The interactive roles played between plants and microbes enhance rhizosphere development, which can be used for in situ bioremediation of toxic chemicals such as PCBs (polychlorinated biphenyls). We are currently evaluating Alfalfa (Medicago sativa) for PCB phytoremediation due to its extensive root system and nitrogen fixation capacity by nodulation. Alfalfa plants were grown in Leonard jars containing soil spiked with 100 ppm of 2, 3, 4-PCB and inoculated with either (a) E.coli (non-rhizospheric bacteria) engineered with the PCB biodegradation ohb genes, (b) Sinorhizobium meliloti (nitrogen-fixing, rhizospheric bacteria) engineered with the ohb genes, or (c) a mixed microbial consortia isolated from PCB impacted soils. After 6 weeks, plant shoots, roots, treated soils and water displayed undetectable levels of 2, 3, 4-PCB. However, alfalfa plants grown in soils inoculated with only the E.coli or Sinorhizobium meliloti GEMs showed reduced growth, possibly due to toxic PCB metabolite residues from incomplete mineralization. On the other hand, plants grown in soils inoculated with the mixed microbial consortia showed vigorous growth of roots and shoots and no apparent PCB metabolites. Therefore, we conclude that the microbial consortia accelerated PCB biodegradation through co-metabolism in the alfalfa rhizosphere. Ongoing research is underway to assay the phytotoxicity of the PCB metabolic byproducts observed in the single-inoculum treatments and to characterize the PCB-degrading rhizosphere consortia using 16S rDNA T-RFLP analyses.
Scientific and engineering investigations of alternative constructed wetland configurations are ongoing in locations across the United States to maximize the capacity of such wetlands to reduce concentrations of phosphorus, volatile organic compounds (VOCs), and metals. Two recent constructed wetland projects, one completed in Florida and another in Indiana, illustrate the unique applications of wetlands to address contamination from stormwater and groundwater sources.
A portion of the phosphorus-contaminated stormwater from the Village of Wellington, located in southeastern Florida, currently is pumped to the Loxahatchee National Wildlife Refuge near the Everglades. By 2006, stormwater discharges into the Everglades must meet a total phosphorus water quality standard of 10 micrograms per liter (µg/L). The Village conducted a treatment technology demonstration project to evaluate the benefits of placing constructed treatment wetland cells in series to promote optimal hydraulics and improved treatment performance. Two treatment trains were designed and built using data supporting constructed wetland design criteria for phosphorus removal. One treatment train consisted of a floating aquatic vegetation (FAV) cell, followed by an emergent aquatic vegetation (EAV) cell, followed by a periphyton-based stormwater treatment area (PSTA). The second treatment train consisted of an EAV cell, followed by a submerged aquatic vegetation (SAV) cell, followed by a PSTA. Water quality studies monitored treatment performance for a 1-year period. Treatment performance exceeded expectations, with influent concentrations of 300 to 400 µg/L of total phosphorus reduced to outflow concentrations of 10 to 15 µg/L. These engineering optimization efforts provided useful data needed to better understand the Village's options for achieving compliance with the Everglades Forever Act (EFA).
Mishawaka, Indiana, extends approximately 3,800 feet southwest of the landfill. A Remedial Action Plan has been implemented that involves capping the landfill, installing five groundwater extraction wells to contain the contaminant plume, and treating extracted groundwater using surface flow wetlands. The treatment wetland system has operated in start-up mode since May 2000. The average influent flow rate has been 360 gallons per minute. The most prevalent contaminant is trichloroethene (TCE). Preliminary results indicated that the treatment wetland system successfully removed TCE from the extracted groundwater; the average influent TCE concentration was 4 µg/L, and the average effluent TCE concentration was 1 µg/L. Monthly analytical results indicated that the treatment wetland system successfully decreased influent VOC concentrations to levels below detection limits (~1 µg/L). Arsenic concentrations for the wetland effluent were consistently below 5 µg/L. During the 2001-2002 monitoring year, wetland effluent concentrations for all contaminants of concern (COCs) were consistently below National Pollution Discharge Elimination System (NPDES) discharge limits established for nearby Juday Creek.
A demonstration project to test the equivalence of alternative landfill covers was established in 1998 at the Rocky Mountain Arsenal in Denver, CO. Four vegetative covers were planted to a mixture of grasses and forbs adapted to the region. The covers included two soil types and three soil depths for one of the soil types. A one-year performance test of these test covers was conducted from September 2000 (T0) through August 2001 (T1) to estimate leachate produced under conditions where natural precipitation was supplemented with irrigation to reach predetermined monthly goals. We assessed initial and final vegetation conditions to document changes in plant growth. To avoid disturbance of soil over lysimeter pans, vegetation was sampled in the buffer area to the north of the lysimeter pans. Soil was sampled in 15 cm intervals to the depth of each cover. At T1, additional samples were collected over lysimeter pans to determine if vegetation growth was different in the soil over the lysimeter pans. We estimated vegetation cover, plant species composition, aboveground biomass production, root biomass, root length density, and gravimetric soil moisture.
From T0 to T1, total plant coverage increased for all covers as might be expected with supplemental irrigation. Western wheatgrass was the dominant species followed by sideoats grama. At T1, the net number of species increased by two. A main objective of the growth analysis was to determine if root growth increased from T0 to T1. In buffer area samples, 24 of 32 soil cores showed an increase in root length density while 26 showed an increase in root mass from T0 to T1. A limited number of the differences were significant by t-test. Analysis of variance used to test for overall differences between T0 and T1 treatment means resulted in p-values of 0.034 for the test of root length differences between T0 and T1 and 0.075 for root mass. This analysis supported a general increase in root growth from T0 to T1. At T1, samples from the buffer area were compared to samples over lysimeter pans. Mean values from 24 of 32 cores showed higher root length density in the buffer soil and 27 cores showed higher root mass. Analysis of variance to test for overall differences between buffer and lysimeter means resulted in p-values of 0.105 for root length and 0.079 for root mass suggesting differences in growth in the two sample areas. Plant growth analysis showed that diverse prairie communities established on the alternative vegetative cover plots. Plants rooted to the full depth of the cover soils and rooting increased during a year with supplemental irrigation. There was evidence that plant growth may be affected by the presence of lysimeter pans used to collect leachate. Plant growth data can be useful for assessment of alternative landfill cover performance.
Leachate from a historical vegetation-capped landfill near a Teck Cominco lead zinc smelter in Trail, British Columbia contains high concentrations of zinc, cadmium and arsenic and has a pH ranging from 5.1 to 5.5. To evaluate an alternative treatment technology for the decontamination of the leachate, Nature Works Remediation Corporation was contracted by Teck Cominco to design and build a demonstration scale engineered wetland system. The single-train engineered wetland consists of six cells: two anaerobic bioreactors, followed by three horizontal sub-surface flow (HSSF) cells and a pond wetland cell. Pulp mill biosolids, mixed with sand and manure were used as carbon source for sulphate- and iron-reducing bacteria in the anaerobic bioreactors. HSSF cells were planted with Tripsicum dactyloides, Typha latifolia and Calamagrostis canadensis. The system was designed for 20,000 l/day, the mean flow rate was between 15,000 and 16,400 l/day.
