Phytoremediation efficiency of a PAH-contaminated industrial soil using ryegrass,white clover,and celery as mono- and mixed cultures

Purpose  

Phytoremediation has been recognized as a promising technology for the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils. However, little is known about how plant species and cropping patterns affect the process of phytoremediation removing PAHs. Therefore, the aim of this study was to investigate further the effects of monocultures or mixed cultures of different plant species on PAH phytoremediation.     

Effects of bacteria on metal bioavailability,speciation, and mobility in different metal mine soils: a column study

Purpose  

Successful phytoremediation depends mainly on the bioavailability of heavy metals in the soil. Recently, soil microbes possess several mechanisms that are able to change metal bioavailability in the soil, which provides a new strategy for investigating biogeochemical cycling of metals in contaminated soils. Three metal mines soils with elevated concentrations of Cd, Pb, and Zn from China were applied in this column study to (1) evaluate the effects of metal tolerant bacterial inoculation (Burkholderia cepacia, accession number: AB051408) on metal release, (2) monitor the migration of metals in the rhizospheric horizon (0–20 cm), and (3) investigate metal speciation and sequential fractions in soil.     

Physiological and biochemical responses of <Emphasis Type="Italic">Dolichos lablab</Emphasis> L. to cadmium support its potential as a cadmium phytoremediator

Purpose

This study aims to investigate the response of a high biomass producer non-hyperaccumulator legume plant species, Dolichos lablab L., to cadmium (Cd) stress for phytoremediation process.

Materials and methods

Three individual experiments were carried out to assess physiological and biochemical parameters to support the use of this plant species as a phytoremediator. The first experiment was carried out in Cd-contaminated soil while the second and third experiments were conducted in sand in which Cd was applied to study biochemical responses. Analysis of mineral nutrition, phytoremediation parameters, antioxidant response, and protein identification by gel-based proteomics were performed.

Results and discussion

Good tolerance to Cd under moderate level of contamination was observed. Mineral nutrition was little affected, and phytoremediation index was satisfactory. Additionally, biochemical responses based on antioxidant enzyme analysis were well responsive in roots, reflecting the capacity of Cd stress attenuation in this organ. A proteomic analysis revealed positive regulation of root proteins involved in carbohydrate, amino acids, nitrogen metabolism, and abiotic/biotic stress response, which together may contribute to create a scenario to overcome Cd-induced stress.

Conclusions

Based on the physiological and biochemical results, we concluded that D. lablab L. is suitable for phytoremediation/phytostabilization purposes.

     

Fertilizer amendment for improving the phytoextraction of cadmium by a hyperaccumulator <Emphasis Type="Italic">Rorippa globosa</Emphasis> (Turcz.) Thell

Purpose  

Two main pathways of phytoremediation of heavy metal-contaminated soils are phytostabilization and phytoextraction. Some soil amendments can strengthen phytostabilization or phytoextraction through either reducing heavy metal bioavailability in soil or increasing the heavy metal accumulation capacity of the hyperaccumulator (enhancing heavy metal concentration or shoot biomass of the hyperaccumulator). Urea and chicken manure are often used as fertilizers. This research will explore their effects on a newly found hyperaccumulator, Rorippa globosa (Turcz.) Thell., phytoremediating cadmium (Cd).     

Phytoremediation of Pb in the sediment of a mangrove ecosystem

Purpose

Coal-fuelled power plants can discharge hazardous materials, particularly heavy metals such as lead (Pb). An alternative way of reducing Pb concentration from contaminated sediments is through phytoremediation. Presently, there are few research findings on the phytoremediation potential of mangroves on metals like Pb. The study was conducted to survey and identify mangroves that thrive near the coal-fired power plant and to assess the phytoremediation potential of mangroves on Pb in sediment.

Materials and methods

The study sites were located in the mangrove ecosystems of Sitio Oyon and Sitio Asinan in Masinloc, Zambales, Philippines. The first stage of our study was to survey and identify the mangrove species. The second stage was to assess the levels of Pb in the sediments, water, and tissues of mangrove trees. The diversity assessment of the mangrove species was done through the use of 10?×?12 m quadrat technique. Water and sediment samples from each mangrove ecosystem were collected using composite sampling methods.

