Poplar for the phytomanagement of boron contaminated sites

Green solution to riparian pollution: Populus alba L. potential for phytoremediation and bioindication of PTEs along the Sava river

This study addresses the potential of Populus alba L. for bioindication and phytoremediation of the contaminated lower part of the Sava River. The main objectives are to assess soil contamination with potentially toxic elements (PTEs: As, B, Cd, Cr, Cu, Li, Ni, Pb, Sr, and Zn), evaluate their availability, and assess the phytoremediation and bioindication potential of Populus alba. Quantification of the PTE contents was performed using inductively coupled plasma optical emission spectroscopy (ICP-OES), while bioindication and phytoremediation potential were evaluated using accumulation indices. The study revealed phytotoxic contents of Cr, Cu, Ni and Zn in the riparian soils of the lower Sava River. The percentage of available Cd was high, but due to its low total content, its phytotoxic potential is limited. According the metal accumulation index, Populus alba exhibits significant potential to accumulate the PTEs studied (with accumulated toxic contents of B, Cr, Li, Sr, and Zn). The ability of Populus alba to accumulate and bioindicate Cd, Cr, and Ni is promising, as is its ability to potentially remediate B, Cd, and Zn. Copper deficiency in leaves resulted in a reduction in photosynthetic performance, but without visible morphological symptoms. The reduced photosynthetic capacity serves as an adaptive strategy for this species in response to toxic levels of PTEs. Since Populus alba is widely distributed in European riparian forests, it is a good candidate to address soil contamination through phytoremediation and bioindication techniques.

Differential effects of tree species identity on rhizospheric bacterial and fungal community richness and composition across multiple trace element-contaminated sites

Soil microbial communities play a key role in plant nutrition and stress tolerance. This is particularly true in sites contaminated by trace metals, which often have low fertility and stressful conditions for woody plants in particular. However, we have limited knowledge of the abiotic and biotic factors affecting the richness and composition of microbial communities inhabiting the rhizosphere of plants in contaminated sites. Using high-throughput amplicon sequencing, we studied the rhizospheric bacterial and fungal community structures of 14 woody plant families planted in three contrasting sites contaminated by metals (Pb, Cd, Zn, Mn, Fe, S). The rhizospheric bacterial communities in the given sites showed no significant difference between the various woody species but did differ significantly between sites. The Proteobacteria phylum was dominant, accounting for over 25 % of the overall relative abundance, followed by Actinobacteria, Bacteroidetes and Gemmatimonadetes. Site was also the main driver of fungal community composition, yet unlike bacteria, tree species identity significantly affected fungal communities. The Betulaceae, Salicaceae and Fagaceae families had a high proportion of Basidiomycota, particularly ectomycorrhizal fungi, and the lowest diversity and richness. The other tree families and the unplanted soil harboured a greater abundance of Ascomycota and Mucoromycota. Consequently, for both bacteria and fungi, the site effect significantly impacted their community richness and composition, while the influence of plants on the richness and composition of rhizospheric microbial communities stayed consistent across sites and was dependent on the microbial kingdom. Finally, we highlighted the importance of considering this contrasting response of plant rhizospheric microbial communities in relation to their host identity, particularly to improve assisted revegetation efforts at contaminated sites.

Ecophysiological response of Populus alba L. to multiple stress factors during the revitalisation of coal fly ash lagoons at different stages of weathering

The enormous quantities of fly ash (FA) produced by thermal power plants is a global problem and safe, sustainable approaches to reduce the amount and its toxic effects are still being sought. Vegetation cover comprising long-living species can help reduce FA dump-related environmental health issues. However, the synergistic effect of multiple abiotic factors, like drought, low organic matter content, a deficit of essential nutrients, alkaline pH, and phytotoxicity due to high potentially toxic element (PTE) and soluble salt content, limits the number of species that can grow under such stressful conditions. Thus, we hypothesised that Populus alba L., which spontaneously colonised two FA disposal lagoons at the 'Nikola Tesla A' thermal power plant (Obrenovac, Serbia) 3 years (L3) and 11 years (L11) ago, has high restoration potential thanks to its stress tolerance. We analysed the basic physical and chemical properties of FA at different weathering stages, while the ecophysiological response of P. alba to multiple stresses was determined through biological indicators [the bioconcentration factor (BCF) and translocation factor (TF) for PTEs (As, B, Cr, Cu, Mn, Ni, Se, and Zn)] and by measuring the following parameters: photosynthetic efficiency and chlorophyll concentration, non-enzymatic antioxidant defence (carotenoids, anthocyanins, and phenols), oxidative stress (malondialdehyde (MDA) concentrations), and total antioxidant capacity (IC50) to neutralise DPPH free radical activity. Unlike at L3, toxic As, B, and Zn concentrations in leaves induced oxidative stress in P. alba at L11, shown by the higher MDA levels, lower vitality, and reduced synthesis of chlorophyll, carotenoids, and total antioxidant activity, suggesting its stress tolerance decreases with long-term exposure to adverse abiotic factors. Although P. alba is a fast-growing species with good metal accumulation ability and high stress tolerance, it has poor stabilisation potential for substrates with high As and B concentrations, making it highly unsuitable for revitalising such habitats.

Boron contamination and its risk management in terrestrial and aquatic environmental settings

Boron (B) is released to terrestrial and aquatic environments through both natural and anthropogenic sources. This review describes the current knowledge on B contamination in soil and aquatic environments in relation to its geogenic and anthropogenic sources, biogeochemistry, environmental and human health impacts, remediation approaches, and regulatory practices. The common naturally occurring sources of B include borosilicate minerals, volcanic eruptions, geothermal and groundwater streams, and marine water. Boron is extensively used to manufacture fiberglass, thermal-resistant borosilicate glass and porcelain, cleaning detergents, vitreous enamels, weedicides, fertilizers, and B-based steel for nuclear shields. Anthropogenic sources of B released into the environment include wastewater for irrigation, B fertilizer application, and waste from mining and processing industries. Boron is an essential element for plant nutrition and is taken up mainly as boric acid molecules. Although B deficiency in agricultural soils has been observed, B toxicity can inhibit plant growth in soils under arid and semiarid regions. High B intake by humans can be detrimental to the stomach, liver, kidneys and brain, and eventually results in death. Amelioration of soils and water sources enriched with B can be achieved by immobilization, leaching, adsorption, phytoremediation, reverse osmosis, and nanofiltration. The development of cost-effective technologies for B removal from B-rich irrigation water including electrodialysis and electrocoagulation techniques is likely to help control the predominant anthropogenic input of B to the soil. Future research initiatives for the sustainable remediation of B contamination using advanced technologies in soil and water environments are also recommended.

Field evaluation of industrial non-food crops for phytomanaging a metal-contaminated dredged sediment

Phytomanagement is a concept fit for a bio-based circular economy that combines phytotechnologies and biomass production for non-food purposes. Here, ten annual and perennial industrial non-food crops (Sorghum Biomass 133, Sorghum Santa Fe red, Linum usitatissimum L., Eucalyptus sp., Salix Inger, Salix Tordis, Beta vulgaris L., Phacelia tanacetifolia Benth., Malva sylvestris L., and Chenopodium album L.) were studied under field conditions for phytomanaging a metal (Cd, Cu, Pb, and Zn)-contaminated dredged sediment in the North of France. The crops were selected according to their relevance to pedoclimatic and future climatic conditions, and one or more non-food end-products were proposed for each plant part collected, such as biogas, bioethanol, compost, natural dye, ecocatalyst, and fiber. Based on the soil-plant transfer of metals, eight out of the crops cultivated on field plots exhibited an excluder behavior (bioconcentration factor, BCF < 1), a trait suitable for phytostabilization. However, these crops did not change the metal mobilities in the dredged sediment. The BCF < 1 was not sufficient to characterize the excluder behavior of crops as this factor depended on the total dredged-sediment contaminant. Therefore, a BCF group ranking method was proposed accounting for metal phytotoxicity levels or yield decrease as a complemental way to discuss the crop behavior. The feasibility of the biomass-processing chains was discussed based on these results and according to a survey of available legislation in standard and scientific literature.

