Nanoscale zero-valent iron (nZVI) is a promising material tool for the remediation of metal(loid)-contaminated soils since it reduces metal(loid) availability and plant uptake, thereby enhancing the development of the plants. However, the effects of nZVI as nanoparticles on soil properties, plants, and the microbial rhizosphere in unpolluted soils are poorly understood. Here we tested the impact of nZVI at different doses (0.5 and 5% of commercial suspension) on soil properties, lettuce plants, and their microbial rhizosphere in two non-contaminated soils with distinct physico-chemical properties (alkaline versus acidic soil). To this end, a pot experiment was performed with lettuce plants in a growth chamber for a month. Both soils showed an increase in of pH and available Fe after nZVI application. However, these effects were more marked in the acidic soil. In this regard, the plants in this soil showed increased biomass and Fe content. TEM analysis revealed that although the roots and leaves of plants grown in the alkaline soil showed better cell integrity than those in acidic soil-an observation that was consistent with the visual appearance of the plants-the former were more affected by the nZVI treatment. Regarding the microbial rhizosphere, in general, nZVI enhanced enzyme activity regardless of the soil type. Microbial functional diversity showed a significant decline in response to nZVI in alkaline soil. In contrast, the 0.5% nZVI treatment had a positive effect on this parameter in acidic soil. Bacterial genetic diversity was less affected by the presence of nZVI than fungal diversity, which was higher in nZVI-treated acidic soils. In addition, alterations of bacterial and fungal communities were associated with available Fe in acidic soil. In conclusion, soil properties play a key role in determining the effects of nZVI on lettuce plants and their rhizosphere.

Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). The present study evaluates the effectiveness of different types of commercial iron nanoparticles (nanoscale zero valent iron (nZVI), bimetallic nZVI-Pd, and nano-magnetite (nFe 3 O 4 )), for the remediation of an industrial soil co-contaminated with Cr and PCBs. Soil samples were mixed with nZVI, nZVI-Pd, or nFe 3 O 4 at doses selected according to their reactivity with PCBs, homogenized, saturated with water and incubated at controlled conditions for 15, 45 and 70 days. For each sampling time, PCBs and chromium were analyzed in aqueous and soil fractions. Cr(VI) and Cr leachability (TCLP test) were determined in the soil samples. The treatment with the three types of iron nanoparticles showed significant reduction in Cr concentration in aqueous extracts at the three sampling times (> 98%), compared to the control samples. The leachability of Cr in treated soil samples also decreased and was stable throughout the experiment. Results suggested that nZVI and nZVI-Pd immobilized Cr through adsorption of Cr(VI) on the shell and reduction to Cr(III). The mechanism of interaction of nFe 3 O 4 and Cr(VI) included adsorption and reduction although its reducing character was lower than those of ZVI nanoparticles. PCBs significantly decreased in soil samples (up to 68%), after 15 days of treatment with the three types of nanoparticles. However, nFe 3 O 4 evidenced reversible adsorption of PCBs after 45 days. In general, nZVI-Pd reduced PCB concentration in soil faster than nZVI. Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days). This is likely due to natural bioremediation, although it was not effective for Cr remediation. Results suggest that the addition of nZVI or nZVI-Pd and pseudo-anaerobic conditions could be used for the recovery of soil co-contaminated with Cr and PCBs.

The use of nanofertilizers could be a potential solution to address the current challenges of agriculture (global hunger, increase of world population, highly inefficient use of fertilizer, soil nutrient deficiency and scarcity of raw materials). Most available literature focuses on the effects of some nanomaterials synthesized at lab scale and detailed information about commercial nanofertilizer is lacking. The aim of the present study was to characterize two commercial nanofertilizers (NF-A and NF-B) and evaluate the effect of their foliar application at increasing doses (recommended dose (RD), 10RD, 100RD and 500RD) on spinach plants. Both nanofertilizers differed greatly in composition, colloidal stability and morphology. Their impact on spinach leaves depended on nanofertilizer composition and dose and they did not have negative effects at the recommended dose or at 10RD. However, NF-B at the highest doses (100RD and 500RD) had major negative effects on leaves compared to NF-A and induced a reduction in the content of chlorophyll, polyphenols, flavonols and antioxidant activity, an increase in oxidative damage, and the deterioration of the cellular ultrastructure according to TEM analysis. In contrast, leaves treated with NF-A showed few changes and only at the highest dose (500RD) were some adverse effects detected. Foliar application of the two commercial nanofertilizers modified the surface composition as well as the nutrient content of the leaves, adding new elements and increasing the content of others, especially at the highest doses tested. The present study will contribute to the establishment of safe levels of nanofertilizer exposure and provides a starting point for studies on the mechanisms involved in nanoparticle uptake by leaves.

