Open Access Scientific Reports

The Phytoattenuation of the Soil Metal Contamination: The Effects of Plant Growth Relgualtors (GA3 and IAA) by Employing Wetland Macrophyte Vetiver and Energy Plant Sunflower

Research Article Open Access

C. F. Chen, T. Y. Yeh* and C. F. Lin

Department of Civil and Environmental Engineering, National University of Kaohsiung, Taiwan

*Corresponding authors: TY Yeh Professor, Department of Civil and Environmental Engineering National University of Kaohsiung, Taiwan Tel: 886-7- 591-9536 Fax: 886-7-591-9376 E-mail: tyyeh@nuk.edu.tw

Received December 11, 2012; Published June 30, 2012

Citation: Chen CF, Yeh TY, Lin CF (2012) The Phytoattenuation of the Soil Metal Contamination: The Effects of Plant Growth Relgualtors (GA3 and IAA) by Employing Wetland Macrophyte Vetiver and Energy Plant Sunflower. 1: 176. doi:10.4172/scientificreports.176

Copyright: © 2012 Kumar JP, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

The phytoattenuation, a novel green remediation concept, has been successfully demonstrated while employing vetiver and biostimulator (gibberellic acid GA3 and indol-3-acetic acid IAA) to gradually mitigate the soil Cu levels. The effectiveness of stimulator GA3 and IAA was in the descending sequence GA3 > IAA. Biostimulator has been demonstrated plant growth enhancement and been employed for agricultural operation. The on-site tests demonstrated Cu levels were gradually decreasing during 4 months monitoring time periods. The soil metal level reduction achieved a satisfactory level which complied with local environmental standards. After more rounds of planting and harvesting, the soil metal concentration expected to be further dropped while on-site operation was executed. Green remediation concepts such as the phytoattenuation need to be taken as serious concern while the Earth has faced recent unpresdent damage Japan tsunami, Green house effect, unpredicted weather fluctuation worldwide, and serious endangered species issues.

Keywords

The phytoattenuation; Heavy metals; Vetiver (Vetiveria zizaniodides); Sunflower; Biostimulator; Gibberellic acid (GA3); Indol- 3-acetic acid (IAA)

Introduction

The soil and groundwater remediation act has been enacted and executed since year 2000. It has been ten good years till today where lots of remediation techniques progressively employed to improve Taiwan the soil and groundwater resource quality. Regulatory agencies, academia, remediation consulting firms, on-site professional engineers all contribute the proud ten years in terms of the soil and groundwater clean-up contribution. However, some of technologies were unenvironmental friendly even detrimental and damage to Taiwan precious the soil and groundwater resources. In Article one of the current Taiwan the soil and groundwater Act, it clearly stated which the soil is a precious nature resources. The soil definitely is not a waste, shame on us most of current most commonly employed remediation are unlawful and merely aiming to save time and money consideration without any care to our land. Dig-and-dump and the soil acid washing are damage employed in almost every single local environment agency the soil clean-up project. Lot of money, effort and time has been spent during past ten years. Most of the spending is not improving the soil quality.

It is really confusing regarding the lesson learned and gained while used these chemical physical, not environmental friendly treatment techniques. Two remediation approaches, namely dig-and-dump and the soil acid washing simply treat the soil as garbage, waste, and junk, not the soil law indicated the soil is a resource. The purpose of this paper is aimed to raise all you concerns and care toward our precious the soil property, toward remediation engineers and particularly those governmental authorities who have so far never taken it as deep thought of current serious situation regarding the soil damage.

A novel green remediation approach intends to convey in this paper by employing plant to gradually reduce the soil metal contamination through several rounds of planting and harvesting. Unlike phytoextraction, the phytoattenuation aims to reduce the soil metal pollution in a gradually and less aggressive approach such as chelator assisted remediation. The initial pollution level generally is lower than most the soil contamination sites. Therefore, plant is easier to propagate to increase biomass inducing reliable metal uptake. The conceptual model is shown in figure1.

Figure 1: The conceptual model of plant propagation.

