Remediation of contaminated soils by enhanced nanoscale zero valent iron

Nano Zero Valent Iron (nZVI) as an Amendment for Phytostabilization of Highly Multi-PTE Contaminated Soil

In recent years, a lot of attention has been given to searching for new additives which will effectively facilitate the process of immobilizing contaminants in the soil. This work considers the role of the enhanced nano zero valent iron (nZVI) strategy in the phytostabilization of soil contaminated with potentially toxic elements (PTEs). The experiment was carried out on soil that was highly contaminated with PTEs derived from areas in which metal waste had been stored for many years. The plants used comprised a mixture of grasses-Lolium perenne L. and Festuca rubra L. To determine the effect of the nZVI on the content of PTEs in soil and plants, the samples were analyzed using flame atomic absorption spectrometry (FAAS). The addition of nZVI significantly increased average plant biomass (38%), the contents of Cu (above 2-fold), Ni (44%), Cd (29%), Pb (68%), Zn (44%), and Cr (above 2-fold) in the roots as well as the soil pH. The addition of nZVI, on the other hand, was most effective in reducing the Zn content of soil when compared to the control series. Based on the investigations conducted, the application of nZVI to soil highly contaminated with PTEs is potentially beneficial for the restoration of polluted lands.

Effects of in situ Remediation With Nanoscale Zero Valence Iron on the Physicochemical Conditions and Bacterial Communities of Groundwater Contaminated With Arsenic

Nanoscale Zero-Valent Iron (nZVI) is a cost-effective nanomaterial that is widely used to remove a broad range of metal(loid)s and organic contaminants from soil and groundwater. In some cases, this material alters the taxonomic and functional composition of the bacterial communities present in these matrices; however, there is no conclusive data that can be generalized to all scenarios. Here we studied the effect of nZVI application in situ on groundwater from the site of an abandoned fertilizer factory in Asturias, Spain, mainly polluted with arsenic (As). The geochemical characteristics of the water correspond to a microaerophilic and oligotrophic environment. Physico-chemical and microbiological (cultured and total bacterial diversity) parameters were monitored before and after nZVI application over six months. nZVI treatment led to a marked increase in Fe(II) concentration and a notable fall in the oxidation-reduction potential during the first month of treatment. A substantial decrease in the concentration of As during the first days of treatment was observed, although strong fluctuations were subsequently detected in most of the wells throughout the six-month experiment. The possible toxic effects of nZVI on groundwater bacteria could not be clearly determined from direct observation of those bacteria after staining with viability dyes. The number of cultured bacteria increased during the first two weeks of the treatment, although this was followed by a continuous decrease for the following two weeks, reaching levels moderately below the initial number at the end of sampling, and by changes in their taxonomic composition. Most bacteria were tolerant to high As(V) concentrations and showed the presence of diverse As resistance genes. A more complete study of the structure and diversity of the bacterial community in the groundwater using automated ribosomal intergenic spacer analysis (ARISA) and sequencing of the 16S rRNA amplicons by Illumina confirmed significant alterations in its composition, with a reduction in richness and diversity (the latter evidenced by Illumina data) after treatment with nZVI. The anaerobic conditions stimulated by treatment favored the development of sulfate-reducing bacteria, thereby opening up the possibility to achieve more efficient removal of As.

Nanomaterials in the environment, human exposure pathway, and health effects: A review

Nanomaterials (NMs), both natural and synthetic, are produced, transformed, and exported into our environment daily. Natural NMs annual flux to the environment is around 97% of the total and is significantly higher than synthetic NMs. However, synthetic NMs are considered to have a detrimental effect on the environment. The extensive usage of synthetic NMs in different fields, including chemical, engineering, electronics, and medicine, makes them susceptible to be discharged into the atmosphere, various water sources, soil, and landfill waste. As ever-larger quantities of NMs end up in our environment and start interacting with the biota, it is crucial to understand their behavior under various environmental conditions, their exposure pathway, and their health effects on human beings. This review paper comprises a large portion of the latest research on NMs and the environment. The article describes the natural and synthetic NMs, covering both incidental and engineered NMs and their behavior in the natural environment. The review includes a brief discussion on sampling strategies and various analytical tools to study NMs in complex environmental matrices. The interaction of NMs in natural environments and their pathway to human exposure has been summarized. The potential of NMs to impact human health has been elaborated. The nanotoxicological effect of NMs based on their inherent properties concerning to human health is also reviewed. The knowledge gaps and future research needs on NMs are reported. The findings in this paper will be a resource for researchers working on NMs all over the world to understand better the challenges associated with NMs in the natural environment and their human health effects.

Successful remediation of soils with mixed contamination of chromium and lindane: Integration of biological and physico-chemical strategies

Soils contaminated by organic and inorganic pollutants like Cr(VI) and lindane, is currently a main environmental challenge. Biological strategies, such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, and nanoremediation with nanoscale zero-valent iron (nZVI) are promising approaches for polluted soil health recovery. The combination of different remediation strategies might be key to address this problem. For this reason, a greenhouse experiment was performed using soil without or with an organic amendment. Both soils were contaminated with lindane (15 mg kg^-1) and Cr(VI) (100 or 300 mg kg^-1). After one month of aging, the following treatments were applied: (i) combination of bioaugmentation (actinobacteria), phytoremediation (Brassica napus), and vermiremediation (Eisenia fetida), or (ii) nanoremediation with nZVI, or (iii) combination of biological treatments and nanoremediation. After 60 days, the wellness of plants and earthworms was assessed, also, soil health was evaluated through physico-chemical parameters and biological indicators. Cr(VI) was more toxic and decreased soil health, however, it was reduced to Cr(III) by the amendment and nZVI and, to a lesser extent, by the biological treatment. Lindane was more effectively degraded through bioremediation. In non-polluted soils, nZVI had strong deleterious effects on soil biota when combined with the organic matter, but this effect was reverted in soils with a high concentration of Cr(VI). Therefore, under our experimental conditions bioremediation might be the best for soils with a moderate concentration of Cr(VI) and organic matter. The application of nZVI in soils with a high content of organic matter should be avoided except for soils with very high concentrations of Cr(VI). According to our study, among the treatments tested, the combination of an organic amendment, biological treatment, and nZVI was shown to be the strategy of choice in soils with high concentrations of Cr(VI) and lindane, while for moderate levels of chromium, the organic amendment plus biological treatment is the most profitable treatment.

Synthesis, characterization and application of novel MnO and CuO impregnated biochar composites to sequester arsenic (As) from water: Modeling, thermodynamics and reusability

The present study aimed at enhancing the adsorption potential of novel nanocomposites of Sesbania bispinosa biochar (SBC) with copper oxide (SBC/CuO) and manganese oxide nanoparticles (SBC/MnO) for the efficient and inexpensive removal of environmentally concerned contaminant arsenic (As) from contaminated water at batch scale. The scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray (EDX), X-ray diffraction (XRD) and point of zero charge (PZC) analyses proved successful impregnation of the metallic nanoparticles on SBC surface. The results revealed the maximum As removal (96 %) and adsorption (12.47 mg/g) by SBC/CuO composite at 10 mg As/L, optimum pH-4, dose 1.0 g/L and ambient temperature (25 ± 1.5 °C) as compared with SBC (7.33 mg/g) and SBC/MnO (7.34 mg/g). Among four types of adsorption isotherms, Freundlich isotherm demonstrated best fit with R² > 0.997. While pseudo second-order kinetic model revealed better agreement with kinetic experimental data as matched with other kinetic models. The thermodynamic results depicted that As adsorption on the as-synthesized adsorbents was endothermic and spontaneous in nature with increased randomness. The SBC/CuO displayed excellent reusability and stability over four adsorption/desorption cycles and proved that the as-synthesized SBC/CuO composite may be the efficient adsorbent for practical removal of As from contaminated water.