Results and discussion

Three mangrove species were identified in the study sites: Avicennia marina, Rhizophora stylosa, and Sonneratia alba. The order of importance of the mangrove trees in the two sampling locations, based on an importance value index (IVI), were as follows: SA (IVI?=?171.20)?>?AM (77.79)?>?RS (51.01). The total uptake of Pb from sediments near the power plants varied significantly (p?≤?0.001) among the three mangrove species. S. alba had the highest Pb uptake of 48.4 kg ha^?1 followed by A. marina (23.1 kg ha^?1), and R. stylosa (2.4 kg ha^?1). These three mangrove species have the potential to phytoremediate Pb in the sediment.

Conclusions

The three mangrove species present in the coastal ecosystem near the electric power plant—A. marina, R. stylosa, and S. alba—were potential phytoremediators of sediment Pb. The present study indicated that the mangroves possess beneficial characteristics that remove Pb from contaminated sediments in areas directly affected by coal-fired power plants, and thus have potential phytoremediation properties.     

Assessing phytoremediation potentials of selected tropical plants for acrylamide

Purpose  

Environmentally hazardous and health risk substances in animals and humans in the environment have increased as a result of continuing anthropogenic activities. Examples of these activities are food processing, laboratory, food production, industrial, and other relative activities that use various forms of acrylamide. All acrylamide in the environment are manmade. It is the building block for the polymer, polyacrylamide, which is considered to be a nontoxic additive. However, if the polymerization process is not perfect and complete, the polyacrylamide may still contain acrylamide which is toxic and may pose risks and hazards to the environment. Another form of acrylamide that may pose danger as well in the environment is the acrylamide monomer, which is also a very toxic organic substance that could affect the central nervous system of humans and is likely to be carcinogenic. Phytoremediation could be a tool to somehow absorb this neurotoxic agent and lessen the contamination in the soil. This technology could lessen the soil and water contamination by acrylamide thereby limiting the exposure of animals and humans. This study may also help solve the problem of disposing contaminated acrylamide waste materials. This study was conducted to achieve the following objectives: (1) to evaluate phytoremediation potentials of some selected tropical plants in acrylamide-contaminated soil, (2) to compare the performance of tropical plants in absorbing acrylamide through accumulation in their roots and shoots, and (3) to determine the outcome of acrylamide in the soil after treatment using the test plants with phytoremediation potentials.     

Development of an express method for measuring soil nitrate,phosphate, potassium,and pH for future in-field application

Background

In practical farming, there is often a need for short-term availability of information on the soil nutrient status.

Aims

To develop a new express method for the extraction of major plant-available nutrients and measurement of soil nutrients. In future, this method shall serve for in-field measurements of soil samples with an ion-sensitive field-effect transistor (ISFET).

Methods

Various extraction conditions such as type of extractant, soil-to-solution ratio, time, and intensity were investigated on a broad selection of dried soil samples in the laboratory. Based on 83 field-moist soil samples with varying clay contents, these conditions were compared to standard laboratory methods.

Results

With increasing extraction time, the nutrient concentrations increased. When the soil-to-solution ratio was reduced, a greater share of nutrients was extracted, independent of soil type. H₂O and 0.01 M CaCl₂ and standard calcium-acetate-lactate (CAL) solution proved to be too weak in the short period to reach the ISFET sensor measurement range. Higher concentrated CAL solutions performed much better. Finally, a 5-min CaCl₂ extraction followed by the removal of an aliquot for the determination of soil pH and NO₃⁻ was found to be effective. The remaining solution was then mixed with 0.20 M CAL solution for the analysis of H₂PO₄⁻ and K⁺ at 10 min of extra extraction time. This extraction method showed very good correlations with the values based on the German laboratory reference methods for pH (R² = 0.91) and for nitrate (R² = 0.95). For phosphorus and potassium, we obtained an R² of 0.70 and 0.81, respectively, for all soils. When soils were grouped according to clay content higher correlations were found.

