Phytoremediation of petroleum hydrocarbons in tropical coastal soils II. microbial response to plant roots and contaminant

GOAL, SCOPE AND BACKGROUND: The goal of this study was to understand the interaction between plants and microorganisms during petroleum-hydrocarbon bioremediation in Pacific Islands coastal soils. Total bacteria and hydrocarbon-degrading microorganisms population dyanamics were examined in the rhizospheres of tropical trees and shrubs, which were evaluated for their phytoremediation potential in a greenhouse experiment. The respective and combined effects of plant roots and diesel contaminant on the microbial populations were determined in relation to diesel fuel depletion. An increase in the grading populations size of the hydrocarbon-degrading populations of microbes, elicited by rhizodeposition, is generally regarded as conducive to an enhanced degradation of petroleum hydrocarbon pollutants in vegetated soil. METHODS: The soil was a coastal sandy loam (pH 7.8) which was artificially contaminated with 10 g of No. 2 diesel fuel/kg soil or left uncontaminated. The pots were irrigated with fertilizer and 1% NaCl. The enumerations were carried out in the contaminated and uncontaminated rhizospheres of three trees, kiawe (Prosopis pallida), milo (Thespesia populnea), and kou (Cordia subcordata) and three shrubs, beach naupaka (Scaevola sericea), false sandalwood (Myoporum sandwicense), and oleander (Nerium oleander). Unplanted control soils were included in the experiment. Total bacteria and phenanthrene-degrading bacteria were enumerated on plates. Diesel- and pristane-degrading microorganisms were enumerated by the most-probable-number technique in tissue-culture plates. RESULTS AND DISCUSSION: All four types of microorganisms responded to the rhizosphere of the 6 plants in uncontaminated soil and to the diesel contaminant in unplanted soil. In contaminated rhizospheres, no effect of the plant on the hydrocarbon-degrader numbers was visible. Total bacteria responded more to the plant roots than to the contaminant. The phenanthrene-degrading bacteria and pristane-degrading microorganisms were more influenced by the contaminant than by the plants. The diesel-degrading microorganisms were equally stimulated by the plants and the contaminant. The numbers of hydrocarbon degraders were similar in the contaminated rhizospheres of the three effective plants (kiawe, kou, and milo) and in those of the three ineffective shrubs. CONCLUSION: The results suggest the quality of the rhizodeposition is plant-dependent and governs the type of diesel-degrader populations that will be enhanced by a given plant. RECOMMENDATIONS AND OUTLOOK: In the proposed phytoremediation-benefit model plant roots maintain high levels of hydrocaron degraders in uncontaminated soil. When the root enters a contaminated zone of soil, those hydrocarbon degraders that prefer the contaminant would switch to the contaminant as a carbon source, effectively removing the hydrocarbons. If the root exudates and the contaminant are equally attractive to the hydrocarbon degraders, the contaminant degradaton would be less effective.     

Bioremediation of a soil contaminated by hydrocarbon mixtures: the residual concentration problem

The phenomenon of residual concentration was investigated in the aerobic biodegradation of three different petroleum commercial products (i.e., kerosene, diesel fuel and a lubricating mineral oil) in static microcosms. Two different soils exhibiting different physical-chemical characteristics were used (i.e., a biologically treated hydrocarbon-contaminated soil and a pristine soil). Residual concentrations were observed and a simple way to take this phenomenon into account was proposed.     

Age-dating Diesel Fuel Spills: Using the European Empirical Time-based Model in the U.S.A.

