Assessing the Phytoremediation Potential of Tall Fescue and Sericea Lespedeza for Organic Contaminants in Soil

The phytoremediation potential of using tall fescue (Festuca arundinacea Schreb.) grass and sericea lespedeza (Lespedeza cuneata [Dum. ‐Cours.]) legume species was assessed using three different groups of organic contaminants in soil. One hundred parts per million (ppm) each of a nitroaromatic compound (TNT), a polycyclic aromatic hydrocarbon (Pyrene), and a polychlorinated biphenyl (Aroclor 1248) were used to contaminate the soils. The experiments were conducted using soils with high and low organic‐matter content. The results indicate that recoveries of Pyrene and TNT were very low in all treatments in soil with high organic‐matter content (6.3 percent) compared with recoveries in soil with low organic‐matter content (2.6 percent). In contrast, recoveries of PCB from soil were not dependent on the soil's organic‐matter content. Planting both the legume and grass species had significant effect on the transformations of TNT and PCB in the soil with low organic‐matter content and did not affect the fate of Pyrene in both soils. The amount of TNT transformed in the four months of plant growth was 63 percent in the tall fescue and 46 percent in the sericea‐planted soils, compared with only a 15 percent unaccounted loss in the unplanted control soils. Furthermore, the grass species, with its massive root system, was significantly better at causing TNT dissipation compared with the legume species, which has less root vegetative mass. The plant biomass, particularly the shoot weight of the tall fescue grass, was significantly increased as a result of TNT treatment. Tall fescue and sericea biomass did not appear to have any significant effect on Pyrene transformation. Planting sericea provided a significantly high level of PCB transformation in soils with either high or low amounts of organic matter. Tall fescue did not appear to have any significant effect on PCB transformation. © 2002 Wiley Periodicals, Inc.     

The controlling of landfill leachate evapotranspiration from soil-plant systems with willow: Salix amygdalina L.

The use of willows (Salix amygdalina L) to manage landfill leachate disposal is an effective and cost-effective method due to the high transpiration ability of the willow plants. A 2-year lysimetric experiment was performed to determine an optimum leachate hydraulic loading rate to achieve high evapotranspiration but exert no harmful influence on the plants. The evapotranspiration rate of a soil-plant system planted with the willow was 1.28-5.12-fold higher than the rate measured on a soil surface lacking vegetation, suggesting that soil-willow systems with high volatilization rates are a viable landfill leachate treatment method. Of the soil-willow systems, the one with willow growing on sand amended with sewage sludge soil at an hydraulic loading rate of 1 mm day(-1) performed best, with evapotranspiration ranging from 2.25 to 3.02 mm day(-1) and a biomass yield of 8.0-9.85 Mg dry matter ha(-1). The organic fraction of the soil increased as much as 2.5% of dry matter, due to the sewage sludge input, which exerted a positive effect on the biomass yield as well as on transpiration and evaporation. It was observed that the plants in the sand-and-sewage sludge soil systems displayed higher resistance to toxic effects from the applied landfill leachate relative to plants in the sand-soil systems.     

Field trial experiment: Phytoremediation with Salix sp. on a dredged sediment disposal site in Flanders,Belgium

Remediation of heavy metal contamination in soil is a widespread environmental issue. Conventional remediation techniques are invasive and often too expensive, particularly if large areas of soil are contaminated. Phytoremediation is the use of plants to remediate soil and groundwater. Phytoremediation of inorganic comtaminants such as metals can be further catagorized into phytostabilization and phytoextraction. These techniques have gained an increasing amount of attention and research over the last ten years. Phytoextraction of heavy metals and periodical removal of harvestable plant parts results in a gradual decrease of pollutant levels in the top soil. Woody species such as Salix sp. (willow) do not represent the fastest phytoextraction procedure compared to uptake by herbaceous species; however, they offer the added advantage of possible reuse of the produced biomass (wood) for the production of renewable energy. Here we present the results of a field experiment conducted to evaluate the use of Salix to remediate soil contaminated with cadmium and zinc at a dredged sediment disposal site in Flanders, Belgium. © 2003 Wiley Periodicals, Inc.     