Recent Developments in the Application of Nanomaterials in Agroecosystems

Nanotechnology implies the scientific research, development, and manufacture, along with processing, of materials and structures on a nano scale. Presently, the contamination of metalloids and metals in the soil has gained substantial attention. The consolidation of nanomaterials and plants in ecological management has received considerable research attention because certain nanomaterials could enhance plant seed germination and entire plant growth. Conversely, when the nanomaterial concentration is not properly controlled, toxicity will definitely develop. This paper discusses the role of nanomaterials as: (1) nano-pesticides (for improving the plant resistance against the biotic stress); and (2) nano-fertilizers (for promoting the plant growth by providing vital nutrients). This review analyzes the potential usages of nanomaterials in agroecosystem. In addition, the adverse effects of nanomaterials on soil organisms are discussed. We mostly examine the beneficial effects of nanomaterials such as nano-zerovalent iron, iron oxide, titanium dioxide, nano-hydroxyapatite, carbon nanotubes, and silver- and copper-based nanomaterials. Some nanomaterials can affect the growth, survival, and reproduction of soil organisms. A change from testing/using nanomaterials in plants for developing nanomaterials depending on agricultural requirements would be an important phase in the utilization of nanomaterials in sustainable agriculture. Conversely, the transport as well as ecological toxicity of nanomaterials should be seriously examined for guaranteeing its benign usage in agriculture.

Nano-scale zero valent iron modulates Fe/Cd transporters and immobilizes soil Cd for production of Cd free rice

In recent decades, nanoscale zero valent iron (nZVI) has been found to be a promising approach for heavy metal remediation. This study is the first report highlighting the role of nZVI to ameliorate Cadmium (Cd) stress in rice along with its effects in expressions of transporter genes, agronomic parameters and grain nutrient status. Initially, 3 concentration of Cd (10, 50, 250 μM) and nZVI (50, 100, 200 mg L^-1) were selected. PCA analysis based on growth parameters, photosynthetic pigment contents and lipid peroxidation rate confirmed that 100 mg L^-1 nZVI was most suitable for remediation of 10 μM Cd. It was evident that, nZVI can alleviate Cd-induced toxic effects by enhancing antioxidant defense mechanisms and other physiological processes in plants. nZVI treated rice seedlings also showed upregulation of phytochelatins which aided in Cd chelation within vacuoles. Study of root morphology with scanning electron microscopy and ROS imaging with confocal microscopy confirmed that nZVI could alleviate oxidative stress due to Cd uptake. In nZVI treated rice seedlings, gene expressions of iron (Fe) transporters (like, IRT1,IRT2,YSL2,YSL15) which are responsible for both Fe and Cd uptake were significantly down-regulated whereas, OsVIT1 and OsCAX4 genes were over expressed which lead to sequestration of Cd in vacuoles. Cd localization assay with leadmium proved that Cd translocation was reduced with nZVI treatment. To further validate our findings a pot experiment was carried out where it was found that nZVI could immobilize Cd in soil prevented accumulation of Cd in rice grains in addition to improving yield.

Mercapto propyltrimethoxysilane- and ferrous sulfate-modified nano-silica for immobilization of lead and cadmium as well as arsenic in heavy metal-contaminated soil

Nano-silica as an important part of soil is an ideal carrier of passivator material. In this paper, nano-silica was modified by silane coupling agent containing mercapto group and iron (II) salt to afford an organic-inorganic hybrid containing -S-Fe-S functional group (coded as RNS-SFe) on the surface of nano-silica. Results demonstrate that the RNS-SFe nanoparticle has network-like spheroidal shape and a primary particle size is about 18.0 nm. The RNS-SFe hybrid as a potential immobilization agent for heavy metal in soil shows excellent performance for the remediation of the contaminated soil. Specifically, with a dosage of 3.0% (mass ratio) in the soil, it can immobilize bioavailable Pb, Cd, and As by 97.1%, 85.0%, and 80.1%, respectively. Namely, the RNS-SFe hybrid can transform the bioavailable Pb, Cd, and As into insoluble mercapto metal compounds (-S-Pb-S- and -S-Cd-S-) and less soluble iron arsenate (Fe₃(AsO₄)₂, FeAsO₄) precipitate on the surface of nano-silica particle, thereby reducing the toxicity and mobility of the toxic contaminant fractions. In the meantime, the immobilized products of the Pb, Cd and As fractions have good resistance against acid leaching. These results are contributive to the application of RNS-SFe for the remediation of multi-heavy metal-contaminated soils in field.

Differential growth and metabolic responses induced by nano-scale zero valent iron in germinating seeds and seedlings of Oryza sativa L. cv. Swarna

Since development of antioxidant defence system is high energy demanding event, innate defence system and stress tolerance of plant is strictly governed by plant age. This study is aimed towards evaluating variation of tolerance in germinating seeds and seedlings of Oryza sativa L. cv. Swarna against nano-scale zero valent iron (nZVI). A comparative study of several physiological and biochemical parameters have been carried out among 2 distinct plant groups, Group I treated with variable concentrations of nZVI (50, 100, 150 and 200 mg L^-1) during germination and Group II treated with similar nZVI doses on 7th day after germination. Upon treatment with higher nZVI concentrations, Group I seedlings showed susceptibility towards oxidative stress while Group II seedlings showed tolerance against these higher doses of nZVI. Significant growth enhancement was observed upon treatment with 50-150 mg L^-1 nZVI, since up-regulation of plant's endogenous antioxidant system protected relatively aged Group II seedlings from oxidative damages. Hierarchical clustering based on overall physiological, biochemical and stress parameters confirmed that in Group I seedlings 100-200 mg L^-1 nZVI treatments were toxic where as in Group II seedlings 50-150 mg L^-1 nZVI treatments showed growth promoting effects. This differential response is due to developmental stage related resistance in plants.

Reduction and stabilization of Cr(VI) in soil by using calcium polysulfide: Catalysis of natural iron oxides

Cr(VI)-contaminated soils could be remediated by using calcium polysulfide (CPS), while natural iron oxides as a main composition of soil would influence the pathways of the remediation. Through kinetic batch tests, the kinetics of Cr(VI) removal from soil, the effects of the contents of natural iron oxides, soil environmental conditions and mechanisms of Cr(VI) removal by using CPS with the presence of natural iron oxides were investigated. The results show that the removal of Cr(VI) by using CPS in soil fitted the pseudo-second-order model best, and the appearance of goethite increased the apparent rate constant from 0.0002 kg mg^-1 h^-1 to 0.0005 kg mg^-1 h^-1. The presence of iron oxides enhanced the removal of Cr(VI) by using CPS, and an extended reductive atmosphere of soil was created. The enhancement of Cr(VI) removal increased with the contents of iron oxides from 0 to 9 g kg^-1, and declined from 9 to 12 g kg^-1. Acidic environment favored the removal of Cr(VI) from soil by using CPS with or without the iron oxides compared to neutral soil and increased it from 87% to 100% because of proton-consuming reactions and electrostatic attraction. Twenty-nine percent of exchangeable and bound-to-carbonates species of chromium declined after the remediation, while 24% bound-to-iron-and-manganese-oxide species increased simultaneously. The findings of the study indicate that natural iron oxides in soils catalyze the reduction of Cr(VI) in soil and facilitate significantly the remediation of Cr(VI)-contaminated soil by using CPS.