Conclusions

A new express method based on a wet-chemical approach with a soil preparation procedure was successfully developed and validated. This seems to be a valuable basis for future in-field measurements via ISFET.     

Potential of willow and its genetically engineered associated bacteria to remediate mixed Cd and toluene contamination

Purpose

The purpose of this study was to investigate if bacteria with beneficial properties that were isolated from willow growing on a metal-contaminated site can be further equipped with genes coding for a specific degradation pathway to finally obtain transconjugants that can be inoculated in willow to improve phytoremediation efficiency of mixed contaminations.

Materials and methods

Cultivable rhizosphere bacteria and root endophytes were isolated from willow (cv. Tora) growing on a metal-contaminated soil. All isolated strains were tested for their metal resistance and potential to promote plant growth. The two most promising strains were selected and were equipped with the pTOM plasmid coding for toluene degradation. Both transconjugants were inoculated separately and combined in willow cuttings exposed to mixed Cd–toluene contamination, and their effect on phytotoxicity, Cd uptake, and toluene evapotranspiration was evaluated.

Results and discussion

Many of the isolated strains tested positive for the production of siderophores, organic acids, and indole acetic acid (IAA) and showed increased Cd resistance. The Cd-resistant, siderophore-producing rhizosphere strain Burkholderia sp. HU001 and the Cd-resistant root endophyte Pseudomonas sp. HU002, able to produce siderophores, organic acids, and IAA, were selected as receptors for conjugation with the toluene-degrading Burkholderia vietnamiensis BU61 as a donor of the pTOM-TCE plasmid. Although inoculation with the individual transconjugant strains had no effect on plant growth and negatively affected Cd uptake, their combined inoculation resulted in an increased shoot biomass upon Cd–toluene exposure did not affect Cd uptake and strongly reduced evapotranspiration of toluene to the atmosphere.

Conclusions

In this study, inoculation of willow with a consortium of plant-associated bacteria equipped with the appropriate characteristics resulted in an improved phytoremediation of a mixed Cd–toluene contamination: the degradation of toluene was improved leading to a decreased toxicity and evapotranspiration, while Cd uptake and translocation were not affected.     

Glyphosate and glufosinate-based herbicides: fate in soil,transfer to,and effects on land snails

Purpose  

The aim of this work was to assess the transfer and effects of two widely used herbicides on the land snail Helix aspersa during long-term exposure under laboratory conditions.     

Field-applying an inexpensive, 13C-depleted,labile carbon source to study in situ fate and short-term effects on soils

Background

Labile carbon (C_labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C_labile additions use laboratory incubations. We need to field-apply C_labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and ¹³C-depleted source of C_labile—crude glycerol carbon (C_glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied C_glyc at three rates (0, 216, and 866 kg C ha⁻¹) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C_glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO₃⁻–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

C_glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C_glyc added). The δ¹³C values of the other measured C pools were too variable to accurately track the C_labile fate. NO₃⁻–N was decreased by 13%–57% with the 216 and 866 kg C ha⁻¹ rates, respectively, and was strongly related to greater microbial uptake of C_glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, C_labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO₃⁻–N.     

Phytoremediation of a PCB-contaminated soil by alfalfa and tall fescue single and mixed plants cultivation

Purpose

Two plant species (tall fescue and alfalfa) grown alone and in combination was investigated to evaluate phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil and the impact on the catabolic genes and soil enzyme activities in the rhizosphere.

Materials and methods

Surface soil was collected from Xiaoshan (a PCB-containing capacitors and transformers storage site). The phytoremediation experiment was carried out in an agricultural greenhouse experiment station at Huajiachi campus, Zhejiang University. Soil dressing method and fertilizers were applied to improve soil quality for the pot experiment. Soil dehydrogenase activity was measured spectrophotometrically by the reduction of 2, 3, 5-triphenylterazolium chloride (TTC) to triphenyl formazane (TPF) and catalase activity was determined by back-titrating residual H₂O₂ with KMnO₄. Quantitative real-time PCR using SYBR green I was employed with the individual primer sets to determine the relative abundance of the biphenyl dioxygenase genes. Total bacterial numbers were determined by CFU counting and amplification of 16S rDNA.

