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Trichloroethylene (TCE) is a widespread environmental pollutant common in groundwater plumes associated with industrial manufacturing areas. We had previously isolated and characterized a natural bacterial endophyte, Enterobacter sp. strain PDN3, of poplar trees, that rapidly metabolizes TCE, releasing chloride ion. We now report findings from a successful three-year field trial of endophyte-assisted phytoremediation on the Middlefield-Ellis-Whisman Superfund Study Area TCE plume in the Silicon Valley of California. The inoculated poplar trees exhibited increased growth and reduced TCE phytotoxic effects with a 32% increase in trunk diameter compared to mock-inoculated control poplar trees. The inoculated trees excreted 50% more chloride ion into the rhizosphere, indicative of increased TCE metabolism in planta. Data from tree core analysis of the tree tissues provided further supporting evidence of the enhanced rate of degradation of the chlorinated solvents in the inoculated trees. Test well groundwater analyses demonstrated a marked decrease in concentration of TCE and its derivatives from the tree-associated groundwater plume. The concentration of TCE decreased from 300 μg/L upstream of the planted area to less than 5 μg/L downstream of the planted area. TCE derivatives were similarly removed with cis-1,2-dichloroethene decreasing from 160 μg/L to less than 5 μg/L and trans-1,2-dichloroethene decreasing from 3.1 μg/L to less than 0.5 μg/L downstream of the planted trees. 1,1-dichloroethene and vinyl chloride both decreased from 6.8 and 0.77 μg/L, respectively, to below the reporting limit of 0.5 μg/L providing strong evidence of the ability of the endophytic inoculated trees to effectively remove TCE from affected groundwater. The combination of native pollutant-degrading endophytic bacteria and fast-growing poplar tree systems offers a readily deployable, cost-effective approach for the degradation of TCE, and may help mitigate potential transfer up the food chain, volatilization to the atmosphere, as well as direct phytotoxic impacts to plants used in this type of phytoremediation.

Abatement of soil-lead hazards may also reduce human exposure to other soil toxins, thereby achieving significant collateral benefits that are not accounted for today. This proposition was tested with the specific case of soil-arsenic, where 1726 residential soil samples were collected and analyzed for lead and arsenic. The study found that these two toxins coexisted in most samples, but their concentrations were weakly correlated, reflecting the differing sources for each toxin. Collateral benefits of 9% would be achieved during abatement of the lead-contaminated soils having elevated arsenic concentrations. However, a hidden hazard of 16% was observed by overlooking elevated arsenic concentrations in soils having lead concentrations not requiring abatement. This study recommends that soil samples collected under HUD programs should be collected from areas of lead and arsenic deposition and tested for arsenic as well as lead, and that soil abatement decisions consider soil-arsenic as well as soil-lead guidelines.

ウランのように放射性および化学的毒性が懸念され, 汚染域が広範に及ぶ土壌の改良には, 安全性および経済性に優れたファイトレメディエーションが有効であることが提案されている。本研究の目的は, 性質の異なる土壌において, ファイトレメディエーションのキレート添加剤としてのクエン酸が, 植物のウラン吸収に及ぼす影響を評価することである。供試植物として, カラシナ, ホウキギ, ヒマワリの3種を選択し, 性質の異なるウラン汚染土壌にクエン酸溶液 (20mmol kg-1) を添加することにより, 植物が吸収するウラン量を試験した。ウラン汚染土壌は, アメリカ合衆国の湿潤地域 (湿潤土: 542mg U kg-1) および乾燥地域 (砂漠土: 137mg U kg-1) に位置する軍事基地内から採取した。全ての供試植物のウラン吸収は, クエン酸溶液の土壌添加により増加する傾向が見られた。特に湿潤土の添加処理におけるカラシナのウラン濃度 (2476mg U kg-1) は, 無処理の315倍に達した。一方, 砂漠土において, クエン酸添加が植物のウラン濃度を増加させる効果は, 湿潤土と比較して顕著に低く, 2～5倍の増加率に留まった。土壌によりクエン酸の効果が異なる要因は, 砂漠土に高濃度に含有する炭酸カルシウムが, クエン酸によるウランの溶解効果を抑制した可能性が推察された。クエン酸溶液の土壌添加は, 湿潤土におけるカラシナの乾物重量を顕著に減少し, その結果土壌からのウラン除去量が低下し得ることが確認された。一方, ホウキギやヒマワリは, 単位重量当のウラン蓄積量がカラシナと比較して低値を示したが, これら植物の乾物生産量に優れた特性は, 結果として土壌からのウラン除去量を増加させた。