In 1993, a paper was published by Christensen and Larsen that offered a method for determining the age of diesel oil spills in soil (Christensen and Larsen, 1993 Ground Water Mount. R . Fall , 142-149). It presented an empirical time-based model of the degradation of diesel fuel in soils using chemical data gathered at petroleum release sites in Denmark and the Netherlands. Now, evaluation of the validity of the application of this work to subsurface petroleum releases in other countries remains. In the U.S.A., investigations assessing date(s) of release of diesel fuel in soils, e.g. age dating of subsurface petroleum contamination, have considerable interest. Litigation-driven scientific investigations with accompanying expert testimony in a court of law are underway. The number of instances where application of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties is growing in the U.S.A. This paper presents two case studies which evaluate the applicability of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties in general. It illustrates the approach using gas chromatographic data from two recently-completed projects evaluating the applicability of the Christensen and Larsen model to a No. 2 fuel oil/diesel fuel surface spill in the U.S.A. Results showed that the application of the model to petroleum-contaminated soils was scientifically valid, provided its applicability was evaluated using hypothesis testing for specific changes in the characteristics of the petroleum hydrocarbon distribution in a number of soil samples collected over time at one site. The paper offers observations on the application of the Christensen and Larsen model to petroleum found in the light non-aqueous phase liquid (LNAPL) phase and groundwater.     

Age-dating Diesel Fuel Spills: Using the European Empirical Time-based Model in the U.S.A.

In 1993, a paper was published by Christensen and Larsen that offered a method for determining the age of diesel oil spills in soil (7Ground Water Mount.R . Fall, 142–149). It presented an empirical time-based model of the degradation of diesel fuel in soils using chemical data gathered at petroleum release sites in Denmark and the Netherlands. Now, evaluation of the validity of the application of this work to subsurface petroleum releases in other countries remains.In the U.S.A., investigations assessing date(s) of release of diesel fuel in soils, e.g. age dating of subsurface petroleum contamination, have considerable interest. Litigation-driven scientific investigations with accompanying expert testimony in a court of law are underway. The number of instances where application of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties is growing in the U.S.A.This paper presents two case studies which evaluate the applicability of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties in general. It illustrates the approach using gas chromatographic data from two recently-completed projects evaluating the applicability of the Christensen and Larsen model to a No. 2 fuel oil/diesel fuel surface spill in the U.S.A. Results showed that the application of the model to petroleum-contaminated soils was scientifically valid, provided its applicability was evaluated using hypothesis testing for specific changes in the characteristics of the petroleum hydrocarbon distribution in a number of soil samples collected over time at one site. The paper offers observations on the application of the Christensen and Larsen model to petroleum found in the light non-aqueous phase liquid (LNAPL) phase and groundwater.     

Improvement of the hydrocarbon phytoremediation rate by Cyperus laxus Lam. inoculated with a microbial consortium in a model system

Hydrocarbon phytoremediation by Cyperus laxus Lam. growing on perlite and inoculated with hydrocarbon-degrading microorganisms was evaluated. Total petroleum hydrocarbons (TPH) were extracted from weathered soil (60.7 g of TPH kg(-1) of dry soil) and spiked on perlite at initial concentration of 5 g of TPH kg(-1) of dry perlite. Phenological characteristics, total microbial viable counts, hydrocarbon degraders and residual hydrocarbons were determined through 180 days of culture. Phenological characteristics of inoculated plants were improved as compared with non-inoculated plants: root biomass was 1.6 times greater, flowering time was reduced (13%), and the number of inflorescences was 1.5 times higher. The rhizospheric bacterial and fungi counts were higher for planted treatments (inoculated and not inoculated) than for unplanted pots. The maximum phytoremediation rate (0.51 mg of TPH g(-1) of dry plant d(-1)) for inoculated plants was reached at 60 days of culture, and was two times higher than for non-inoculated plants (55% TPH removal). Similar hydrocarbon phytoremediation extent values for inoculated (90%) and non-inoculated (85%) plants were obtained at 180 days of culture. The present study demonstrated that mutual benefits between C. laxus and inoculated hydrocarbon-degrading microorganisms are improved during phytoremediation. It is pertinent to note that this is the first report of hydrocarbon phytoremediation by Cyperus laxus Lam., a native plant growing in highly contaminated swamps.     