Most of the metals were removed from the water in the two anaerobic bioreactors by microbially mediated precipitation as sulphides: 92.8% of arsenic, 98.0% of cadmium and 84.4% of zinc were removed in this way. After flowing through the HSSF cells and the pond wetland cell, the total metals removed were 98.1% of total Arsenic, 99.4% of total cadmium and 95.7 % of Zinc. The pH increased throughout the wetland system from around 5 to around 7 at the wetland outlet.
Data from this pilot study show that engineered wetland systems which have anaerobic bioreactors as components are very effective in removing metals from landfill leachate, even under winter conditions.
There is an increasing awareness in Turkey for solid waste problems particularly in cities further on scientific bases and on implications. Biological restoration is the main tool to control the environmental risks of solid waste disposal sites and to transfer these areas into nature. Being the 4th biggest city of Turkey, Sofulu solid waste disposal site is one of the main problem in Adana Environmental problems in Sofulu solid waste dumping area are; dispersion of wastes and pathogens around, direct touch/handling, unattractive smells, gases, leaking waters, stabilisation of wastes, visual pollution.
In order to minimize those negative effects there is an “upper surface covering” implication which helped to control waste dispersion and to minimize unattractive smell and as a result upper surface gas concentration have been lessened in considerable amount. But the bare surfaced areas are still open to erosion without any vegetation on. As long as plantation work is done without the most suitable species, the idea will stand on the agenda that planting implication will become unaffected by the erosion in a shorter term.
In the rehabilitation work and implications of Sofulu solid waste dumping area, there is very little research particularly for protecting by plant cover. As the species was chosen for the plantation without taking into account the local and the regional conditions and implication of the species without pre-experiments there is an obvious failure in the early rehabilitation works.
In this research Cynodon dactylon, Melilotus officinalis Lam., Inula viscosa, Thymbra spicata var spicata L., Althea rosea are chosen for plantation. During the one-year plants are irrigated with clean and leakage water at the drought weather conditions. As a conclusion Cynodon dactylon, Melilotus officinalis Lam, Althea rosea were succesful for rehabilitation of Sofulu disposal site. But Inula viscosa could not grow. We need one year more to say about Thymbra spicata var spicata.
Successful implementation and regulatory acceptance of phytoremediation strategies require fundamental study to identify process metabolites and kinetics to ensure adequate protection of human and environmental health. In support of this goal, experiments were conducted to measure uptake and metabolism of nucleophilic contaminants by aquatic plants. The model system contained simulated natural water, L. minor and associated microbes. In these studies, 2,4-di and 2,4,5-tri-chlorophenol were rapidly assimilated into plant tissues from surrounding media. Competing processes, i.e., photolysis and microbial transformation, were insignificant in accounting for observed removals. LC-MS studies of tissues extracts indicated three major metabolites in plant tissues. MS, NMR techniques were employed to identify metabolites of 2,4-dichlorophenol as 2,4-dichlorophenyl-D-glucopyranoside, 2,4-dichlorophenyl-(6-O-malonyl)-D-glucopyranoside and 2,4-dichlorophenyl-D-glucopyranosyl-b-D-apiofuranoside. Identical results were obtained with 2,4,5-trichlorophenol. Structures were confirmed by comparison to reference compounds synthesized in the laboratory. The identification of these compounds indicated that these contaminants were detoxified through storage in plant vacuoles (malonyl glycosides) and complex polysaccharides (apiosides). In no case were metabolites found in the surrounding media. Deliberate introduction of representative metabolites resulted in hydrolysis and re-assimilation of contaminants by the observed pathway. Quantitative techniques were developed using the synthesized compounds to generate time-series data. From these data, a novel technique was used to examine metabolic transformations as function of contaminant removed from the aqueous phase (conversion). Conversion normalized kinetic data variations arising from plant activity, pH and other factors and indicated that plant metabolism was the primary, if not exclusive, mode of contaminant removal in the system.
The application of phytoremediation techniques in the treatment of polluted waters (rhizofiltration or rhizosphere bioremediation) seems particularly promising in all those situations in which isolated settlements have difficulties in connecting or in utilizing conventional water treatment plants (large scale depuration). This is the case, for instance, of agro-industrial plants like milk and cheese production farms. Two horizontal subsurface flow reed beds of 75 m2 each, treating dairy parlor effluent and domestic sewage (about 6.5 m3 day-1), were set up to determine the efficiency of this system in reducing the polluting load in an isolated mountain rural settlement. A total suspended solids value of about 0.70 g/l and COD and BOD5 values of about 1200 and 450 mg l-1 O2, respectively, were characteristic of the influent waters. Removal of suspended solids and organic load constantly remained at levels above 90%, while those of the nutrients N and P were about 50% and 60%, respectively. The total number of coliform bacteria and Escherichia coli was reduced by more than 99% and fecal streptococci by more than 98%. Nitrates, chlorides, sulfates, anionic and non-ionic surface-active agents and heavy metals were detected only in low concentrations. Concentration and localization of metals was also quantified in Phragmites tissues by microanalysis with Scanning Electron Microscope equipped with Energy Dispersive X-ray detector (SEM/EDX). Significant differences could be found for the zinc content in reed stems and roots. SEM/EDX analyses evidenced the precipitation of iron on the outside surface of the root periderm, reported to be acting as a barrier towards uptake of other metals. Results demonstrated the use of reed beds as an appropriate treatment to reduce pollutants in wastewater from rural activities to values acceptable for discharge into surface waters.
Blast-furnace slag, a by-product of steel production, is recycled and often used as fill material for roads and other transportation structures. In and around I-65 and I-80/94 in Northwestern Indiana, this material is generating unsightly leachate with an extremely unpleasant smell. The resulting reaction stems from under-weathered slag mixing with runoff to produce a greenish leachate, exhibiting high pH and hydrogen sulfide odor. This leachate has become a nuisance because of its occurrence in public parks, and has forced the Indiana Department of Transportation to take remedial action. The overall objective of this project is to explore the use of constructed wetlands as a means to biologically and chemically eliminate the negative properties of the leachate. Field scale constructed wetlands have been designed to treat the slag leachate at two locations. The design calls for subsurface wetland cells to create anoxic conditions that would best reduce total sulfur, high pH, and other pollutants, along with limiting open water exposure and nuisances, such as insects. Laboratory and greenhouse studies will also test the leachability of the slag material, constituents of the slag leachate, as well as possible substrates and plant combinations to use within the constructed wetland system. We will discuss the rationale for our approach to remediate this problem, the mechanisms of remediation, and the advantages and known limitations of the proposed system.