Treatment of dredged sediments contaminated by polyaromatic hydrocarbons (PAHs) is a significant problem in the New York/New Jersey (NY/NJ) Harbor. 0.5 m3-scale slurry-phase bioreactors were used to determine whether bioaugmentation with a PAH-degradative bacterial consortium, or with the salt marsh grass S. alterniflora, could enhance the biodegradation of PAHs added to dredged estuarine sediments from the NY/NJ Harbor. The results were compared to biodegradation effected by the indigenous sediment microbial community. Sediments were diluted 1:1 in tap water and spiked to a final concentration of 20 mg/kg dry weight sediment of phenanthrene, anthracene, acenaphthene, fluorene, fluoranthene, and pyrene. The sediment slurry was then continuously sparged with air over 3 months. In all bioreactors a rapid reduction of greater than 95% of the initial phenanthrene, acenaphthene, and fluorene occurred within 14 days. Pyrene and fluoranthene reductions of 70 to 90% were achieved by day 77 of treatment. ...

Edible plants enhanced with minerals were tested to determine whether these plants could be used as a new source of mineral dietary supplements that provide essential minerals in a more available form than current, inorganically based mineral supplements. A select cultivar of Brassica juncea was identified that can be cultivated under hydroponic conditions to contain high levels of nutritionally important minerals such as Cr, Fe, Mn, Se, and Zn. Sequential extraction, simulated gastric fluid digestion, and simulated intestinal fluid digestion were used to assess the degree of solubility and potential availability of each metal examined. Results from these solubility experiments indicate that the accumulated trace elements achieve greater soluble concentrations than those provided in popular mineral supplements. The consistent high concentration of minerals in the edible plant tissue allows processing small quantities of these enriched plants into capsules or tablets that supply 100% of the recommended daily intake of these elements in soluble form from a natural, vegetative source.

Previous studies have shown that EDTA is necessary to solubilize soil Pb and facilitate its transport from the soil to the above ground plant tissues. These studies have also suggested that Pb is accumulated in the plant tissue with transpiration as the driving force. We conducted further studies to evaluate the relationship between EDTA soil treatment, plant transpiration, and plant accumulation of Pb and EDTA. Indian mustard (Brassica juncea) plants were grown in soils containing Pb at three different concentrations (1.5, 3.0 and 4.8 mmol/kg) for 5 weeks before being treated with EDTA concentrations ranging from 0 to 10 mmol/kg. Plant shoots and xylem sap were collected and analyzed for Pb and EDTA content using ICP and HPLC, respectively. Water loss was measured for 7 days following EDTA application. Transpiration was not affected at

Uranium phytoextraction, the use of plants to extract U from contaminated soils, is an emerging technology. We report on the development of this technology for the cleanup of U-contaminated soils. In this research, we investigated the effects of various soil amendments on U desorption from soil to soil solution, studied the physi ological characteristics of U uptake and accumulation in plants, and developed techniques to trigger U hyperac cumulation in plants. A key to the success of U phytoextraction is to increase soil U availability to plants. We have found that some organic acids can be added to soils to increase U desorption from soil to soil solution and to trigger a rapid U accumulation in plants. Of the organic acids (acetic acid, citric acid, and malic acid) tested, citric acid was the most effective in enhancing U accumulation in plants. Shoot U concentrations of Brassica juncea and Brassica chinensis grown in a U-contaminated soil (total soil U, 750 mg kg-1) increased from less than 5 mg kg-1 t...

Phytoremediation is emerging as a potential cost-effective solution for the remediation of contaminated soils. Because contaminants such as lead (Pb) have limited bioavailability in the soil, a means of solubilizing the Pb in the soil and facilitating its transport to the shoots of plants is vital to the success of phytoremediation. Indian mustard (Brassica juncea) was used to demonstrate the capability of plants to accumulate high tissue concentrations of Pb when grown in Pb-contaminated soil. Concentrations of 1.5% Pb in the shoots of B. juncea were obtained from soils containing 600 mg of Pb/kg amended with synthetic chelates such as EDTA. The accumulation of Pb in the tissue corresponded to the concentration of Pb in the soil and the concentration of EDTA added to the soil. The accumulation of Cd, Cu, Ni, and Zn from contaminated soil amended with EDTA and other synthetic chelators was also demonstrated. The research indicates that the accumulation of metal in the shoots of B. juncea can be enhanced t...