Irrigation restrictions due to drought periods related to climate change, would affect different crops, especially to non-food crops. In this regard the effect of irrigation reduction should be studied in energy crops in order to obtain a sustainable bioenergy cropping system. Arundo donax, has been considered a crop with high water requirements, it has nevertheless been proven to be drought tolerant. However, there is a lack of knowledge on the effect of reduced irrigation combined with the use of different fertilizers. This work studied the combined effect of value-added products (VAPs) from wastewater (treated sewage sludge) or traditional inorganic fertilizers, and irrigation reduction in Arundo donax crop in a 2-year pot experiment. Plant biometric characteristics, chemical properties and biomass yield were studied as well as the effect of treatment on soil properties. Results showed that under reduced irrigation conditions, biomass production was reduced, especially during the second year. Organic treatments from sewage sludge minimize the effect of irrigation reduction. In these treatments, biomass yield for reduced irrigation was similar to that of the control treatment with irrigation at field capacity. For this reason, it is recommended to use VAPs from wastewater as organic amendments enabling water restriction with lower effect on Arundo production.

Iron nanoparticles have been successfully used to remove metals from contaminated water. However, most research in this field has been performed with nanoparticles synthesized at the lab-scale. This study compares the capacity of three types of commercial iron nanoparticles, nanoscale zero-valent iron (nZVI), nano-magnetite (nFe(3)O(4)) and iron sulfide (nFeS) nanoparticles to remove Hg2+ from artificially contaminated water over a range of pH, dose, and time of contact. The three types of commercial nanoparticles removed Hg2+ from aqueous solutions being the immobilization processes stable for at least 48 h nZVI particles were faster and more efficient than nFe(3)O(4) and nFeS in terms of Hg removal per unit of iron mass under the experimental conditions tested. The nZVI suspension (0.18 g Fe/L) immobilized 98% of Hg2+ after 15 min, removal ranging between 94 and 98% at the times tested, regardless of the pH (pH 3 to 9). X-ray photoelectron spectroscopy (XPS) analysis revealed that the mechanism by which nZVI immobilizes Hg2+ depends on the dose and includes reduction to Hg-0 and adsorption and/or complexation of Hg2+ to the nZVI shell. In contrast, adsorption was the main mechanism for nFeS (1.6 g Fe/L) and nFe(3)O(4) (3.9 g Fe/L), which removed almost 85 and 80% of Hg2+, respectively, after 3 h of contact. The effectiveness of nFe(3)O(4) and nFeS increased slightly over time (until 48 h). The Hg(2+)removal capacity of nFe(3)O(4) increased with the pH, while that of nFeS peaked at neutral and alkaline pH. Given these findings, the three types of iron nanoparticles emerge as potential candidates for the decontamination of Hg-polluted waters. The choice of nanoparticle depends on the efficacy required, the degree of pollution, the cost and length of the process.