The United States Army Corps of Engineers (USACE) frequently dredges sediments from the waterways of the United States in an effort to maintain navigation. The USACE created a large number of Confined Disposal Facilities (CDFs) in the 1970s to store dredged sediments that contain organic and metal pollutants. The majority of these CDFs are either full or very near their capacity; therefore, a method needs to be developed to remediate or otherwise reduce the volume of the sediments in the current CDFs to allow continued placement of contaminated dredged sediments in the CDFs. A research team from Purdue University, University of South Carolina, and Central State University (Ohio) is attempting to reduce the total volume of contaminated sediments by removing the water from the sediments and by remediating the sediments. Remediated sediments can then be removed from the CDF and used as fill material, potting mixes, habitat restoration, and other beneficial uses. The objectives of this project are to evaluate the relative ability of various plants to rapidly and efficiently dewater contaminated dredged sediments, and to test the remediation potential of various plants to degrade the polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) contained in the dredged sediments. These objectives will be met through field trials and supporting greenhouse studies. The field site is located on the Jones Island CDF in Milwaukee, WI. The experimental design includes 7 vegetation treatments with four replicates. The treatments are Carex aquatilis (vigorously and densely rhizomatous wetland plant), Salix nigra (willow shown to have high transpiration rates), Cephalanthus occidentalis (woody species capable of handling high moisture soil), Hibiscus laevis (high biomass aquatic plant), and Scirpus fluviatilis (rush shown to tolerate pollution well), natural attenuation, and an unvegetated control. The dewatering phase and the remediation will be studied together until the termination of the project. Supporting greenhouse studies at Purdue University and the University of South Carolina are identifying plants with a high potential to meet the objectives of the field study. Dewatering will be evaluated by taking weekly samples at depths of 0 to 10 cm, 10 to 20 cm, and 20 to 40 cm, and determining the gravimetric moisture percentage. Remediation potential is evaluated by quarterly sampling of the soils and quantifying residual contaminants using solvent extraction followed by GC-FID for PAHs and GC-ECD for PCBs.
Three field sites, one each in Michigan, California, and West Virginia are being used to document the extent of attenuation of hydrocarbon-impacted soils and waters using phytoremediation. The Michigan site planted to hybrid poplar and willow has crude oil impacted shallow groundwater adjacent to a wetland. The West Virginia site planted with hybrid poplar is a former refinery and contains a mix of hydrocarbons that have impacted both soils and shallow groundwater. The California site planted with willow is a former oil field in coastal sand dunes with diesel-range hydrocarbon impacted groundwater. All of the sites are older than 10 years and each has had trees growing at least two seasons.
We collected geochemical data from upgradient, within plume and downgradient from the hydrocarbon plume at each site. At the Michigan and West Virginia sites we also collected soil samples before planting and after the next two growing seasons. A field protocol was established for groundwater sample analysis onsite to guide the investigations. This procedure ensured that most samples needed were collected prior to leaving the field. We utilize a three dimensional (3-D) approach through the collection of vertical profile samples in both vadose and saturated zones. Groundwater samples are collected for iron, sulfate, nitrate, Eh and conductivity using field portable instruments when possible. Once these analyses are complete, groundwater samples are collected for analysis by an offsite laboratory for hydrocarbons and dissolved gases (CH4, CO2, and O2). We also collect vertical profile soil gas samples in those areas where groundwater is deeper than approximately 3 feet, which are also analyzed for carbon dioxide, oxygen, and methane.
Active degradation of the hydrocarbon-impacted groundwater has been documented at all sites by the presence of high values of methane, carbon dioxide, and ferrous iron plus the low values of oxygen and Eh. Indications that phytoremediation is having an effect include: 1) increased levels of carbon dioxide in soils (West Virginia site), 2) increased growth rates in trees growing directly over the groundwater plume (CA site), 3) elimination of sheening in adjacent wetland (Michigan site).
We seek to delineate the potential of specific plants for use in phytoremediation of PAH-contaminated soils. The reporter strain, Pseudomonas fluorescence HK44 with a nah-lux fusion was used to investigate the effect of root extracts on the expression of naphthalene dioxygenase. Hybrid poplar and milo extracts had a negative effect on bioluminescence when HK44 was concurrently exposed to naphthalene. However, willow and mint extracts significantly enhanced bioluminescence, presumably due to the presence of nah inducers such as salicylate. Further experiments with substrates found in root extracts (e.g., sugars, carboxylic acids and phenolics) suggest that the presence of easily degradable substrates in the rhizosphere of most plants might repress PAH degrading genes. However, enhanced growth of desirable genotypes and the presence of inducers in the rhizosphere might result in faster PAH degradation rates than in unplanted soil.
Effluent dams located along the NW boundary of the Umbogintwini Industrial Complex in South Africa, have been used for the disposal of the site’s effluent since the early 1960’s and were finally decommissioned in 1998. Field investigations indicated that due to hydraulic loading from the dams, springs located in a village adjacent to the site boundary were contaminated by chlorinated hydrocarbons which originated from the effluent dams, in spite of an hydraulic divide between the dams and the village. Management measures implemented included alternative supply of water to the community, the commissioning of a hydraulic containment system within and external to the dams, improved surface and subsurface water control and studies of natural attenuation in diminishing the source, as physical removal is not an option. In addition, experimental trials are currently underway to investigate the feasibility of using an evapo-transpiration cap to limit infiltration of precipitation from reaching the groundwater. The evapo-transpiration cap is proposed as an alternative to the conventional RCRA capping design required for closure of the site. The benefits of the evapo-transpiration cap over the conventional cover, is that not only are they more cost effective to construct and maintain, but they have also been shown to provide long term protection to the environment. The long-term mean annual potential evaporation (1528mm) exceeds the mean annual rainfall (1025mm) at the site, which merited a detailed water balance evaluation. Hence, a study was designed, particularly to define the flux of liquid below the root zone, whether into or out of the lower layers of the impoundment. The study comprised four parts: 1) the monitoring of atmospheric variables and the monitoring of the soil water tensions by automated tensiometers within 2m of the surface of the slimes dam under areas of different vegetation, a bare area and a plastic lined area, 2) the characterization of the hydraulic properties of the slimes dam material, 3) the interpretation of the data to define gradients and fluxes within and below the root zone and the calibration of a model, (HYDRUS), to simulate the fluxes in the profile during the monitoring period and 4) the prediction of the long-term performance of the cover using the model. Preliminary indications are that, over the monitored period, there was a net uptake of water from the profile within and below the root zone at all vegetated sites, the evaporation from the bare surface is significant, but not sufficient to prevent deep drainage. Recharge of the groundwater has been estimated by integrating the simulated fluxes at 8m below the surface. For one of the vegetated sites (ficus thonningii), the net drainage amounts to a net 17mm over the 28-year period of simulation, while for the bare surface the total recharge is 7500mm, some 26% of the total rainfall, reflecting the merits of the evapo-transpiration cap.
Anecdotal evidence indicates that remediating hybrid poplar stands face high rates of mortality. This may in part be due to the challenging edaphic conditions found under brownfield conditions such as rocky, debris-ridden or compacted soil; extreme pH; and nutrient and water deficits.
To determine the relationship between nutrient and water availability and tree size, seven hybrid poplar clones (DN74) were planted along a septic plume gradient. After three years, results showed significant negative correlations (using Pearson product moment correlation coefficients) in all aspects of tree size: height (rp = -0.93939, p = 0.0017), stem diameter (rp = -0.83035, p = 0.0207) and mean leaf size (rp = 0.92503, p = 0.0028) decreased with increasing distance from the nutrient/water source. Large trees are also significantly correlated with large leaves (rp = 0.92075, p = 0.0033 for the correlation between tree size and leaf size).
These results suggest that actively managing phytoremediating poplar stands through nutrient enhancement and irrigation overcomes limiting edaphic factors, and contributes to increased survival. Actively managing these and other ecological variables may also enhance growth and increase the capacity of trees to degrade or transform contaminants, thereby expediting remediation.