Uptake of perchlorate by vegetation growing at field sites in arid and subhumid climates

Previous greenhouse and field studies show that terrestrial and aquatic vegetation, including trees, grasses, and agricultural produce grown on perchlorate‐contaminated soil or with perchlorate‐contaminated irrigation water, accumulate perchlorate mainly in their leaf tissue. The phytoaccumulated perchlorate poses potential ecological risk by either contaminating the food chain of humans and animals or recycling in the ecosystem as leaf litter fall that accumulates on topsoil. In this study, the uptake and phytoaccumulation of perchlorate in terrestrial and aquatic vegetation growing at two perchlorate‐contaminated sites (the Longhorn Army Ammunition Plant [LHAAP] in Karnack, Texas, and the Las Vegas Wash [LVW], Nevada) was monitored during multiple growing seasons. The LHAAP site is located in a subhumid climate, while the LVW site is located in an arid climate. All vegetation species collected from both sites contained quantifiable levels of perchlorate. The detected concentrations varied with the type of plant species, amount of perchlorate concentration in soil, and season and stage of plant maturity. The highest perchlorate concentrations were measured in willows (Salix nigra), crabgrass (Digitaria spp.), and Bermuda grass (Cynodon dactylon) at the LHAAP, while salt cedar (Tamarix ramosissima) at the LVW phytoaccumulated the highest mass of perchlorate. The concentrations of perchlorate measured in plant leaves growing over contaminated soils at multiple LHAAP locations did not reveal the strong seasonal variability observed at the LVW site. The slow rate of phytodegradation of the perchlorate fraction taken up by plants during the growing season explained the detection of higher perchlorate concentrations in leaves collected later in the growing season (fall) and in senesced leaves compared to younger, live leaves. This proves that senesced plant leaves potentially recycle perchlorate back into the soil on which plant litter collects. To minimize the potential recycling of perchlorate during phytoremediation, it is recommended that senesced leaves be collected and composted or phytoremediation be designed to enhance rapid rhizodegradation (rhizoremediation). © 2007 Wiley Periodicals, Inc.     

Biomass and Nutrient Dynamics of Restored Neotropical Forests

Restoring species-rich tropical forests is an important activity because it helps mitigate land deforestation and degradation. However, scientific understanding of the ecological processes responsible for forest restoration is poor. We review the literature to synthesize the current state of understanding of tropical forest restoration from a biogeochemical point of view. Aboveground biomass and soil carbon accumulation of restored tropical forests are a function of age, climate, and past land use. Restored forests in wet life zones accumulate more biomass than those in moist or dry life zones. Forests restored on degraded sites accumulate less aboveground biomass than forests restored on pastures or agricultural land. Rates of aboveground biomass accumulation in restored forests are lower than during natural succession, particularly during the first decades of forest establishment. Rates of litterfall, biomass production, soil carbon accumulation, and nutrient accumulation peak during the first few decades of restored forest establishment and decline in mature stages. Changes in species composition and canopy closure influence the rate of primary productivity of older restored stands. Species composition also influences the rate and concentration of nutrient return to the forest floor. The ratio of primary productivity to biomass is high in young restored forests and low in mature stands irrespective of climate. The ratio is low when past land use has little effect on biomass accumulation, and high when past land uses depresses biomass accumulation. This effect is due to a high rate of litterfall in restored forests, which helps restore soil by circulating more nutrients and biomass per unit biomass accumulated in the stand. The degree of site degradation and propagule availability dictates the establishment and growth of tree species. Reestablishment of forest conditions and the enrichment of sites by plant and animal species invasions lead to faster rates of succession, aboveground primary productivity, and biomass accumulation in restored forests. Our review demonstrates that nutrient cycling pathways and nutrient use efficiency are critical for interpreting the suitability of tree species to different conditions in forest stands undergoing restoration.     

