Tungsten (W) is a rare element and present in the earth's crust mainly as iron, aluminium, and calcium minerals including wolframite and scheelite. This review aims to offer an overview on the current knowledge on W pollution in complex environmental settlings, including terrestrial and aquatic ecosystems, linking to its natural and anthropogenic sources, behavior in soil and water, environmental and human health hazards, and remediation strategies. Tungsten is used in many alloys mainly as wafers, which have wide industrial applications, such as incandescent light bulb filaments, X-ray tubes, arc welding electrodes, radiation shielding, and industrial catalysts. The rigidity and high density of W enable it to be suitable for defence applications replacing lead. In soil, W metal is oxidised to the tungstate anion and occurs in oxidation states from ? 2 to + 6, with the most prevalent oxidation state of + 6. However, recently, people have been alerted to the risk posed by W alloys and its particulates, which can cause cancer and have other detrimental health effects in animals and humans. The population is subject to W pollution in the workplace by breathing, ingestion, and dermal contact. Remediation of W-polluted soil and aquatic environments can be accomplished via stabilization or solubilization. Stabilization of W in soil and groundwater using immobilizing agents inhibits the bioavailability of W, thereby preventing the contaminant from reaching the food chain, while solubilization of W in soil involving mobilizing materials accelerates the elimination of W via soil washing and root absorption. Future research opportunities covering risk-based remediation of W pollution in these complex settings are presented.

The effect of aging on cadmium (Cd) bioavailability and bioaccessibility was investigated in naturally aged field soil within a contaminated site. The results, which are based on a comparison of investigations carried out in 2018 and 2022 on the same soil samples, provide a realistic evaluation of the variation in Cd chemical forms due to long-term aging. The data obtained show a significant reduction (from approximately 30% to 60%) in the mobile and bioavailable forms of cadmium, while the total quantity in soil did not change significantly. The effect of aging on the bioavailable fractions is also reflected in the reduction in the amount of the metal absorbed by plants. On the one hand, this indicates a reduction in the potential contamination of the food chain, while on the other, it highlights the limitations of the use of phytoextraction as a clean-up technology in this specific site. In the case under study, it should also be noted that there was no decrease in cadmium bioaccessibility over time, which remained very high even after four years of cadmium aging in the soil, which was about 60% of the total content in the most contaminated soil samples. This highlights the potential health risks related to the incidental ingestion of Cd-contaminated soil, which could become the main exposure route in the case of the final use of the site as a park or public green area.

Phytoremediation is an appropriate and sustainable technology used to clean up pollutants from soils and waters through plant species. They are naturally capable of absorbing metals and degrading organic molecules, but often, the presence of contaminants causes suffering to plants driving limited growth. In these situations, thanks to the production of specific root exudates, the plants can engage the most suitable bacteria capable of supporting their growth according to the particular environmental stress. These rhizobacteria (PGPR) promote the growth and development of plants with numerous beneficial effects, even more evident when plants are grown in critical environmental conditions, such as toxic contaminants. A better and deeper understanding of the interactions between plants-microorganisms directly in the matrix of interest, especially in the presence of persistent contamination, could provide new opportunities for phytoremediation. PGPR can alleviate the phytotoxicity of metals in the soil by altering their bioavailability and increasing the translocation of metals within the plant or excluding their uptake. Lead (Pb), mercury (Hg) and arsenic (As) are among the most toxic metals (metalloids). We report some phytoextraction results with three different soils contaminated by i) As and Hg , (ii) As and iii) Pb.