Non-food crops provide an alternative renewable energy source. The high yield of Arundo donax makes this crop a suitable candidate for this purpose. Sewage sludge can be repurposed as an organic amendment to recover soil fertility and improve crop yield. This study sought to evaluate the effect of treated sewage sludge (SS) amendment on the production and heating value of A. donax as a source of biomass for energy production. The study was developed in experimental plots in Central Spain. As organic amendment, sewage sludge composted with pruning waste (CP) and treated by thermal drying (TD) were applied at a dose of 50 t ha- 1, in comparison to a mineral fertilizer treatment (F) and a control soil without treatment (C). After two growing seasons, plant biomass, production parameters and heating value were examined, as well as the effect of the amendments on soil properties. Most parameters increased in plants grown in sewage sludge-treated plots, including heating value reaching 19.19 MJ kg- 1. Moreover, the leaves of these plants had a higher chlorophyll (from 0.39 to 0.52 mg cm-2) and nitrogen content (2%) and a lower ash content (0.9 % reduction). This reduction in ash and the increase of heating value favor the use of this biomass for thermochemical applications. Moreover, the increase in soil organic carbon (around 40 %) due to the organic treatments contributes to increase the carbon stock in soil. The findings support that the application of treated sewage sludge emerges as a suitable strategy not only for enhancing the production of A. donax for energy uses but also for maintaining soil fertility in Mediterranean conditions.

The determination of soil metal(loid) availability presents controversy and there is no consensus or uniformity on used analytical methods. In this study nine single extraction methods (H2O, CaCl2, NaNO3, NH4NO3, DTPA, EDTA, HCl, LMWOA, TCLP) and four sequential extraction procedures (Tessier, BCR, Wenzel and Fernández-Martínez) have been compared to estimate the availability of As and Hg in two soils from a highly polluted brownfield, especially with As. The metal(loid) concentrations were also determined in three native plant species (Lotus corniculatus, Betula celtiberica and Dactylis glomerata) collected in the habitat under study. Each single extractant showed a particular capacity of As/Hg extraction because they do not extract the same forms of each element. The availability of As and Hg depended on the element characteristics, soil properties, type of extractant and degree of pollution, thus the use of a single extraction procedure provides limited information of metal(loid) availability and to reach general conclusions is difficult. Regarding the sequential extractions, each procedure showed a specific pattern for As and Hg regardless of the soil. Thus, the choice of one or other method depends on the environmental conditions, metal(loid) and soil properties. In risk assessment studies it would be recommendable to select one of the more aggressive extractants, so as not to underestimate the environmental risk. In this regard, the sequential extraction procedures render more detailed information about metal(loid) potential availability in relation to soil properties. The analysis of native plant species showed higher metal(loid) concentrations in roots than in aerial parts and differences were observed depending on the metal(loid) and the species. In general, plants showed a higher BCFs for Hg than As even though the total and available As concentrations were higher than those found for Hg, which highlights the influence of plant species on the metal(loid) uptake.

Soil pollution is one of the ten major soil threats identified in the 2015 Status of the World's Soil Resources by the Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils. The presence of high concentration of metals and metalloids (metal(loid)s) is one of the main causes of soil pollution and action to reduce this contamination is urgently needed, especially in agricultural soils. Metal(loid)s cannot be chemically degraded, and consequently persist in soil for extended periods after their introduction. There is a wide variety of strategies for the remediation of soils polluted with metals and metalloids based on physicochemical or biological technologies. The physicochemical technologies can be in situ or ex situ and may have a great impact on the edaphic environment. Among the biological techniques, phytoremediation is referred to the use of plants for decontamination purposes. Since its introduction in the 1980s, a considerable number of research and review papers on phytoremediation processes has been published. The capacity of plants for absorption of metal(loid)s depends on their characteristics and availability, plant species, soil properties, and environmental factors. Cereals such as barley and wheat are widely present across different soil typologies and climatic conditions. This chapter collects the main researches on phytoremediation capacity of barley and wheat plants to metal(loid) pollution.

Arundo donax L. has been recognized as a promising biomass crop for bioenergy and biobased applications. Previous nitrogen fertilization studies of this crop were based on conventional fertilizer application (broadcast). Fertigation is considered an efficient strategy to reduce nutrient loss in irrigated crops. The objective of this study was to investigate the effect of nitrogen fertigation on A.donax grown in low fertility soil, under a continental Mediterranean climate. Three levels of nitrogen supply (N) were studied: 0 N (0 kg ha(-1) year(-1)) 60 N (60 kg ha(-1) year(-1)) and 120 N (120 kg ha(-1) year(-1)) Biometric parameters, leaf chlorophyll content, leaf weight percentage, biomass production and biomass quality as well as soil macronutrient concentration were evaluated. Nitrogen use efficiency and energy yield increase due to fertilization were also determined. Compared with unfertilized plants, fertigation increased plant height, basal diameter of stem, chlorophyll content, biomass production and fiber composition. However, the increase in N rate from 60 to 120 kg ha(-1) year(-1) did not affect biomass yield. Energy increase due to N fertigation and nitrogen use efficiency led to the recommendation of using a fertigation N rate of 60 kg ha(-1) for the A. donax cultivation in these experimental conditions.