Laboratory development and field demonstration of self-sealing/self-healing landfill liner

The self-sealing/self-healing (SS/SH) barrier concept is based on the principle that two or more parent materials placed in vertical or horizontal layers will react at their interfaces to form insoluble reaction products. These products constitute a seamless impermeable seal, which is resistant to the transmission of leachate and contaminants. A SS/SH liner formulation was developed in the laboratory and demonstrated at the Sudokwon landfill site in South Korea. Laboratory testing results indicated that a seal with a hydraulic conductivity less than 10(-9) m/s formed after two to four weeks of curing at room temperature, and the seal healed itself after it was fractured. The use of the soil from the Sudokwon landfill site instead of sand as the matrix of the parent materials in the SS/SH liner retarded the sealing and healing of the seal, but did not show an obvious effect on the overall sealing and healing capacity of the seal at early stages. The construction and installation of the field demonstration SS/SH liner were carried out in the same way as for a soil cement liner. The quality of the liner was ensured by the enforcement of quality analysis/quality control procedures during installation. A single sealed ring infiltration test was performed on the field demonstration liner 36 days after the installation was completed. The measurement of water infiltration rate indicated that the liner healed after it was fractured. However, the long-term sealing and healing capacity needs to be further investigated.     

Phytoremediation of a Petroleum‐Hydrocarbon Contaminated Shallow Aquifer in Elizabeth City,North Carolina,USA

A former bulk fuel terminal in North Carolina is a groundwater phytoremediation demonstration site where 3,250 hybrid poplars, willows, and pine trees were planted from 2006 to 2008 over approximately 579,000 L of residual gasoline, diesel, and jet fuel. Since 2011, the groundwater altitude is lower in the area with trees than outside the planted area. Soil‐gas analyses showed a 95 percent mass loss for total petroleum hydrocarbons (TPH) and a 99 percent mass loss for benzene, toluene, ethylbenzene, and xylenes (BTEX). BTEX and methyl tert‐butyl ether concentrations have decreased in groundwater. Interpolations of free‐phase, fuel product gauging data show reduced thicknesses across the site and pooling of fuel product where poplar biomass is greatest. Isolated clusters of tree mortalities have persisted in areas with high TPH and BTEX mass. Toxicity assays showed impaired water use for willows and poplars exposed to the site's fuel product, but Populus survival was higher than the willows or pines on‐site, even in a noncontaminated control area. All four Populus clones survived well at the site. © 2014 Wiley Periodicals, Inc.*     

Phytoremediation of lead-contaminated soil at a New Jersey Brownfield site

Phytoremediation is a new technology that uses specially selected metal-accumulating plants as an attractive and economical method to clean up soils contaminated with heavy metals and radionuclides. The integration of specially selected metal-accumulating crop plants (Brassica juncea (L) Czern.) with innovative soil amendments allows plants to achieve high biomass and metal accumulation rates. In a recent study conducted at a lead-contaminated site in Trenton, New Jersey, the soil was treated with phytoremediation using successive crops of B. juncea combined with soil amendments. Through phytoremediation, the average surface soil lead concentration was reduced by 13 percent. In addition, the target soil concentration of 400 mg/kg was achieved in approximately 72 percent of the treated area in one cropping season.     