Uranium Removal from Groundwater and Wastewater Using Clay-Supported Nanoscale Zero-Valent Iron

The peculiarities of sorption removal of uranium (VI) compounds from the surface and mineralized groundwater using clay-supported nanoscale zero-valent iron (nZVI) composite materials are studied. Representatives of the main structural types of clay minerals are taken as clays: kaolinite (Kt), montmorillonite (MMT) and palygorskite (Pg). It was found that the obtained samples of composite sorbents have much better sorption properties for the removal of uranium from surface and mineralized waters compared to natural clays and nZVI.It is shown that in mineralized waters uranium (VI) is mainly in anionic form, namely in the form of carbonate complexes, which are practically not extracted by pure clays. According to the efficiency of removal of uranium compounds from surface and mineralized waters, composite sorbents form a sequence: montmorillonite-nZVI > palygorskite-nZVI > kaolinite-nZVI, which corresponds to a decrease in the specific surface area of the pristine clay minerals.

Metal immobilization and nitrate reduction in a contaminated soil amended with zero-valent iron (Fe0)

Technologies based on zero-valent iron (Fe⁰) are increasingly being used to immobilize metals in soils and remove metals and nitrate from waters. However, the impact of nitrate reduction on metal immobilization in metal contaminated soils has been poorly investigated so far. Here, different concentrations of Fe⁰ filings (1%, 2% and 5%; wt%) were applied to a metal contaminated soil. The resulting nitrate reduction and metal (Cd and Zn) immobilization was investigated using a column leaching experiment for 12 weeks. Corrosion of Fe⁰ filings and precipitation of Fe oxyhydroxydes (FeOOH) on the surfaces of the filings were observed using SEM-EDS and EMPA-WDS at the end of the experiment. Compared to the untreated soil, total nitrate amounts released were lowered by 47%, 59% and 87% in the presence of 1%, 2% and 5% of Fe⁰, respectively. Concomitantly with nitrate reduction, Cd and Zn concentrations in leachates were strongly alleviated in the presence of Fe⁰, which was partly attributed to the rise of soil pH subsequent to nitrate reduction. More importantly, biotests with Lupinus albus L. revealed that the mechanisms involved in metal immobilization are stable to root-induced acidification. However, Fe⁰ was not efficient to reduce Cd concentration in Lolium multiflorum Lam., indicating that root processes other than acidification may re-mobilize metals.

Developments in the Application of Nanomaterials for Water Treatment and Their Impact on the Environment

Nanotechnology is an uppermost priority area of research in several nations presently because of its enormous capability and financial impact. One of the most promising environmental utilizations of nanotechnology has been in water treatment and remediation where various nanomaterials can purify water by means of several mechanisms inclusive of the adsorption of dyes, heavy metals, and other pollutants, inactivation and removal of pathogens, and conversion of harmful materials into less harmful compounds. To achieve this, nanomaterials have been generated in several shapes, integrated to form different composites and functionalized with active components. Additionally, the nanomaterials have been added to membranes that can assist to improve the water treatment efficiency. In this paper, we have discussed the advantages of nanomaterials in applications such as adsorbents (removal of dyes, heavy metals, pharmaceuticals, and organic contaminants from water), membrane materials, catalytic utilization, and microbial decontamination. We discuss the different carbon-based nanomaterials (carbon nanotubes, graphene, graphene oxide, fullerenes, etc.), and metal and metal-oxide based nanomaterials (zinc-oxide, titanium dioxide, nano zerovalent iron, etc.) for the water treatment application. It can be noted that the nanomaterials have the ability for improving the environmental remediation system. The examination of different studies confirmed that out of the various nanomaterials, graphene and its derivatives (e.g., reduced graphene oxide, graphene oxide, graphene-based metals, and graphene-based metal oxides) with huge surface area and increased purity, outstanding environmental compatibility and selectivity, display high absorption capability as they trap electrons, avoiding their recombination. Additionally, we discussed the negative impacts of nanomaterials such as membrane damage and cell damage to the living beings in the aqueous environment. Acknowledgment of the possible benefits and inadvertent hazards of nanomaterials to the environment is important for pursuing their future advancement.

Characterization of bimetallic Fe/Ni nanoparticles supported by amphiphilic block copolymer and its application in removal of 1,1,1-trichloroethane in water

The iron and nickel bimetallic nanoparticles supported by the block copolymer polystyrene-block-poly (acrylic acid) (PS-b-PAA-nZVI-Ni) were synthesized successfully and were applied to assess the degradation of 1,1,1-trichloroethane (1,1,1-TCA) in water. An optimal dose of Ni loading was 2 wt%, while an optimal mass ratio of PS-b-PAA to Ni/Fe, i.e., 0.5:1, at which the dechlorination efficiency was a maximum. The size of PS-b-PAA-nZVI-Ni nanoparticles (average size ~ 50 nm) was three times smaller than that of nZVI-Ni due to the prevention of agglomeration of the resultant zerovalent iron nanoparticles by PS-b-PAA. In the applying aspect, the pseudo-first-order rate constant (Kobs) of 1,1,1-TCA removal by PS-b-PAA-nZVI-Ni was 0.0142 min-1 within 240 min, which was approximately five times higher than nZVI. Meanwhile, PS-b-PAA-supported nZVI-Ni nanoparticles penetrated much deeper in quartz sand columns than nZVI-Ni nanoparticles, indicating PS-b-PAA had significant influence on nZVI transport. The findings from this study suggested that PS-b-PAA-nZVI-Ni, with its high reactivity, selective screening for 1,1,1-TCA, could be one significant potential for use as remedial agent to treat chlorinated solvents in water.

Effective sequestration of Cr (VI) from wastewater using nanocomposite of ZnO with cotton stalks biochar: modeling, kinetics, and reusability

The disposal of chromium (Cr) containing wastewater in surface water bodies without prior treatment is a serious threat to humans, animals, and plants. A novel nanocomposite (CSB/ZnO) of cotton stalks biochar (CSB) with ZnO nanoparticles was synthesized for the removal of Cr (VI) ions from contaminated water at batch scale. The impact of adsorbent dosage (1-4 g/L), initial Cr (VI) levels (25-200 mg/L), pH (2-8), and interaction time (0-180 min) was assessed for the removal of Cr (VI) from contaminated water. The Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and point of zero charge (PZC) characterization showed successful impregnation of ZnO particles on CSB with improved surface characteristics. The maximum adsorption (qmax) of CSB and CSB/ZnO was 54.95 and 107.53 mg Cr/g, respectively that is relatively higher than various previously studied adsorbents. The experimental isothermal data better fitted with the Freundlich model in comparison with other isotherm models while adsorption kinetics well corroborated with the pseudo-second-order model. The results revealed that doping of biochar with metallic nanoparticles (CSB/ZnO) proved very effective (99.6% at 50 mg/L) with high reusability (91%) after five adsorption/desorption cycles and seems a suitable strategy for the decontamination of Cr (VI) contaminated waters.

FeS-biochar and Zn(0)-biochar for remediation of redox-reactive contaminants

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis. These biochars significantly promoted the removal of 2,4-dichlorophenol (DCP) by means of sorption and reduction. Compared to direct reduction with FeS and Zn(0), the formation of reduction intermediates and product was enhanced from 21% and 22% of initial DCP concentration to 41% and 52%, respectively. 2,4-Dinitrotoluene (DNT), chromate (CrO₄²⁻) and selenate (SeO₄²⁻) were also reductively transformed to reduction products (e.g., 2,4-diaminotoluene [DAT], Cr³⁺, and selenite [SeO₃²⁻]) after they sorbed onto the biochars including FeS and Zn(0). Mass recovery as DAT, Cr³⁺ and selenite was 4–20%, 1–3%, and 10–30% under the given conditions. Electrochemical and X-ray analyses confirmed the reduction capability of the biochars including FeS and Zn(0). Fe and S in the FeS–biochar did not effectively promote the reductive transformation of the contaminants. Contrastingly, the stronger reducer Zn(0) yielded faster reductive transformation of contaminants over the Zn(0)-containing biochar, while not releasing high concentrations of Zn²⁺ into the aqueous phase. Our results suggest that biochars including Zn(0) may be suitable as dual sorbents/reductants to remediate redox-reactive contaminants in natural environments.