A combined approach utilizing UAV 3D imaging methods, in-situ measurements, and laboratory experiments to assess water evaporation and trace element uptake by tree species growing in a red gypsum landfill

The extractive industry is increasingly faced with problems of managing contaminated sites. The red gypsum landfill at the Ochsenfeld site is representative of the typology byproduct storage of the Ti-extraction activity. The management of the elemental content and the water body are the issues at this site. The aim of this study was to evaluate the canopy conductance (g_cmax) of various tree species and the content of elements in the leaves, utilizing the opportunity of a demonstration plantation setup in 2014 with sixteen tree species, combined with a growth chamber experiment. We combined the gas exchange measurements with the data from two multispectral cameras with RGB and NIR bands embarked on an unmanned aerial vehicle (UAV). In the field, Ostrya carpinifolia, Maclura pomifera, and Rhus copallina had the highest g_cmax of all planted tree species, and the high transpiration rate in O. carpinifolia was confirmed in a pot-based controlled experiment. Except R. copallina, the species with a high Mn content (O. carpinifolia, Betula pendula, and Salix aquatica grandis) had high stomatal conductance. O. carpinifolia could therefore be a species to exploit in the management of landfill leachates, especially in the context of climate change since this species is well adapted to dry environments.

A risk management framework for Gentle Remediation Options (GRO)

Gentle Remediation Options (GRO) are remediation measures involving plants, fungi, bacteria, and soil amendments that can be applied to manage risks at contaminated sites. Several studies and decision-support tools promote the wider range of benefits provided by GRO, but there is still skepticism regarding GRO implementation. Key issues that need to be better communicated are the various risk mitigation mechanisms, the required risk reduction for an envisioned land use, and the time perspective associated with the risk mitigation mechanisms. To increase the viability and acceptance of GRO, the phytomanagement approach implies the combination of GRO with beneficial green land use, gradually reducing risks and restoring ecosystem services. To strengthen the decision basis for GRO implementation in practice, this paper proposes a framework for risk management and communication of GRO applications to support phytomanagement strategies at contaminated sites. The mapping of the risk mitigation mechanisms is done by an extensive literature review and the Swedish national soil guideline value model is used to derive the most relevant human health exposure pathways and ecological risks for generic green land use scenarios. Results indicate that most of the expected risk mitigation mechanisms are supported by literature, but that knowledge gaps still exist. The framework is demonstrated to support the identification of GRO options for the case study site given two envisioned land uses: biofuel park and allotment garden. A more easily understandable risk management framework, as proposed here, is expected to act as a communication tool to educate decision-makers, regulatory bodies and other stakeholders for better understanding of risk mitigation mechanisms and preliminary timeframes of various GRO, particularly in the early stages of a brownfield redevelopment project.

An Assessment of the Phytoremediation Potential of Planted and Spontaneously Colonized Woody Plant Species on Chronosequence Fly Ash Disposal Sites in Serbia—Case Study

In this study, the potential of planted (Tamarix tetrandra Pall. ex M.Bieb. and Robinia pseudoacacia L.) and spontaneously colonized (Amorpha fruticosa L. and Populus alba L.) woody species for the phytoremediation of potentially toxic trace elements (TEs) such as As, B, Cr, Cu, Mn, Ni, Se, and Zn, from the chronosequence fly ash (FA) deposit lagoons (L1 and L2) at the ‘Nikola Tesla A’ Thermal Power Plant (TENT-A) in Serbia were analyzed. The differences in the pseodototal and bioavailable (DTPA-extractable) concentrations and mobility (AR index) of TEs in FA at the examined lagoons are a result of the time-conditioned influence of weathering (3 and 11 years respectively) and vegetation development on changing the basic physical and chemical properties of FA (texture, pH, EC, CEC, C, N, and bioavailable P and K) and its toxicity. This resulted in differences in the concentration of TEs in the roots and leaves of the examined plants at L1 and L2. All examined species accumulated Cr the most in the root (BAF > 1 and TF < 1), which suggests that they are good stabilizers of this element. Biological indices for As (BAF > 1 and TF < 1) identified T. tetrandra and A. fruticose as good stabilizers of As. P. alba stood out as accumulating the highest levels of B, Ni, and Zn, T. tetrandra the highest levels of Cu, Mn, and Se, and R. pseudoacacia the highest levels of As and B in leaves (BAF > 1; TF > 1), which makes them good extractors of these elements from the FA at TENT-A. However, due to toxic concentrations of As, B, Se, and Zn in their leaves, they are not recommended for the phytoremediation of the investigated lagoons through the process of phytostabilization. Under conditions of elevated total Cu and Ni concentration in FA, the content of these elements in the leaves of A. fruticosa at both lagoons were within the normal range. This, in addition to a good supply of essential Zn, the stabilization of As and Cr in the roots, an increase in BAF, and a decrease in TF for B with a decrease in its mobility in ash over time, singles this invasive species out as the best candidate for the phytostabilization of TEs in FA at the TENT-A ash deposit site.

Boron Bioaccumulation by the Dominant Macrophytes Grown in Various Discharge Water Environments

Turkey has the largest boron (B) reserves in the world (> 70 %). Therefore, the land and water resources in Turkey contaminated with high concentration of B Pollution due to mining and industrial operations. This study investigates the accumulation of B in aquatic macrophytes soil and water in the both mining and municipal waste water discharges. For this purpose, soil, plant and water samples were collected from the streams at the areas of mining and municipal waste water discharge sites and analyzed for B using ICP-MS. Results show that the Xanthium strumarium, Eupatorium cannabinum, Lythrum salicaria, Tamarix tetrandra, Typha latifolia, and Salix sp. hyperaccumulate B. These hyperaccumulator plants have a great capacity to accumulate and transport B to plant parts from the soil and water. Therefore, these plants can be useful for decontaminating or rehabilitation of soils and waters polluted with B.

Myriophyllum elatinoides: A potential candidate for the phytoremediation of water with low level boron contamination

Phytoremediation is considered to be a cost-effective strategy for removing boron (B) from polluted water. In this study, Myriophyllum elatinoides, a widespread submerged or floating macrophyte, was found to survive in 40 mg B/L. Time-dependent kinetics show that the shoot exhibits a much longer period of B uptake and a much higher maximal tissue B concentration than the root. High values of the bioconcentration factor (BCF) and translocation factor (TF) indicate that M. elatinoides is a potential hyperaccumulator of B. Transmission electron micrographs show that excess B damages the cells of M. elatinoides, and the major target organelles are the chloroplast (leaf), mitochondria (stem and root), and nucleolus (root). Energy dispersive spectroscopy (EDS) shows that B is mainly deposited in the cytoplasm and on the surface of the chloroplast of the leaf cell. In the stem and root cells, B is mainly deposited on the mitochondrial membrane and in the vacuoles, respectively. This study indicates that the mechanisms of B toxicity, tolerance, and accumulation in M. elatinoides are involved in the cellular localization of B. Future work should focus on the evaluation of the physiological and genetic mechanisms involved in B tolerance and accumulation in M. elatinoides under different conditions.