Low molecular weight organic acids (LMWOA) from root exudates, decomposing organic matter, and other sources are important ligands involved in solution complexation reactions as well as ligand exchange reactions at mineral surfaces. The purpose of this study was to (i) develop an ion chromatography method that could be used to determine LMWOA in soil solutions from Spodosols, (ii) assess methods for preserving LMWOA in soil solutions, and (iii) evaluate LMWOA concentrations in forest floor solutions during a growing season. Solutions were collected weekly from zero-tension lysimeters installed within the forest floor (forest floor leachate collectors). Limits of quantitation for acetic, formic, malonic, oxalic, phthalic, and citric acids were 0.35, 0.14, 0.43, 0.41, 0.07, and 0.04 μM, respectively, which in some cases are an order of magnitude lower than reported in previous studies. Freezing soil solutions after filtering resulted in the best recoveries (between 90 and 100% for all LMWOA); other methods of preservation, such as filtering alone and filtering and storing at 4°C, resulted in lower recoveries. The average concentrations of LMWOA in the forest floor solutions were 10 μM acetic acid, 0.7 μM formic acid, and 3.3 μM oxalic acid. Dissolved organic C from the forest floor contained a maximum concentration of 2.0% acetic acid, 0.01% formic acid, and 0.15% oxalic acid. There were no apparent temporal patterns in LMWOA concentrations, except for a decrease in LMWOA concentrations from late September to a minimum in October.

To better understand the potential toxicity of Se, it is necessary to know the concentration of different Se ionic species (e.g., SeO 3 2- and SeO 4 2- ). The hydride generation atomic absorption spectrophotometry (HGAAS) method of Se analysis cannot separate Se into individual ionic species. Ion chromatography (IC) can determine SeO 3 2- and SeO 4 2- concentrations simultaneously ; however, common anions, such as sulfate (S0 4 2- ), in groundwater interferes with SeO 3 2- and SeO 4 2- speciation. The purpose of this study was to measure the concentration of ionic SeO 3 2- and SeO 4 2- species in groundwater, thereby determining the chemical speciation of dissolved Se. Three groundwater samples with high concentrations of Mg 2+ and SO 4 2- were used in this study. The ionic SeO 3 2- and SeO 4 2- species in groundwatersamples were selectively adsorbed onto copper oxide (CuO) particles by lowering the pH to 5.5. These ionic species were desorbed from the surface of CuO particles by increasing the pH to 12.5. Subsequently, the concentrations of SeO 3 2- and SeO 4 2- ionic species in solutions were determined with HGAAS and IC. The effect of divalent cations (e.g., Mg 2+ ) on the concentration of SeO 4 2- in aqueous solutions was also evaluated. The dissolved Se concentration in three groundwater samples ranged from 22 to 151 μg/L. The CuO particles extracted 97% of SeO 3 2- from groundwater samples, suggesting that Se(lV) concentrations were dominated by the SeO 3 2- ion. However, CuO particles extracted 80% of SeO 4 2- from groundwater samples. These results suggest that Se(Vl) concentrations consisted of SeO 4 2- and metal SeO 4 2- solution species. The dissolved Mg 2+ in groundwater samples formed a strong neutral ion pair with SeO 4 2- (MgSeO 4 0 ), which was not adsorbed by the CuO particles. Overall chemical speciation of dissolved Se, extracted with CuO particles, suggests that groundwater samples consisted of SeO 3 2- (6-36%), SeO 4 2- (32-65%), organic Se species (14-23%), and neutral ion pairs (9-16%). An important aspect of the proposed method is that CuO can be used in the field to extract both SeO 3 2- and SeO 4 2- ionic species from groundwater samples, and these species could be desorbed from CuO and measured using HGAAS or IC methods, depending upon the concentrations of these species.