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis.

Effects of environmental factors on the removal of heavy metals by sulfide-modified nanoscale zerovalent iron

Sulfide-modified nanoscale zerovalent iron (S-nZVI) has excellent reducing performance for heavy metals in water. The influence of environmental factors on the reactivity can be used to explore the practical feasibility of S-nZVI and analyze the reaction mechanism in depth. This study compared the removal effect and mechanism of Cu²⁺ and Ni²⁺ by nanoscale zerovalent iron (nZVI), S-nZVI, and carboxymethyl cellulose-modified nanoscale zerovalent iron (CMC-nZVI). The results show that the pseudo-first-order kinetic constant of Cu²⁺ removal by nZVI, S-nZVI, and CMC-nZVI was 1.384, 1.919, and 2.890 min^-1, respectively, and the rate of Ni²⁺ removal was 0.304, 0.931, and 0.360 min^-1, respectively. The removal mechanism of S-nZVI was similar to that of nZVI and CMC-nZVI. Specifically, Cu²⁺ was predominantly removed by reduction, while Ni²⁺ removal included adsorption and reduction. Environmental factors had a specific inhibitory effect on the removal of Cu²⁺ but had a negligible impact on Ni²⁺. The condition of low pH, the presence of Cl^- and humic acid (HA) promoted the corrosion consumption of Fe⁰, in which H⁺ directly corroded Fe⁰ at low pH. At the same time, Cl^- and HA inhibited the adsorption or binding of heavy metal ions on the particle surface, thereby reducing the electron transfer and utilization efficiency. The passivation of NO₃^- reduced the anaerobic corrosion of the material in water but suppressed the release of electrons, thereby reducing the reduction efficiency of the three types of materials. The anaerobic corrosion of S-nZVI was less affected by environmental factors, and it can still maintain more than 80% of the electronic utilization efficiency under different environmental factors, which illustrates that S-nZVI has broad prospects for practical applications in heavy metal polluted water.

Bioelectrochemical remediation of Cr(VI)/Cd(II)-contaminated soil in bipolar membrane microbial fuel cells

Heavy-metal contaminated soils post great environmental and health concerns. In this study, Cr and Cd which are frequently observed in contaminated soils, were selected as representatives of hazardous heavy metals because of their different redox potentials and electric charges. Cr(VI)-, Cd(II)-, Cr(VI)/Cd(II)-contaminated soils were remediated in two-chamber air-cathode MFCs, in order to investigate the remediation of soil contaminated by single heavy metal and mixed heavy metals. Four ion exchange membranes (IEMs) were first evaluated to find out that bipolar membrane (BPM) was able to well maintain pH in both anolyte and catholyte, which was beneficial to support biological metabolism and heavy metal removal. It was also found that heavy metal ions (Cr, Cd or Cr/Cd) could migrate toward the cathode forming a concentration gradient under the weak electric field. The interaction between negatively charged Cr and positively charged Cd had no major effect to hinder each other on the migration, suggesting that the reduction reaction and electric field should be the main motivation for metal ion migration. The remediation performance of mixed heavy metal contaminated soil was superior to that of single heavy metal contaminated soil, for the possible reason of smaller internal resistance under mixed heavy metal condition.

Applying modified biochar with nZVI/nFe3O4 to immobilize Pb in contaminated soil

Lead (Pb) pollution in soil has become one of the most serious environmental problems, and it is more urgent in areas where acid rain is prevalent. Curing agents to solidify heavy metals in soil are efficiently applied to remediate Pb-contaminated soil. In this study, we prepared biochar, biochar loaded with nano-zero-valent iron (BC-nZVI), and biochar loaded with nano-ferroferric oxide (BC-nFe₃O₄), and investigated the Pb-immobilizing efficiency in contaminated soil in the condition of acid rain by them. The results showed that 8 g/kg is the best added dosage of curing agents for immobilizing Pb, which of the immobilizing efficiency of Pb were 19% (biochar), 42% (BC-nZVI), and 23% (BC-nFe₃O₄), respectively. Besides, the curing agents had positive effects on immobilizing Pb under acid rain condition, which could significantly reduce the content of acid extractable Pb, especially BC-nZVI (1.5%). And the immobilization efficiency of modified biochar was better than biochar, especially BC-nZVI (66%). BC-nZVI showed a more ideal effect on decreasing the leaching amount of Pb in the condition of acid rain. The results highlighted that biochar-loaded nano-iron-based materials, especially BC-nZVI, was promising and environmentally friendly materials for remediating Pb-contaminated soils, which provided scientific reference and theoretical basis for the treatment of Pb-contaminated soils around industrial sites particularly in acid rain area.

Effects of Different In Situ Remediation Strategies for an As-Polluted Soil on Human Health Risk, Soil Properties, and Vegetation

The demand for soils for recreational uses, gardening, or others in urban and periurban areas is increasing, and thus the presence of polluted technosols in these areas requires nature-based in situ remediation technologies. In this context, the capacity of three amendments, namely zero valent iron nanoparticles (nZVI), compost and a mixture of compost and biochar, to immobilise As in a polluted technosol simultaneously cultivated with Lolium perenne L. were tested and compared. The characteristics of the soil were comprehensively characterised by chemical and X-ray analysis to determine As contents, distribution, and mineralogy. As mobility was evaluated by the RBA methodology and then potential human health risks, both carcinogenic and non-carcinogenic, were assessed in all treatments. The nZVI treatment reduced risks due to the As immobilisation obtained (41% As decrease, RBA test), whereas the organic amendments did not imply any significant reduction of the RBA values. As to soil properties, the organic treatments applied lowered the pH values, increasing cation exchange capacity, and carbon and nutrient contents. To determine impacts over plant production, fresh biomass, As, Ca, Fe, K, Mg, Na and P were measured in Lolium under the different treatments. Notably, organic amendments improved As extraction by plants (57% increase), as well as fresh biomass (56% increase). On the contrary, nZVI diminished As extraction (65% decrease) and promoted a fresh biomass decrease of 57% due to nutrients immobilisation (61% decrease of P in plants tissues).

Preparation, environmental application and prospect of biochar-supported metal nanoparticles: A review

Biochar is a low-cost, porous, and carbon-rich material and it exhibits a great potential as an adsorbent and a supporting matrix due to its high surface activity, high specific surface area, and high ion exchange capacity. Metal nanomaterials are nanometer-sized solid particles which have high reactivity, high surface area, and high surface energy. Owing to their aggregation and passivation, metal nanomaterials will lose excellent physiochemical properties. Carbon-enriched biochar can be applied to overcome these drawbacks of metal nanomaterials. Combining the advantages of biochar and metal nanomaterials, supporting metal nanomaterials on porous and stable biochar creates a new biochar-supported metal nanoparticles (MNPs@BC). Therefore, MNPs@BC can be used to design the properties of metal nanoparticles, stabilize the anchored metal nanoparticles, and facilitate the catalytic/redox reactions at the biochar-metal interfaces, which maximizes the efficiency of biochar and metal nanoparticles in environmental application. This work detailedly reviews the synthesis methods of MNPs@BC and the effects of preparation conditions on the properties of MNPs@BC during the preparation processes. The characterization methods of MNPs@BC, the removal/remediation performance of MNPs@BC for organic contaminants, heavy metals and other inorganic contaminants in water and soil, and the effect of MNPs@BC properties on the remediation efficiency were discussed. In addition, this paper summarizes the effect of various parameters on the removal of contaminants from water, the effect of MNPs@BC remediation on soil properties, and the removal/remediation mechanisms of the contaminants by MNPs@BC in water and soil. Moreover, the potential directions for future research and development of MNPs@BC have also been discussed.