Attenuation is borrowing from the concept “natural attenuation” which has been commonly proposed as a remediation approach for organic pollutants such as DNAPL (dense non-aqueous liquid) solvent TCE (tri-chloro ethylene) and PCE (tetra-chloro ethylene) or LNAPL (light non-aqueous liquid) petroleum product BTEX (benzene, toluene, ethyl benzene, and xylene. Natural attenuation mainly used natural pollution mitigation mechanism including microbial degradation, adsorption, volatilization, etc. This approach is targeted to pollutant which is not degraded in a reasonable time using conventional remediation techniques, technical imperfectability, or the cost beyond the affordable monetary amounts, economical imperfectability.

Cu is used as the fodder additives for preventing swine diarrhea and skin abrasion. Cu has been reported the toxicity to phytoplankton and been employed as algaecide for serious eutrophication mitigation. The careless management of Cu wastewater from swine industries could damage the water and the soil environment. The choice of plant is more flexible than pytoextration. Plant is not necessary to be a hyper accumulator and biomass production is not required to be enormous. Using several sessions of agricultural planting and harvesting, the metal contamination is gradually to reduce to an acceptable the soil background concentration. The only concern is the time requirement for the whole attenuation operation. If the site has the emergent health and ecological damage concern, the aggressive remediation takes into the substation list to be conducted to ensure public health and ecological protection.

Possible ideal plants include wetland water pollution mitigation the macrophytes such as the vetiver, the cattail, and the reed which has been demonstrated to be easily propagation and capable to reduce water and sediment metal levels. The harvested plant wastes should be properly managed to prevent the secondary environmental contamination. An alternative plant is the energy macrophytes such as sunflower and Chinese cabbage. After harvesting, the residue plant can be reused to produce bio-fuel which is green and substitute to petroleum fuels to lesson current energy concern.

Vetiver is known for its effectiveness in the soil erosion control due to its unique morphological and physiological characteristics. Vetiver is also a high biomass plant with remarkable photosynthetic efficiency which renders it tolerant against various harsh environmental conditions. Vetiver with deep-rooted and higher water-use can effectively stabilize soluble metals in the soils. These properties enable vetiver to be an ideal candidate for the phytoattenuation and have been investigated in the study. Sunflower (Helianthus annuus) is a fastgrowing crop which has been commonly used for phytoextraction of metal contaminated the soils. Sunflower has the potential as biofuel to become the substitute of fossil fuels, especially the increasing oil prize in recent years. The higher biomass production of sunflower, contribute them being the candidates of phytoextration contaminant and then harvested as potential fuel substitution.

The biostimulator has been facilitated the plant growth enhancement and been employed for agricultural operation. The stimulators can be borrowed to enhance the vetiver propagation leading to expect the phytoattenuation purpose. Two biostimlators, namely Gibberellic Acid (GA3) and Indol-3-Acetic Acid (IAA), were tested to evaluate vetiver metal attenuation enhancement. In recent year, lots of researches related to the phytoextration have been conducted. The metal removal results were very optimistic the most updater researched results are shown in table 1. Few if any study was focused on the biostimulator assisted the phytoattenuation. The objectives of this study were aimed to observe the planting and harvesting attenuation cycles were required to achieve feasible the soil metal levels. The effects of the biostimulators, GA3 and IAA were also scrutinized to reveal the stimulator effect.

Table 1: Different state of copper concentration (mg/kg).

Materials and Methods

Plant, the biostimulators, and the soil preparation

Vetiver and sunflower were collected from the University of Kaohsiung campus wetlands (22°73’N, 120°28’E) pre cultured for 5 days and carefully washed with distilled water. Plant samples were dried at 103°C in an oven until completely dried.

Harvested Plant tissue and final the soil metal content analysis

Plant after last session of operation was harvested, carefully washed, and air dried for metal analysis. Plant samples were dried at 103°C in an oven until completely dried. Dried plant samples were divided into root and shoot for metal accumulation assessment. These pretreated plants were digested in a solution containing 11:1 HNO3: HCl solution via a microwave digestion apparatus (Mars 230/60, CEM Corporation) and diluted to 100 mL with the deionized water. 0.2 g of dried the soil adding aquaregia rending for microwave digestion and 2.5g of dried for sequential extraction experiments. Metals analyses were conducted via an atomic absorption spectrophotometry (AAS, Perkin Elmer).