Selenite (SeO 3 2− ) sorption in soils has been correlated with pH, soil mineralogy, and soil solution composition, factors that are often highly variable with respect to mine soil materials. Selenite equilibrium and adsorption batch studies were conducted with four mine soil materials to determine adsorption parameters that could be used to develop a model to predict Se retention. Initial mass, Freundlich, Langmuir, and other relationships were explored to describe adsorption and retention of Se in these soils. For equilibrium and adsorption studies, 25 ml of solution was added to 2.5 g of soil in a polyethylene centrifuge tube. Time-dependent analysis consisted of duplicate treatments of two SeO 3 2− levels and reaction times of 2, 6, 24, 48, 168, 336, and 504 h. Adsorption studies were arranged in a 3 × 10 × 4 factorial design (three replications, 10 SeO 3 2− concentrations, four soils) and equilibrated for 14 d. Selenite sorption as a function of pH in each material was also examined. Selenite sorption of 10 μg Se/g soil was not greatly affected by pH between pH 4 and 8, except in one sample where sorption decreased at pH 6. Initial mass isotherms were very similar for Se additions up to 20 mg/kg for all soils and predicted Se sorption very similar to the experimental data for these and 12 additional soils. The Freundlich and Langmuir isotherms did not effectively predict Se sorption

Batch studies were conducted with Mn oxides (birnessite-hausmannite mixture, BHM) and samples of four soil series from the Mid-Atlantic region of the USA to determine effects of reducing organic acids, similar to those found in the rhizosphere, on the SeO3/SeO4 distribution. Jackland (Typic Hapludalf), Myersville (Ultic Hapludalf), Christiana (Aeric Paleaquult), and Evesboro (Typic Quartizipsamment) A and B horizon soil samples with and without prior Mn oxide reduction were incubated aerobically for 10 d with 0.1 mmol kg-1 SeO3 and 0 or 25 mmol kg-1 of ascorbic acid, gallic acid, oxalic acid, or citric acid. Selenite was also added to BHM (10 mmol kg-1) with 0 or 0.1 mmol kg-1 ascorbic acid. The availability of Se for plant uptake as a result of root-soil interactions was examined using growth chamber studies with barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seedlings grown in 150-mL cone-shaped containers to maximize root-soil surface interactions and to create ‘rhizosphere’ soil throughout the root zone. In the BHM system ascorbic acid increased oxidation of SeO3 to SeO4 to 33% of added SeO3. In the presence of ascorbic and gallic acids and Mn oxides, oxidation of SeO3 to SeO4 occurred in the B horizons of all the soils and in the A horizons of Jackland and Myersville soils. Removal of Mn oxides decreased the oxidation in some samples. Wheat and barley plants were able to accumulate up to 20 μmol Se kg-1 from the Jackland soil when soluble Se was not measurable. The root-soil interactions in the Jackland soil with barley and wheat provided the plant with Se from insoluble sources. The results also indicate that Mn oxides coming in contact with reducing root exudates have a greater ability to oxidize SeO3 to SeO4. Thus, rhizosphere processes play an important role in the availability of Se for plant uptake.

The need for a routine, inexpensive method with nanomolar detection limits for soluble SeO 3 3- and SeO 4 2- is increasing as Se research on soil-plant-water systems intensifies and speciation of Se valence states is required. This study was undertaken to compare hydride generation-atomic absorption spectrometry, colorimetry using 2,3-diaminoaphthalene, and ion chormatography as suitable methods for analysis of SeO 3 2- and SeO 4 2- in soil extracts and water samples. Selenium standards in solutions of either 1.0 mM KH 2 PO 4 , CaSO 4 , and KNO 3 , or in distilled water were analyzed to determine detection limits, limits of quantitation, and practicality for routine use of the above methods (...)

The phytoremediation of recalcitrant metals such as lead and uranium rely on soil amendments to enhance metal availability within the rhizosphere. Because these amendments may persist in soils, agents that not only biodegrade rapidly but also are effective in triggering metal uptake in plants are needed for metals phytoextraction to be considered as an accepted practice. In this study, several biodegradable organic acids and chelating agents were assessed to determine if these amendments can be used in an effective manner, and if their activity and use is consistent with a proposed class of soil amendments for phytoextraction, here termed transient phytoextraction agents (TPAs). A TPA is proposed as an agent that would exhibit both effectiveness in triggering plant accumulation of the targeted metal while minimizing the risk of migration through rapid degradation or inactivation of the soluble complex. Eleven candidate TPAs (acetic acid, ascorbic acid, citric acid, malic acid, oxalic acid, succinic acid, ethylenediaminedisuccinic acid, dicarboxymethylglutamic acid, nitrilotriacetic acid, BayPure CX 100, and the siderophore desferrioxamine B) were tested in batch studies to evaluate their complexation behavior using contaminated soils, with uranium and lead as the target metals. A growth chamber study was then conducted with Brassica juncea (Indian mustard), Helianthus annuus (sunflower), and Festuca arundinacea (tall fescue) grown in a lead-contaminated soil that was treated with the candidate TPAs to assess phytoextraction effectiveness. For the soils tested, citric acid, oxalic acid, and succinic acid were found to be effective complexing agents for uranium phytoextraction, whereas Baypure CX 100 and citric acid exhibited effectiveness for lead phytoextraction.