Phytoremediation of petroleum hydrocarbons in tropical coastal soils II. microbial response to plant roots and contaminant

Goal, Scope and Background.  The goal of this study was to understand the interaction between plants and microorganisms during petroleum-hydrocarbon bioremediation in Pacific Islands coastal soils. Total bacteria and hydrocarbon-degrading microorganisms population dynamics were examined in the rhizospheres of tropical trees and shrubs, which were evaluated for their phytoremediation potential in a greenhouse experiment. The respective and combined effects of plant roots and diesel contaminant on the microbial populations were determined in relation to diesel fuel depletion. An increase in the size of the hydrocarbon-degrading populations of microbes, elicited by rhizodeposition, is generally regarded as conducive to an enhanced degradation of petroleum hydrocarbon polutants in veaetated soil. Conclusion  The results suggest the quality of the rhizodeposition is plant-dependent and governs the type of diesel-degrader populations that will be enhanced by a given plant. Recommendations and Outlook  In the proposed phytoremediation-benefit model plant roots maintain high levels of hydrocarbon de-graders in uncontaminated soil. When the root enters a contaminated zone of soil, those hydrocarbon degraders that prefer the contaminant would switch to the contaminant as a carbon source, effectively removing the hydrocarbons. If the root exudates and the contaminant are equally attractive to the hydrocarbon degraders, the contaminant degradation would be less effective.     

Influence of diesel fuel on seed germination

The use of plant-based systems to remediate contaminated soils has become an area of intense scientific study in recent years and it is apparent that plants which grow well in contaminated soils need to be identified and screened for use in phytoremediation technologies. This study investigated the effect of diesel fuel on germination of selected plant species. Germination response varied greatly with plant species and was species specific, as members of the same plant family showed differential sensitivity to diesel fuel contamination. Differences were also seen within plant subspecies. At relatively low levels of diesel fuel contamination, delayed seed emergence and reduced percentage germination was observed for the majority of plant species investigated. Results suggest the volatile fraction of diesel fuel played an influential role in delaying seed emergence and reducing percentage germination. In addition, the remaining diesel fuel in the soil added to this inhibitory effect on germination by physically impeding water and oxygen transfer between the seed and the surrounding soil environment, thus hindering the germination response.     

Phytoremediation in the tropics--influence of heavy crude oil on root morphological characteristics of graminoids

When studying species for phytoremediation of petroleum-contaminated soils, one of the main traits is the root zone where enhanced petroleum degradation takes place. Root morphological characteristics of three tropical graminoids were studied. Specific root length (SRL), surface area, volume and average root diameter (ARD) of plants grown in crude oil-contaminated and uncontaminated soil were compared. Brachiaria brizantha and Cyperus aggregatus showed coarser roots in polluted soil compared to the control as expressed in an increased ARD. B. brizantha had a significantly larger specific root surface area in contaminated soil. Additionally, a shift of SRL and surface area per diameter class towards higher diameters was found. Oil contamination also caused a significantly smaller SRL and surface area in the finest diameter class of C. aggregatus. The root structure of Eleusine indica was not significantly affected by crude oil. Higher specific root surface area was related to higher degradation of petroleum hydrocarbons found in previous studies.     

The effects of perennial ryegrass and alfalfa on microbial abundance and diversity in petroleum contaminated soil

Enhanced rhizosphere degradation uses plants to stimulate the rhizosphere microbial community to degrade organic contaminants. We measured changes in microbial communities caused by the addition of two species of plants in a soil contaminated with 31,000 ppm of total petroleum hydrocarbons. Perennial ryegrass and/or alfalfa increased the number of rhizosphere bacteria in the hydrocarbon-contaminated soil. These plants also increased the number of bacteria capable of petroleum degradation as estimated by the most probable number (MPN) method. Eco-Biolog plates did not detect changes in metabolic diversity between bulk and rhizosphere samples but denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified partial 16S rDNA sequences indicated a shift in the bacterial community in the rhizosphere samples. Dice coefficient matrices derived from DGGE profiles showed similarities between the rhizospheres of alfalfa and perennial ryegrass/alfalfa mixture in the contaminated soil at week seven. Perennial ryegrass and perennial ryegrass/alfalfa mixture caused the greatest change in the rhizosphere bacterial community as determined by DGGE analysis. We concluded that plants altered the microbial population; these changes were plant-specific and could contribute to degradation of petroleum hydrocarbons in contaminated soil.     

