Phytostabilization-Management Strategy for Stabilizing Trace Elements in Contaminated Soils

A combined bibliometric and sustainable approach of phytostabilization towards eco-restoration of coal mine overburden dumps

Extraction of coal through opencast mining leads to the buildup of heaps of overburden (OB) material, which poses a significant risk to production safety and environmental stability. A systematic bibliometric analysis to identify research trends and gaps, and evaluate the impact of studies and authors in the field related to coal OB phytostabilization was conducted. Key issues associated with coal extraction include land degradation, surface and groundwater contamination, slope instability, erosion and biodiversity loss. Handling coal OB material intensifies such issues, initiating additional environmental and physical challenges. The conventional approach such as topsoiling for OB restoration fails to restore essential soil properties crucial for sustainable vegetation cover. Phytostabilization approach involves establishing a self-sustaining plant cover over OB dump surfaces emerges as a viable strategy for OB restoration. This method enhanced by the supplement of organic amendments boosts the restoration of OB dumps by improving rhizosphere properties conducive to plant growth and contaminant uptake. Criteria essential for plant selection in phytostabilization are critically evaluated. Native plant species adapted to local climatic and ecological conditions are identified as key agents in stabilizing contaminants, reducing soil erosion, and enhancing ecosystem functions. Applicable case studies of successful phytostabilization of coal mines using native plants, offering practical recommendations for species selection in coal mine reclamation projects are provided. This review contributes to sustainable approaches for mitigating the environmental consequences of coal mining and facilitates the ecological recovery of degraded landscapes.

Biological and green remediation of heavy metal contaminated water and soils: A state-of-the-art review

Contamination of the natural ecosystem by heavy metals, organic pollutants, and hazardous waste severely impacts on health and survival of humans, animals, plants, and microorganisms. Diverse chemical and physical treatments are employed in many countries, however, the acceptance of these treatments are usually poor because of taking longer time, high cost, and ineffectiveness in contaminated areas with a very high level of metal contents. Bioremediation is an eco-friendly and efficient method of reclaiming contaminated soils and waters with heavy metals through biological mechanisms using potential microorganisms and plant species. Considering the high efficacy, low cost, and abundant availability of biological materials, particularly bacteria, algae, yeasts, and fungi, either in natural or genetically engineered (GE) form, bioremediation is receiving high attention for heavy metal removal. This report comprehensively reviews and critically discusses the biological and green remediation tactics, contemporary technological advances, and their principal applications either in-situ or ex-situ for the remediation of heavy metal contamination in soil and water. A modified PRISMA review protocol is adapted to critically assess the existing research gaps in heavy metals remediation using green and biological drivers. This study pioneers a schematic illustration of the underlying mechanisms of heavy metal bioremediation. Precisely, it pinpoints the research bottleneck during its real-world application as a low-cost and sustainable technology.

Removal of Heavy Metals from Mine Tailings in Central Chile Using Solidago chilensis Meyen, Haplopappus foliosus DC, and Lycium chilense Miers ex Bertero

Mining activities have been a part of the history of Chile since time immemorial, generating pollution and environmental liabilities. Due to the lack of regulation, many tailings are deposited close to rivers or/and on unstable ground, near which towns have been built, generally in locations with no budget for their treatment. This study tested three plant species from Northern and Central Chile to remove total chromium, nickel, and zinc from tailings: Solidago chilensis, Haplopappus foliosus, and Lycium chilense, which complements the few existing studies on heavy metals removal with native or endemic Chilean shrubs. The experiments were conducted ex situ, and the initial and final concentrations of metals were determined in tailings and plants to obtain the removal efficiency, translocation and bioconcentration factors. Among these species, the best performance was obtained using Solidago chilensis, achieving removal efficiencies of 24% for Cr, 19% for Ni, and 17% for Zn, showing the ability to phytostabilize chromium and the higher resistance concerning the toxicity threshold. Haplopappus foliosus and Lycium chilense presented a slight tendency to stabilize chromium. Only Solidago chilensis showed little ability to extract Zn.