Synthesis and bioactivity of (13Z,15E)-octadecadienal: A sex pheromone component from Micromelalopha siversi Staudinger (Lepidoptera: Notodontidae)

BACKGROUND

Micromelalopha siversi (Staudinger) (Lepidoptera: Notodontidae) is a defoliator of poplar trees, Populus spp. (Salicaceae). In our previous study, 13,15-octadecadienal has been conformed as a female-produced candidate sex pheromone component of M. siversi, but the Z/E stereochemistry of the 1,3-diene system has not been identified so far.

RESULTS

Four unsaturated aliphatic aldehydes, Z13,E15-18:Ald, Z13,Z15-18:Ald, E13,E15-18:Ald, and E13,Z15-18:Ald, were synthesized from the commercially available 12-bromo-1-decanol mainly by alkylation of lithium alkyne, normal Wittig or Wittig-Schlosser olefination, and hydroboration-protonolysis. According to gas chromatography (GC) analysis of pheromone gland extracts, Z13,E15-18:Ald was the main component, and a small amount of Z13,Z15-18:Ald was also detected, with a ratio of approximately 7:3. However, the results of GC-electroantennographic detection (GC-EAD) showed that Z13,E15-18:Ald was the only compound with electrophysiological activity, whereas Z13,Z15-18:Ald elicited no activity. In the field, traps baited with only Z13,E15-18:Ald resulted in much superior results to those with Z13,Z15-18:Ald as well as the Z13,E15-18:Ald and Z13,Z15-18:Ald binary mixture.

CONCLUSIONS

Based on geometrically selective synthesis and bioactivity tests, the active sex pheromone component of M. siversi has been identified as Z13,E15-18:Ald, the pheromone component that has not been identified in Lepidoptera before. The synthetic component was attractive to male moths in preliminary field traps, which provides novel technologies to monitor and control this pest.

Analysis of physiological responses and expression profiling of boron transporter-like genes in response to excess boron in Populus russkii

Poplars (Populus species) are tolerant to boron (B) toxicity and have phytoremediation potential in B-contaminated soils. However, the detoxification strategy is largely unknown. To screen the key B transporter-like (BOR-like) genes for B compartmentation, Populus russkii plants were exposed to different levels of excess B and the plant growth, physiological responses, B distribution, and the expression patterns of BOR-like genes were characterized. P. russkii showed moderate tolerance to excess B although the plant growth was inhibited. The enhanced proline level and well-regulated antioxidant defense system were associated with B tolerance in leaves. The B absorbed by plants was predominantly allocated to leaves. Ten BOR-like genes were identified and seven of them showed tissue-specific expression patterns. PrBOR7 was identified as an important BOR-like gene possibly involved in the export of B from leaf cytoplasm because it was expressed specifically in leaves and induced by excess B. Yeast experiment assays verified that PrBOR7 functions as an efflux-type transporter and strongly improved cell tolerance to excess B. The expression patterns of BOR-like genes highlight the diversity of the family members in P. russkii, and PrBOR7 has potential as a candidate gene for B detoxification.

Boron tolerance and accumulation potential of four salt-tolerant plant species

Boron (B) is an essential element for plants, but excess B is phytotoxic. Since excess B often occurs along with high salinity in the environment, the purposes of the experiments are to screen plants that tolerate both excess B and high salinity for the remediation of B-contaminated saline water or soils. Here we tested the capacities of B tolerance and accumulation of four salt-tolerant plant species, Tripolium pannonicum, Suaeda glauca, Iris wilsonii, and Puccinellia tenuiflora using hydroponic culture systems, and compared their potential for application in phytoremediation. The maximum B supply concentrations for the survival of T. pannonicum, S. glauca, I. wilsonii, and P. tenuiflora are 40, 250, 700, and 300 mg/L, respectively. The maximum B concentrations in the shoot tissue of these plants are 0.45, 2.48, 15.21, and 8.03 mg/g DW, and in the root are 0.23, 0.70, 6.69, and 2.63 mg/g DW, respectively. Our results suggest that S. glauca, I. wilsonii, and P. tenuiflora are capable of tolerating and accumulating high levels of B, and I. wilsonii is a most promising candidate for the remediation of B-contaminated sites. This study will provide evidence in support of our future pilot studies (e.g., constructed wetlands) on the phytoremediation of B-contaminated water and soil.

Biowastes to augment the essential oil production of Leptospermum scoparium and Kunzea robusta in low-fertility soil

Biowastes are unwanted materials of biological origin. They include biosolids, dairy shed effluent, and sawdust. When applied to soil, biowastes can provide plant nutrients, but also introduce heavy metals, pathogens, or xenobiotics. Biowastes could improve degraded or low-fertility soils and generate revenue through the production of non-food products such as essential oils. We grew New Zealand native plants, mānuka (Leptospermum scoparium J.R. Forst & G. Forst) and kānuka (Kunzea robusta de Lange & Toelken) in series of greenhouse experiments in low-to-medium-fertility soils (Bideford clay loam, Lismore stony silt loam, and Pawson silt loam) amended with either biosolids (up to 13500 kg N ha^-1 equiv.), biosolids + sawdust (1:0.5-1250 kg N ha^-1 equiv.) and dairy shed effluent (200 kg N ha^-1 equiv.). Two types of biosolids from Kaikoura (KB) and Christchurch City Council (CB) were used in the experiments. CB (1500 kg N ha^-1 equiv.) and dairy shed effluent (200 kg N ha^-1 equiv.) increased the biomass of L. scoparium by up to 120% and 31%, and K. robusta by up to 170% and 34%, respectively. Adding sawdust to KB increased the biomass of L. scoparium and K. robusta although it offset the L. scoparium growth increase in the KB-only treatment. The growth response of K. robusta to biowastes was greater than L. scoparium with oil production in K. robusta increasing by up to 211% when 1500 kg N ha^-1 equiv. of CB was applied to Lismore stony silt loam. Generally, the treatments had a negligible effect on oil concentration in all the soil types, except for the KB + sawdust treatment, which increased the oil concentration by 82%. Most of the EOs' major components were unaffected by biowaste addition in the soils, although some components increased in the Bideford clay loam following KB and KB + sawdust application. Biosolids increased foliar concentrations of Zn, Cu, and Cd, but these were below risk-threshold concentrations. Applying CB (up to 1500 kg N ha^-1 equiv.) to low-fertility soils is recommended to establish ecosystems dominated by L. scoparium and K. robusta that annually would produce ca. 100 kg ha^-1 of EOs worth US$ 26k and 24k, respectively. Adding sawdust to CB could have environmental benefits through reduction of N leaching. Field trials are warranted to elucidate critical ecological variables and production economics in biowaste management.

Overcoming limitation of "recalcitrant areas" to phytoextraction process: The synergistic effects of exogenous cytokinins and nitrogen treatments

The aim of the present work was to test the efficiency of the phytoextraction process involving the use of exogenous phytohormone (cytokinins, CKs) and fertilizer (nitrogen, N) treatments in phytotechnologies to address risk management in "recalcitrant areas". The CKs and N treatments, alone or combined (CKs + N) in a Modulated Application (MA), were tested on the crop plant Helianthus annuus, common to Mediterranean area, fast growing and with high biomass production. Plants were grown on boron (B) contaminated sediments (collected from a geothermal area located in Tuscany (Italy). Plant growth, B uptake, together with plant stress parameters were investigated. Boron is easily taken up and translocated by some crop plants, but the high phytotoxicity can dramatically impact the plant growth and consequently the applicability and efficiency of the phytoextraction process. As indicators of plant stress, oxidative balance and photosynthetic parameters were investigated to give a deeper insight of phytotoxic mechanisms. Results showed that while each treatment (CKs and N alone) had significantly positive effects on plant health, the MA treatment provided a synergistic effect on morphological parameters and biomass production as a whole. After MA treatment, plants showed antioxidant activity comparable to that of the control (unpolluted sediments) and showed an increase of net photosynthesis. Moreover, our data showed very high values of B uptake and translocation (about 800 mg kg^-1 in shoots), without any alteration triggered by the treatments (CKs and N alone or combined in MA). B phytoextraction resulted increased about fivefold with the MA treatments, while each treatment alone increased only two or three folds when treated with either CKs or N. The MA treatment is not "contaminant specific", so it could be applied in other "recalcitrant areas" where different types of contaminations occur, in order to overcome limitations of plant growth.