Remediation of Cr(VI)-Contaminated Soil by Nano-Zero-Valent Iron in Combination with Biochar or Humic Acid and the Consequences for Plant Performance

Nano-scale zero-valent iron (nZVI) is among the most common nanoparticles widely used for the treatment of various environmental contaminants. However, little is known about the combined effects of nano-zero-valent iron (nZVI) and other soil amendments on soil remediation and plant performance. For the first time, we studied the remediation of Cr(VI)-contaminated soil using bare nZVI (B-nZVI) and starch-supported nZVI (S-nZVI) in combination with either biochar (BC) or humic acid (HA), and the consequent effects on plant growth and Cr accumulation. Both S-nZVI and B-nZVI decreased the contents of Cr(VI) and available Cr in soil, but increased available Fe content, with S-nZVI generally showing more pronounced effects at a higher dose (1000 mg/kg). B-nZVI exerted no inhibition and even stimulation on plant growth, but 1000 mg/kg S-nZVI produced significant phytotoxicity, resulting in decreased plant growth, low chlorophyll content in leaves, and excessive accumulation of Fe in roots. Each nZVI decreased shoot and root Cr concentrations. BC and HA produced synergistic effects with nZVI on Cr(VI) removal from soil, but HA decreased soil pH and increased the availability of Cr and Fe, implying a potential environmental risk. Addition of BC or HA did not alter the effects of either nZVI on plant growth. In conclusion, combined application of 100 mg/kg nZVI and BC could be an ideal strategy for the remediation of soil contaminated with Cr(VI), whereas high-dose S-nZVI and HA are not recommended in the remediation of agricultural soils for crop production or in the phytostabilization of Cr(VI).

Influence of nanoscale zero-valent iron on hydraulic conductivity of a residual clayey soil and modeling of the filtration parameter

Contaminated clay soils pose problems to public health and the environment in several parts of the world. Very little is known about the transport of decontaminating agents used in remediation process under natural, undisturbed conditions. Nanomaterials, especially those made of nanoscale zero-valent iron (nZVI), have been most frequently used for remediation of contaminated soils because of their higher reactivity, lower toxicity, and lower cost than other metallic nanoparticles. Even though the nanoparticle size is smaller than soil pores, clogging may occur over time due to agglomeration of nanoparticles, which could reduce the soil's natural permeability and thereby cause filtration of the nanoparticles. The use of a stabilizer in the nanoparticles can modify the reactivity but improves their mobility in the soil system. Thus, the objective of this work was to evaluate the hydraulic conductivity of residual clay soil under the injection of different types and concentrations of nZVI with and without surfactant stabilizer (NANOFER 25, NANOFER 25S, and NANOFER STAR in powder at 1 g/L, 4 g/L, 7 g/L, and 10 g/L concentrations), and to model transport of these nZVI suspensions in this soil system. Undisturbed cylindrical soil samples collected from the field were used, and hydraulic conductivity tests were performed using a column apparatus. The results showed that the presence of the stabilizer in the nZVI influenced the nanoparticles' mobility. The nZVI concentrations of 1 and 4 g/L did not affect the natural soil hydraulic conductivity. However, higher concentrations reduced the hydraulic conductivity value, which retarded the migration of nZVI as reflected in the value of filtration parameter.

Evaluation of nanoremediation strategy in a Pb, Zn and Cd contaminated soil

We addressed the efficiency of a nanoremediation strategy using zero-valent iron nanoparticles (nZVI), in a case of co-mingled heavy metals (HM) pollution (Pb, Cd and Zn). We applied a combined set of physical-chemical, toxicological and molecular analyses to assess the effectiveness and ecosafety of nZVI (5% w/w) for environmental restoration. After 120 days, nZVI showed immobilization capacity for Pb (20%), it was scarcely effective for Zn (8%) and negligibly effective for Cd. The HMs immobilization in the nZVI treated soils (compared to control soil), reaches its maximum after 15 days (T3) as reflected in the decrease of HM toxicity towards V. fischeri. The overall abundance of the microbial community was similar in both sets of samples during all experiment, although an increase in the number of metabolically active bacteria was recorded 15 days post treatment. We studied the induced impact of nanoremediation on the soil microbial community structure by Next Generation Sequencing (NGS). Even when higher HM immobilization was recorded, no significant recovery of the microbial community structure was found in nZVI-treated soil. The most marked nZVI-induced structural shifts were observed at T3 (increase in the Firmicutes population with a decrease in Gram-negative bacteria). Predictive metagenomic analysis using PICRUSt showed differences among the predicted metagenomes of nZVI-treated and control soils. At T3 we found decrease in detoxification-related proteins or over-representation of germination-related proteins; after 120 days of nZVI exposure, higher abundance of proteins involved in regulation of cellular processes or sporulation-related proteins was detected. This study highlights the partial effectiveness of nanoremediation in multiple-metal contaminated soil in the short term. The apparent lack of recovery of biodiversity after application of nZVI and the decreased effectiveness of nanoremediation over time must be carefully considered to validate this technology when assurance of medium- to long-term immobilization of HMs is required.

Mobility of Cellulose Nanocrystals in Porous Media: Effects of Ionic Strength, Iron Oxides, and Soil Colloids

Understanding the dispersivity and migration of cellulose nanocrystals (CNCs) in porous media is important for exploring their potential for soil and water remediation. In this study, a series of saturated column experiments were conducted to investigate the coupled effects of ionic strength, iron oxides (hematite), and soil colloids on the transport of CNCs through quartz sand and natural soils (red earth and brown earth). Results showed that CNCs had high mobility in oxide-free sand and that iron oxide coating reduced the mobility of CNCs. An analysis of Derjaguin-Landau-Verwey-Overbeek interactions indicated that CNCs exhibited a deep primary minimum, nonexistent maximum repulsion and secondary minimum on hematite-coated sand, favorable for the attachment of CNCs. The maximum effluent percentage of CNCs was 96% in natural soils at 5 mM, but this value decreased to 4% at 50 mM. Soil colloids facilitated the transport of CNCs in brown earth with larger effect at higher ionic strength. The ionic strength effect was larger in natural soils than sand and in red earth than brown earth. The study showed that CNCs can travel 0.2 m to 72 m in porous media, depending on soil properties, solution chemistry, and soil colloids.

Use of Nanoscale Zero-Valent Iron for Remediation of Clayey Soil Contaminated with Hexavalent Chromium: Batch and Column Tests

This study investigated the reduction of hexavalent chromium (Cr(VI)) in a clayey residual soil using nanoscale zero-valent iron (nZVI). Five different ratios between nZVI and Cr(VI) were tested in batch tests (1000/11; 1000/23; 1000/35; 1000/70, and 1000/140 mg/mg) with the soil. With the selected proportion resulting best efficiency, the column tests were conducted, with molded specimens of 5 cm in diameter and 5 cm in height, with different nZVI injection pressures (10, 30, and 100 kPa). The soil was contaminated with 800 mg/kg of Cr(VI). The Cr(VI) and Cr(III) analyses were performed following the USEPA 3060A and USEPA 7196A standards. The results show that the reduction of Cr(VI) is dependent on the ratio between nZVI and Cr(VI), reaching 98% of efficiency. In column tests, the pressure of 30 kPa was the most efficient. As pressure increased, contaminant leaching increased. The permeability decreased over time due to the gradual increase in filtration and formation of oxyhydroxides, limiting nZVI mobility. Overall, nZVI is efficient for soil remediation with Cr(VI), but the injection process can spread the contaminated if not properly controlled during in situ application.