Over time, contaminants can become fixed or sequestered in soil. This fixation (or stabilization) lowers contaminant availability, making bioremediation of aged soils difficult. The risk posed by exposure to soil, however, is also reduced by sequestration. Under a low-risk scenario, plant succession and ecological restoration should be allowable choices for site management. To support that line or reasoning, the bioavailability of metals and PAHs were investigated on a site where contaminants had approximately 10-20 years to age and sequester into the matrix. Site soils were sampled at two depths from established study plots. These samples were extracted (using single and sequential procedures), and analyzed for metals and PAHs. In addition, the activity, biomass, and PLFA profiles of the microbial communities, as well as the metal content in plant tissues, were determined. In studies conducted under controlled conditions, select plant species were grown in hydroponic metal solutions or in site soils, assessed for phytotoxicity, and then analyzed for metals. Characterization of the site soils by extraction indicated that levels of metal removed by mild steps of the sequential procedure were between 80 to 100 times lower than total loadings. Concurrent with this, little metal was found in the tissues of plants grown in the soil. Plants growing onsite and in potted soils showed no signs of reduced growth or phytotoxicity. When these same species were grown in solutions (where the metals were freely available), levels less than half that found in the field killed the plants. At lower (non-lethal) concentrations, plant tissue accumulations were higher than any found in soil-grown plants. Collectively, the results of these studies indicated that the contaminants in the aged soils were essentially unavailable. Results of microbial characterization and PAH availability will be presented.
Previous field studies from our laboratory indicate that zucchini and cucumber are good and poor accumulators, respectively, of persistent organic pollutants from soil. We have hypothesized that exuded organic acids facilitate the uptake of persistent organic pollutants by increasing contaminant bioavailability to the plants. The objective of this study was to compare DDE uptake and organic acid exudation by zucchini and cucumber under various cultivation and nutrient conditions. When grown under dense planting conditions (5 plants in a 5-kg pot of DDE-contaminated soil), zucchini accumulated significant and expected amounts of DDE with a BCF (bio-concentration factor, the ratio of DDE concentration in plant tissue to that in soil) of 17 for roots and 8 for stems. Surprisingly under these stressed conditions, cucumber accumulated greater DDE in the roots with a BCF of 33, but translocation to aboveground tissues was negligible. The typical root BCF for cucumber species grown under field conditions is usually less than 1. The concentrations of citric, malic, formic and acetic acids in the rhizosphere soil of cucumber was significantly higher than that of zucchini, suggesting that the increased DDE uptake by cucumber was likely due to increased organic acid exudation under nutrient stressed conditions. Under these dense planting conditions, cucumber developed an extensive fibrous root system that has not been observed under field conditions. When analyzed separately, the DDE concentration in cucumber fine roots s was six times greater than the concentration in the composited root system. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake is currently being assessed.
Phytoremediation, the use of plants for contamination clean-up, is an inexpensive, low-maintenance remediation alternative. Of concern is that phytoremediation and other bioremediation technologies may not result in complete degradation of the contaminants and often the ultimate fate of the metabolic by-products is unknown. In some cases, however, remediated soils may reach an acceptable endpoint if the contaminants (or associated by-products) can be shown to be biologically unavailable. Plants can influence bioavailability in many ways, including increasing organic matter through root exudates, humification in the rhizosphere, or through root exploration of areas with physical restrictions resulting in contaminant entrapment. Although phytoremediation is showing great promise as a clean-up technology, environmentally significant pathways of contaminant dissipation and resulting toxicity have not been clearly assessed in soil-plant systems. The potential effects of plant roots on bioavailability (and associated toxicity) have not been clearly defined.
This study will focus on the phytoremediation of polycyclic aromatic hydrocarbons (PAHs) from manufactured gas plant (MGP) impacted soil using sweet clover (Melilotus officinalis), fescue (Festuca arundinacea Schreb), and zucchini (Cucurbita pepo Raven). Two treatments, phytoremediation, bioremediation, and an untreated control (natural attenuation) will be assessed for overall remediation efficiency and residual ecotoxicity. The pots will be sacrificed for analytical and ecotoxicity analyses every three months over an 18-month study. In this study, several standard and newly developed toxicity tests will be used to determine bioavailability and acceptable endpoints in the phytoremediated soil. Invertebrate toxicity assays will include the 14-d biomass production test using the earthworm, Eisenia foetida and the 24-h mortality test using the soil dwelling nematode, Caenorhabditis elegans. The plant bioassays will include germination tests with lettuce (Lactuca sativa), millet (Panicum miliaceum), radish (Raphanus L.), and root elongation analyses to evaluate toxicity of targeted compounds. In addition, microbial respiration will be conducted to evaluate the residual toxic effects of contaminants on overall microbial communities. Microbial assays, such as most probable number (MPN) of contaminant degraders, will be performed. Several chemical extractions will also be conducted to assess the labile contaminant fraction. Strong correlations have been shown between bioavailable and butanol extractable fractions of PAHs in planted and unplanted soils, as well as butanol extraction and bioavailability. The results from this research project will allow for determination of the benefits of phytoremediation through traditional measures such as evaluation of contaminant concentrations, along with non-traditional measures of success (i.e. ecotoxicity).
Phytoremediation of trichloroethylene (TCE) from contaminated groundwater has been performed using fast-growing tree species that maintain a high water demand. Tree species with these characteristics make excellent candidates for phytoremediation applications due to their ability to uptake large amounts of groundwater, and therefore contaminant. Several metabolites of TCE have been identified in the tissue of poplars including trichloroethanol (TCEtOH), di- and trichloroacetic acids (DCAA, TCAA). The presence of these metabolites indicates that TCE degradation is taking place through natural metabolism of exogenous compounds in the plant system. However, it is important to expand the range of plants that can be utilized in varying areas of the country for phytoremediation. By screening native tree species for the ability to take up and degrade TCE we hoped to identify phytoremediation candidates suitable for the Southeast. This study was a greenhouse-based project that simulates the effects of groundwater TCE on the plant system. In this study, we examined native tree and plant species of the Southeast by studying their interaction with TCE. Tissue analysis by gas chromatography revealed the presence of both TCE and TCEtOH in various samples. While overall growth did not appear to be affected by TCE treatment, some species possess more potential for phytoremediation field applications.
This study used an experimental model of a constructed wetland to evaluate the risk of mercury methylation when the soil is amended with sulfate. The model was planted with Schoenoplectus californicus and designed to reduce copper, mercury, and metal-related toxicity in a wastestream. The soil of the model was varied during construction to provide a control and two sulfate treatments, thus allowing characterization of sulfate’s effect on the removal efficiency of copper and mercury from the wastestream, as well as the risks from methylmercury formation in water and sediment. Total mercury concentrations were reduced by an average of 37%, and copper was reduced by 59% as wastewater passed through the system. The control and both sulfate treatments were equally efficient at overall mercury and cooper removal. Methylmercury concentrations in porewater were up to three times higher in the sulfate treatments (0.5 to 1.6 ng/L) than in the control (<0.02 ng/L to 0.5 ng/L). Mean percent methylmercury was 9.0% in the control with 18.5 and 16.6% in the low and high sulfate treatments, respectively. Methylmercury concentrations measured in the model’s surface water, however, did not reflect the differences between the control and the sulfate treatments that were noted in porewater, and there were no differences between methylmercury flowing into and out of the system. The mean bulk sediment methylmercury concentration in the top 6 cm of the low sulfate treatment was significantly higher than all other sediment means. Total mercury body burdens were elevated in two species of fish which had been held in the sulfate treated tanks. There was no added benefit from the sulfate additions, as the non-sulfate-amended control was equally effective in removing metals while keeping mercury methylation low.