Temporal changes of metal bioavailability and extracellular enzyme activities in relation to afforestation of highly contaminated calcareous soil

Metal bioavailability and extracellular enzyme activity are two important indicators of soil quality in metal-contaminated soil. However, it is unclear how the chronosequence effect modifies these two factors in highly contaminated calcareous soils undergoing afforestation. We used Populus simonii Carr. and the calciphilous Ulmus macrocarpa Hance as contrasting tree species to study the chronosequence effect. We found that afforestation significantly increased soil total nitrogen (N) content as well as soil carbon (C)/phosphorus (P) and N/P ratios, but decreased soil total P content and soil C/N ratio, regardless of the tree species and stand age, suggesting strong P limitation. However, available P did not change significantly with stand age. In both tree species, P mobilization depleted soil organic matter through the priming effect of dissolved organic carbon, whereas the decrease in soil pH in the U. macrocarpa stands enhanced CaCO₃ dissolution, collectively reducing the capacity of the soil to immobilize metals, resulting in increased metal bioavailability with stand age. The activity of oxidase (dehydrogenase) was positively correlated with bioavailable zinc concentration, soil electrical conductivity, and soil total N content. Hydrolase activities (alkaline phosphatase, β-glucosidase, and urease) were significantly positively correlated with the ratios of soil C/N and C/P, soil pH, and CaCO₃, but negatively correlated with soil N/P ratio and bioavailable cadmium concentration. Increasing stand age was associated with the gradual recovery of oxidase activity and remarkable inhibition of hydrolase activity. Our results suggest that the combination of soil hydrolase activity and metal bioavailability can predict soil quality in the afforestation of highly contaminated soils.

Phytoremediation potential of poplar and willow species in small scale constructed wetland for boron removal

Boron (B) pollution is an expanding environmental problem throughout the world due to intensive mining practices and extensive usage of B in agricultural chemicals and industrial products in recent years. The purpose of this study was to investigate B removal performance of four poplar and four willow species in small scale Constructed Wetland (CW). Rooted cuttings of tested species were treated with simulated wastewater having five elevated B concentrations (0.5, 5, 10, 20 and 40 ppm). All the tested species could resist up to 20 ppm wastewater B supply and could regrow from their roots in the soil having maximum 15 mg/kg B content. The result of the study indicated that 65% ± 5.3 of B was removed from the wastewater in 5 ppm B treatment while the same efficiency decreased to 45% ± 4.6 at 40 ppm B supply. The average effect of sediment on B removal was found to be approximately 20% for all B treatments while the remaining part of the loaded B was removed from the CW within effluent (35-54%). Therefore, actual effects of plant species on B removal was ranged from 45% to 25% between 5 and 40 ppm B treatments. Mass B removal within plant body (phytextraction) comprised the 13-10% of total loaded B in CW while the remaining part of the loaded B (31-15%) was stabilized into the sediment with the effects of poplar and willow roots. These results presented clear understanding of effective B purification mechanisms in CWs. Boron phytextraction capacity of a plant species was less effective than its phytstabilization efficiency which increase filtering capacity of the sediment and stabilization of more B around the rhizosphere. In terms of their B removal ability, P.nigra and S.anatolica had the highest B removal capacities with phytextraction (20-11%) while S.alba, P.alba and S.babylonica had more phytstabilizaiton performance (40-15%) in CW. Disposal of B loaded plant material create another environmental costs for CW applications. Therefore, B loaded wood and leaf tissues were mixed and used for production of wooden panels in the study. Then a combustion test was applied on these panels to test their fire resistance. The results of the tests revealed much higher burning tolerance of the B loaded panels (5-20%) compared to controls. Annual harvesting, fast growing and deep rooting ability of the poplar and willow species with their high phytstabilization and phytextraction efficiencies make these species excellent tools to remove B from the polluted waters. Utilization of these species for B removal in large scale CWs is quite possible which should be also investigated in further studies.

Evaluation of two hybrid poplar clones as constructed wetland plant species for treating saline water high in boron and selenium, or waters only high in boron

Wetland mesocosms were constructed to assess two hybrid poplar clones (Populustrichocarpa×P. deltoides×P. nigra '345-1' and '347-14') for treating saline water high in boron (B) and selenium (Se), and a hydroponic experiment was performed to test the B tolerance and B accumulation in both clones. In the mesocosm experiment, clone 345-1 exhibited no toxic symptoms at an EC of 10mScm^-1, while clone 347-14 showed slight toxic symptoms at 7.5mScm^-1. The removal percentages of B, Se, sodium (Na), and chloride (Cl) ranged from 26.7-45.6%, 50-69.4%, 18.4-24.0%, and 15.8-23.2%, respectively, by clone 345-1, and from 22.9-29.4%, 31.7-43.8%, 16.5-24.2%, and 14.9-23.9%, respectively, by clone 347-1. In the hydroponic experiment, B toxic symptoms were observed at treatments of 150 and 200mg B L^-1 for clones 345-1 and 347-14, respectively. The greatest leaf B concentrations of 3699 and 1913mgkg^-1 were found in clone 345-1 and clone 347-14, respectively. The translocation factor (TF) of clone 347-14 was less than clone 345-1. Clone 345-1 only showed significantly greater (P<0.05) B removal percentages than clone 347-14 when B treatment was <20mg B L^-1. In conclusion, both tested poplar clones competitively accumulated and removed B and Se in constructed wetlands.

Photosynthesis and aboveground carbon allocation of two co-occurring poplar species in an urban brownfield

Phytoremediation, a technique used to reclaim heavy metal-contaminated soils, requires an understanding of plant physiological responses to heavy metals. However, the majority of studies documenting heavy metal impact on plant functioning have been performed in laboratory or greenhouse settings. We predicted that increased soil heavy metal concentrations reduce photosynthesis and biomass production in trees growing in metal contaminated soil in a naturally re-vegetated urban brownfield. Leaf gas exchange, leaf carbon and nitrogen concentration, and tree biomass were recorded and compared for Populus deltoides and Populus tremuloides growing in an urban brownfield. The CO₂ compensation point (CCP) differed significantly between soil metal concentrations and species, with P. deltoides displaying a greater CCP and P. tremuloides displaying a lower CCP as soil metal concentration increased, despite no changes in dark respiration for either species. In terms of biomass, only total branch weight (TBW) and leaf area (LA) differed significantly between soil metal concentrations, though the difference was largely attributable to variation in diameter at breast height (DBH). Furthermore, TBW and LA values for P. deltoides did not decrease with increasing soil metal concentration. Soil metal concentration, thus, had minimal effect on the relationship between tree age and DBH, and no effect on relationships of tree age and height or LA, respectively. Significant differences between soil metal concentrations and species were found for δ¹⁵N (isotopic nitrogen ratio) while leaf nitrogen content (% N) also differed significantly between species. Long-term water use efficiency derived from carbon isotope analysis (iWUE_isotope) differed significantly between trees grown on different soil metal concentrations and a significant species-metal concentration interaction was detected indicating that the two study species responded differentially to the soil metal concentrations. Specifically, P. tremuloides enhanced while P. deltoides reduced long-term iWUE_isotope as soil metal concentration increased, further emphasizing the importance of species and possible genotype selection for phytoremediation.