Composted sewage sludge utilization in phytostabilization of heavy metals contaminated soils

In phytostabilization, heavy metal-tolerant plants (e.g.,grasses) can be used to reduce the mobility of heavy metals in soils. The most important step in phytostabilization is the selection of the suitable plant species, in which growth and development can be supported by soil amendments. Sewage sludge compost could be a suitable additive, which provides nutrients for the plant species used for phytostabilization and contributes to an alternative solution for sewage sludge utilization. The aim of the study was to examine the potential of sewage sludge compost in phytostabilization for heavy metal contaminated matrices: identify the optimal ratio of sewage sludge compost to decrease phytotoxicity of the matrices, and assessment of feasible plant species for phytostabilization based on its bioaccumulation properties. In this research, perennial ryegrass (Lolium perenne), broad-leaved sorrel sorrel (Rumex acetosa), lettuce (Lactuca sativa) and cabbage (Brassica oleracea var. capitata) were used for phytotoxicity experiments as well as for testing sewage sludge compost amended phytostabilization of polluted flotation sludge and mine tailings. Sewage sludge compost increased the pH and electric conductivity of the matrices. High salt content and low acidity, altogether with heavy metals caused harmful physiological effects on plant species grown without any compost addition. In the root development test, as in the germination test, the application of 5% sewage sludge compost proved to be optimal. The lower translocation factors of broad-leaved sorrel and perennial ryegrass showed a higher rate of heavy metal accumulation in the roots. Perennial ryegrass, cabbage, and lettuce plant species reached their maximum biomass by adding 5% of sewage sludge compost. Based on the bioaccumulation, translocation and biomass properties, application of perennial ryegrass is recommended for phytostabilization of heavy metal contaminated sites. Furthermore, composted sewage sludge also had a significant effect on the reduction of heavy metal uptake by cabbage and lettuce, which highlights their role as indicator plants in ecotoxicological measurements.

Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

Multiscale imaging on Saxifraga paniculata provides new insights into yttrium uptake by plants

Yttrium (Y) has gained importance in high tech applications and, together with the other rare earth elements (REEs), is also considered to be an emerging environmental pollutant. The alpine plant Saxifraga paniculata was previously shown to display high metal tolerance and an intriguing REE accumulation potential. In this study, we analysed soil grown commercial and wild specimens of Saxifraga paniculata to assess Y accumulation and shed light on the uptake pathway. Laser ablation inductively coupled plasma mass spectrometry and synchrotron-based micro X-ray fluorescence spectroscopy was used to localise Y within the plant tissues and identify colocalized elements. Y was distributed similarly in commercial and wild specimens. Within the roots, Y was mostly located in the epidermis region. Translocation was low, but wild individuals accumulated significantly more Y than commercial ones. In plants of both origins, we observed consistent colocalization of Al, Fe, Y and Ce in all plant parts except for the hydathodes. This indicates a shared pathway during translocation and could explained by the formation of a stable organic complex with citrate, for example. Our study provides important insights into the uptake pathway of Y in S. paniculata, which can be generalised to other plants.

Arbuscular Mycorrhiza Alters Metal Uptake and the Physio-biochemical Responses of Glycyrrhiza glabra in a Lead Contaminated Soil

Arbuscular mycorrhizal (AM) fungi can affect the host's ability to cope with several environmental stresses, such as heavy metal stress. Therefore, an experiment was conducted to assess the effect of the Funneliformis mosseae inoculation on growth and physio-biochemical parameters and lead (Pb) accumulation in liquorice (Glycyrrhiza glabra L.) under Pb stress. A factorial experiment was performed with the combination of two factors, fungi (inoculated and non-inoculated (NM)) and soil Pb levels (0, 150, 300, and 450 mg kg-1 soil) with four replicates. In the presence of Pb, symbiosis with F. mosseae exert positive effect on growth parameters, which was more significant in shoots than roots. Mycorrhization improved fresh and dry weights and length in shoot by 147, 112.5 and 83%, respectively, compared to NM plants at Pb150 level. Moreover, F. mosseae significantly increased tolerance index and the concentrations of soluble sugars and flavonoids in shoots and proline, phosphorus, potassium, calcium, zinc and manganese in shoots and roots but decreased their malondialdehyde concentrations under Pb stress. The Pb concentrations, transfer and bioaccumulation factors of mycorrhizal plants were less than non-mycorrhizal ones. A positive correlation was also observed between glomalin secretion and colonization rate in Pb treated soils. These results indicate the importance of mycorrhizal colonization in alleviating the Pb-induced stress in liquorice, mainly through improving the nutrition, modifying reactive oxygen species detoxifying metabolites and reducing the translocation of Pb to shoots. Observations revealed that mycorrhization of liquorice would be an efficient strategy to use in the phytoremediation practices of Pb-contaminated soils.