Vinegar residue supported nanoscale zero-valent iron: Remediation of hexavalent chromium in soil

A composite material comprising of nanoscale zero-valent iron (nZVI) supported on vinegar residue (nZVI@VR) was prepared and applied for remediation of soils contaminated by hexavalent chromium (Cr(VI)). Sedimentation test results revealed that the nZVI@VR displayed enhanced stability in comparison to the bare-nZVI. Remediation experiments exhibited the immobilization efficiency of Cr(VI) and Cr_total was 98.68% and 92.09%, respectively, when using 10 g nZVI@VR (nZVI 5%) per 200 g Cr-contaminated soil (198.20 mg kg^-1 Cr(VI), 387.24 mg kg^-1 Cr_total) after two weeks of incubation. Further analyses demonstrated that almost all the exchangeable Cr was transformed into Fe-Mn oxide bound and organic matter bound. Moreover, the application of nZVI@VR enhanced soil organic carbon content and reduced redox potential. After granulation, the immobilization efficiency of Cr(VI) and Cr_total achieved 100% and 91.83% at a dosage of 10% granular nZVI@VR. Granular nZVI@VR also accelerated the transform of more available Cr (exchangeable and bound to carbonates) into less available fractions (Fe-Mn oxide bound and organic matter bound), thus resulting in a remarkable reduction in the Cr bioavailability. These results prove that nZVI@VR can be an effective remediation reagent for soils contaminated by Cr(VI).

Removal of labile arsenic from flooded paddy soils with a novel extractive column loaded with quartz-supported nanoscale zero-valent iron

Efficient removal of labile arsenic (As) from paddy soil is a fundamental pathway mitigating As accumulation in rice from a long-term perspective. In this study, a porous and pencil-shaped column prepacked with quartz-supported nanoscale zero-valent iron (NZVI) was designed to extract elevated porewater As from paddy soil under flooded condition. With fine quartz as supporting medium in the core layer, only 0.07% out-migration of the loaded NZVI occurred in arsenite As(III) solution. At pH 5-9, removal of aqueous As(III) with NZVI-column was 73-78%, while silicic acid and phosphate at their environmentally realistic concentrations exhibited 27-30% and 14-17% inhibition on As(III) extraction, respectively. For two paddy soils with slight (S-As) and moderate (M-As) As contamination, four cycles of intermittent extraction with NZVI-column induced steady and marked decrease in porewater As. By the end of four successive extractions, profiles of DGT-labile As in S-As and M-As soils decreased by 22% and 29% on average with simultaneous decline of the most available fraction of soil As (including soluble and exchangeable fraction) by 26% and 17%, respectively. For the post-extracted two soils, As accumulation of rice seedlings declined by 29-57% than those in control. These results identify the effectiveness of NZVI-column in extracting elevated labile As from paddy soils with the aid of flooding. Targeting fast removal of high porewater As, column-extraction could serve as the first step in "remediation train" of paddy soils with relatively high As to shorten cleanup time by rendering much lowered soil As burden for the following phytoextraction and other measures.

Evaluating phytotoxicity of bare and starch-stabilized zero-valent iron nanoparticles in mung bean

Zero-valent iron nanoparticles (nZVI) are among the most widely used nanoparticles in nanoremediation of various environmental pollutants. Environmental fate and impact of nZVI has attracted increasing concerns due to their potential risks. However, phytotoxicity of nZVI still remains poorly understood. Here, the phytotoxic effects of bare nZVI (B-nZVI) and starch-stabilized nZVI (S-nZVI) were evaluated on the germination of mung bean seeds exposed to suspensions with different doses of 0-1000 mg/L and the growth of hydroponically cultured seedling at 600 mg/L. In most cases, B-nZVI had no inhibition on seed germination, and even promotion on shoot and root elongation. However, S-nZVI displayed dose-dependent effects, with a decreased germination rate at 600-750 mg/L. B-nZVI at 600 mg/L showed no obvious phytotoxic but even stimulatory effects on seedling growth. Comparatively, S-nZVI at 600 mg/L produced significant phytotoxicity on mung bean plants, leading to decreased seedling growth, altered nutritional balance, and excess Fe accumulation in roots (>400 mg/kg). S-nZVI were observed to form a coating of insoluble Fe(III) compounds on root surface. Simultaneously, some nZVI penetrated and accumulated into root cells, but did not move to shoots. In conclusion, B-nZVI easily aggregate into larger particles in solution, leading to decreased adhesion to root surface and lower uptake by roots, whereas the higher dispersity and hydrophilicity of S-nZVI makes them more readily be adhered to root surface forming a coating, and penetrated into roots, resulting in excess Fe accumulation, consequently interfering with root functions such as the adsorption and transport of water and nutrients.

Effects of Zerovalent Iron Nanoparticles on Photosynthesis and Biochemical Adaptation of Soil-Grown Arabidopsis thaliana

Nanoscale zerovalent iron (nZVI) is the most widely used nanomaterial for environmental remediation. The impacts of nZVI on terrestrial organisms have been recently reported, and in particular, plant growth was promoted by nZVI treatment in various concentrations. Therefore, it is necessary to investigate the detailed physiological and biochemical responses of plants toward nZVI treatment for agricultural application. Here, the effects of nZVI on photosynthesis and related biochemical adaptation of soil-grown Arabidopsis thaliana were examined. After treatment with 500 mg nZVI/kg soil, the plant biomass increased by 38% through enhanced photosynthesis, which was confirmed by the gas-exchange system, carbon isotope ratio and chlorophyll content analysis. Besides, the iron uptake of the plant increased in roots and leaves. The magnetic property measurements and transmission electron microscopy showed that the transformed particles were accumulated in parts of the plant tissues. The accumulation of carbohydrates such as glucose, sucrose and starch increased by the enhanced photosynthesis, and photosynthetic-related inorganic nutrients such as phosphorus, manganese and zinc maintained homeostasis, according to the increased iron uptake. These findings suggest that nZVI has additional or alternative benefits as a nano-fertilizer and a promoter of CO₂ uptake in plants.

Immobilization of heavy metals in vegetable-growing soils using nano zero-valent iron modified attapulgite clay

Nowadays, the problem of heavy metal pollution in vegetables is received wide attention. In this work, attapulgite clay (ATTP), as a cheap and readily available inorganic mineral material, was modified with nano zero-valent iron (nFe⁰@ATTP) for heavy metal immobilization in soil. Batch experiments were employed to evaluate the optimal remediation performance by ATTP before and after modified with nFe⁰ through planting Pakchoi (Brassica chinesis L.) in Cd, Cr, and Pb contaminated soil from Changsha. The results showed that amendments can all increase the pH value of soils, and notably decrease the concentration of extractable Cd, Cr, and Pb in soil. The germination rate and root length of Pakchoi were promoted, and the activities of peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) contents were notably reduced besides superoxide dismutase (SOD) activity after treatments with ATTP and nFe⁰@ATTP. Vicia faba-micronucleus test indicated that the application of amendments reduced the toxicity of heavy metals on the genetic material of Vicia faba root tip cells. The nFe⁰@ATTP were found to well convert Cd, Cr, and Pb into less bioavailable state in soil, thus blocking heavy metal uptake by plants. This material could be a promising amendment for heavy metals contaminated soil.