Native herbaceous plant species with potential use in phytoremediation of heavy metals, spotlight on wetlands - A review

Soil, air and water pollution caused by the mobility and solubility of heavy metals significantly damages the environment, human health, plants and animals. One common in situ method used for the decontamination of heavy metals is phytoremediation. This usually involves the use of exotic species. However, these species may exhibit invasive behavior, thereby, affect the environmental and ecological dynamics of the ecosystem into which they are introduced. This paper focuses on some native herbaceous plant species reported on the wetlands of Bogota, Colombia, with potential use in phytoremediation of heavy metals. To do that, the authors identified and searched a bibliography based on key words related to heavy metal decontamination. In addition, authors gathered and analyzed relevant information that allowed the comprehension of the phytoremediation process. This paper suggests the study of 41 native or endemic species regarding their behavior towards heavy metal contamination. From a survey of herbaceous plants reported in Bogota, native and endemic species that belong to predominant families in heavy metal accumulation processes were selected. Although found in Colombian's wetlands, these can also be found worldwide. Therefore, they are of great interest due to their global presence and their potential for use in phytoremediation. The current research about the development of phytoremediation focuses on the identification of new herbaceous species able to decontaminate substratum polluted with heavy metals to contribute with the investigation of the ecology and environment of the nature's remnants in urban wetland ecosystems.

Removal of boron from wastewater: Evaluation of seven poplar clones for B accumulation and tolerance

Boron (B) contamination of wastewater is a serious environmental and health problem, which has proved difficult to remediate. One potential approach is phytoremediation, i.e., the use of plants to extract B into the shoot systems, which can then be harvested and removed. The purpose of this study was to investigate the ability of seven hybrid poplar clones to accumulate and tolerate B at different levels of B and salinity. The clones were grown in quarter strength Hoagland's nutrient solution and exposed to four B treatments: 0.25, 25, 75 and 125 mg B L^-1 in factorial combination with three salinity treatments: 0, 0.5 and 5 g L^-1. Measurements were made of biomass (dry weight) and B concentrations (analyzed by inductively coupled plasma-optical emission spectroscopy) of plant tissues. The results showed that, with increasing level of B supply, the B concentrations in the shoot tissue of the poplar clones increased, while shoot biomass decreased. Comparison of the seven different poplar clones revealed that the clone designated 195-529 exhibited the greatest ability for B accumulation and tolerance. Generally, the 0.5 g L^-1 level of salinity was beneficial for poplar growth and B removal, while the high salinity level of 5 g L^-1 significantly inhibited poplar growth and B translocation from roots to shoots. Based on the results obtained with this hydroponic system, the clone 195-529 (P. trichocarpa × P. deltoides) is likely to be the most useful for the removal of B from B contaminated wastewater.

Genome-wide transcriptome profiling of black poplar (Populus nigra L.) under boron toxicity revealed candidate genes responsible in boron uptake, transport and detoxification

Boron (B) is an essential nutrient for normal growth of plants. Despite its low abundance in soils, it could be highly toxic to plants in especially arid and semi-arid environments. Poplars are known to be tolerant species to B toxicity and accumulation. However, physiological and gene regulation responses of these trees to B toxicity have not been investigated yet. Here, B accumulation and tolerance level of black poplar clones were firstly tested in the current study. Rooted cutting of these clones were treated with elevated B toxicity to select the most B accumulator and tolerant genotype. Then we carried out a microarray based transcriptome experiment on the leaves and roots of this genotype to find out transcriptional networks, genes and molecular mechanisms behind B toxicity tolerance. The results of the study indicated that black poplar is quite suitable for phytoremediation of B pollution. It could resist 15 ppm soil B content and >1500 ppm B accumulation in leaves, which are highly toxic concentrations for almost all agricultural plants. Transcriptomics results of study revealed totally 1625 and 1419 altered probe sets under 15 ppm B toxicity in leaf and root tissues, respectively. The highest induction were recorded for the probes sets annotated to tyrosine aminotransferase, ATP binding cassette transporters, glutathione S transferases and metallochaperone proteins. Strong up regulation of these genes attributed to internal excretion of B into the cell vacuole and existence of B detoxification processes in black poplar. Many other candidate genes functional in signalling, gene regulation, antioxidation, B uptake and transport processes were also identified in this hyper B accumulator plant for the first time with the current study.

Boron stress response and accumulation potential of the extremely tolerant species Puccinellia frigida

Phytoremediation is a promising technology to tackle boron toxicity, which restricts agricultural activities in many arid and semi-arid areas. Puccinellia frigida is a perennial grass that was reported to hyperaccumulate boron in extremely boron-contaminated sites. To further investigate its potential for phytoremediation, we determined its response to boron stress under controlled conditions (hydroponic culture). Also, as a first step towards understanding the mechanisms underlying its extreme tolerance, we evaluated the presence and expression of genes related with boron tolerance. We found that P. frigida grew normally even at highly toxic boron concentrations in the medium (500mg/L), and within its tissues (>5000mg/kg DW). We postulate that the strategies conferring this extreme tolerance involve both restricting boron accumulation and an internal tolerance mechanism; this is consistent with the identification of putative genes involved in both mechanisms, including the expression of a possible boron efflux transporter. We also found that P. frigida hyperaccumulated boron over a wide range of boron concentrations. We propose that P. frigida could be used for boron phytoremediation strategies in places with different soil characteristics and boron concentrations. Further studies should pave the way for the development of clean and low-cost solutions to boron toxicity problems.

Biowaste Mixtures Affecting the Growth and Elemental Composition of Italian Ryegrass ()

Biosolids (sewage sludge) can be beneficially applied to degraded lands to improve soil quality. Plants grown on biosolids-amended soils have distinct concentrations of macronutrients and trace elements, which can be beneficial or present a risk to humans and ecosystems. Potentially, biosolids could be blended with other biowastes, such as sawdust, to reduce the risks posed by rebuilding soils using biosolids alone. We sought to determine the effect of mixing biosolids and sawdust on the macronutrient and trace element concentration of ryegrass over a 5-mo period. was grown in a low fertility soil, typical for marginal farm areas, that was amended with biosolids (1250 kg N ha), biosolids + sawdust (0.5:1) and urea (200 kg N ha), as well as a control. Biosolids increased the growth of from 2.93 to 4.14 t ha. This increase was offset by blending the biosolids with sawdust (3.00 t ha). Urea application increased growth to 4.93 t ha. The biowaste treatments increased N, P, Cu, Mn, and Zn relative to the control, which may be beneficial for grazing animals. Although biowaste application caused elevated Cd concentrations (0.15-0.24 mg kg) five- to eightfold higher than control and urea treatments, these were below levels that are likely to result in unacceptable concentrations in animal tissues. Mixing biosolids with sawdust reduced Cd uptake while still resulting in increased micronutrient concentrations (P, S, Mn, Zn, Cu) in plants. There were significant changes in the elemental uptake during the experiment, which was attributed to the decomposition of the sawdust.