An Assessment of the Metal Removal Capability of Endemic Chilean Species

In Chile, there are several abandoned mine tailing impoundments near population centers that need to be remediated. In this study, the ability of Oxalis gigantea, Cistanthe grandiflora, and Puya berteroniana to remove Zn, Ni, and Cr from mine tailings was evaluated. The plants’ removal efficiency, bioconcentration, and translocation factors regarding these metals were determined to assess the ability of certain endemic species from Northern and Central Chile to extract or stabilize metals. After a period of seven months, the chemical analysis of plants and tailings, together with the statistical treatment of data, indicated the inability of all the species to translocate Ni, Cr, or Zn with a translocation factor lower than one. The results showed the stabilizing character of Oxalis gigantea, Puya berteroniana, and Cistanthe grandiflora for Zn, with a bioconcentration factor close to 1.2 in all cases, and the same ability of the latter two species for Cr, with a bioconcentration factor of 1.5 in the case of Cistanthe grandiflora and 1.7 for Puya berteroniana. Finally, a removal efficiency of 9.3% was obtained with Cistanthe grandiflora for Cr and 15% for Ni; values lower than 6.4% were obtained for Zn in all cases. Improvements in the process should be sought to enhance the performance of these species for the accumulation of the target metals.

Plant-Mycorrhizal Fungi Interactions in Phytoremediation of Geogenic Contaminated Soils

Soil contamination by geogenic contaminants (GCs) represents an imperative environmental problem. Various soil remediation methods have been successfully employed to ameliorate the health risks associated with GCs. Phytoremediation is considered as an eco-friendly and economical approach to revegetate GC-contaminated soils. However, it is a very slow process, as plants take a considerable amount of time to gain biomass. Also, the process is limited only to the depth and surface area of the root. Inoculation of arbuscular mycorrhizal fungi (AMF) with remediating plants has been found to accelerate the phytoremediation process by enhancing plant biomass and their metal accumulation potential while improving the soil physicochemical and biological characteristics. Progress in the field application is hindered by a lack of understanding of complex interactions between host plant and AMF that contribute to metal detoxification/(im)mobilization/accumulation/translocation. Thus, this review is an attempt to reveal the underlying mechanisms of plant-AMF interactions in phytoremediation.

Phytoremediation technology and food security impacts of heavy metal contaminated soils: A review of literature

Heavy metal accumulation in soil and water is one of major problems caused by inorganic contaminants. Their presence in agricultural soils in high quantities have impacted the food security significantly and, by extension, the human health. Amongst various physico-chemical methods available for remediation of heavy-metals-polluted-sites, phytoremediation approaches have been found to be safe and environment friendly. This review gathered scattered information on heavy metal phytoremediation studies published in both review and research articles. It described the impact of heavy metals on food security and comprehensively discussed the application of different phytoremediation approaches for treatment of heavy metal-polluted soils, the basic principles underlining them, their strengths and weaknesses. Our findings indicated that, while hundreds of hyper-accumulator plants are being reported yearly, only few describe limitations inherent in them, such as low growth rate, low biomass production, and low metal tolerance. Hence, this review also gave a detailed overview of research gaps in phytotechnology and advocates consideration of the 'omics' studies; genomics, proteomics, metabolomics and likes in selecting and enhancing potential plants for phytoremediation. For a sustainable large-scale phytoremediation application, we established a multi-technology repair strategy via the combination of different methods like application of biological composts, plant-growth promoting microorganisms, and phytohormones for stimulation of the plant-growth during phytoremediation. We also gave comprehensive insights to proper disposal of plants used for phytoremediation, this subject is often not well considered/planned while deciding the application of plants for removal of heavy metals from polluted environments.

Cu Dynamics in the Rhizosphere of Native Tropical Species: Assessing the Potential for Phytostabilization in Mining-Impacted Soils