Fate of saline ions in a planted landfill site with leachate recirculation

Recirculation of leachate on a covered landfill site planted with willows or other highly evapotranspirative woody plants is an inexpensive option for leachate management. In our study, a closed landfill leachate recirculation system was established on a rehabilitated municipal solid waste landfill site with planted landfill cover. The main objective of the study was to evaluate the sustainability of the system with regard to high hydraulic loads of the landfill leachate on the landfill cover and high concentrations of saline ions, especially potassium (K⁺), sodium (Na⁺) and chloride (Cl^?), in leachate.The results of intensive monitoring, implemented during May 2004 and September 2007, including leachate, soil and plant samples, showed a high sustainability of the system regarding saline ions with the precipitation regime of the studied region. Saline ion concentrations in leachates varied between 132 and 2592 mg Cl^? L^?1, 69 and 1310 mg Na⁺ L^?1 and between 66 and 2156 mg K⁺ L^?1, with mean values of 1010, 632 and 686 mg L^?1, respectively. Soil salinity, measured as soil electrical conductivity (EC), remained between 0.17 and 0.38 mS cm^?1 at a depth between 0 and 90 cm. An average annual precipitation of 1000 mm provided sufficient leaching of saline ions, loaded by irrigation with landfill leachate, from the soil of the landfill cover and thus prevented possible salinity shocks to the planted willows.     

An application of a phytoremediation technology in Bulgaria—The Kremikovtzi Steel Works experiment

The first in‐field phytoremediation trial in Bulgaria was initiated in the summer of 1998 at two highly polluted heavy‐metal sites within the industrial region of Kremikovtzi Steel Works, near the capital town of Sofia. The experiment targeted phytoextraction of lead, according to the selection of Brassica juncea seed material and technology, generously provided by Phytotech, Inc. The metal concentrations in soil samples were measured before planting and after harvest. Leaf and stem plant samples were investigated by laser mass spectrometry in search of metal accumulation depots. The results of the one‐planting experiment show a very uneven decrease between 0 and 25.9 percent of the initial lead concentration at various sample locations. The trial, which was initially planned for three consecutive years, was unfortunately terminated in the second year because the Steel Works entered a privatization procedure. Nevertheless, the experimental data obtained confirmed the general applicability of phytoremediation to treat soil polluted with heavy metals. The experiment was further successful, because it confirmed the proposal to clean the three‐kilometer ecological zone around the Steel Works with two plantings per year in two years to levels below the maximum permissible level for lead of 25 to 80 g/t for pH 4, according to the Bulgarian Environmental Standards. © 2006 Wiley Periodicals, Inc.     

Evaluation of a soil‐amendment process demonstration for reducing the bioavailability of lead

The U.S. Environmental Protection Agency (EPA) evaluated an in‐situ application of a soil‐amendment process at a residential site that was contaminated with lead. The goal of the evaluation was to determine if the soil‐amendment process resulted in lower concentrations of bioavailable lead in the contaminated soils. The relative bioavailability of lead (bioaccessible lead) was measured by an in vitro test procedure that uses a highly acidic extraction procedure to simulate human digestive processes. The soil‐amendment demonstration showed that the 11.2 percent mean reduction in bioavailable lead concentration between untreated and treated soils was not statistically different. © 2002 Wiley Periodicals, Inc.     

Phytoremediation experimentation with the herbicide bentazon

An experiment was performed on six species of trees to determine the feasibility of remediating groundwater contaminated with an agricultural herbicide, bentazon, at a site in southern Louisiana. Fate studies on bentazon support that it is translocated to the plant leaves where it is degraded by photolysis to lower-order derivative compounds within short periods of time. Both transpiration observations and dosing tests suggest that the most favorable phreatophyte and tolerant specie of tree to bentazon exposure was the black willow (Salix nigra).     

A field trial of a bentonite landfill liner

Field and laboratory trials were carried out for a bentonite amended weathered granite landfill liner. The trials were undertaken to gain experience in the installation method, and to establish the appropriate mixing techniques and mix design. It was established that a bentonite-amended weathered granite liner could be constructed on steep slopes. This paper presents the results of the trials, which included both field and laboratory permeability testing. It was found that the success of a soil bentonite liner is critically dependent on the mixture having the right moisture content at the time of compaction.     