In the last few years, the effectiveness of nanoscale zero-valent iron (nZVI) as a treatment for polluted waters and soils has been widely studied. However, little data are available on its efficacy for metal immobilization at low and moderate doses. In this study, the effectiveness of two doses of commercial nZVI (1 and 5%) to immobilize Cu and/or Ni in water and acidic soil samples was evaluated. The influence of the nanoremediation technology on iron availability, physico-chemical soil properties and soil phytotoxicity was also assessed. The results show that the effectiveness of nZVI to immobilize Cu and Ni in water and soil samples was determined by the dose of the nanomaterial and the presence of both metals. Nickel immobilization was significantly decreased by the presence of Cu but the opposite effect was not observed. nZVI showed better immobilization capacity in water than in soil samples. In water, the dose of 5% completely removed both metals, whereas at a lower dose (1%) the percentage of immobilized metal decreased, especially for Ni in Cu + Ni samples. In soil samples, 5% nZVI was more effective in immobilizing Ni than Cu, with a 54% and 21% reduction of leachability, respectively, in single contaminated samples. In Cu + Ni soil samples, nZVI treatment led to a significant decrease in Ni immobilization, similar to that observed in water samples. The application of nZVI induced a dose-dependent increase in available Fe-a relevant effect in the context of soil rehabilitation. Germination assays of Medicago sativa and Vicia sativa seeds revealed that treatment with nZVI did not induce phytotoxicity under the experimental conditions tested, and that the phytotoxicity induced by Ni decreased significantly after the treatment. Thus, the use of nZVI emerges as an interesting option for Cu and/or Ni immobilization in water samples. The effectiveness of nZVI to remove Cu from acidic soil samples was moderate, while for Ni it was strongly dependent on the presence of Cu. These observations therefore indicate that the results in water samples cannot be extrapolated to soil samples.

Phytoremediation using high production crops could be an alternative for the recovery of metals polluted soils. In this sense, the Arundo donax L. energy crop has shown tolerance to moderate concentrations of heavy metals. The objective of this work was to test the tolerance of micropropagated plants of Arundo donax to increasing concentrations of cadmium, chromium, cooper, nickel and lead, in an in vitro culture medium. Biomass production and concentration of heavy metal in shoots and roots were analyzed. Results showed that heavy metals were accumulated mostly in subterranean organs. The increase in heavy metal concentration was dose dependent and not always follows a linear relationship. Arundo donax showed a broad tolerance to cadmium (0.5 mM), chromium (0.2 mM), cooper (2 mM), nickel (0.5 mM) and lead (1 mM). In relation to cooper, Arundo donax showed a hyperaccumulative potential. These results suggest the potential use of Arundo donax in the phytomanagement of polluted soils although further studies should be carried out using polluted soils.

Commercial magnetite nanoparticles (NPs) were used to immobilize As and organic pollutants, mainly PAHs, in a polluted soil. The composition, structure and morphology of the NPs were examined by means of electron microscopy, X-ray analysis, infrared spectroscopy, dynamic light scattering, thermogravimetric analysis, and magnetic property determination. To evaluate the immobilization of As and organic pollutants, soil subsamples were treated with the magnetite NPs at different doses (0.2%, 1%, 2% and 5%). The availability of As was then examined by the TCLP test and the Tessier sequential extraction procedure, whereas TPH and PAHs were measured by GC–MS. Notable results for As immobilization were achieved at a dose of 1% NPs (42.5% decrease in As, TCLP test), although the best result was obtained at the highest dose of 5% (92.3% decrease in As, TCLP test) without significant variations in As speciation. Regarding organic pollutants, a decrease in TPH and PAHs content was detected even at the lowest dose of NPs tested (49% and 89% respectively). The treatments had no negative effects on soil parameters such as soil pH and electrical conductivity. In turn, the increase in Fe availability after application of NPs was insignificant whereas soil phytotoxicity assessed by germination test was reduced. In conclusion, the use of magnetite NPs opens up new nanoremediation options to treat soils affected by both organic and metal(loid) pollution.