The phytoremediation of an organic and inorganic polluted soil: A real scale experience

A phytoremediation process with horse manure, plants (Populus alba, Cytisus scoparius, Paulownia tomentosa) and naturally growing vegetation was carried out at a real-scale in order to phytoremediate and functionally recover a soil contaminated by metals (Zn, Pb, Cd, Ni, Cu, Cr), hydrocarbons (TPH) and polychlorobiphenyls (PCB). All the plants were effective in two years in the reclamation of the polluted soil, showing an average reduction of about 35%, 40%, and 70% in metals, TPH and PCB content, respectively. As regards the plants, the poplar contributed the most to organic removal. In fact, its ability to take up and detoxify organic pollutants is well known. Paulownia tomentosa, instead, showed high metal removal. The Cytisus scoparius was the least effective plant in soil decontamination. The recovery of soil functionality was followed by enzyme activities, expressing the biochemical processes underway, and nutrient content useful for plant growth and development. Throughout the area, an enhancement of metabolic processes and soil chemical quality was observed. All the enzymatic activities showed a general increase over time (until 3-4 fold than the initial value for urease and β-glucosidase). Moreover, Cytisus scoparius, even though it showed a lower decontamination capability, was the most effective in soil metabolic stimulation.

Effect of Pine Waste and Pine Biochar on Nitrogen Mobility in Biosolids

Humanity produces ∼27 kg of dry matter in biosolids per person per year. Land application of biosolids can improve crop production and remediate soils but may result in excessive nitrate N (NO-N) leaching. Carbonaceous materials can reduce the environmental impact of biosolids application. We aimed to ascertain and compare the potentials for Monterey pine ( D. Don)-sawdust-derived biochars and raw sawdust to reduce NO-N leaching from biosolids. We used batch sorption experiments 1:10 ratio of material to solution (100 mg kg of NH or NO) and column leaching experiments with columns containing biosolids (2.7% total N, 130 mg kg NH and 1350 mg kg NO) mixed with soil, biochar, or sawdust. One type of low-temperature (350°C) biochar sorbed 335 mg kg NH, while the other biochars and sawdust sorbed <200 mg kg NH. None of the materials sorbed NO. Biochar added at rates of 20 to 50% reduced NH-N (<1% of total N) leaching from columns by 40 to 80%. Nitrate leaching (<7% of total N) varied little with biochar form or rate but was reduced by sawdust. Incorporating dried sawdust with biosolids showed promise for mitigating NO-N leaching. This effect likely is due to sorption into the pores of the biochar combined with denitrification and immobilization of N rather than chemical sorption onto surfaces.

Long-term field phytoextraction of zinc/cadmium contaminated soil by Sedum plumbizincicola under different agronomic strategies

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment "S. plumbizincicola intercropped with maize" was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha(-1) gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.

Copper nanoparticles/compounds impact agronomic and physiological parameters in cilantro (Coriandrum sativum)

The environmental impacts of Cu-based nanoparticles (NPs) are not well understood. In this study, cilantro (Coriandrum sativum) was germinated and grown in commercial potting mix soil amended with Cu(OH)2 (Kocide and CuPRO), nano-copper (nCu), micro-copper (μCu), nano-copper oxide (nCuO), micro-copper oxide (μCuO) and ionic Cu (CuCl2) at either 20 or 80 mg Cu per kg. In addition to seed germination and plant elongation, relative chlorophyll content and micro and macroelement concentrations were determined. At both concentrations, only nCuO, μCuO, and ionic Cu, showed statistically significant reductions in germination. Although compared with control, the relative germination was reduced by ∼50% with nCuO at both concentrations, and by ∼40% with μCuO, also at both concentrations, the difference among compounds was not statistically significant. Exposure to μCuO at both concentrations and nCu at 80 mg kg(-1) significantly reduced (p≤ 0.05) shoot elongation by 11% and 12.4%, respectively, compared with control. Only μCuO at 20 mg kg(-1) significantly reduced (26%) the relative chlorophyll content, compared with control. None of the treatments increased root Cu, but all of them, except μCuO at 20 mg kg(-1), significantly increased shoot Cu (p≤ 0.05). Micro and macro elements B, Zn, Mn, Ca, Mg, P, and S were significantly reduced in shoots (p≤ 0.05). Similar results were observed in roots. These results showed that Cu-based NPs/compounds depress nutrient element accumulation in cilantro, which could impact human nutrition.

Genotypic variations in the dynamics of metal concentrations in poplar leaves: a field study with a perspective on phytoremediation

Poplar is commonly used for phytoremediation of metal polluted soils. However, the high concentrations of trace elements present in leaves may return to soil upon leaf abscission. To investigate the mechanisms controlling leaf metal content, metal concentrations and expression levels of genes involved in metal transport were monitored at different developmental stages on leaves from different poplar genotypes growing on a contaminated field. Large differences in leaf metal concentrations were observed among genotypes. Whereas Mg was remobilized during senescence, Zn and Cd accumulation continued until leaf abscission in all genotypes. A positive correlation between Natural Resistance Associated Macrophage Protein 1 (NRAMP1) expression levels and Zn bio-concentration factors was observed. Principal component analyses of metal concentrations and gene expression levels clearly discriminated poplar genotypes. This study highlights a general absence of trace element remobilization from poplar leaves despite genotype specificities in the control of leaf metal homeostasis.

Phytoremediation of metals: a numerical analysis

A finite element code was used for investigating the effect of some relevant characteristics of a phytoremediation project (crop type and density, presence of an irrigation system, soil capping and root depth). The evolution of the plume of contamination of Cd2+, Pb2+, and Zn2+ was simulated taking into account reactive transport and root processes. The plant contaminant uptake model was previously calibrated using data from greenhouse experiments. The simulations adopted pedological and climatological data representative of a sub-tropical environment. Although the results obtained were specific for the proposed scenario, it was observed that, for more mobile contaminants, poor water conditions favor stabilization but inhibit plant extraction. Otherwise an irrigation system that decreases crop water stress had an opposite effect. For less mobile contaminants, the remediation process did not have appreciable advantages. Despite its simplifying assumptions, particularly about contaminant sorption in the soil and plant system, the numerical analysis provided useful insight for the phytoextraction process important in view of field experiments.

Boron accumulation and tolerance of hybrid poplars grown on a B-laden mixed paper mill waste landfill

Paper mill wastes are a mixture of by-products from pulp production and on-site energy production, consisting of paper mill sludge, ash and cinders. Landfilling of these highly boron (B) and heavy metal laden waste products carries environmental risks. Poplars have been successfully employed in the phytomanagement and hydraulic control of B contaminated sites. Here, we assess the performance of hybrid poplars on a paper-mill waste landfill, investigate the accumulation of B by the trees and explore the relationship between local-scale root growth and substrate properties. Leaf and root tissue samples were collected on three plots and analyzed for their chemical properties and root traits. Additionally, we sampled four soil cores in the vicinity of each of the trees and determined chemical and physical properties. Using a principal component analysis followed by a cluster analysis, we identified three substrate types. This method delineated the soil effects on tree survival and growth, although correlations with individual soil element concentrations were weak. Despite signs of B toxicity in some leaves, B was not the key limiting factor for poplar growth. Instead, Ca deficiency caused by a Mg:Ca imbalance was the primary reason for the poor performance of some trees. Root growth was not limited by toxicity effects of soil contaminants. Our results show that hybrid poplars perform well under the harsh growing conditions on a multi-contaminated, B-laden substrate in a hemiboreal climate. Exploiting the differences in the performance of the four clones in relation to the soil types, could increase the success of revegetation on this and other landfills.