Arsenic contamination of drinking water poses serious health risks to millions of people worldwide. To reduce such risks, the United States Environmental Protection Agency recently lowered the Maximum Contaminant Level for arsenic in drinking water from 50 to 10 microgL(-1). The majority of water systems requiring compliance are small systems that serve less than 10,000 people. Current technologies used to clean arsenic-contaminated water have significant drawbacks, particularly for small treatment systems. In this pilot-scale demonstration, we investigated the use of arsenic-hyperaccumulating ferns to remove arsenic from drinking water using a continuous flow phytofiltration system. Over the course of a 3-month demonstration period, the system consistently produced water having an arsenic concentration less than the detection limit of 2 microgL(-1), at flow rates as high as 1900 L day(-1) for a total treated water volume of approximately 60,000 L. Our results demonstrate that phytofiltration provides the basis for a solar-powered hydroponic technique to enable small-scale cleanup of arsenic-contaminated drinking water.

Several species of fern from the Pteris genus are able to accumulate extremely high concentrations of arsenic (As) in the fronds. We have conducted short-term unidirectional As influx and translocation experiments with 73As-radiolabeled arsenate, and found that the concentration-dependent influx of arsenate into roots was significantly larger in two of these As-hyperaccumulating species, Pteris vittata (L.) and Pteris cretica cv. Mayii (L.), than in Nephrolepis exaltata (L.), a non-accumulating fern. The arsenate influx could be described by Michaelis-Menten kinetics and the kinetic parameter Km was found to be lower in the Pteris species, indicating higher affinity of the transport protein for arsenate. Quantitative analysis of kinetic parameters showed that phosphate inhibited arsenate influx in a directly competitive manner, consistent with the hypothesis that arsenate enters plant roots on a phosphate-transport protein. The significantly augmented translocation of arsenic to the shoots that was seen in these As hyperaccumulator species is proposed to be due to a combination of the increased root influx and also decreased sequestration of As in the roots, as a larger fraction of As could be extracted from roots of the Pteris species than from roots of N. exaltata. This leaves a larger pool of mobile As available for translocation to the shoot, probably predominantly as arsenite.

Iron‐efficient T3238FER tomato (Lycopersicon esculentum Mill.) and A7 soybean [Glycine max (L.) Merr.] were unable to respond to iron (Fe) deficiency stress in the absence of potassium (K) in growth solutions. The lack of response in both FER tomato and A7 soybean was a diminished exudation of hydrogen (H+) ions and reductants and a lower level of Fe(III) reduction at the roots. This lack of Fe‐stress response resulted in reduced levels of leaf Fe and greater chlorosis in the absence of K in both species. Solution K was replaced with vary.ing equimolar levels of both sodium (Na) and rubidium (Rb) in growth solutions, but neither effectively substituted for K which appears essential in eliciting the Fe‐stress response mechanism resulting in the uptake of Fe by the plant. Potassium seems to have a very specific role in the plant for maximum utilization of Fe.

The glycoside hydrolase family 5 endocellulase, E1 (Cel5A), from Acidothermus cellulolyticus was transformed into both Nicotiana tabacum and Zea mays with expression targeted to the cell wall under a constitutive promoter. Here we explore the possibility that in planta expression of endocellulases will allow these enzymes to access their substrates during cell wall construction, rendering cellulose more amenable to pretreatment and enzyme digestion. Tobacco and maize plants were healthy and developed normally compared with the wild type (WT). After thermochemical pretreatment and enzyme digestion, transformed plants were clearly more digestible than WT, requiring lower pretreatment severity to achieve comparable conversion levels. Furthermore, the decreased recalcitrance was not due to post-pretreatment residual E1 activity and could not be reproduced by the addition of exogenous E1 to the biomass prior to pretreatment, indicating that the expression of E1 during cell wall construction altered the inherent recalcitrance of the cell wall.