The use of native plants for reforestation and/or remediation in areas contaminated by mining is a technique with low implantation and maintenance costs. The success of this practice depends on the plant species and geochemical processes at the soil–plant interface (e.g., rhizosphere). This study evaluated the potential of spontaneous species for mobilizing and altering mineral and metal dynamics in the rhizosphere of Cu-rich soils resulting from the abandoned Pedra Verde mine in NE Brazil. Rhizosphere and bulk soil samples were collected from five shrubby/arboreal species. The pH, organic matter content, Cu fractionation, mineralogical characterization, and Cu content in the leaves and roots of all studied species were determined. In addition, the bioaccumulation factor (BCF) and translocation factor (TF) were used to evaluate the potential of these species for Cu hyperaccumulation. The Cu concentration in leaf plant tissues varied from 18 to 34 mg kg−1, and all plants presented TF and BCF < 1, indicating that the species were not Cu hyperaccumulators. However, the root exudates induce mineral dissolution, indicating potential Cu accumulation in the roots (from 36 to 249 mg kg−1). Combretum aff. pisoniodes Taub was the species with the greatest potential for decreasing Cu bioavailability and phytostabilization. Our findings indicate the potential of native Brazilian plants for growth in Cu-contaminated soil. These findings may be used for reforestation programs.

Uptake patterns of critical metals in alpine plant species growing in an unimpaired natural site

The range of metals used for industrial purposes - electrical engineering, solar panels, batteries - has increased substantially over the last twenty years. Some of these emerging metals are the subject of geopolitical conflict and are considered critical as their unique properties make them irreplaceable. Many of these elements are poorly studied and their biogeochemical cycles still raise many questions. Aim of this study is to analyse the soil-to-plant transfer of some of these chemical elements and to shed light on their uptake pathways. For this purpose, the geological site of Jas Roux (France) was chosen as this alpine site is naturally rich in critical and potentially toxic elements such as As, Sb, Ba and Tl, but nevertheless is host to a high diversity of plants. Elemental concentrations were analysed in the topsoil and in 12 selected alpine plant species sampled in situ. Statistical tools were used to detect species dependent characteristics in elemental uptake. Our analyses revealed accumulation of rare earth elements by Saxifraga paniculata, selective oxyanion absorption by Hippocrepis comosa, accumulation of Tl by Biscutella laevigata and Galium corrudifolium and an exclusion strategy in Juniperus communis. These findings advance our understanding of the environmental behaviour of critical metals and metalloids such as V, As, Y, Sb, Ce, Ba and Tl and might bare valuable information for phytoremediation applications.

Assessment of differences in anatomical and hydraulic properties of the root and xylem of three willow (Salix L.) clones during phytostabilization after exposure to elevated cadmium

An anatomical study of adventitious roots of three Salix clones, B-44, SV068 and SM4041, treated with 3 and 6 mg Cd kg-1 dry weight in soil in a greenhouse experiment. The aim was to analyze the anatomical characteristics of roots in response to pollution by cadmium and to assess the potential application of anatomical and hydraulic characteristics in the selection of the most suitable Salix clones for phytostabilization of pollutants in soils. Anatomical parameters measured in this study included root crosssectional area, root diameter, the proportion of periderm, secondary phloem (cortex) and wood (secondary and primary xylem), and parameters of the vessels (lumen area, diameter and frequency). Based on the measurements of individual vessel lumens and the number of vessels, the theoretical hydraulic conductivity (kh) of roots was calculated. The effects of applied Cd concentrations on root traits were studied in clones and control plants. Following treatments with both Cd concentrations, plants of clone B-44 had the highest values of most parameters and significantly higher kh in comparison with control samples due to the significantly larger root cross-sectional area and lumen of vessels. It was concluded that these characteristics can serve for effective evaluation and selection of clones for remediation of sites contaminated with cadmium.

Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor

The main objective of this study was to achieve the continuous biorecovery and bioreduction of Pb(II) using an industrially obtained consortia as a biocatalyst. An upflow anaerobic sludge blanket reactor was used in the treatment process. The bioremediation technique that was applied made use of a yeast extract as the microbial substrate and Pb(NO3)2 as the source of Pb(II). The UASB reactor exhibited removal efficiencies of between 90 and 100% for the inlet Pb concentrations from 80 to 2000 ppm and a maximum removal rate of 1948.4 mg/(L·d) was measured. XRD and XPS analyses of the precipitate revealed the presence of Pb0, PbO, PbS and PbSO4. Supporting experimental work carried out included growth measurements, pH, oxidation–reduction potentials and nitrate levels.