Spills of petroleum products resulting from illegal pipeline extraction also affect agricultural areas. These areas must be subject to remediation interventions to bring the concentrations of contaminants below the alarm levels and avoid further damage to the environment and living beings. In these cases, green technologies such as bioremediation and phytoremediation are an excellent approach to reduce impacts on agriculture. This contribution evaluates the effectiveness of combining some green techniques in managing soil contaminated by oil spills. A feasibility test of phytoremediation at a microcosm scale with three plant species (corn, lupine and alfalfa) was conducted, combining the approach with plant growth-promoting rhizobacteria (PGPR). Particular attention was given to the reclamation from polycyclic aromatic hydrocarbons (PAHs). At the end of the experiments, biomass production and PAHs concentration in the soil and plants (roots and aerial parts) were determined. The remediation strategy was aimed at two concurrent objectives: the need to remove the maximum amount of contaminants from the soils affected by oil spills and the restoration of the agricultural activity to be carried out in absolute safety. The results show a decrease in the concentration of hydrocarbons in the soil favored by the presence of tested plants, which manage to grow satisfactorily on the soil under examination, albeit with an inevitable decrease in yield compared to uncontaminated soil. Looking at the concentration of pyrene, which is usually considered as indicator of PAHs contamination, the removal reaches values higher than 50 % in vegetated soils. The addition of the selected PGPR counteract the negative effect of contamination, favoring the growth of plants and allowing the production of fresh biomass comparable to that obtained on the uncontaminated control soil. This results in a further reduction of the contaminant in question up to an additional 20 %. Therefore, the presence of organic contaminants can be concretely reduced in a sustainable and cost-effective way by the joint action of plants and microorganisms that promote the processes of rizodegradation.

Many agricultural areas are contaminated by heavy metals to such a level that the growth of plants is drastically reduced. Based on the site's specific characteristics, feasibility studies were carried out to choose the most effective technologies. Feasibility tests showed that soil washing and phytoremediation technologies could be used at the agricultural site under study. The efficiency of the technologies is highly dependent on soil characteristics, which determine the chemical form of the metals. The results indicate that water-based soil washing can be successfully used with the possibility of reaching the remediation objectives quickly. However, the technology in the first step essentially breaks down the soil. Moreover, phytoremediation cannot be used directly to overcome the toxicity derived from the very high bioavailability of the heavy metals. Still, there is the need to use "assisted" phytoremediation by adding compost that reduces metal bioavailability, allowing phytoextraction. In this case, a longer time is needed to reach the remediation target. The results provide a preliminary scenario for decision-makers and stakeholders to assess possible technologies applicable and a possible scheme to be applied in similar cases of polluted agricultural areas.

A feasibility study is presented for a bioremediation intervention to restore agricultural activity in a field hit by a diesel oil spill from an oil pipeline. The analysis of the real contaminated soil was conducted following two approaches. The first concerned the assessment of the biodegradative capacity of the indigenous microbial community through laboratory-scale experimentation with different treatments (natural attenuation, landfarming, landfarming + bioaugmentation). The second consisted of testing the effectiveness of phytoremediation with three plant species: Zea mays (corn), Lupinus albus (lupine) and Medicago sativa (alfalfa). With the first approach, after 180 days, the different treatments led to biodegradation percentages between 83 and 96% for linear hydrocarbons and between 76 and 83% for branched ones. In case of contamination by petroleum products, the main action of plants is to favor the degradation of hydrocarbons in the soil by stimulating microbial activity thanks to root exudates. The results obtained in this experiment confirm that the presence of plants favors a decrease in the hydrocarbon content, resulting in an improved degradation of up to 18% compared with non-vegetated soils. The addition of plant growth-promoting bacteria (PGPB) isolated from the contaminated soil also promoted the growth of the tested plants. In particular, an increase in biomass of over 50% was found for lupine. Finally, the metagenomic analysis of the contaminated soil allowed for evaluating the evolution of the composition of the microbial communities during the experimentation, with a focus on hydrocarbon- oxidizing bacteria.

Pollution from numerous contaminants due to many anthropogenic activities affects soils quality. Industrialized countries have many contaminated sites; their remediation is a priority in environmental legislation. The aim of this overview is to consider the evolution of soil remediation from consolidated invasive technologies to environmentally friendly green strategies. The selection of technology is no longer exclusively based on eliminating the source of pollution but aims at remediation, which includes the recovery of soil quality. "Green remediation" appears to be the key to addressing the issue of remediation of contaminated sites as it focuses on environmental quality, including the preservation of the environment. Further developments in green remediation reflect the aim of promoting clean-up strategies that also address the effects of climate change. Sustainable and resilient remediation faces the environmental challenge of achieving targets while reducing the environmental damage caused by clean-up interventions and must involve an awareness that social systems and environmental systems are closely connected.