Effects of in-situ ozonation on indigenous microorganisms in diesel contaminated soil: survival and regrowth

Soil column experiments were conducted to investigate the effects of chemical oxidation on the survival of indigenous microbes (i.e., heterotrophic microbes, phenanthrene-degrading microbes, and alkane-degrading microbes) for field soil contaminated with diesel fuel. Rapid decreases of total petroleum hydrocarbons (TPH) and aromatics of diesel fuel were observed within the first 60 min of ozone injection; after 60 min, TPH and aromatics decreased asymptotically with ozonation time. The three types of indigenous microbes treated were very sensitive to ozone in the soil column experiment, hence the microbial population decreased exponentially with ozonation time. The numbers of heterotrophic, alkane-degrading, and phenanthrene-degrading bacteria were reduced from 10(8) to 10(4), 10(7) to 10(3), and 10(6) CFU g soil(-1) to below detection limit after 900 min of ozonation, respectively. Except for the soil sample ozonated for 900 min, incubation of ozone-treated soil samples that were not limited by oxygen diffusion showed further removal of TPH. The soil samples that were ozonated for 180 min exhibited the lowest concentration of TPH and the highest regrowth rate of the heterotrophic and alkane-degrading populations after the 9 weeks of incubation.     

陕北黄土区土壤石油污染物对玉米生长影响研究

为研究陕北黄土区土壤石油污染物对玉米种子出苗率和幼苗生长的影响,采用盆栽试验的方法,设置土壤不同石油浓度处理组,培养玉米2个月,测定了各处理组玉米的出苗率、株高、茎宽、生物量和叶片叶绿素浓度.结果表明:(1)土壤石油质量浓度即使为30 g/kg时,各处理组出苗率最终均为100％;土壤石油质量浓度达到20 g/kg及以上时,在一定程度上会推迟玉米种子的出苗时间.(2)土壤石油质量浓度达到1 g/kg就会对玉米茎的生长产生抑制作用,可以显著降低玉米株高,但对玉米茎宽影响不显著.随着土壤石油浓度的升高,对玉米株高的抑制作用显著增加.玉米茎宽总体上是随着土壤石油浓度的升高而减小,但土壤石油质量浓度为0～1g/kg或20～30 g/kg时,玉米茎宽没有显著差异.(3)当土壤石油质量浓度达到5 g/kg以上时,植株干质量随石油浓度升高而减少.土壤石油质量浓度达到20 g/kg时,会显著降低玉米根的含水率;达到30 g/kg时,会显著降低茎和叶的含水率.(4)土壤石油质量浓度为1、5 g/kg时,叶绿素a和叶绿素b浓度与土壤石油质量浓度为0 g/kg时没有显著差异;土壤石油质量浓度为10、20、30 g/kg时,叶绿素a和叶绿素b浓度显著低于土壤石油质量浓度为0 g/kg时,并且随土壤石油浓度的升高呈降低趋势.     

The potential of Thai indigenous plant species for the phytoremediation of arsenic contaminated land

To assess the potential of the native plant species for phytoremediation, plant and soil samples were collected from two areas in Thailand that have histories of arsenic pollution from mine tailings. The areas were the Ron Phibun District (Nakorn Si Thammarat province) and Bannang Sata District (Yala province), and samples were taken in 1998 and 1999 and analysed for total arsenic by atomic absorption spectrophotometry. Arsenic concentrations in soil ranged from 21 to 14,000 microg g(-1) in Ron Phibun, and from 540 to 16,000 microg g(-1) in Bannang Sata. The criteria used for selecting plants for phytoremediation were: high As tolerance, high bioaccumulation factor, short life cycle, high propagation rate, wide distribution and large shoot biomass. Of 36 plant species, only two species of ferns (Pityrogramma calomelanos and Pteris vittata), a herb (Mimosa pudica), and a shrub (Melastoma malabrathricum), seemed suitable for phytoremediation. The ferns were by far the most proficient plants at accumulating arsenic from soil, attaining concentrations of up to 8350 microg g(-1) (dry mass) in the frond.     

Short-term effects of diesel fuel on rhizosphere microbial community structure of native plants in Yangtze estuarine wetland

Purpose

In this work, short-term effects of diesel fuel on Huangpu?CYangtze estuarine wetland soil microbial community structure were studied under simulated conditions through phospholipid fatty acids (PLFAs) analysis. Four native plant species, bulrush (Scirpus tripueter), galingale (Cyperus rotundus), wildrice (Zizania latifolia), and reed (Phragmites australis) were tested in the experiments.