Field evaluation of willow under short rotation coppice for phytomanagement of metal-polluted agricultural soils

Short rotation coppice (SRC) of willow and poplar might be a promising phytoremediation option since it uses fast growing, high biomass producing tree species with often a sufficient metal uptake. This study evaluates growth, metal uptake and extraction potentials of eight willow clones (Belders, Belgisch Rood, Christina, Inger, Jorr, Loden, Tora and Zwarte Driebast) on a metal-contaminated agricultural soil, with total cadmium (Cd) and zinc (Zn) concentrations of 6.5 +/- 0.8 and 377 +/- 69 mg kg(-1) soil, respectively. Although, during the first cycle, on average generally low productivity levels (3.7 ton DM (dry matter) ha(-1) y(-1)) were obtained on this sandy soil, certain clones exhibited quite acceptable productivity levels (e.g. Zwarte Driebast 12.5 ton DM ha(-1) y(-1)). Even at low biomass productivity levels, SRC of willow showed promising removal potentials of 72 g Cd and 2.0 kg Zn ha(-1) y(-1), which is much higher than e.g. energy maize or rapeseed grown on the same soil Cd and Zn removal can be increased by 40% if leaves are harvested as well. Nevertheless, nowadays the wood price remains the most critical factor in order to implement SRC as an acceptable, economically feasible alternative crop on metal-contaminated agricultural soils.

Long-term biomonitoring of soil contamination using poplar trees: accumulation of trace elements in leaves and fruits

Phytostabilization aims to immobilize soil contaminants using higher plants. The accumulation of trace elements in Populus alba leaves was monitored for 12 years after a mine spill. Concentrations of As and Pb significantly decreased, while concentrations of Cd and Zn did not significantly over time. Soil concentrations extracted by CaCl2 were measured by ICP-OES and results of As and Pb were below the detection limit. Long-term biomonitoring of soil contamination using poplar leaves was proven to be better suited for the study of trace elements. Plants suitable for phytostabilization must also be able to survive and reproduce in contaminated soils. Concentrations of trace elements were also measured in P. alba fruiting catkins to determine the effect on its reproduction potential. Cadmium and Zn were found to accumulate in fruiting catkins, with the transfer coefficient for Cd significantly greater than Zn. It is possible for trace elements to translocate to seed, which presents a concern for seed germination, establishment and colonization. We conclude that white poplar is a suitable tree for long-term monitoring of soil contaminated with Cd and Zn, and for phytostabilization in riparian habitats, although some caution should be taken with the possible effects on the food web. Supplemental materials are available for this article. Go to the publisher's online edition of International Journal of Phytoremediation to view the supplemental file.

Fate of trace elements during the combustion of phytoremediation wood

We investigated the fate of trace elements (TE) in poplar wood on the conversion of biomass to heat in a 0.2 MW combustion unit equipped with a fabric filter. The phytoremediation wood was harvested from a TE-contaminated agricultural site planted with a high-density poplar stand. The combustion technology used in the present experiment allows for an efficient separation of the various ash fractions. The combustion process concentrates Cu, Cr, and Ni in the bottom ash, heat exchanger ash, and cyclone ash fractions. Therefore, the impact of the fabric filter is negligible for these elements. Conversely, Cd, Pb, and Zn are significantly recovered in the emission fraction in the absence of the fabric filter above the emission limits. The use of a fabric filter will allow the concentration of these three TEs in the ashes collected below the filter, thus complying with all regulatory thresholds, i.e., those from the large combustion plant EU directive. Because the TE concentrations in the different fractions differed significantly, it is recommended that these fractions be treated separately, especially when recycling of ashes from phytoremediation wood through application in agriculture is envisaged.

Practical salinity management for leachate irrigation to poplar trees

Landfill leachate can be beneficially reused for irrigation of fiber crops with appropriate attention to nutrient and salinity management. The Riverbend Landfill in Western Oregon has been effectively practicing irrigation of landfill leachate to poplar trees since 1993. Over that time, the site has been adaptively managed to control salinity impacts to the tree crop while beneficially utilizing the applied water and nutrients during each growing season. Representative leachate irrigation water has ranged in concentration of total dissolved solids from 777 to 6,940 mg/L, chloride from 180 to 1,760 mg/L and boron from 3.2 to 7.3 mg/L. Annual leachate irrigation applications have also ranged between 102 and 812 mm/yr. Important conclusions from this site have included: 1) Appropriate tree clone selection and tree stand spacing, thinning, and harvest rotations are critical to maintaining a productive tree stand that is resilient and resistant to salt stress. The most effective combinations have included clones DN-34, OP-367, 184-411, 49-177, and 15-29 planted at spacing of 3.7-m x 1.8-m to 3.7-m x 3.7-m; 2) Leaf tissue boron levels are closely correlated to soil boron levels and can be managed with leaching. When leaf tissue boron levels exceed 200 to 250 mg/kg, signs of salt stress may emerge and should be monitored closely; 3) Salinity from leachate irrigation can be managed to sustain a healthy tree crop by controlling mass loading rates and providing appropriate irrigation blending if necessary. Providing freshwater irrigation following each leachate irrigation and targeting freshwater irrigation as 30 percent of total irrigation water applied has successfully controlled salt impacts to vegetation; and 4) Drip irrigation generally requires more careful attention to long-term soil salinity management than spray irrigation. Moving drip irrigation tubes periodically to prevent the formation of highly saline zones within the soil profile is important. In this paper, a fifteen year record of monitoring and operational data are presented that can be used by others in managing irrigation of saline water to poplar trees. When salinity is carefully managed, tree systems can help to provide sustainable leachate management solutions for landfills.

Boron accumulation and toxicity in hybrid poplar (Populus nigra × euramericana)

Poplars accumulate high B concentrations and are thus used for the phytomanagement of B contaminated soils. Here, we performed pot experiments in which Populus nigra × euramericana were grown on a substrate with B concentrations ranging from 13 to 280 mg kg(-1) as H(3)BO(3). Salix viminalis, Brassica juncea, and Lupinus albus were grown under some growing conditions for comparison. Poplar growth was unaffected at soil B treatment levels up to 93 mg kg(-1). Growth was progressively reduced at levels of 168 and 280 mg kg(-1). None of the other species survived at these substrate B levels. At leaf B concentrations <900 mg kg(-1) only <10% of the poplar leaf area showed signs of toxicity. Neutron radiography revealed that chlorotic leaf tissues had B concentrations of 1000-2000 mg kg(-1), while necrotic tissues had >2000 mg kg(-1). Average B concentrations of up to 3500 mg kg(-1) were found in leaves, while spots within leaves had concentrations >7000 mg kg(-1), showing that B accumulation in leaf tissue continued even after the onset of necrosis. The B accumulation ability of P. nigra × euramericana is associated with B hypertolerance in the living tissue and storage of B in dead leaf tissue.

A review of biochars' potential role in the remediation, revegetation and restoration of contaminated soils

Biochars are biological residues combusted under low oxygen conditions, resulting in a porous, low density carbon rich material. Their large surface areas and cation exchange capacities, determined to a large extent by source materials and pyrolysis temperatures, enables enhanced sorption of both organic and inorganic contaminants to their surfaces, reducing pollutant mobility when amending contaminated soils. Liming effects or release of carbon into soil solution may increase arsenic mobility, whilst low capital but enhanced retention of plant nutrients can restrict revegetation on degraded soils amended only with biochars; the combination of composts, manures and other amendments with biochars could be their most effective deployment to soils requiring stabilisation by revegetation. Specific mechanisms of contaminant-biochar retention and release over time and the environmental impact of biochar amendments on soil organisms remain somewhat unclear but must be investigated to ensure that the management of environmental pollution coincides with ecological sustainability.