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Cadmium toxicity in plants: Impacts and remediation strategies

Cadmium (Cd) is an unessential trace element in plants that is ubiquitous in the environment. Anthropogenic activities such as disposal of urban refuse, smelting, mining, metal manufacturing, and application of synthetic phosphate fertilizers enhance the concentration of Cd in the environment and are carcinogenic to human health. In this manuscript, we reviewed the sources of Cd contamination to the environment, soil factors affecting the Cd uptake, the dynamics of Cd in the soil rhizosphere, uptake mechanisms, translocation, and toxicity of Cd in plants. In crop plants, the toxicity of Cd reduces uptake and translocation of nutrients and water, increases oxidative damage, disrupts plant metabolism, and inhibits plant morphology and physiology. In addition, the defense mechanism in plants against Cd toxicity and potential remediation strategies, including the use of biochar, minerals nutrients, compost, organic manure, growth regulators, and hormones, and application of phytoremediation, bioremediation, and chemical methods are also highlighted in this review. This manuscript may help to determine the ecological importance of Cd stress in interdisciplinary studies and essential remediation strategies to overcome the contamination of Cd in agricultural soils.

In situ phytoremediation of heavy metal-contaminated soil and groundwater: a green inventive approach

The heavy metal contamination of soil and groundwater is a serious threat to environment worldwide. The survival of human being primarily relies upon soil and groundwater sources. Therefore, the remediation of heavy metal-contaminated soil and groundwater is a matter of utmost concern. Heavy metals are non-degradable and persist in the environment and subsequently contaminate the food chain. Heavy metal pollution puts a serious impact on human health and it adversely affects our physical body. Although, numerous in situ conventional technologies have been utilized for the treatment purpose, but most of the techniques have some limitations such as high cost, deterioration of soil properties, disturbances to soil native flora and fauna and intensive labour. Despite that, in situ phytoremediation is a cost-effective, eco-friendly, solar-driven and novel approach with significant public acceptance. The past research reflects rare discussion addressing both (heavy metal in situ phytoremediation of soil and groundwater) in one platform. The present review article covers both the concepts of in situ phytoremediation of soil and groundwater with major emphasis on health risks of heavy metals, enhanced integrated approaches of in situ phytoremediation, mechanisms of in situ phytoremediation along with effective hyperaccumulator plants for heavy metals remediation, challenges and future prospects.

Assessment of Native and Endemic Chilean Plants for Removal of Cu, Mo and Pb from Mine Tailings

In Chile, 85% of tailings impoundments are inactive or abandoned and many of them do not have a program of treatment or afforestation. The phytoremediation of tailings with Oxalis gigantea, Cistanthe grandiflora, Puya berteroniana and Solidago chilensis have been tested in order to find plants with ornamental value and low water requirements, which enable reductions in molybdenum (Mo), copper (Cu) or lead (Pb) concentrations creating an environmentally friendly surrounding. Ex-situ phytoremediation experiments were carried out for seven months and Mo, Cu and Pb were measured at the beginning and at the end of the growth period. The capacity of these species to phyto-remedy was evaluated using the bioconcentration and translocation factors, along with assessing removal efficiency. Solidago chilensis showed the ability to phytoextract Mo while Puya berteroniana showed potential for Cu and Mo stabilization. The highest removal efficiencies were obtained for Mo, followed by Cu and Pb. The maximum values of removal efficiency for Mo, Cu and Pb were 28.7% with Solidago chilensis, 15.6% with Puya berteroniana and 8.8% with Cistanthe grandiflora, respectively. Therefore, the most noticeable results were obtained with Solidago chilensis for phytoextraction of Mo.

Securing of an Industrial Soil Using Turfgrass Assisted by Biostimulants and Compost Amendment

This work aimed to study the effects of compost (applied at two rates) and two commercial microbial biostimulants on the mobility and bioavailability of potentially toxic elements (PTEs) in an industrial soil phytostabilized by Dactylis glomerata L. or a mixed stand of grasses (Lolium perenne L., Poa pratensis L. and Festuca arundinacea Shreb.). The soil showed very high pseudototal and bioavailable concentrations of cadmium (Cd) and lead (Pb), due to improper lead-acid batteries storage. Compost amendment in combination with the two biostimulants produced the best outcomes in terms of plant growth and nutrient uptake. The same mix of beneficial microbes improved soil biological fertility enhancing soil nitrogen fixing and ammonia oxidizing bacteria, while reduced the pore water and NH4NO3 extractable concentrations of Cd and at lower extent of Pb in soil. Accordingly, the lower mobility and bioavailability of Cd in soil determined a lower uptake and accumulation of Cd in shoots of different grass species. Our results suggest that a green cap with turfgrass assisted by biostimulants and compost amendment in PTE-contaminated industrial sites could be a reliable and effective practice to protect and restore soil biological fertility and to reduce the risk of PTE dispersion in the surrounding environment.