Functionalized Biochar/Clay Composites for Reducing the Bioavailable Fraction of Arsenic and Cadmium in River Sediment

Biochar has frequently been used for the treatment of heavy metal pollution in water and soil; its effect on contaminated sediments requires further research. To improve the ability of biochar to immobilize heavy metals in sediment, we prepared a functionalized biochar/attapulgite composite by pyrolysis of the clay attapulgite and zinc chloride-pretreated rice straw biomass. Compared with the original biochar, the biochar/attapulgite composite had a large increase in specific surface area, pore volume, oxygen-containing functional groups, and cation exchange capacity. Biochar effectively improved the dispersibility of attapulgite as a matrix. The results showed that the biochar/attapulgite composite effectively reduced the bioavailable fraction of arsenic (As) and cadmium (Cd) in river sediment, which was a great improvement compared with the raw biochar. After the sediment was treated with different biochar/attapulgite composites, the concentrations of As and Cd in the overlying water and the porewater, and the content of acid-extractable and toxicity characteristic leaching procedure (TCLP)-extractable As and Cd in the solid phase of the sediment decreased significantly. Both zinc chloride activation and attapulgite improved As and Cd immobilization in sediment when we used the biochar/attapulgite composite. The results suggest that biochar/attapulgite composite can be used as an efficient in situ sorbent amendment to improve the heavy metal immobilization ability of the sediment. Environ Toxicol Chem 2019;38:2337-2347. © 2019 SETAC.

Remediation performance and mechanism of hexavalent chromium in alkaline soil using multi-layer loaded nano-zero-valent iron

Remediation of soil chromium (Cr) pollution is becoming more and more urgent. In this study, a multi-loaded nano-zero-valent iron (nZVI) material (CNH) was prepared by carboxymethyl cellulose (CMC) and humic acid (HA) as dispersant and support agent, respectively, and the remediation effect of CNH, HA and CN (CNH without HA) for Cr contaminated soil was investigated within 90 d cycle. After 7 d treatment of CNH, the HOAc-extractable Cr decreased significantly. After the 90 d remediation, the HOAc-extractable Cr decreased most in the treatment of 3% CNH, about 74.48% lower than control. All treatments eventually caused different decline of soil pH, with a range of 0.12-0.54, in which the CNH treatment group had the least depression. HA loading significantly weakened the toxicity of nZVI, resulting in the higher soil microbial quantity and enzyme activities compared with CN. Additionally, the improvement of soil microecology by CNH and HA was positively correlated with the ratio of application, while CN was negatively correlated (except FDA enzyme activity) with these indexes. These results emphasized the potential of the synthesized CNH as a promising material to remediate Cr contaminated soil. Furthermore, details of possible mechanistic insight into the Cr remediation were carefully discussed.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe₂O₃·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO₄ and Fe₂O₃·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO₄^-, HO•, and •O₂^-, ¹O₂ are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Effect of multiple iron-based nanoparticles on availability of lead and iron, and micro-ecology in lead contaminated soil

Although iron nanoparticles (NPs) have been used for environmental remediation of heavy metal, their potential to remediate lead (Pb) contaminated soil and effect on soil micro-ecology is unclear. The purpose of this study was to investigate the potential of nanoscale zerovalent iron (nZVI), nanoscale zerovalent iron supported by biochar (nZVI@BC), ferrous sulfide (FeS-NPs), ferrous sulfide supported by biochar (FeS-NPs@BC), ferriferrous oxide (Fe₃O₄-NPs) and ferriferrous oxide supported by biochar (Fe₃O₄-NPs@BC) to remediate Pb contaminated soil and the influences for soil micro-ecology. The results showed that biochar (BC) could improve the crystal shape and superficial area of iron-based nanoparticles. Soil pH values was significantly decreased by FeS-NPs and FeS-NPs@BC, but increased by other iron-nanoparticles. The ability to reduce available Pb concentration showed significant difference among these iron-nanoparticles, that is, the immobilized rate were nZVI by 45.80%, nZVI@BC by 54.68%, FeS-NPs by 2.70%, FeS-NPs@BC by 5.13%, Fe₃O₄-NPs by 47.47%, Fe₃O₄-NPs@BC by 30.51% at day 90. Almost all soil enzyme activities in Fe₃O₄-NPs and Fe₃O₄-NPs@BC groups were increased, but the majority of the enzyme activities were inhibited in other iron-based nanoparticles groups, while the maximum bacterial number was determined in FeS-NPs group. Furthermore, microbial diversity analysis showed that FeS-NPs has significantly changed microbial community richness and diversity, followed by nZVI and Fe₃O₄-NPs. Accordingly, our results suggested that nZVI@BC had the best immobilization effect on Pb in high-concentration Pb-contaminated alkaline soil, but the toxic effect of Fe₃O₄-NPs on soil micro-ecology was relatively minimal.

Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: A critical review

The promising characteristics of nanoscale zero-valent iron (nZVI) have not been fully exploited owing to intrinsic limitations. Carbon-enriched biochar (BC) has been widely used to overcome the limitations of nZVI and improve its reaction with environmental pollutants. This work reviews the preparation of nZVI/BC nanocomposites; the effects of BC as a supporting matrix on the nZVI crystallite size, dispersion, and oxidation and electron transfer capacity; and its interaction mechanisms with contaminants. The literature review suggests that the properties and preparation conditions of BC (e.g., pore structure, functional groups, feedstock composition, and pyrogenic temperature) play important roles in the manipulation of nZVI properties. This review discusses the interactions of nZVI/BC composites with heavy metals, nitrates, and organic compounds in soil and water. Overall, BC contributes to the removal of contaminants because it can attenuate contaminants on the surface of nZVI/BC; it also enhances electron transfer from nZVI to target contaminants owing to its good electrical conductivity and improves the crystallite size and dispersion of nZVI. This review is intended to provide insights into methods of optimizing nZVI/BC synthesis and maximizing the efficiency of nZVI in environmental cleanup.

Behavior, remediation effect and toxicity of nanomaterials in water environments

In recent years, nanotechnology has been developing continuously. Due to their advantageous huge specific surface areas, microinterface characteristics, remediation ability and potential environmental risks, nanomaterials have become a hot topic in the field of environmental research. With the mass production and use of nanomaterials, they will inevitably be discharged or leaked into the water environment. In this paper, we will describe some typical nanomaterials, such as nanoscale zero valent iron (nZVI), graphene nanomaterials (GNMs), TiO₂ nanoparticles (NPs), ZnO NPs, Fe₃O₄ NPs, carbon nanotubes (CNTs), Ag NPs, and other nanomaterials in water environments, focusing on the positive and negative effects of some nanomaterials in water environments. The remediation function and the impact of nanomaterials in water environments, including behavior of nanomaterials and their toxicity to aquatic organisms will be discussed. This will be of great significance for our subsequent research on nanomaterials.

Utilization of nanomaterials for in-situ remediation of heavy metal(loid) contaminated sediments: A review

Heavy metal(loid)s are toxic and non-biodegradable environmental pollutants. The contamination of sediments with heavy metal(loid)s has attracted increasing attention due to the negative environmental effects of heavy metal(loid)s and the development of new remediation techniques for metal(loid) contaminated sediments. As a result of rapid nanotechnology development, nanomaterials are also being increasingly utilized for the remediation of contaminated sediments due to their excellent capacity of immobilizing/adsorbing metal(loid) ions. This review summarizes recent studies that have used various nanomaterials such as nanoscale zero-valent iron (nZVI), stabilizer-modified nZVI, nano apatite based-materials including nano-hydroxyapatite particles (nHAp) and stabilized nano-chlorapatite (nCLAP), carbon nanotubes (CNTs), and titanium dioxide nanoparticles (TiO₂ NPs) for the remediation of heavy metal(loid) contaminated sediments. We also review the analysis of potential mechanisms involved in the interaction of nanomaterials with metal(loid) ions. Subsequently, we discuss the factors affecting the nanoparticle-heavy metal(loid)s interaction, the environmental impacts resulting from the application of nanomaterials, the knowledge gaps, and potential future research.