The fractionation of the soil retained metal was investigated by a sequential extraction technique where the soil samples were placed in a plastic bottle then shaking for proper mixing overnight and subjected to a five-step serial extraction procedure. The procedure of sequential chemical extraction used in this study includes a series of reagents which represented as exchangeable (1 M KNO3), inorganically bound (0.5 M KF), organically bound (0.1 M Na4P2O7), Fe and Mn-oxide bound (0.3 M Na3C6H5O7, 1 M NaHCO3 and 0.5 g Na2S2O4), and sulfide (6 M HNO3) forms, respectively.

Data and statistical analysis

Data were evaluated relative to the control to understand their statistical variation. Metal concentration of plants was recorded as mg of metal per kilogram of dry biomass. A triplicate of the soil and plant samples from each treatment were recorded and used for statistical analyses. Statistical significance was assessed using mean comparison test. Differences between treatment concentration means of parameters were determined by Student’s t test. A level of p < 0.05 considered statistically significant was used in all comparisons. Means are reported mean ± standard deviation. All statistical analyses were performed with Microsoft Office EXCEL 2003.

Results and Discussion

Background the soil concentration including total metal and metal fractionation

The total metal analysis and sequential extraction results after application the chelators are shown in figure 2.

Figure 2: Cu concentration (mg/kg) in different parts of vetiver and sunflower.

The sequential extraction results can be used to depict metal mobility. Generally, the latter three fractions, namely organic, Fe-and Mn-hydroxide, and sulfide are more inert, permanently bound to the soils, and less bioavailable while first two fractions including exchangeable and inorganic have been defined as loosely bound.

The vetiver propagation enhancement and Cu the soil reduction

IAA and GA3 both performed satisfactory vetiver growth enhancement relative to control. GA3 generally possessed better propagation upgrade than IAA. Both biostimulator could employ for the vetiver growth increase which is the merit for further plant uptake. Biostimulators commonly employed in agricultural amendment to enhance produce propagation. Appling in contaminated site mitigation was unpresedent and the results were optimistic. The price the addition the biostimulator needs to further evaluate.

The phytoattenuation evaluation

The results of the attenuation study using the vetiver and two stimulators have demonstrated prominent success. After 4 cycles of planting and harvesting Cu levels had demonstrated gradually metal decreasing. The control, the stimulator, and stimulator remaining copper levers were progressingly decended. These results were very effective and indicted which the phytoattenuation can be a green alternative to mitigate the soil metal contamination with or without the biostimulator assistant.

The phytoattenuation evaluation

Four stage of the phytoattenuation observation demonstrated positive medium to low contaminated level the soil mitigation which can be used for further similar site application. The phytoattenuation though is not effective for high level metal contamination while it is environmental friendly without using dig-and-dump rather EDTA the chelation enhancing expected to be well received worldwide.

PCR analysis

Technologies include: gene probes, the microarrays, and conventional and real-time polymerase chain reaction (PCR), whole genome amplification, sequencing, comparative genomics, and metagenomics. Together these proved unprecedented ability to interrogate the microbial world.

Detection of a specific gene target has become routine practice in most molecular laboratories. The ability to analyze 16S rRNA gene sequence using PCR has resulted in a virtual eaploprerfomeed sample with prior DNA extract from environmental sample. PCR has revolutionized the ability of researches to detect specific nucleic nuclear acid sequences in isolated as well in environmental samples. PCR is extremely sanative able in some cased o detect a single target molecule. PCR assay has been optimized; it is relative fast to get results in only a few hours, to several days or weeks which may be necessary for cultural methods.

• Surface monitoring

• EDX

• SEM

• FTIR

Conclusion

Vetiver has been demonstrated as valid plant for the phytoattenuation ideal plant due to it is great biomass prorogation and metal prominent uptake. This study has demonstrated after several sessions of vetiver planting and harvesting. Biostimulators, GA3 and IAA, have demonstrated effective plant propagation enhancement. Cu descending levels were statistically significant relative to the control. The soil metal level reduction achieved acceptable levels. More rounds of planting and harvesting, the soil metal concentrations expected to be much lessoned in real sites. Green remediation concepts such as the phytoattenuation and phytoextration need to be taken as serious concern.