The regulatory agency for waste disposal and management in South Africa is the Department of Water Affairs and Forestry (DWAF: http://www.dwaf.gov.za/). In 1994 DWAF issued a set of documents titled, “Minimum Requirements for Waste Disposal by Landfill”. These have since been updated in 1998 and further additions are in progress.
Whilst the Minimum Requirements have their primary application in municipal landfills, the guidelines within these documents have also been applied to industrial contamination and hazardous waste situations. Concurrently, there are no guidelines related to remedial goals and what would be considered acceptable levels of risk for contamination situations. Consequently, where appropriate, the Minimum Requirements have fulfilled this role, but have also led to situations where they are inflexible in terms of the application of emerging and innovative technologies, such as vegetative capping and phytoremediation for source and risk reduction.
Recent scientific advances have made it possible to use molecular biological techniques for assessment of microbial communities in complex environmental systems. Molecular techniques, such as PCR amplification, cloning, and sequencing of ribosomal RNA genes, have recently been embraced by environmental science community as important tools for predicting soil and water remediation success. The focus of this study is to evaluate the potential use of a suite of microbiological techniques for assessment of phytoremediation success.
The objective of this research was to study the uptake of nitrate nitrogen by hybrid poplar trees (Populous deltoids´ nigra, DN 34). This research may lead to better management practices for wastewater irrigation operations and greater acceptance of this alternative treatment process for nitrate removal. Uptake was evaluated by exposing hybrid poplar trees to concentrations ranging from 7 to 210 mg/L nitrate as N. Nitrate removal from hydroponic solutions was monitored over time, and nitrate uptake followed a hyperbolic trend. In comparison to barley, maize and ryegrass, poplar was found to have a lower affinity for nitrate removal from soil as indicated by the experimentally determined half-velocity coefficient Ks. Furthermore, active transport of nitrate appeared to be maximized in the 56 to 110 mg/L range as reactors with initial nitrate concentrations that were equal to or greater than 100 mg/L showed gradual increases in concentration over time. The total mass of nitrate removal by the trees is significant, but this research indicated that if high concentrations of nitrate are applied to poplar stands the concentration of nitrate passing through the root zone could actually be higher than the applied concentration.
Hybrid poplar trees (Populas deltoides x nigra DN34), hybrid willow trees (Salix alba ‘Matsudana’), and native grasses (climax timothy, alsike clover, alfalfa, red clover, orchard grass, and landino clover) were grown in a greenhouse using petroleum contaminated soil from phytoremediation sites in Superior, Wisconsin and Heath, Ohio. Amendment studies were conducted to determine appropriate fertilizer applications. Growth of native grasses planted in Superior soils showed enhanced growth with the addition of phosphorus, zinc, and potassium. Sulfur, added as a soil conditioner to control pH, hindered growth. Hybrid poplar and willow trees planted in Superior soils mixed with mulch (2:1) showed little to no growth during a three month period. Inhibition was likely due to soil texture and not soil toxicity. Soil samples from the successful grass study were analyzed for petroleum hydrocarbon concentrations. This analysis demonstrates the effect of amendments and grasses on petroleum degradation. The results of the studies conducted with Superior soils contrasted with the results observed using Heath soils. Hybrid poplar trees were stimulated strongly with the addition of nitrogen using soil from Heath. The combined results of these independent studies illustrate the need for site-specific amendment studies prior to the application of phytoremediation.
The importance of oxygen addition to hybrid poplar vitality was investigated using petroleum contaminated soil from Heath, Ohio. Five passive methods of oxygen delivery were examined, including aeration tubes, gravel addition, and an Oxygen Release Compound (ORC). When ORC was placed in coffee filters above hydrocarbon contaminated soil, increases in poplar biomass and increased root growth in hydrocarbon-stained soils was observed. The positive response of hybrid poplars to oxygen amendments suggests the addition of air or oxygen to the root zone of plants in phytoremediation projects when soil contamination exerts a high biochemical oxygen demand, such as at former refinery sites.
Heavy industrial processes often displace native ecological systems and may release environmentally harmful by-products into their surrounding soils, waters, and air. As part of the Historic Rouge Manufacturing Complex sustainable site renovation project (Dearborn, MI), we have developed a phytoremediation treatment program using only native plant species. Approximately 50 different plant species endemic to the S.E. Michigan area were screened in greenhouse trials for their ability to degrade polyaromatic hydrocarbons from soils impacted by coke manufacturing. Of these, 22 species were planted at an off-site installation in leachate-controlled, lined treatment plots in single-species grids (“cells”) and monitored for PAH degradation and plant growth and vigor. Preliminary results showed elevated rates of PAH biodegradation in most rhizospheres relative to the unplanted control cells. We completed an additional pilot-scale treatment installation adjacent to the Coke Oven Facility at the Rouge Complex in Fall02. This on-site phytoremediation trial covers 1.6 acres in 12 distinct plots containing different plant community mixtures of 22 different plant species (~22,000 total plants) in 2 different water-status habitats. Concurrent laboratory investigations have focused on characterization of rhizosphere microbial communities, effects of soil hydrogeological properties, and beneficial soil management strategies for enhanced phytoremediation. This project has begun the process of soil remediation, site rehabilitation, and habitat restoration at this facility, serving as a model of Brownfield Development for other industrial properties.
The recently discovered hyperaccumulating fern Pteris vittata (tradename edenfern™) has great potential for remediation of arsenic contaminated soils. This fern has been shown to concentrate arsenic, in the fronds, as high as 22,000 mg/kg without any measurable phytotoxicity symptoms (Ma et al., 2000). This plant has also shown to bioconcentrate arsenic from soil with only moderately elevated soil arsenic concentrations. The potential for phytoextraction is highly dependent on a number of site characteristics. These including: meteorology, geology, and contaminant concentration in the soil, contaminant speciation, and the physical form of the contaminant. At the site discussed, single plants, under field conditions have been found to contain 1800 mg/kg arsenic from soil with an initial arsenic concentration of less than 200 mg/kg. A two-year field study has been conducted to evaluate the field performance of three edenfern species at an apple orchard using soil with elevated arsenic concentrations.
This field study was designed to assess soil and agronomic characteristics, quantify plant uptake of arsenic and identify production parameters that affect plant performance (growth characteristics, biomass production, and arsenic accumulation). Six pilot field plots have been established at Picatinny Arsenal in a former apple orchard that was historically treated with a lead arsenate pesticide. Three different species of the Pteris fern, mayii, parkerii, and vittata, were planted in triplicate in each of the six plots. The ferns were planted at two different plant densities, 12 and 6-inch spacings to determine the rate of soil arsenic clean-up. During the first year of study, selected ferns were harvested at 8, 12 and 16 and 20 weeks. In the second year of study, all plants were harvested at 20 weeks. The variations of arsenic uptake, biomass production and total arsenic mass phytoextraction within the field experimental variables, will be presented. Soil samples were collected prior to planting and again after each year of study. Statistically significant reductions in soil arsenic concentrations have been observed following each year of plant harvesting. The Army Risk Assessment Modeling System (ARAMS) has been used to determine the reduction of environmental risk from arsenic at the site after each year of harvest.