Remediation of persistent organic pollutants (POPs) in two different soils

Persistent organic pollutants (POPs) are a set of chemicals that are toxic, persist in the environment for long periods of time, and biomagnify as they move up through the food chain. The most widely used method of POP destruction is incineration, which is expensive and could result in undesirable by‐products. An alternative bioremediation technology, which is cheaper and environ‐mentally friendly, was tested during this experiment. Two different soil types containing high and low organic matter (OM) were spiked with 100 mg/kg each of pyrene and Aroclor 1248 and planted with three different species of grasses. The objective of the study was to determine residue recovery levels (availability) and potential effectiveness of these plant species for the remediation of POPs. The results showed that recovery levels were highly dependent on the soil organic matter content—very low in all treatments with the high OM content soil compared to recoveries in the low OM soil. This indicates that availability, and, hence, biodegradability of the contaminants is dependent on the organic matter content of the soil. Moreover, the degree of availability was also significantly different for the two classes of chemicals. The polyaromatic hydrocarbon (PAH) recovery (availability) was extremely low in the high organic matter content soil compared to that of the polychlorinated biphenyls (PCBs). In both soil types, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls. Planting did not have any significant effect on the transformation of the PAHs in both soil types; however, planting with switchgrass was the best remedial option for both soil types contaminated with PCB. © 2005 Wiley Periodicals, Inc.     

U（Ⅵ）在处置场地质环境中迁移规律的模拟研究

以西南某极低放射性废物处置场土壤为研究对象,采用静态吸附和动态吸附实验获取处置场地质特征参数,结合PHREEQC软件和地下水数值模拟系统（GMS）预测U（Ⅵ）在处置场环境中的化学种态和迁移规律。结果表明：U（Ⅵ）在处置场土壤中的吸附平衡时间为20 d,吸附分配系数为358 mL/g;U（Ⅵ）在处置场地下水环境中主要以UO₂（CO₃）₂^2-和UO₂（CO₃）₃^4-形式存在;处置场关闭后安全运行30 a,处置场中心U（Ⅵ）质量浓度下降4.20%,外围50 m与下游河流边界处U（Ⅵ）质量浓度分别为初始给定值的3.40%和1.32%;在12 a时有0.10%的U（Ⅵ）到达河边。     

Use of Large‐Scale Electrokinetic and ZVI Treatment for Chlorinated Solvent Remediation at an Active Industrial Facility

The combination of electrokinetic and zero‐valent iron (ZVI) treatments were used to treat soils contaminated with chlorinated solvents, including dense nonaqueous phase liquid (DNAPL), at an active industrial site in Ohio. The remediation systems were installed in tight clay soils under truck lots and entrances to loading docks without interruption to facility production. The electrokinetic system, called Lasagna^TM, uses a direct current electrical field to mobilize contaminant via electroosmosis and soil heating. The contaminants are intercepted and reduced in situ using treatment zones containing ZVI. In moderately contaminated soils around the Lasagna^TM‐treated source areas, a grid of ZVI filled boreholes were emplaced to passively treat residual contamination in decades instead of centuries. The remediation systems were installed below grade and did not interfere with truck traffic during the installation and three years of operation. The Lasagna^TM systems removed 80 percent of the trichloroethylene (TCE) mass while the passive ZVI borings system has reduced the TCE by 40 percent. The remediation goals have been met and the site is now in monitoring‐only mode as natural attenuation takes over. © 2014 Wiley Periodicals, Inc.     

Cost-effective contaminant plume delineation using multilevel drive point samplers

Over the past several years, environmental professionals have sought new and innovative field techniques to allow on-site plume delineation and in-field location of monitoring wells. One technique adopted for site characterization is the multilevel drive point sampler (MLDPS). This technology allows sampling of soil gas and groundwater and measurement of aquifer permeability. MLDPSs offer a cost-effective solution to the high cost of plume delineation by providing in-field data for decisions on monitoring well location and depth. MLDPS technologies can increase the effectiveness of monitoring well installation programs, decrease the cost of site characterization, and accelerate the time between initial site assessment and implementation of a remediation program. MLDPS technologies offer distinct advantages over other field techniques, and a cost comparison is offered. A case study describing application of the MLDPS to the delineation of a TCE-contaminated plume is described.     