Arsenic accumulation by red fescue (Festuca rubra) growing in mine affected soils - Findings from the field and greenhouse studies

Soils strongly enriched in arsenic in historical mining sites pose the environmental risk. Phytostabilization is a reasonable method for their remediation. A suitability of red fescue (Festuca rubra L.) for this purpose was examined. Plant and soil material was collected from four study objects: mine dumps in Złoty Stok and Czarnów and two areas formerly flooded by tailings. Total As in soils ranged 72-48900 mg/kg, while the shoots and roots of red fescue contained 1.5-65.5 and 2.3-824 mg/kg As, respectively. Bioaccumulation BAF and translocation TF factors were typical for excluders, however, in most cases, As in shoots exceeded 4 mg/kg, an EU threshold for As in fodder. A greenhouse experiment, that involved treatment with mineral fertilizers, manure, and forest litter, was performed to closer examine the factors governing As uptake by red fescue. A stress-resistant cultivar Leo-Pol was used as a test plant. Grass shoots were harvested after 6 and 12 weeks. Manure treatment increased strongly As extractability but did not increase As uptake by plants. Though, As concentrations in plants were in the pot experiment by manifold higher than those in the field. Particularly high (66.5-1580 mg/kg) was As in the second shoot harvest. Differences between the field and greenhouse data indicate that the populations of red fescue, that develop in As rich sites, are specifically As-tolerant. Possible mechanisms of tolerance are discussed. The conclusion is that the commercial cultivar, despite declared stress-resistance, cannot be used for phytostabilization of barren As-rich soils.

Immobilization of Potentially Toxic Elements (PTE) by Mineral-Based Amendments: Remediation of Contaminated Soils in Post-Industrial Sites

In many post-industrial sites, the high contents and high mobility of different potentially toxic elements (PTEs) make the soils unsuitable for effective management and use. Therefore, immobilization of PTE seems to be the best remediation option for such areas. In the present study, soil samples were collected in post-industrial areas in Northeastern Poland. The analyzed soil was characterized by especially high contents of Cd (22 mg·kg−1), Pb (13 540 mg·kg−1), and Zn (8433 mg·kg−1). Yellow lupine (Lupinus luteus L.) and two types of mineral-based amendments were used to determine their combined remediation effect on PTE immobilization. A greenhouse pot experiment was conducted to evaluate the influence of chalcedonite and halloysite on plant growth, chlorophyll a fluorescence, the leaf greenness index (SPAD), PTE uptake, and the physicochemical properties and toxicity of soil. The application of chalcedonite resulted in the greatest increase in soil pH, whereas halloysite contributed to the greatest reduction in the contents of Ni, Pb, Zn, and Cr in soil, compared with the control treatment. The addition of halloysite significantly increased plant biomass. The application of mineral-based amendments increased the ratio of variable fluorescence to maximum chlorophyll fluorescence (Fv/Fm) in yellow lupine leaves. The leaf greenness index was highest in plants growing in soil amended with chalcedonite. The results of this study suggest that mineral-based amendments combined with yellow lupine could potentially be used for aided phytostabilization of multi-PTE contaminated soil in a post-industrial area.

The combined effect of phytostabilization and different amendments on remediation of soils from post-military areas

Army bases and battle fields are areas of high pollution due to the chemicals released there. Soils in these areas suffer from these uses of the land, and ecosystem services are affected. Although, in the 20th century, the production of bombs and the locations of battle fields and army bases were widespread, there is little research on the impact of war on nature. Moreover, there is a need to rehabilitate the disturbed soils. The contents and ecological risks of Cu, Ni, Cd, Pb, Zn, and Cr in the topsoil from a post-military area (north-eastern Poland) were investigated. In addition, a vegetation experiment was performed with the technique of aided phytostabilization on soils from the study area. The novelty of this study is the assessment of the usefulness of soil amendments (chalcedonite, limestone, activated carbon) in heavy metal (HM) phytostabilization in contaminated soils from post-military areas. Soil samples were also examined for pollution quantification indicators, including the index of geoaccumulation (I_geo), contamination factor (CF), and degree of contamination, and subjected to the Ostracodtoxkit test. The mean contents of the tested HMs were higher than those stipulated in soil environmental quality standards. The highest I_geo (7.38) and CF (346) values were those of Cr and Zn, respectively. The highest increase in soil pH was observed after the application of limestone to the soil. The greatest reduction in Cu, Ni, and Cd contents was caused by addition of limestone. The contents of HMs in Festuca rubra were higher in its roots than in its above-ground parts.