Phytoirrigation provides a relatively inexpensive means of moving impaired water to a planted area or forest for treatment, greatly expanding the ways in which phytoremediation can be used. A long term solution for leachate management at Riverbend Landfill in Yamhill County, Oregon was needed. After evaluating treatment options including membrane filtration, distillation, landfill gas-fired evaporation, and treatment in a municipal wastewater reclamation facility, it was determined that using the leachate to irrigate a poplar tree farm was the preferred solution. Using information gathered from the landfill's existing 14-acre spray-irrigated leachate poplar tree application site, a new poplar tree plantation was designed with significant improvements including expanded land area to reduce nutrient and hydraulic loading, a state-of-the-art drip irrigation system, extensive environmental monitoring, and a sustainable tree plantation plan to ensure consistent harvesting and leachate capacity far into the future. The system was installed in 2001, and has been successfully operated for two years.
Warm climate can enhance phytoremediation strategies. Tropical and sub-tropical environments may have an advantage in that long plant growing seasons and increased soil temperature can accelerate phyto-processes. Diverse situations in Hawaii have been addressed through the technology. Seven sites were investigated for action on one or more of the following remediation needs: explosives residues, hydrocarbons, pesticide residues, soil stabilization, and slaughterhouse wastewater. Over 100 plant species were investigated.
Many researchers have dismissed the possibility of remediating polychlorinated biphenyls (PCBs) using plants due to their highly hydrophobic nature. Previous studies have, however, identified that a large variety of plant species can flourish in PCB contaminated soil. During routine site assessment work at various Mid-Canada Line (MCL) sites located in northern Ontario, PCB levels exceeding 500 ppm in the tissues of some plants were recorded. The discovery of these plants (which appear to be natural PCB accumulators) led to greenhouse studies to investigate the potential for remediating PCB contaminated sites. Ongoing greenhouse studies in a specially designed facility control for parameters including volatilization and atmospheric deposition of PCBs on plant surfaces, and for shoot to soil contact. Genera-specific differences in PCB uptake, partitioning of PCBs amongst different plant tissues, and congener-specific uptake of PCBs were examined. Results indicate PCB uptake of up to 2200 ppm in the roots of the MCL species, with a translocation factor (TLF) of 0.56. A 45-72% drop in soil [PCB] was also observed over an 8 week period when planted with this species. Other plants screened included zucchini, soybeans and tall fescue. Congener-specific analysis reveal that lower chlorinated congeners may experience preferential uptake or accumulate in plant tissues.
A phytoremediation study was conducted on a 1-acre MGP brownfield site at the Niagara Mohawk's Harbor Point Research Facility, 1-mile north of the central business district, Utica, New York. A split plot, randomized block field design was installed in June 1999 with four treatments in four blocks. Plot sizes were 20 x 20 feet with a 10 foot unplanted buffer strip separating all plots. Treatments were: (1) unvegetated control, (2) plantings of white clover, red fescue, Kentucky bluegrass, and annual rye, (3) volunteer, old-field vegetation, and (4) plantings of willow and poplar. Results-to-date from the Harbor Point study are producing clear, positive results of operational-level phytoremediation effects. It appears that PAH-contaminants in the soil are being reduced with cultured plant communities.
Premier Environmental Services, Inc. (Premier) is conducting a Pilot-scale Phytoremediation Study on a former wood-treating site located in central Louisiana. The wood treating facility operated from the early 1970s to the early 1980s during which time the facility treated timber products through the application of CCA and creosote. As a result of operations, CCA and creosote constituents were released to the surrounding soils. After facility decommissioning in 1992, various remedial activities were conducted at the site between 1994 and 1996 to remove structures and grossly impacted soils. Investigations conducted after these activities indicated that PAHs and CCA are mostly present in the shallow soil (0-4 feet). Typical concentrations for Cr ranged up to 2,300 mg/kg, As up to 1,900 mg/kg, and PAHs up to 930 mg/kg. Groundwater at a depth of 40 feet has been impacted locally by PAH constituents and Cr and As.
The objective of the pilot study is to evaluate the reduction of contaminant mass and mobility, decrease human health/ecological risk, and return the land to beneficial use through biostabilization and rhizosphere biodegradation. The objectives are being monitored through the evaluation of changes in infiltration rates, changes in chemical concentrations in soil and leachate, and changes in leachability in soils. The study is also characterizing stabilization and biodegradation mechanisms. In order to monitor these parameters a treatment plot and a control plot were established. Infiltration monitoring is being conducted using suction lysimeters, reflectometers, and an electronic rain gauge. A telemetry system (cellular) measures precipitation and percolation and the information is downloaded remotely. The data collected from the site will eventually be used for a GIS-simulation of the study area. The spatial model will integrate measures of contaminant concentration, bioavailability, toxicity as well as soil characteristics.
Site preparation occurred in November 1999 to remove all native vegetation that may initially compete with the newly planted trees. Raised planting beds were established using a bedding plow to construct 3-ft deep windrows. Loblolly pines were hand-planted at a density of 500 per acre over the entire30 acre site, with the exception of the control plot. In addition to the remote monitoring and annual porewater and groundwater sampling, changes in nature and mass of contaminants will be based upon evaluation of the control and treatment plots. These evaluations are being performed during years 1, 3, 5, 10, 15, 20, and 30. If after year 10, trends in toxicity and contaminant mass are not satisfactory, more traditional remedial alternatives will be employed.
Natural succession onto contaminated sites has gained recent attention because the plant community that forms may aid in remediation (defined here as successional remediation). As opposed to managed agricultural-based phytoremediation, successional remediation offers several advantages: it is self-sustainable, maintenance-free, more economical and may result in ecological restoration. This study focused on the early succession of an aged land treatment unit with elevated levels of PAHs and heavy metals (Cr, Pb, Zn, Ni, Cu). Twelve test plots, left unmanaged, were established to parallel the RTDF study on the 5.5 acre Chevron Land Treatment Unit in Hooven, OH. Plants colonizing these unmanaged plots were identified and analyzed for trends in richness, diversity and community similarity over a three-year period. These ecological characteristics were also analyzed with regard to spatial distribution and contaminant loading. Information from this research will be useful in optimizing phytoremediation technologies where successional remediation is adopted.
Phytoremediation involves the use of plants to remove or neutralize chemicals from contaminated soils, sediments or water. This emerging technology has a promising future in the hazardous wastes clean-up industry because it is inexpensive, unobtrusive and more esthetically pleasing in comparison to other remediation strategies.
Four plant species (zucchini, tall fescue, alfalfa, and rye grass) were grown in DDT-contaminated soil in the greenhouse. Treatments consisted of soils contaminated with high levels (2500-7000 ppb) and low levels (50-150 ppb) of DDT. All trays were covered with laboratory parafilm to limit volatilization. Zucchini plants in the high DDT soil treatment took up some of the highest concentrations of DDT (2270 ppb in roots and 2990 ppb in shoots), and in addition had the highest bioaccumulation factors (BAFs) and translocation factors (TLFs). Zucchini is therefore a promising phytoremediator for DDT.