Results and discussion

Planting treatment significantly enhanced bacterial numbers and PCB removal. The copy numbers of the bphA, bphD.1.B, bphD.2.A, and bphD.2.A/B genes, total bacteria counts, and dehydrogenase activity were the highest in mixed cropping soil, which indicated that tall fescue (forage grass) and alfalfa (legume) mixed cropping was most beneficial to soil bacteria, the potential PCB degraders, and enzyme activity. However, the highest removal of PCBs was found in tall fescue single plant cultivation, followed by combined plant cultivation, probably because tall fescue had greater biomass and could extract more PCBs from soil. Compared with nutrients amended unplanted control, the removals of tri-, tetra-, and penta-CBs in tall fescue single-planted and tri-CBs in combined planted soils were significantly enhanced (p?<?0.01).

Conclusions

The presence of vegetation significantly promoted the dissipation of PCBs and growth of total bacteria and the potential PCBs degraders in soils. Tall fescue and alfalfa mixed cropping was most beneficial to soil bacteria and enzyme activity. Tall fescue showed highest ability for remediation of PCBs in a poor quality soil.     

Phytoremediation of a multi contaminated soil: mercury and arsenic phytoextraction assisted by mobilizing agent and plant growth promoting bacteria

Purpose

The possibility of using chemical and microbial additives to enhance the phytoextraction of mercury (Hg) and arsenic (As) from a multi-contaminated soil could be very effective, leading to a significant saving in terms of time and costs of the reclamation. The aim of this study was to evaluate the efficacy of the addition of (i) thiosulfate and (ii) metal-tolerant bacteria isolated from the polluted soil having plant growth promotion (PGP) potential to perform As and Hg phytoextraction by Brassica juncea and Lupinus albus.

Materials and methods

A collection of 13 bacterial isolates able to tolerate As and Hg was obtained from the contaminated soil, identified by partial 16S rRNA gene sequencing and tested in vitro for PGP activities. The most promising strains were further tested in vivo for the evaluation of plant growth ability and rhizocompetence on model plants. Pot experiments were conducted in microcosms, with polluted soil vegetated with B. juncea and L. albus. Ammonium thiosulfate and potassium dihydrogen phosphate were used as mobilizing agents, together with a bacterial consortium composed by the most promising PGP isolates.

Results and discussion

Thirteen indigenous metal-tolerant bacterial strains were isolated, and their in vitro characterization highlighted their great potential in assisting the phytoremediation process; most of them tolerated both trace elements and showed, at the same time, multiple PGP traits. The results were confirmed in vivo on model plants and lead to the selection of the most promising PGP strains to be applied in microcosm-scale phytoextraction experiments. Thiosulfate addition significantly increased the mobilization of both elements, promoting bioavailability and phytoextraction. When a selected bacterial consortium was supplemented in addition to thiosulfate, the efficacy of the phytoaccumulation was increased up to 85 % for As and up to 45 % for Hg.

Conclusions

The use of the common fertilizer thiosulfate appeared to have great potential in phytoextraction practices since it was able to facilitate the uptake by plants of both Hg and As. Moreover, the application of a consortium of indigenous PGP bacteria (PGPB) produced a further positive effect on the plant biomass, supporting and enhancing the phytoextraction strategy, thus demonstrating their potential in a microbe-assisted phytoremediation intervention.

     

Metal tolerance in barley and wheat cultivars: physiological screening methods and application in phytoremediation

Purpose

The objective of the study was to evaluate the tolerance of barley (Hordeum vulgare) and wheat (Triticum aestivum) in soil contaminated with different concentrations of Cd and Cr, the effect of these metals on some physiological characteristics and the biomass produced in order to assess their potential application in phytoremediation of contaminated soils.