Revegetating industrial waste disposal sites

Short-rotation tree plantations were established at seven industrial waste disposal sites in southern Finland. Altogether 31,500 willow cuttings were planted between 1984 and 1989. Neutralized residue from a titanium dioxide pigment process had an unfavourable influence on growth. Biological sludges from a municipal sewage treatment plant, and pulp and paper mills were too compact to be used alone as substrate, but gave a good supply of nutrients. Sand, bark and de-inking waste were sufficiently porous, but were low in nutrients. A mixture of different waste materials is therefore recommended as a substrate for willow stands. Replacement of a natural soil cover with waste material allows disposal of a greater volume of refuse and diminishes the costs of revegetation. The landfill characteristics have to be taken into account. The high temperature of bark also disturbed the growth of willow stands. Ferrous sulphate in the landfill limits the possibility of irrigating the stand. The highest biomass production of the stands exceeded that of normal Finnish forest. Willow stands can be used for landscaping industrial waste disposal sites, for increasing evapotranspiration and minimizing leachate discharge.     

Effect of Humic Acids and Fungal Inoculations on Cesium and Lead Concentrations in Lettuce Plants Grown in Contaminated Soils

A study was carried out to evaluate the effect of humic acid additives, applied either individually or in combination with Fusarium oxysporum fungi, on uptake and translocation of cesium and lead in cultivated Lettuce (Lactuca sativa) grown on Mostorud (clayey) and El‐Gabal El‐Asfar (sandy loam soil) soils in a complete randomized block experimental design. The selected soils from contaminated areas (Mostorud soil was irrigated with contaminated industrial water for more than 30 years and El‐Gabal EL‐Asfar soil was irrigated with sewage effluent for more than 50 years). The results indicated that the cesium and lead content was reduced by all treatments of humic acid application individually or when combined with Fusarium oxysporum inoculations, especially at 200 mmol/kg compared to a control and other treatments. On the other hand, retention of cesium and lead occurred in roots more than shoots. ©2016 Wiley Periodicals, Inc.     

In-Situ Phytoremediation of Pahs Contaminated Soils Following a Bioremediation Treatment

Phytoremediation of pollutants in soils is an emerging technology, using different soil-plant interaction properties. For organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), phytodegradation seems to be the most promising approach. It occurs mostly through an increase of the microbial activity in the plant rhizosphere, allowing the degradation of organic substances, a source of carbon for soil microbes. Despite a large amount of available data in the literature concerning laboratory and short term PAH phytodegradation experiments, no actual field application of such technique was previously carried out. In the present study, a soil from a former coking plant was used to evaluate the feasibility and the efficiency of PAH phytodegradation in the field during a three years trial and following a bioremediation treatment. Before the phytoremediation treatment, the soil was homogenized and split into six independent plots with no hydrological connections. On four of these plots, different types of common plant species were sowed: mixture of herbaceous species, short cut (P1), long cut (P2), ornamental plants (P3) and trees (P4). Natural vegetation was allowed to grow on the fifth plot (P5), and the last plot was weeded (P6). Each year, representative sampling of two soil horizons (0–50 and 50–100 cm) was carried out in each plot to characterize the evolution of PAHs concentration in soils and in soils solution obtained by lixiviation. Possible impact of the phytoremediation technique on ecosystems was evaluated using different eco- and genotoxicity tests both on the soil solid matrix and on the soil solution. For each soil horizon, comparable decrease of soil total PAHs concentrations were obtained for three plots, reaching a maximum value of 26% of the initial PAHs concentration. The decrease mostly concerned the 3 rings PAHs. The overall low decrease in PAHs content was linked to a drastic decrease in PAHs availability likely due to the bioremediation treatment. However, soil solutions concentration showed low values and no signficant toxicity was characterized. The mixture of the herbaceous species seemed to be the most promising plants to be used in such procedure.