This work investigates the mechanisms determining Cr speciation and availability in two different soils polluted with two chromium sources (an industrial sludge, highly polluted with Cr, and Cr(VI) solution) and the influence of these parameters on the recovery of the soil functions related with biological quality and plant growth. The experiment was carried out in greenhouse conditions using 36 pots of 17 kg for the growth of Silene vulgaris for 21 months. Logistic Regression Model using Lasso estimator shows that soil organic matter (SOM) and pH control Cr availability in studied soils. In soils treated with the sludge, X ray Absorption spectroscopy showed that Cr was present as Cr(III), biological quality indicators increased and plants were able to grow. However, in soils polluted with Cr(VI), Cr availability was significantly different in the two soils. In the alkaline and poor in organic matter soil, 12% of Cr(VI) remained in the soil leading to the decrease of soil quality indicators and the total inhibition of plant growth. In the neutral soil, Cr(VI) was totally reduced to Cr(III) by soil organic matter (SOM), quality indicators were not affected and plants grown properly. Infrared Spectroscopy showed that different functional groups reacted with Cr in the two soils. This study highlights the importance to understand the mechanisms underlaying Cr redox and adsorption reactions in Cr polluted soils as they determine the potential recovery of the functions related with biological quality indicators and plant growth. The methodology proposed allows this study in complex soil samples at realistic concentrations and may be useful for risk assessment and for the planning of managing strategies in Cr polluted soils.

In the last decade, several laboratory-scale experiments have shown the use of nanoscale zero-valent iron (nZVI) to be effective in reducing metal(loid) availability in polluted soils. The present study evaluates the capacity of nZVI for reducing the availability of As and Hg in brownfield soils at a pilot scale, and monitors the stability of the immobilization of these contaminants over a 32 month period. To the best of our knowledge, this is the first study to apply nZVI to metal(loid)-polluted soils under field conditions. Two sub-areas (A and B) that differed in pollution load were selected, and a 5 m2 plot was treated with 2.5% nZVI (by weight) in each case (Nanofer 25S, NanoIron). In sub-area A, which had a greater degree of pollution, a second application was performed eight months after the first application. Overall, the treatment significantly reduced the availability of both As and Hg, after only 72 h, although the effectiveness of the treatment was highly dependent on the degree of initial contamination. Sub-area B (with a lower level of pollution) showed the best and most stable immobilization results, with As and Hg in toxicity characteristics leaching procedure (TCLP) extracts decreasing by 70% and 80%, respectively. In comparison, the concentrations of As and Hg in sub-area A decreased by 65% and 50%, respectively. Based on our findings, the use of nZVI at a dose of 2.5% appears to be an effective approach for the remediation of soils at this brownfield site, especially in sub-area B. For sub-area A, a higher dose of nZVI-or its use in combination with other remediation strategies-should be tested.

The capacity of two iron-based nanomaterials, namely goethite nanospheres (nGoethite) and zero valent iron nanoparticles (nZVI), to immobilize As in a polluted soil was evaluated and compared. The composition and morphology of the products were studied by energy dispersive X-ray analysis and transmission electron microscopy, while zeta potential and average sizes were determined by dynamic light scattering. To assess As immobilization, soil subsamples were treated with nGoethite or nZVI at a range of Fe doses (0.5%, 2%, 5% and 10%) and then studied by the TCLP test and the Tessier sequential extraction procedure. The influence of both nanoparticles on As speciation was determined, as was impact on soil pH, electrical conductivity, Fe availability and phytotoxicity (watercress germination). For nZVI, notable results were achieved at a dose of 2% (89.5% decrease in As, TCLP test), and no negative effects on soil parameters were detected. Indeed, even soil phytotoxicity was reduced and only at the highest dose was a slight increase in As3+ detected. In contrast, excellent results were obtained for nGoethite at the lowest dose (0.2%) (82.5% decrease in As, TCLP test); however, soil phytotoxicity was increased at higher doses, probably due to a marked enhancement of electrical conductivity. For both types of nanoparticle, slight increases in Fe availability were observed. Thus, our results show that both nZVI and nGoethite have the capacity to effectively immobilize As in this brownfield. The use of lower doses of nGoethite emerges as a promising soil remediation strategy for soils affected by As pollution.