The remediation of contaminated soils started years ago using consolidates technologies (incineration, inertization, etc.) usually employed in the waste treatment. This has contributed to consider a contaminated soil as a hazardous waste. This approximation was unfortunately transferred in many European legislations and on this basis soil quality have been used only marginally considered in the clean-up procedures. For many years, soil quality has been identified by the concentration values of contaminant and excavation and landfill disposal of soil has been largely used. In recent years, the knowledge of technologies has rapidly grown and soil remediation is now based on innovative technologies, which are largely dependent on soil properties. The new environmental policies are increasingly promoting "Green remediation" and "Natural Based Solution" strategies: which consider all environmental effects of remedy and incorporate all the options to maximize environmental benefit. These remediation strategies restore contaminated sites to productive use with a great attention to the global environmental quality, including the preservation of soil functionality by the use of minimally invasive technologies such as bioremediation and phytoremediation. Moving from the definition of remedial targets based on contaminant concentrations, it is essential to select technologies with low environmental impact to avoid the destruction in a very short time of an essential non-renewable resource, such as the soil.

Lead (Pb) is one of the most common metal pollutants in soil, and phytoextraction is a sustainable and cost-effective way to remove it. The purpose of this work was to develop a phytoextraction strategy able to efficiently remove Pb from the soil of a decommissioned fuel depot located in Italy by the combined use of EDTA and endophytic bacteria isolated from indigenous plants. A total of 12 endophytic strains from three native species (Lotus cornicolatus, Sonchus tenerrimus, Bromus sterilis) were isolated and selected to prepare a microbial consortium used to inoculate microcosms of Brassica juncea and Helianthus annuus. As for B. juncea, experimental data showed that treatment with microbial inoculum alone was the most effective in improving Pb phytoextraction in shoots (up to 25 times more than the control). In H. annuus, on the other hand, the most effective treatment was the combined treatment (EDTA and inoculum) with up to three times more Pb uptake values. These results, also validated by the metagenomic analysis, confirm that plant-microbe interaction is a crucial key point in phytoremediation.

The increasing use of tungsten in the production of green energy in the aerospace and military industries, and in many other hi-tech applications, may increase the content of this element in soil. This overview examines some aspects of the behavior of tungsten in soil, such as the importance of characteristics of soils in relation to bioavailability processes, the chemical approaches to evaluate tungsten mobility in the soil environment and the importance of adsorption and desorption processes. Tungsten behavior depends on soil properties of which the most important is soil pH, which determines the solubility and polymerization of tungstate ions and the characteristics of the adsorbing soil surfaces. During the adsorption and desorption of tungsten, iron, and aluminum oxides, and hydroxides play a key role as they are the most important adsorbing surfaces for tungsten. The behavior of tungsten compounds in the soil determines the transfer of this element in plants and therefore in the food chain. Despite the growing importance of tungsten in everyday life, environmental regulations concerning soil do not take this element into consideration. The purpose of this review is also to provide some basic information that could be useful when considering tungsten in environmental legislation.

Phytoremediation is a sustainable technology capable of efficiently removing low or moderate contamination. However, complex pollution conditions can drastically reduce efficiency, as plants can show themselves sensitive to organic contaminants, growing slowly and thus impairing metals' absorption. In cases where the action of indigenous bacteria degrading hydrocarbons and promoting plant growth is not sufficient, more sophisticated strategies are necessary. This investigation aims to evaluate the effectiveness of a train of technologies that sees advanced phytoremediation in combination with other biological approaches to remediate soil from a disused industrial area contaminated by N-containing compounds, alkyl aromatic hydrocarbons, copper, and nickel. In particular, a stepwise procedure was used with a pre-treatment (landfarming and bioaugmentation), significantly affecting the soil's fertility, increasing germinability up to 85%, and allowing the plants to extract the metals adequately. Furthermore, with EDTA as a mobilizing agent, nickel absorption has increased up to 36% in Helianthus annuus and up to 88% in Zea mays. For copper, an increase of up to 262% in Helianthus annuus and up to 202% in Zea Mays was obtained. Analysis through Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry highlighted the biodegradation of some of the N-containing compounds recording, after phytoremediation, a decrease of up to almost 90%. Metagenomic analysis of the soil showed a typical microbial population of oxidizing hydrocarbon strains with a prevalence of the Nocardiaceae family (43%). The results obtained appear to confirm the usefulness of the approach developed, and the employed cutting-edge analytical techniques allowed a top-notch characterization of the remediation scenario.

