effects of rhizosphere bacteria on absorption and metal concentration in wil-lows and identified 10 strains from contaminated soils of lead mine. Among identified bacteria, bacteria of six type were as follow: pseudomonas, agromyces, strep-tomyces, flavobacterium, servatia and janthinobacterium. Among strains, four strains (from pseudomonase, serratia type) and two strains (from streptomyces type) have the ability of siderophore production and three strains (two from janthinobacterium type and one from serratia type) have the ability of auxin production. Also none of the ten strains have the ability of ACC deaminase enzyme pro-duction. The resistance of these bacteria to zinc, lead and cadmium were assessed too. Yan-de et. al., (2007), provided the list of growth stimuli strains and their effects on plant including control of phytopathogen, growth and nutrition absorption improvement, resis-tant once to cadmium, zinc, copper, lead, nickel, co-balt, chrome contamination, root production and also resistant once to salinity and drought tension, how-ever, rhizobacteria in addition to metal transmission from soil to plant can increase phytoremediation efficiency by effects on soil pH, iron supply through siderophore production, phosphorus solubility in-crease, effects on phytopathogen, resistant once to salinity and drought tension, and indole acetic acid (IAA) production.

According to [Figure - 1], shoot highest cadmium con-centration and also the most absorption were observed for amaranthus. It seems that, the result of inoculants application was not identical in three plants and amaranthus did not significantly respond to inoculants application. In terms of root cadmium concentration, the most amounts were observed at alfalfa and with B1 inoculants consumption. Also, the highest root and shoot iron concentration was observed at alfalfa and the same inoculants. As a whole, the wet weight of root was observed for alfalfa, the wet weight of shoot for sunflower and the most transmission factor and cadmium absorption for amaranthus. According to these findings, applicability of plants with high biom-ass production and inoculants effects on growth pro-motion and plant development was proved. Other re-searchers including Madejon et al., (2003) and Cheng (2003) and Mathe- Gasper and Anton (2005) have re-ported the same findings. According to study of Madejon et al., (2003), shoot biomass and root of sun-flower were significantly less in contaminated soil than non contaminated soil. But, this effect was not impor-tant at maturation, of the product. Oil production was more in contaminated soil. These researchers declared that toxic effect of arsenic, cadmium, copper, lead, thal-lium was not observed at plants of the soil around mine. In this study, the potential phytoremediation of sunflower was affirmed, and with regard to its lower potential for phytoextraction, there were suggestion on sunflower application for soil protection and oil production for industrial consumption. According to results of this study, total cadmium concentration at sunflower was 125 mg/kg, which including 80 mg/kg at shoot, 13 mg/kg at root and 25 mg/kg at seeds. Ac-cording to Cheng's report (2003), heavy metal accu-mulation and distribution in plant depends on differ-ent elements such as: environmental elements as plant species, type of element, chemical form, bioavailability, oxidation- reduction potential, pH, cation exchange capacity, solute oxygen, and temperature and root dis-tribution. Song et al., (1996), by assessing heavy metal concentration such as cadmium, zinc, lead in espio-nage organ, has illustrated the relation between metal amount in espionage edible organ and forms of these metal in soil as several equations. These researchers expressed the process of metal accumulation as fol-low: cadmium> zinc> lead. Products that research's focus on them due to their high biomass production include: sunflower, cotton, oil seed, corn, Indian mus-tard, cereal (Vassiller et al., 2002). The extent of cad-mium concentration at corn in phytoremediation was mentioned as 25 to 150 mg/kg of shoot dry material.

Conclusion

Based on these results, plant type was effective in phytoextraction efficiency increase and also, inocu-lants application was useful and effective in phytoextraction efficiency increase. For conformation of the results we can point to the reports of Lasat (2002), Glick (2003), Aleem et al., (2003), Yan- de et al., (2007), Ansari and Malik (2007) and Kuffner et al.,(2008) which deals with the effect of growth stimuli bacteria through indirect and direct effect on root growth, root growth stimulation through siderophore production [Figure - 3],[Figure - 4] and phosphorous and iron supply and other nutrients [Figure - 7],[Figure - 9],[Figure - 10], control of heavy metal stress through ACC deaminase enzyme production and tension ethylene decrease, ability of auxin (IAA) production, control of salinity and drought stress, absorption stimulation and heavy metal transmission from rhizosphere environ-ment to plant and pathogen element effect decrease and also declares the useful effects of plant growth stimuli bacteria and its synergistic effect with plant in Green remediation.

Alfalfa, as a whole, is considered as an appropri-ate plant for stabilization of pollutant metals and pre-serving their distribution, due to its high potential in biomass production. Also, there was no significant risk in terms of its shoot metal concentration. The same results mentioned for sunflower too. So we can suc-cessfully use this plant for phytoremediation technol-ogy with plant stabilization method. Amaranthus can be considered as a potential option for removing of pollutants and land remediation, due to its resistance to weather conditions and also its ability in metal ac-cumulation and transmission from root to shoot by phytoextraction mechanism and low risk of nutrition in food cycle. As mentioned above, contaminated soil phytoextraction is a relatively new and developing tech-nology with special advantages. Economical use of native and cultivated plants for phytoremediation of moderately polluted soils with heavy metals should be approached with more research and field evaluations.^[43]

References

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