Biochar for the mitigation of nitrate leaching from soil amended with biosolids

Countries with sewage treatment plants produce on average 27 kg of dried biosolids/person/yr. Concerns about nitrate leaching limit the rate at which biosolids are added to soil. We sought to determine whether biochar, a form of charcoal that is added to soil, could reduce nitrate leaching from biosolids amended soil. We set up 24 (0.5 m × 0.75 m) lysimeters, filled with two soil types (Templeton Silt Loam and Ashley Dene silt loam) and amended with combinations of biochar (102 t/ha equivalent) and biosolids (600 and 1200 kg N/ha equivalent). Pasture and leachates were sampled over 5 months. Nitrate leaching from biochar plus biosolids amended soils were reduced to levels at or below the control treatments. Pasture N concentrations were similarly affected by biochar addition. Future research should focus on unravelling the mechanism responsible for the change in the nitrogen cycle in soils amended with biosolids and biochar.

Evaluating the role of vegetation on the transport of contaminants associated with a mine tailing using the Phyto-DSS

We identified contaminants associated with the Cata mine tailing depot located in the outskirts of the city of Guanajuato, Mexico. We also investigated strategies for their phytomanagement. Silver and antimony were present at 39 and 31 mg kg(-1), respectively, some twofold higher than the Dutch Intervention Values. Total and extractable boron (B) occurred at concentrations of 301 and 6.3 mg L(-1), respectively. Concentrations of B in soil solution above 1.9 mg L(-1) have been shown to be toxic to plants. Plant growth may also be inhibited by the low concentrations of extractable plant nutrients. Analysis of the aerial portions of Aloe vera (L. Burm.f.) revealed that this plant accumulates negligible concentrations of the identified contaminants. Calculations using a whole system model (Phyto-DSS) showed that establishing a crop of A. vera would have little effect on the drainage or leaching from the site. However, this plant would reduce wind and water erosion and potentially produce valuable cosmetic products. In contrast, crops of poplar, a species that is tolerant to high soil B concentrations, would mitigate leaching from this site. Alternate rows of trees could be periodically harvested and be used for timber or bioenergy.

Boron removal and recovery from concentrated wastewater using a microwave hydrothermal method

Boron compounds are widely-used raw materials in industries. However, elevated boron concentrations in aqueous systems may be harmful to human and plants. In this study, calcium hydroxide (Ca(OH)(2)) alone and Ca(OH)(2) with phosphoric acid (H(3)PO(4)) addition (P-addition) were used to remove and recover boron from wastewater using hydrothermal methods. A microwave (MW) hydrothermal method was used and compared with the conventional heating (CH) method in batch experiments. Physicochemical properties of the precipitates obtained from both methods were analysed by XRD, SEM with EDX and BET. For the case of Ca(OH)(2) alone and the MW method, experimental results showed that boron recovery efficiency reached 90% within 10 min, and crystals of Ca(2)B(2)O(5)·H(2)O were found in the precipitates as indicated by the XRD analysis. For the case of P-addition and the MW method, boron recovery efficiency reached 99% within 10 min, and calcium phosphate species (CaHPO(4)·H(2)O, CaHPO(4) and Ca(10)(PO(4))(6)(OH)(2)) were formed. The experimental results of this study indicate that the required reaction time of the MW method was much less than that of the CH method, and the MW method is an effective and efficient method for boron removal and recovery from concentrated wastewater.

Study on adsorption and remediation of heavy metals by poplar and larch in contaminated soil

INTRODUCTION

Field experiments at the Shenyang Experimental Station of Ecology were conducted to study the adsorption, accumulation, and remediation of heavy metals by poplar and larch grown in artificially contaminated soil.

MATERIALS AND METHODS

The soil was spiked with a combination of Cd, Cu, and Zn at concentrations of 1.5, 100, and 200 mg.kg(-1), respectively.

RESULTS

The results showed that the biomass of poplar (Populus canadensis Moench) was lower by 26.0% in the soil spiked with a mixture of Cd, Cu, and Zn, compared with the control. Concentrations of Cd in poplar leaf and Cu in poplar roots in the treated soil were 4.11 and 14.55 mg kg(-1), respectively, which are much greater than in corresponding controls. The migration of heavy metals in woody plant body was in the order Cd > Zn > Cu. Poplar had higher metal concentrations in aboveground tissues and a higher biomass compared with larch of the same age and therefore is potentially more suitable for remediation. In the heavy metal-polluted soil of this study, phytoremediation by poplar may take 56 and 245 years for Cd and Cu, respectively, for meeting the soil standards of heavy metals, and the corresponding phytoremediation times by larch would take 211 and 438 years.

CONCLUSION

The research findings could be used as a basis to develop ecological engineering technologies for environmental control and remediation of pollution caused by heavy metals in soils.

Evaluating the tolerance of young hybrid poplar trees to recycled waters high in salinity and boron

The successful adoption of water recycling strategies in many arid regions will require crops able to tolerate poor-quality waters. We evaluated different clones for salt and boron (B) tolerance within each of seven genetically distinct genomic groups (e.g., deltoides, deltoides x nigra, trichocarpa x deltoides, trichocarpa x deltoides x maximowizcii, trichocarpa x deltoides x nigra, trichocarpa x nigra, trichocarpa x maximowizcii). During each evaluation period, different clones within each of the groups were irrigated with high sodium chloride (NaCl) salinity (i.e., 10-30 dS m(-1)) and B (i.e., 10 mg L(-1)) water up to a maximum of 150 days, for a 4-year testing period under micro-field plot conditions. Excessive accumulation (up to 6%) of chloride (Cl) likely caused toxicity symptoms (necrosis of the leaves) observed in the less tolerant clones, while leaf B concentrations rarely exceeded 300 mg kg(-1) DM in any clone. Increased soil salinity likely hindered the uptake of B by the clones. Our results show that a wide range of selected Populus clones, of parentage trichocarpa x nigra, followed by deltoides x nigra show potential salt and B tolerance as young trees to recycled waters high in salinity and B.

PHYTOREMEDIATION OF INORGANICS: REALISM AND SYNERGIES

There are very few practical demonstrations of the phytoextraction of metals and metalloids from soils and sediments beyond small-scale and short-term trials. The two approaches used have been based on using 1) hyperaccumulator species, such as Thlaspi caerulescens (Pb, Zn, Cd, Ni), Alyssum spp. (Ni, Co), and Pteris vittata (As) or 2) fast-growing plants, such as Salix and Populus spp. that accumulate above-average concentrations of only a smaller number of the more mobile trace elements (Cd, Zn, B). Until we have advanced much more along the pathway of genetic isolation and transfer of hyperaccumulator traits into productive plants, there is a high risk in marketing either approach as a technology or stand-alone solution to clean up contaminated land. There are particular uncertainties over the longer-term effectiveness of phytoextraction and associated environmental issues. Marginally contaminated agricultural soils provide the most likely land use where phytoextraction can be used as a polishing technology. An alternative and more useful practical approach in many situations currently would be to give more attention to crops selected for phytoexclusion: selecting crops that do not translocate high concentrations of metals to edible parts. Soils of brownfield, urban, and industrial areas provide a large-scale opportunity to use phytoremediation, but the focus here should be on the more realistic possibilities of risk-managed phytostabilization and monitored natural attenuation. We argue that the wider practical applications of phytoremediation are too often overlooked. There is huge scope for cross-cutting other environmental agenda, with synergies that involve the recovery and provision of services from degraded landscapes and contaminated soils. An additional focus on biomass energy, improved biodiversity, watershed management, soil protection, carbon sequestration, and improved soil health is required for the justification and advancement of phytotechnologies.