Materials and methods

A greenhouse experiment using two cultivars of barley, CB502 and Pedrezuela, and one of wheat, Albares, was conducted. The pots were watered with different concentrations of Cd or Cr during the period of plant growth. Cellular membrane damage, content and fluorescence of chlorophyll, and plant biomass were evaluated. After harvesting, the content of metals in the roots, shoots and grains was analysed as well as the available metal concentration in soil samples.

Results and discussion

The results show that the Cd treatments did not significantly affect the growth and physiology of the plants, but they were affected by the Cr treatments. At the highest concentration of Cr, the decrease in chlorophyll content compared to the control was 44, 77 and 83 % for the CB502 and Pedrezuela barleys and the Albares wheat respectively. A reduction in biomass was also observed (74, 81 and 85 % respectively). The amount of Cd and Cr accumulated in the root was higher than that accumulated in the aerial part for the three cultivars. The barleys accumulated the highest amount of metal in the roots. The transfer factor was lower in barley than in the wheat for both metals.

Conclusions

Cadmium treatments do not affect plant development. In the case of Cr, plant development and physiological traits were significantly affected. For the highest concentration of Cr, the CB502 barley had the highest tolerance index, 26 %, and the Albares wheat had the lowest one, 15 %. The two barleys were more effective in phytoremediation of soil contaminated with Cd or Cr than the wheat, presenting a higher tolerance to these metals in the assayed conditions.

     

Holocene sediment accretion in the Trinity River delta,Texas, in relation to modern fluvial input

Purpose  

This study uses sediment cores to quantify Holocene sedimentation rates in the Trinity River delta, Texas. An important question is whether modern fluvial sediment input from the Trinity River is adequate to sustain sedimentation in the delta, thereby combating subsidence and further wetland loss. Our objective was to quantify sedimentation rates within the delta in order to assess whether the delta is in- or out-of-phase with modern sediment delivery rates.     

Impact of in-season split application of nitrogen on intra-panicle grain dynamics,grain quality,and vegetative indices that govern nitrogen use efficiency in sorghum

Background

The correct rate and timing of nitrogen (N) has the potential to improve sorghum productivity through modified grain yield components and quality. The impacts of in-season split application of N have little documentation.

Aim

An experiment was conducted to determine the optimum rate and timing of N to relate vegetative indices that govern nitrogen use efficiency and to maximize grain yield and quality under different soil types.

Methods

Pioneer 86P20 was grown in three environments on two different soil types following a completely randomized block design with nine N application treatments. Treatments included differing N rates applied at critical developmental stages of sorghum (planting, panicle initiation, and booting), accompanied with high temporal aerial phenotyping.

Results

Opportunities to increase grain protein content while using split N applications were observed, with panicle initiation identified as a critical developmental stage. In-season split application of N enhances grain yield under low soil mineral N. Split application of 31 kg N ha⁻¹ each at the time of planting, panicle initiation, and booting emerged as optimum N treatment to increase protein content in sorghum. Vegetative indices, that is, normalized difference vegetation index and normalized difference red edge index are capable of predicting grain yield and protein content, respectively. Intra-panicle grain numbers and weights were altered significantly at different portions within panicles, with an opportunity to enhance yield potential at the bottom portion. The strong stay-green trait in this hybrid locked a large proportion of nitrogen in the leaves, which warrants the need for balancing stay-green and senescence in sorghum improvement programs.

Conclusions

Findings highlight that in grain sorghum remobilization of residual leaf N into grain is a target to increase yield and grain quality. An optimized stay-green trait balanced with senescence is recommended for enhancing sorghum yield potential.     

Biochar-application rate and method affect nutrient availability and retention in a coarse-textured,temperate agricultural Cambisol in a microcosm experiment

Background

Agricultural soils often require organic amendments, which improve crop yield and ecosystem services. Biochar has been proven to increase nutrient availability and retention in fine-textured, tropical soils.