The applicability of compost, zeolite and calcium oxide in assisted remediation of acidic soil contaminated with Cr(III) and Cr(VI)

The effect of soil amendments, i.e., compost, zeolite, and calcium oxide, on the chemical properties of soil contaminated with Cr(III) and Cr(VI) and the uptake of selected heavy metals by spring barley (Hordeum vulgare L.) and maize (Zea mays L.) was determined in a pot experiment. The content of all investigated heavy metals in the tested plants varied significantly in response to the tested soil amendments and increasing concentrations of Cr(III) and Cr(VI). Compost, zeolite, and calcium oxide contributed to an increase in the average yield of the aerial parts of maize plants only in treatments contaminated with Cr(III). The concentrations of Cr, Zn, and Ni in the aerial parts of spring barley and maize were higher in treatments contaminated with Cr(III) than in treatments contaminated with Cr(VI). Calcium oxide induced a significant increase in soil pH relative to the control treatment. In treatments without soil amendments, the average Cr content of soil was higher in pots contaminated with Cr(VI). The concentrations of Zn and Cu in non-amended treatments were negatively correlated with increasing doses of Cr(III) and Cr(VI). Calcium oxide decreased the average content of Cr, Cu, and Ni in all experimental variants. Compost increased the average content of Zn in treatments contaminated with Cr(III) and Cr(IV) relative to non-amended soil.

Remediation techniques for heavy metal-contaminated soils: Principles and applicability

Globally there are over 20millionha of land contaminated by the heavy metal(loid)s As, Cd, Cr, Hg, Pb, Co, Cu, Ni, Zn, and Se, with the present soil concentrations higher than the geo-baseline or regulatory levels. In-situ and ex-situ remediation techniques have been developed to rectify the heavy metal-contaminated sites, including surface capping, encapsulation, landfilling, soil flushing, soil washing, electrokinetic extraction, stabilization, solidification, vitrification, phytoremediation, and bioremediation. These remediation techniques employ containment, extraction/removal, and immobilization mechanisms to reduce the contamination effects through physical, chemical, biological, electrical, and thermal remedy processes. These techniques demonstrate specific advantages, disadvantages, and applicability. In general, in-situ soil remediation is more cost-effective than ex-situ treatment, and contaminant removal/extraction is more favorable than immobilization and containment. Among the available soil remediation techniques, electrokinetic extraction, chemical stabilization, and phytoremediation are at the development stage, while the others have been practiced at full, field scales. Comprehensive assessment indicates that chemical stabilization serves as a temporary soil remediation technique, phytoremediation needs improvement in efficiency, surface capping and landfilling are applicable to small, serious-contamination sites, while solidification and vitrification are the last remediation option. The cost and duration of soil remediation are technique-dependent and site-specific, up to $500ton^-1 soil (or $1500m^-3 soil or $100m^-2 land) and 15years. Treatability studies are crucial to selecting feasible techniques for a soil remediation project, with considerations of the type and degree of contamination, remediation goals, site characteristics, cost effectiveness, implementation time, and public acceptability.

Concept of Aided Phytostabilization of Contaminated Soils in Postindustrial Areas

The experiment was carried out in order to evaluate the effects of trace element immobilizing soil amendments, i.e., chalcedonite, dolomite, halloysite, and diatomite on the chemical characteristics of soil contaminated with Cr and the uptake of metals by plants. The study utilized analysis of variance (ANOVA), principal component analysis (PCA) and Factor Analysis (FA). The content of trace elements in plants, pseudo-total and extracted by 0.01 M CaCl₂, were determined using the method of spectrophotometry. All of the investigated element contents in the tested parts of Indian mustard (Brassica juncea L.) differed significantly in the case of applying amendments to the soil, as well as Cr contamination. The greatest average above-ground biomass was observed when halloysite and dolomite were amended to the soil. Halloysite caused significant increases of Cr concentrations in the roots. The obtained values of bioconcentration and translocation factors observed for halloysite treatment indicate the effectiveness of using Indian mustard in phytostabilization techniques. The addition of diatomite significantly increased soil pH. Halloysite and chalcedonite were shown to be the most effective and decreased the average Cr, Cu and Zn contents in soil.