Phyto-irrigation is a method that combines natural processes and air-stripping phenomena to remove volatile organic compounds from contaminated waters. Phyto-irrigation is a viable alternative to conventional phytoremediation technologies when there is some barrier between the expected root mass of the trees and the contaminated aquifer; i.e., a confining layer or depth considerations. This is suitable for use at sites where VOC contamination in the water exceeds regulatory levels but, when volatilized into the atmosphere, contamination levels remain below allowable limits in the air. This method has the potential to remediate large volumes of VOC-contaminated groundwater at costs considerably lower than those of conventional VOC remediation methods such as air sparging and vacuum exhausting.
In order to investigate the effectiveness of this method, a pilot-scale study has been initiated in a 4-acre test area on the Savannah River Site (SRS) in Aiken, South Carolina. The goal of this study is to determine the efficiencies of phyto-irrigation in plots containing two different mixtures of vegetation and root systems. An above-ground mini-sprinkler system provides irrigation to plots with vegetation native to the Southeastern parts of the United States and to plots planted with hybrid poplar tree clones that were previously found to have a high tolerance for the target contaminants at this site, trichloroethylene (TCE) and tetrachloroethylene (PERC). The primary source of this contamination was from manufacturing facilities during the height of activity on the SRS from the 1950’s to the 1980’s. The SRS was constructed during the early 1950’s to produce the basic materials used in the fabrication of nuclear weapons, primarily tritium and plutonium-239, in support of United States defense programs. Since then, the SRS has become a hotbed of research to clean up the contamination left behind by these operations, which includes the vast amounts of trichloroethylene and tetrachloroethylene used as solvents during this time.
Present concentrations in the groundwater at the study site range from 900 to 1400 ppb of TCE and below 200 ppb of PERC. Regulatory limits mandated by the United States Environmental Protection Agency (US EPA) for both TCE and PERC are set at 5 ppb, which is considerably lower than the measured levels at the study site. Operations for this study began in October 2001 and are scheduled to operate for three years. VOC separation from the groundwater will be achieved by the aboveground sprinkler system, foliage from the vegetation will act as a filter to trap the VOCs, and the root system will act as a barrier to prevent contamination from entering a clean aquifer that lies between the contaminated aquifer and the ground surface. The baseline phase of this project was completed in November 2002 with approximately 1.5 million gallons of contaminated water irrigating the site. The next phase, the variation of irrigation water and contaminant amounts, will commence in April 2003.
Hourly water level data collected by Pro2Serve® Technical Solutions and Environmental Quality Management, Inc. in conjunction with Bechtel Jacobs Company LLC, and U.S. Department of Energy indicate uptake of trichloroethene (TCE) contaminated groundwater by hybrid poplar trees from a 32 foot deep aquifer at the Portsmouth Gaseous Diffusion Plant, Piketon, Ohio. The engineered planting design utilizes sand-filled borings (sand pipes) and the hydraulics of the semi-confined aquifer to allow upwelling of the contaminated groundwater to the root zone of the trees planted within trenches.
Potentiometric surface measurements were collected hourly from four wells through July 2001. Cyclic potentiometric draw down levels of up to one foot per day correlate with expected evapo-transpiration rates. The daily change in potentiometric surface elevation was most apparent in well X740-17G, located within the poplar grove just down gradient from the trenches. The draw down typically peaked in the early evening (between the hours of 1600 and 1900) each day.
The remediation target is a groundwater plume (approximately 3.5 acres) composed mostly of TCE in a thin layer (<2 feet) of unconsolidated alluvial sand and gravel (Gallia Member of the Teays Formation [Gallia]) located on bedrock approximately 32 feet below land surface. The Gallia is overlain by lacustrian silts and clays of the Minford Member of the Teays Formation (Minford). TCE concentrations in the Gallia plume range from 2 mg/L to 2200 mg/L.
Construction and planting of the full-scale Corrective Measures Implementation was completed on the two-acre site in June 1999. Eleven two foot-wide trenches, with a total length of approximately 2400 feet, were installed to a depth of 10 feet. Previously drilled, eight-inch diameter boreholes filled with coarse sand extend through the bottom of the trenches to bedrock. These “sand pipes” provide a highly conductive conduit for the contaminated groundwater in the semi-confined Gallia to upwell to the tree roots in the trench. During construction, groundwater was observed to flow from the sand pipes into the bottom of the open trenches. Draw down in the Gallia potentiometric surface was more pronounced than in the shallower Minford. This indicates that the sand pipes are successfully enabling the trees to remove contaminated groundwater from the 32-foot deep aquifer below the root zone.
Biodegradation of polycyclic aromatic hydrocarbons (PAH) is often enhanced in the root zone of plants. The mechanisms responsible, however, are unknown. Here, plant root products (exudates, water soluble extracts) repressed phenanthrene-degrading activity (PDA) of P.putida (ATCC 17484) following a 4-hr exposure period. Osage orange and Willow root extracts produced ~10 fold and ~5 fold reductions of PDA, respectively. Similar repression of PDA was observed for the simple carbon sources, acetate, lactate, succinate, and pyruvate. These results suggest simple carbon sources present in plant root products serve as preferential carbon sources, potentially making induction of PDA by aromatic root exudate components (e.g. (e.g. salicylate).
A greenhouse study was conducted over 12 months to investigate the dissipation of PAHs in soil from a manufactured gas plant (MGP) using phytoremediation as a tertiary treatment. The soil was pretreated via composting for 12 weeks, and then planted with either tall fescue (Festuca arundinacea), annual ryegrass (Lolium multiflorum), or yellow sweet clover (Melilotus officinalis). Two sets of unvegetated controls were also used, one fertilized and one unfertilized.
Total PAH concentrations decreased in the tall fescue, annual ryegrass, and yellow sweet clover by 23.9%, 15.3%, and 9.1%, respectively. The smaller 2- and 3-ringed compounds; naphthalene, acenaphthylene, acenaphthene, fluorene, and anthracene, were not found at detectable concentrations in any of the treatments. MPN analysis for PAH degraders did not show any statistically significant differences in microbial populations between treatments. Tall fescue had the largest root and shoot biomass, followed by annual ryegrass and yellow sweet clover, and also had the lowest percentage of PAHs remaining after 12 months. There were significant differences seen between treatments (P < 0.05) in the percent remaining concentrations of five of the targeted PAHs. Surface area measurements indicate that tall fescue and annual ryegrass both had significantly higher root surface area than yellow sweet clover, although the two species were not significantly different from one another.
This research has shown that there were significant reductions in PAH concentrations in the planted soil versus the unplanted soil. Tall fescue, which has a fibrous root system, resulted in the largest biomass, root surface area, and PAH reductions compared to that of yellow sweet clover.
The presence of large quantities of TNT, a toxic nitro-substituted explosive, in the soil and water at many military bases in North America is a growing concern ecologically. TNT is recalcitrant when it comes to biodegradation, which leads to its accumulation in the environment. On average, explosive-contaminated soils can contain up to 10,000 mg kg-1 TNT. The Environmental Protection Agency (EPA) lists TNT as a priority pollutant and gives a lifetime health advisory of 2µg L-1 TNT in drinking water.
Phytoremediation, a cost-effective alternative to traditional remediation methods, uses plants to take up pollutants and transform them. Poplar trees have successfully been used to take up TNT and biotransform it into its less toxic daughter-compounds. These metabolized products of TNT are found within the plant tissues, stems and leaves.