The increasing use of non-renewable resources to supply the growing energy demand has shifted the recent researches towards the development of new sustainable strategies to mitigate the consequent environmental impacts. The use of biomass lignocellulosic as a renewable energy source is among the most widespread solutions to face this problem. However, this practice is subject to further improvement. The new integrated phytoremediation-bioenergy strategy, based on the cultivation of the crops on contaminated soil for energy purposes, could be a possible sustainable solution. The main objective of this methodology is the valorization of biomass produced by phytoremediation systems to provide sustainable energy resources. In this way can be obtained the remediation of contaminated areas simultaneously with bioenergy production. This integrated approach offers an innovative and concrete contribution to the resolution of the current energy problem in full agreement with the sustainability concept

Phytoextraction is currently investigated to effectively remediate soil contaminated by metals and provide highly competitive biomass for energy production. This research aimed to increase arsenic (As) removal from contaminated soil using industrial Cannabis sativa L., a suitable energy crop for biofuel production. Assisted phytoextraction experiments were conducted on a microcosm scale to explore the ability of two friendly treatments, sodium sulphate (SO) and exogenous cytokinin (CK), in increasing As phytoextraction efficiency. The results showed that the treatments significantly increased As phytoextraction. Cytokinin was the most effective agent for effectively increasing translocation and the amount of As in aerial parts of C. sativa. In fact, the concentration of As in the shoots of CK-treated plants increased by 172% and 44% compared to untreated and SO-treated plants, respectively. However, the increased As amount accumulated in C. sativa tissues due to the two treatments negatively affected plant growth. Arsenic toxicity caused a significant decrease in aerial C. sativa biomass treated with CK and SO of about 32.7% and 29.8% compared to untreated plants, respectively. However, for our research purposes, biomass reduction has been counterbalanced by an increase in As phytoextraction, such as to consider C. sativa and CK an effective combination for the remediation of As-contaminated soils. Considering that C. sativa has the suitable characteristics to provide valuable resources for bioenergy production, our work can help improve the implementation of a sustainable management model for As contaminated areas, such as phytoremediation coupled with bioenergy generation.

The latest developments in photovoltaic studies focus on the best use of the solar spectrum through Luminescent Solar Concentrators (LSC). Due to their structural characteristics, LSC panels allow considerable energy savings. This significant saving can also be of great interest in the remediation of contaminated sites, which nowadays requires green interventions characterized by high environmental sustainability. This study reported the evaluation of LSC panels in phytoremediation feasibility tests. Three plant species were used at a microcosm scale on soil contaminated by arsenic and lead. The experiments were conducted by comparing plants grown under LSC panels doped with Lumogen Red F305 (BASF) with plants grown under polycarbonate panels used for greenhouse construction. The results showed a higher production of biomass by the plants grown under the LSC panels. The uptake of the two contaminants by plants was the same in both the growing conditions, thus resulting in an increased total accumulation (defined as metal concentration times produced biomass) in plants grown under LSC panels, indicating an overall higher phytoextraction efficiency. This seems to confirm the potential that LSCs have to be building-integrated on greenhouse roofs, canopies, and shelters to produce electricity while increasing plants productivity, thus reducing environmental pollution, and increasing sustainability.

The adsorption and desorption process of the tungstate ion was studied in three soils characteristic of the Mediterranean area, with particularly reference to bioavailability pathways. In the three soils examined, the tungstate adsorption was described by a Langmuir-type equation, while the desorption process showed that not all the adsorbed tungstate was released, probably due to the formation of dierent bonds with the adsorbing soil surfaces. The pH was found to be the main soil property that regulates the adsorption/desorption: The maximum adsorption occurred in the soil with the acidic pH, and the maximum desorption in the most basic soil. In addition, the organic matter content played a fundamental role in the adsorption of tungstate by soils, being positively correlated with the maximum of adsorption. These results indicate that the lowest bioavailability should be expected in the acidic soil characterized by the highest adsorption capacity. This is confirmed by the trend of the maximum buer capacity (MBC) of soils which is inversely related to bioavailability, and was the highest in the acidic soil and the lowest in the most basic soil. Our data could contribute in drafting environmental regulations for tungsten that are currently lacking for Mediterranean soils.