Aims

Here we determine how coarse-textured, temperate soils react to different biochar-application rates in different tillage systems.

Methods

We conducted a 6-month laboratory incubation experiment in microcosms filled with a coarse-textured, temperate agricultural soil to determine the effects of biochar-application rate (none, low, or high, i.e., 0, 20, or 40 t dw ha⁻¹, respectively) and application method (mixed into the soil or applied to the soil surface) on microbial activity and biomass, and nutrient availability and leaching.

Results

Microbial activity and biomass and contents of carbon, nitrogen, and phosphorus in leachates were higher in biochar-addition treatments (by 134%, 37%, 372%, 28%, and 801%, respectively) than in the no-addition treatment. The effect was stronger with the low than with the high biochar-application rate. Biochar applied by both methods acted as a slow-release fertilizer, but this effect was stronger when biochar was mixed into the soil. Although available nutrient contents in the soil remained high, nutrient leaching decreased with incubation time. This effect was especially evident when biochar was mixed into the soil.

Conclusions

Biochar is an effective organic amendment in coarse-textured soils providing available nutrients. On the other hand, nutrient-retention mechanisms develop slowly after biochar application and may be greater when biochar is mixed into the soil than applied on the soil surface.     

Soil shrinkage and hydrostructural characteristics of three swelling soils in Shaanxi,China

Purpose  

Knowledge of soil shrinkage is important for a better understanding of water and solute transport in swelling soils. The objective of this study was to investigate the shrinkage processes and characteristics of three typical swelling soils in Shaanxi, China, with different height treatment using a modified core method and to analyze their agronomic properties.     

Widespread endocrine activity in river sediments in Hesse, Germany, assessed by a combination of in vitro and in vivo bioassays

Purpose  

There is a growing concern regarding the effects of endocrine disrupting compounds on humans and wildlife. Since some of them have the ability to bind to particulate matter, high concentrations can be reached in sediments of surface waters. The objective of this study was an assessment of 50 sediment samples from predominantly small rivers in the German federal state of Hesse with emphasis on endocrine activity.     

Accumulation,transfer, and environmental risk of soil mercury in a rapidly industrializing region of the Yangtze River Delta,China

Purpose  

Mercury (Hg) accumulation and transfer in soil ecosystems has been altered on local, regional, and even global scales, and their environmental risk has increasingly been a concern to the public and the scientific community.     

Enhancing maize grain yield under salt-affected field conditions using salt-resistant maize hybrids and higher planting density

Background

In arid and semiarid countries, grain yield of maize is increasingly impaired by soil salinity. Beside soil amelioration, the development of salt-resistant cultivars is a possibility to enhance crop yield on salt-affected soils.

Aims

This study aimed at testing yield performance in the field of salt-resistant maize hybrids on a salt-affected soil. In addition, planting density was optimized under the saline conditions.

Methods

Four salt-resistant maize hybrids (Zea mays L. SR-05, SR-12, SR-15, and SR-16) were grown under control (EC = 2.0–2.5 dS m⁻¹) and saline (EC = 10.0–12.0 dS m⁻¹) field conditions and compared to the salt-sensitive maize cv. Pioneer-3906. Planting density (5, 8, or 11 plants m⁻²) was optimized for saline soil conditions for SR-12 and the local hybrid EV-78.

Results

Yield of Pioneer-3906 was significantly reduced under salinity because of inhibited kernel setting, whereas the SR hybrids showed no decrease in grain yield. Based on grain yield, the optimum planting density was 8 plants m⁻² with no further increase with 11 plants m⁻². In contrast to SR-12, for cv. EV-78 no increase of harvest index with 8 relative to 5 plants m⁻² was observed.

Conclusions

Vegetative growth of Pioneer-3906 and the SR hybrids was decreased due to Phase-I effects but neither due to water deficiency nor ion toxicity. The experiment corroborated the salt resistance of the SR hybrids under field conditions. Under saline conditions, optimum planting density of salt-resistant cultivars may be higher than under nonsaline conditions when sufficient water supply by artificial irrigation is guaranteed.