Method

In the pot experiment, 20?g rhizosphere soils were mixed with 20?g diesel-blended soils. The concentration of total petroleum hydrocarbon was 16,000?mg/kg. All pots were incubated for 14?days in dark at 28°C and watered with 12?mL sterile distilled water to keep a liquid level. Microbial activity of the samples was assessed by hydrolysis of fluorescein diacetate. Measurements of soil PLFAs and analysis on gas chromatography were performed.

Results

The microbial activity in the samples of reed was highest after the exposure. In all samples, the common PLFA was straight-chain saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA). After the exposure the relative abundance of MUFA and polyunsaturated fatty acid decreased by 20%, and the relative abundance of straight-chain SFA increased by 20%. The results of diversity and PCA indicated that the effect of diesel pollutant on the microbial community was far stronger than the root effect and the reed roots enhanced the tolerance of soil microorganisms to diesel significantly.

Conclusions

All results showed that the soil microbial community structure differed significantly with the exposure to diesel. In reed rhizosphere, the soil microorganisms exhibited a strong resistance to diesel fuel. It confirmed that the root of reed improved the biodegradation ability of soil microorganisms for diesel pollutants and they could be reasonably matched to cure and restore the ecological environment of oil-contaminated wetlands.     

Influence of modified soils on the removal of diesel fuel oil from water and the growth of oil degradation micro-organism

Three soils were modified with two kinds of cationic surfactants in order to increase their sorptive capabilities for organic contaminants. Sorption of diesel fuel oil in water by these modified soils had been investigated. Modified soils can effectively sorb diesel fuel oil from water. The sorption capability of modified soils is: HDTMA-black soil > HDTMA-yellow brown soil > HDTMA-red soil > TMA-black soil > TMA-yellow brown soil > TMA-red soil. Sorption of diesel fuel oil by natural soils and HDTMA modified soils is via partition, the sorption isotherms can be expressed by Henry equation, and logK(SOM) is 2.42-2.80, logK(HDTMA) is 3.37-3.60. Sorption isotherms of TMA modified soils can be expressed by Langmuir equation, the saturation sorption capacities are 1150 (TMA-black soil), 750 (TMA-yellow-brown soil), 171 mg/kg (TMA-red soil), respectively. A diesel fuel oil degradation micro-organism (Pseudomonas sp.) was isolated in the lab. To test the influence of the modified soils on the micro-organism, various growth curves of Pseudomonas in different conditions were drawn. Pseudomonas can grow very well with natural soils and TMA modified soils. The acclimation period of Pseudomonas is reduced. As to HDTMA modified soils, HDTMA loading amount is very important. When HDTMA loading amount is no higher than 0.5 CEC, the micro-organism can grow very well after a long acclimation period.     

Ectomycorrhizas impede phytoremediation of polycyclic aromatic hydrocarbons (PAHs) both within and beyond the rhizosphere

Exploitation of mycorrhizas to enhance phytoremediation of organic pollutants has received attention recently due to their positive effects on establishment of plants in polluted soils. Some evidence exist that ectomycorrhizas enhance the degradation of pollutants of low recalcitrance, while less easily degradable polyaromatic molecules have been degraded only by some of these fungi in vitro. Natural polyaromatic (humic) substances are degraded more slowly in soil where ectomycorrhizal fungi are present, thus phytoremediation of recalcitrant pollutants may not benefit from the presence of these fungi. Using a soil spiked with three polycyclic aromatic hydrocarbons (PAHs) and an industrially polluted soil (1 g kg(-1) of summation operator12 PAHs), we show that the ectomycorrhizal fungus Suillus bovinus, forming hydrophobic mycelium in soil that would easily enter into contact with hydrophobic pollutants, impedes rather than promotes PAH degradation. This result is likely to be a nutrient depletion effect caused by fungal scavenging of mineral nutrients.     