Lead is one of the most potentially toxic metals present in soils. In situ Pb immobilization techniques reducing its bioavailability to soil organisms are of increasing interest. The present work compares the effectiveness of nanoscale zero-valent iron (nZVI), compost, and phosphate for Pb immobilization in an acidic, artificially polluted soil after different contact times (15 and 45 days). The availability and mobility of Pb were evaluated by the Tessier extraction procedure and the toxicity characteristics leaching procedure (TCLP). The impact on soil properties and soil phytotoxicity was also evaluated. The phosphate was the most effective treatment in all sampling times, reaching Pb reductions in more available fractions of 72%, followed by compost (40%) and nZVI (32%). Comparing the two sampling times, a significant reduction of available Pb in phosphate-treated soils was observed at a longer contact time. Soil properties changed depending on the treatment. In general, the application of compost improved the soil fertility, soils treated with nZVI showed an increase of pH and available sodium and iron concentration, and the treatment with phosphate increased available phosphorus concentration in soil, but was less than that obtained by the compost treatment. Regarding the soil phytotoxicity, Vicia sativa showed moderate phytotoxicity to untreated Pb-polluted soils, and the different treatments decreased it. In conclusion, at the experimental conditions, the use of phosphate resulted as more effective than compost and nZVI for reducing Pb availability in an acidic soil. Longer-term assays are necessary to evaluate the stability of the process.

The objective of the study was to evaluate the effect of two types of treated sewage sludge as soil amendment, composted with pruning wastes (CP) and thermally dried (ST) on the production of ten woody perennials species for energy purposes. The species used were: Paulownia tomentosa (princess tree), Populus x euramericana (Canadian poplar), Ulmus minor (field elm, tree clones), Ulmus laevis (European white elm), Prunus x amygdalo-persica (adafuel), Tamarix gallica (tamarisk), Salix alba (white willow) and Platanus x hispanica (plane tree). The increase in plant growth three years after amendment application is evaluated with the aim to analyze the long term effect of the treated sewage sludges application on plant production. In general, the plants developed in the soils treated with ST sludge present the highest values of growth (diameter, height and width), which can be due to the faster supply of nitrogen from this material. However, the growth rate was higher in the CP treatment for the most of the species due to a continuous release of nutrients from the CP degradation. In this sense, the effect of CP treatment on plant production would be observed at the longer time than the ST one.

Plant growth promoting endophytic bacteria (PGPB) isolated from Brassica napus were inoculated in two cultivars of Helianthus tuberosus (VR and D19) growing on sand supplemented with 0.1 mM Cd or 1 mM Zn. Plant growth, concentrations of metals and thiobarbituric acid (TBA) reactive compounds were determined. Colonization of roots of H. tuberosus D19 by Pseudomonas sp. 262 was evaluated using confocal laser scanning microscopy. Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 significantly enhanced growth of H. tuberosus D19 exposed to Cd or Zn. Pseudomonas sp. 228 significantly increased Cd concentrations in roots. Serratia sp. 246, and Pseudomonas sp. 256 and 228 resulted in significantly decreased contents of TBA reactive compounds in roots of Zn exposed D19 plants. Growth improvement and decrease of metal-induced stress were more pronounced in D19 than in VR. Pseudomonas sp. 262-green fluorescent protein (GFP) colonized the root epidermis/exodermis and also inside root hairs, indicating that an endophytic interaction was established. H. tuberosus D19 inoculated with Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 holds promise for sustainable biomass production in combination with phytoremediation on Cd and Zn contaminated soils.