In industrialized countries, there is a growing concern about the possible negative effects on human health induced by high levels of heavy metals in soil. It is recognized that high levels of heavy metals are not necessarily indicative of the adverse effects. These effects are related to bioavailable fractions, which are involved in plant uptake and transfer to the food chain. Bioavailability is a complex issue that is essential to evaluate to determine if heavy metals present in soil may pose hazards to humans and the environment. In the case of direct ingestion of soil, it is essential to consider also bioaccessibility. Bioavailability and bioaccessibility are related to several soil processes and may be largely determined by soil characteristics. This review deals with the influence of soil properties on metal bioavailability and bioaccessibility. A case study on bioavailability and bioaccessibility of heavy metals is reported, considering a large uncontaminated area influenced by deposition from a cement plant.

The phytoremediation efficiency is influenced by contaminant bioavailability in soil, which in turn depends on soil properties. These last, together with rhizosphere processes, regulate the adsorption and release processes of heavy metals in soil. The distribution of metals between solid and liquid soil phases following adsorption/release processes determines the metal amount bioavailable for plant uptake. The use of adsorption isotherms allows evaluating this distribution, in order to describe the soil ability to retain contaminants in the solid phase. The knowledge of sorption processes is of great importance for phytoremediation, since both the specific contaminated soil and the chosen plant species can largely influence the applicability of phytoremediation procedure at field scale. A case study is reported to evaluate adsorption experiments carried out in soils derived from contaminated site with a high heterogeneity of lead concentration. Results obtained by Freundlich equation have demonstrated the possibility of correlating the desorption parameters and the quantity of elements absorbed by the plants.

A careful waste management system should primarily define the final destination of industrial and urban waste in order to help reduce its environmental impact. Many materials, derived from sewage sludge and industrial production, are characterized by considerable adsorbing capacity; thus, they can be used as low-cost adsorbents to remove heavy metals and organic pollutants from water and soil. The adsorption capacity of these sludge-based adsorbents (SBAs) depends on their specific properties, such as surface area and surface functional groups, which can be enhanced by suitable physical and/or chemical activation. The choice of using alternative and ecofriendly adsorbents is a means of exploiting different varieties of sludge, moving from them being waste-management liabilities toward becoming environmentally sustainable resources.

Tungsten is largely used in high-tech and military industries. Soils are increasingly enriched in this element, and its transfer in the food chain is an issue of great interest. This study evaluated the influence of soil characteristics on tungsten uptake by Zea mays grown on three soils, spiked with increasing tungsten concentrations. The soils, classified as Histosol, Vertisol, and Fluvisol, are characteristic of the Mediterranean area. The uptake of the element by Zea mays was strictly dependent on the soil characteristics. As the pH of soils increases, tungsten concentrations in the roots and shoots of the plants increased. Also, humic substances showed a great influence on tungsten uptake, which decreased with increasing organic matter of soils. Tungsten uptake by Zea mays can be described by a Freundlich-like equation. This soil-to-plant transfer model may be useful in promoting environmental regulations on the hazards of this element in the environment.

Proper plant selection and application of suitable strategies are key factors to ensure the effectiveness of a reclamation via phytoremediation approach. In this study, micro- and meso-cosmscale experimentation has been realized to address a persistent contamination by arsenic on a disused industrial site through an assisted phytoremediation intervention. Three crop species, namely Brassica juncea, Helianthus annuus and Zea mays, have been considered and the addition of K2HPO4, a common mobilizing agent for As, or (NH4)S2O3, a promising additive for As mobilization in case of mercury co-presence, evaluated. The use of these additives significantly enhanced the bioavailability of the target contaminant and therefore its phytoextraction up to 80%. Furthermore, in order to maximize the extraction efficiency of the plants, the influence of five indigenous Plant Growth Promoting Bacteria (PGPB), in combination with the mobilizing agents, was measured. The addition of the microbial consortium led to a further increase in the total uptake of arsenic, especially in B. juncea (up to 140%). The combined strategy supports and enhances the arsenic phytoextraction together with an improvement of the soil quality, as shown by phytotoxicity tests. (C) 2018 Elsevier B.V. All rights reserved.