Field Detector Evaluation of Organic Clay Soils Contaminated with Diesel Fuel

Due to numerous types of uncontrolled petroleum releases into the environment such as leaking storage tanks, spills, and improper disposal of petroleum wastes, there is a need for quicker, more efficient methods to determine the levels of soil contamination for site remediation. The portable field detectors used most often in preliminary site evaluations are the flame ionization detector (FID) and the photoionization detector (PID). This research explored the relationship between these two instruments in analysis of two clay soil sites contaminated with diesel fuel. As in previous research, a log-log linear correlation was found between the PID and FID instruments for diesel fuel-contaminated soil at each site (R 2 > 0.91). Also, the correlation factors (0.64 and 0.60) between the field instruments at each site were found to be similar. It was asserted that either field instrument can be used to delineate the diesel fuel contamination at that site based upon a previously calculated correlation between the two instruments, and an overall numerical correlation between the field instruments can be used at various sites of similar soil and contamination characteristics. The implementation of the relationships between these two instruments could facilitate and accelerate site characterization in the future.     

加油站场地油品渗漏探测及土壤污染评估

用洛阳铲采集某地区10座地下贮罐罐龄接近或超过10年的典型加油站场地不同深度土样,并分别用吹脱/捕集/热脱附/气相色谱法和快速溶剂萃取/硅酸镁净化/气相色谱法分析样品中的挥发性和萃取性石油烃,发现2座加油站疑似油品渗漏,其中1座为柴油渗漏,地下贮罐附近1.2 ～3.0 m深度土壤总石油烃含量16.1 ～24.6 g/kg,均超过荷兰土壤清除标准,另1座为汽油和柴油混合渗漏,其地下贮罐附近2.4m深度土壤总石油烃含量较高,但未超标.个别加油站场地较高的土壤天然有机物背景值可能计入EPH的分析结果,但其色谱指纹明显不同于石油烃.     

The influence of association of plant growth-promoting rhizobacteria and zero-valent iron nanoparticles on removal of antimony from soil by Trifolium repens

Using association of plants, nanomaterials, and plant growth-promoting bacteria (PGPR) is a novel approach in remediation of heavy metal-contaminated soils. Co-application of nanoscale zerovalent iron (nZVI) and PGPR to promote phytoremediation of Sb-contaminated soil was investigated in this study. Seedlings of Trifolium repens were exposed to different regimes of nZVI (0, 150, 300, 500, and 1000 mg/kg) and the PGPR, separately and in combination, to investigate the effects on plant growth, Sb uptake, and accumulation and physiological response of the plant in contaminated soil. Co-application of nZVI and PGPR had positive effects on plant establishment and growth in contaminated soil. Greater accumulation of Sb in the shoots compared to the roots of T. repens was observed in all treatments. Using nZVI significantly increased accumulation capacity of T. repens for Sb with the greatest accumulation capacity of 3896.4 μg per pot gained in the “PGPR+500 mg/kg nZVI” treatment. Adverse impacts of using 1000 mg/kg nZVI were found on plant growth and phytoremediation performance. Significant beneficial effect of integrated use of nZVI and PGPR on plant photosynthesis was detected. Co-application of nZVI and PGPR could reduce the required amounts of nZVI for successful phytoremediation of metalloid polluted soils. Intelligent uses of plants in accompany with nanomaterials and PGPR have great application prospects in removal of antimony from soil.

     

Bioremediation of oil-contaminated soil using Candida catenulata and food waste

Even though petroleum-degrading microorganisms are widely distributed in soil and water, they may not be present in sufficient numbers to achieve contaminant remediation. In such cases, it may be useful to inoculate the polluted area with highly effective petroleum-degrading microbial strains to augment the exiting ones. In order to identify a microbial strain for bioaugmentation of oil-contaminated soil, we isolated a microbial strain with high emulsification and petroleum hydrocarbon degradation efficiency of diesel fuel in culture. The efficacy of the isolated microbial strain, identified as Candida catenulata CM1, was further evaluated during composting of a mixture containing 23% food waste and 77% diesel-contaminated soil including 2% (w/w) diesel. After 13 days of composting, 84% of the initial petroleum hydrocarbon was degraded in composting mixes containing a powdered form of CM1 (CM1-solid), compared with 48% of removal ratio in control reactor without inoculum. This finding suggests that CM1 is a viable microbial strain for bioremediation of oil-contaminated soil with food waste through composting processes.     