In two related experiments, plant tissue cultures (from the Populus deltoids x nigra DN34 tree species) were exposed to TNT contamination (in vitro). In the first experiment, cultures were contaminated with 14C(U-ring) labeled TNT to check for metabolites and to identify transformation pathways. Analyses were performed by HPLC and LSC. In the second experiment, the cultures were exposed to 12C-TNT and checked for toxicity. Microtox® analyses, using the bioluminescent bacteria Vibrio fischeri, were performed using the Microtox® Basic Test Method.
In the first experiment, initial TNT disappeared from solution in less than ten days. No significant mineralization was observed. Transient intermediates were identified as reduction derivatives OHADNT, ADNT, DANT and included unknown polar compounds. The process suggests a stepwise reduction of parent TNT. A large percentage, 46%, of the radioactivity remained bound in the plant tissue cultures. This unextractable percentage may cause an initial reduction in toxicity, but could become problematic if the bound fraction were to be released back into the soil and water.
In the second experiment, initial toxicity results showed an EC50= 3.1% (TNT = 50mg/L). A substantial reduction of toxicity, EC50 = 39.2%, was observed. Control experiments did not show significant reduction (EC50 = 4.2%) and controls with no TNT were shown to be essentially non-toxic. Further investigation of the mutagenicity of TNT and its metabolites is underway. Evaluation of the biological hazards associated with a toxic mixture resulting from a biodegradation process may be extremely difficult from the chemical analysis of individual components. In addition to traditional analytical methods, results indicate that microbiotests, and potentially other toxicity tests, may provide useful alternatives in the evaluation of a bioremediation process.
For the purpose of use biomass of aquatic plants from heavy metals Phytoremediation, as fertilizer, we carried out a thermodynamic study of Pb II stable species in order to select a leachant to fulfill the following characteristics: a) to be able to remove Pb from plant biomass, b) to enhance the biomass with nitrogen compounds, and c) to form an electroactive complex so that Pb can be recovered by electrodeposition.
The leachants choice were: ammonium nitrate (NH4NO3), ammonium acetate (CH3COONH4), ammonium oxalate (COONH4)2 , and ammonium sulfate ((NH4)2SO4). These salts were selected because are salts rich in nitrogen compounds, basic constituents of fertilizers, and they are commonly used to remove Pb from polluted soils and sludges.
The thermodynamic study was carried out applying the generalized species and equilibria approach, from which it is possible to draw predominance-zone diagrams (PZD), condensed-phases diagrams (CPD), and predominance-existence diagrams (PED), taken into account the treatment salt (Pb(NO3)2) and leachant salts before stated. Those graphic methods are based in the chemical equilibrium of species presents in the medium or solution, and they are so usefully to characterize an reaction medium, to determine the better separation conditions from a mix, or to optimize the recovering procedures of a particular chemical specie.
Considering the diagrams, we determined that the best leachant salt to remove Pb from the biomass plants is ammonium oxalate because it will form soluble complexes ((PbC2O4 and Pb(C2O4)22-) at low concentrations (0.001 M), which are electroactive complexes that will be presents into the leachate (which will be the supporting electrolyte) and therefore can be recovered by electrodeposition. Ammonium acetate is a good leachant too because the interest complexes (PbCH3COO+ y Pb(CH3COO)2) can be formed at low concentrations (0.01 M) as well. Ammonium nitrate and ammonium sulfate are no good leachants to remove Pb because the first will form an insoluble complex (PbSO4) at low concentrations and the second one will require high concentration to form the soluble complex (PbNO3+).
Acetanilide herbicides are common contaminants in agricultural settings and an attractive option to reduce soil levels of certain pesticides is phytoremediation. Poplar trees can uptake large amounts of subsurface and superficial contaminated waters, converting the herbicides to less toxic metabolites or end products. In the present work, alachlor, S-metolachlor and acetochlor were studied for uptake, translocation and metabolism, toxicity, enzyme activity and immunocytochemistry. Hybrid poplar cuttings (Populus deltoides X P. nigra, DN34) were rooted and grown in half-strength Hoagland’s solution. Uptake, translocation and metabolism study was performed with cuttings exposed to a concentration of 1 mg/L for 14, 10 and 20 days for S-metolachlor, alachlor and acetochlor respectively. Radioactive (14C) derivative of each herbicide was spiked and a gross distribution in the roots, stems and leaves was calculated through mass balances. According to LC-MS analysis, S-metolachlor and its metabolites were detected in very small quantities, indicating that the transformation of this herbicide occurred within the poplar tree. Acetochlor was the most substantially uptaken, whereas alachlor caused great inhibition in poplar growth resulting in a small uptake. Further toxicity experiments were performed for 19 days at 0 mg/L, 1 mg/L and 5 mg/L for S-metolachlor and acetochlor. The toxicity data indicated that acetochlor was more toxic to the poplar tree. A time course experiment for the enzyme analysis was performed where tissues were collected at 1, 3, 6, 12, 24, 48, 96, and 120 hours. Levels of glutathione reductase (GR), peroxidase (PX), glutathione S-transferase (GST) and cytochrome P450 (P450) were measured spectrophotometrically from leaves, stems and root tissues of poplar cuttings exposed to 50 mg/L of S-metolachlor. GR activity fluctuated throughout the experiment forming peaks of activity at 12 and 72 hours after exposure due to the plant response to the first exposure and to the re-spiking of solution. PX analysis also showed an increase of activity after 6 hours of exposure, with some oscillation in root tissue between 1 and 3 hours. The GST activity in leaves and stems samples seemed to decrease towards time, whereas root samples showed a variation of this activity. P450 analysis did not show consistent results, which was related to the small amount of biomass used for this study. Immunocytochemistry analysis after uptake of S-metolachlor was performed in order to demonstrate the herbicide location in the cell. Determining the position of the contaminant may offer important information regarding the detoxification pathway starting with conjugation to glutathione in the cytoplasm followed by the transport of the conjugates into the vacuole.
In recent years, research and application of phytoremediation has resulted in a wealth of data related to this technology. To our knowledge, however, no effort has yet been made to thoroughly compile and mine these data in order to develop effective decision support tools that would aid engineers and remediation professionals in designing phytoremediation strategies. This study examined the use of case-based reasoning (CBR) to develop a decision support tool for phytoremediation design. Case-based reasoning is an artificial intelligence (AI) method based on the way people often solve new problems by recalling the solution to similar problems and adapting the solution accordingly. The integral feature of a CBR methodology is a database of cases that serves as the machine’s memory, but the methods by which a solution works need not be explicitly known. Because of this, CBR is particularly appealing for environmental problems with mechanisms that are not well understood, such as phytoremediation. Significant barriers such as missing, unknown, and non-uniform data complicated the development of the database, which served as the core of the CBR system. To this end, an existing phytoremediation field site database was updated and expanded (from ~170 to ~290 sites). Clearly, more data was needed in order to do a meaningful CBR analysis. In order to fill in missing data and provide ways to measure similarity among field sites, supplementary data from the literature were compiled to construct plant and contaminant hierarchies as well as to construct a database of laboratory-scale cases. Additionally, as a way to estimate data regarding climate, soil types, and plant hardiness zones, sites were linked to a Geographical Information Systems (GIS) interactive map. By taking the initial steps to implement a machine-based CBR system, the cumulative knowledge of many experts was combined in one place.