Phytoremediation potentials of selected tropical plants for Ethidium bromide

Background, Aims and Scope Research and development has its own benefits and inconveniences. One of the inconveniences is the generation of enormous quantity of diverse toxic and hazardous wastes and its eventual contamination to soil and groundwater resources. Ethidium bromide (EtBr) is one of the commonly used substances in molecular biology experiments. It is highly mutagenic and moderately toxic substance used in DNA-staining during electrophoresis. Interest in phytoremediation as a method to solve chemical contamination has been growing rapidly in recent years. The technology has been utilized to clean up soil and groundwater from heavy metals and other toxic organic compounds in many countries like the United States, Russia, and most of European countries. Phytoremediation requires somewhat limited resources and very useful in treating wide variety of environmental contaminants. This study aimed to assess the potential of selected tropical plants as phytoremediators of EtBr. Materials and Methods This study used tomato (Solanum lycopersicum), mustard (Brassica alba), vetivergrass (Vetiveria zizanioedes), cogongrass (Imperata cylindrica), carabaograss (Paspalum conjugatum), and talahib (Saccharum spontaneum) to remove EtBr from laboratory wastes. The six tropical plants were planted in individual plastic bags containing soil and 10% EtBr-stained agarose gel. The plants were allowed to establish and grow in soil for 30 days. Ethidium bromide content of the test plants and the soil were analyzed before and after soil treatment. Ethidium bromide contents of the plants and soils were analyzed using an UV VIS spectrophotometer. Results Results showed a highly significant (p≤0.001) difference in the ability of the tropical plants to absorb EtBr from soils. Mustard registered the highest absorption of EtBr (1.4±0.12 μg kg⁻¹) followed by tomato and vetivergrass with average uptake of 1.0±0.23 and 0.7±0.17 μg kg⁻¹ EtBr, respectively. Cogongrass, talahib, and carabaograss had the least amount of EtBr absorbed (0.2±0.6 μg kg⁻¹). Ethidium bromide content of soil planted to mustard was reduced by 10.7%. This was followed by tomato with an average reduction of 8.1%. Only 5.6% reduction was obtained from soils planted to vetivergrass. Soils planted to cogongrass, talahib, and carabaograss had the least reduction of 1.52% from its initial EtBr content. Discussion In this study, mustard, tomato, and vetivergrass have shown their ability to absorb EtBr from contaminated soil keeping them from expanding their reach into the environment and preventing further contamination. Its downside, however, is that living creatures including humans, fish, and birds, must be prevented from eating the plants that utilized these substances. Nonetheless, it is still easier to isolate, cut down, and remove plants growing on the surface of the contaminated matrices, than to use strong acids and permanganates to chemically neutralize a dangerous process that can further contaminate the environment and pose additional risks to humans. Though this alternative method does not totally eliminate eventual environmental contamination, it is by far produces extremely insignificant amount of by-products compared with the existing processes and technologies. Conclusions Mustard had the highest potential as phytoremediator of EtBr in soil. However, the absorption capabilities of the other test plants may also be considered in terms of period of maturity and productivity. Recommendations and Perspectives It is recommended that a more detailed and complete investigation of the phytoremediation properties of the different plants tested should be conducted in actual field experiments. Plants should be exposed until they reach maturity to establish their maximum response to the toxicity and mutagenecity of EtBr and their maximum absorbing capabilities. Different plant parts should be analyzed individually to determine the movement and translocation of EtBr from soil to the tissues of plants. Since this study has established that some plants can thrive and dwell in EtBr-treated soil, an increased amount of EtBr application should be explored in future studies. It is suggested therefore that a larger, more comprehensive exploration of phytoremediation application in the management of toxic and hazardous wastes emanating from biotechnology research activities should be considered especially on the use of vetivergrass, a very promising tropical perennial grass. ESS-Submission Editor: Professor Zhihong Xu (zhihong.xu@griffith.edu.au: www.griffith.edu.au/centre/cfhr)