Nanomaterials and plants: Positive effects, toxicity and the remediation of metal and metalloid pollution in soil

Currently, the pollution of metals and metalloids in the soil has attracted considerable attention. Phytoremediation is considered an environmentally friendly means of remediating pollution, but often takes a long time to perform. Therefore, the combination of plants and nanomaterials in environmental management has attracted the attention of many researchers because some nanomaterials can promote the germination of plant seeds and the growth of whole plants. However, when the concentration of nanomaterials is not controlled properly, certain toxicity will be produced. This paper reviews research on the combination of plant and nanomaterials for the remediation of contaminated environments, as well as on the effects of nanomaterials on plants.

Opposite influences of mineral-associated and dissolved organic matter on the transport of hydroxyapatite nanoparticles through soil and aggregates

The mechanism by which soil organic matter (SOM) controls nanoparticle transport through natural soils is unclear. In this study, we distinguished the specific effects of two primary SOM fractions, mineral-associated organic matter (MOM) and dissolved organic matter (DOM), on the transport of hydroxyapatite nanoparticles (nHAP) through a loamy soil under the conditions of saturated steady flow and environmentally relevant solution chemistry (1 mM NaCl at pH 7). The results showed that MOM could inhibit the transport of nHAP by decreasing electrostatic repulsion and increasing mechanical straining and hydrophobic interactions. Specifically, the presence of MOM reduced the mobility of nHAP in the bulk soil and its macroaggregates by ~4 fold and ~6 fold, respectively, and this hindered effect became further conspicuous in microaggregates (~36 fold decrease). An analysis of extended Derjaguin-Landau-Vervey-Overbeek (abbreviated as XDLVO) interactions indicated that MOM could decrease the primary energy barrier (Φ_max1), primary minimum (Φ_min1), and secondary minimum (Φ_min2) to promote nHAP attachment. Conversely, DOM (10-50 mg L^-1) favored nHAP mobility due to an increase in electrostatic repulsion among nHAP particles and between nHAP and soil surfaces. Pre-flushing soil with DOM (causing DOM sorption on soil) increased nHAP mobility by ~2 fold in the bulk soil and its macroaggregates, and this facilitated effect was furthered in microaggregates (~11 fold increase). The results of XDLVO interactions showed that DOM increased Φ_max1, Φ_min1, and Φ_min2, producing an unfavorable effect on nHAP attachment. Mass recovery data revealed that the MOM-hindered effect was stronger than the DOM-facilitated effect on nHAP transport. This study suggested that changing SOM fractions could control the mobility of nanoparticles in the subsurface considerably.

The impact of nanoparticles zero-valent iron (nZVI) and rhizosphere microorganisms on the phytoremediation ability of white willow and its response

Soil contaminated with heavy metals (HMs) is a serious problem throughout the world that threatens all living organisms in the soil. Therefore, large-scale remediation is necessary. This study investigated a new combination of remediation techniques on heavy metal contaminated soil, phytoremediation, and soil amendment with nano-sized zero-valent iron (nZVI) and rhizosphere microorganisms. White willow (Salix alba L.) was grown for 160 days in pots containing Pb, Cu, and Cd and amended with 0, 150, and 300 (mg kg^-1) of nZVI and rhizosphere microorganisms, including the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis, and the plant growth promoting rhizobacteria (PGPR), Pseudomonas fluorescens. The results showed that inoculation with PGPR and AMF, particularly dual inoculation, improved plant growth as well as the physiological and biochemical parameters of white willow, and increased the bioconcentration factor (BCF) of Pb, Cu, and Cd. The low dose of nZVI significantly increased the root length and the leaf area of the seedlings and increased the BCF of Cd. In contrast, the high dose of nZVI had negative effects on the seedlings growth and the BCF of Pb and Cu, about - 32% and - 63%, respectively. Our results demonstrate that nZVI at low doses can improve plant performance in a phytoremediation context and that the use of beneficial rhizosphere microorganisms can minimize nZVI stress in plants and make them less susceptible to stress even under high dose conditions.

Shift in Natural Groundwater Bacterial Community Structure Due to Zero-Valent Iron Nanoparticles (nZVI)

Toxic and persistent contaminants in groundwater are technologically difficult to remediate. Remediation techniques using nanoparticles (NPs) such as nZVI (Zero-Valent Iron) are applicable as in situ reduction or oxidation agents and give promising results for groundwater treatment. However, these NP may also represent an additional contamination in groundwater. The aims of this study are to assess the impact of nZVI on the nitrate-reducing potential, the abundance and the structure of a planktonic nitrate-reducing bacterial community sampled in groundwater from a multicontaminated site. An active nitrate-reducing bacterial community was obtained from groundwater samples, and inoculated into batch reactors containing a carbon substrate, nitrate and a range of nZVI concentrations (from 0 to 70.1 mg Fe.L-1). Physical (pH, redox potential), chemical (NO 3 - concentrations) and biological (DNA, RNA) parameters were monitored during 1 week, as well as nZVI size distribution and mortality of bacteria. Nitrate-reducing activity was temporally stopped in the presence of nZVI at concentrations higher than 30 mg L-1, and bacterial molecular parameters all decreased before resuming to initial values 48 h after nZVI addition. Bacterial community composition was also modified in all cultures exposed to nZVI as shown by CE-SSCP fingerprints. Surprisingly, it appeared overall that bacteria viability was lower for lower nZVI concentrations. This is possibly due to the presence of larger, less reactive NP aggregates for higher nZVI concentrations, which inhibit bacterial activity but could limit cell mortality. After 1 week, the bacterial cultures were transplanted into fresh media without nZVI, to assess their resilience in terms of activity. A lag-phase, corresponding to an adaptation phase of the community, was observed during this step before nitrate reduction reiterated, demonstrating the community's resilience. The induction by nZVI of modifications in the bacterial community composition and thus in its metabolic potentials, if also occurring on site, could affect groundwater functioning on the long term following nZVI application. Further work dedicated to the study of nZVI impact on bacterial community directly on site is needed to assess a potential impact on groundwater functioning following nZVI application.

The use of zero-valent Fe for curbing toxic emissions after EDTA-based washing of Pb, Zn and Cd contaminated calcareous and acidic soil

The use of EDTA-based soil washing is prevented by chelant environmental persistence and the hazard of toxic post-remedial emissions. Calcareous and acidic soils with 828 and 673 mg Pb kg^-1, respectively, and co-contaminated with Zn and Cd, were washed with 90 and 60 mM EDTA, respectively, to remove 67 and 80% of Pb. Washed soils were rinsed until 6.5 and 5.1 mM EDTA, respectively, was measured in the final rinsing solutions. Emissions of residual EDTA and chelated metals from remediated soils were mitigated by adsorption on zero-valent Fe (ZVI), which was added (0.5-1.5%, w/w) to the slurry of washed soil immediately before rinsing. ZVI addition prevented the initial post-remedial surge of toxic metals leachability and minimised toxic emissions from calcareous and acidic soil as soon as 6 and 7 days after remediation, respectively. The extractability/leachability of EDTA and toxic metals from remediated and ZVI amended soils diminished to close to emissions from the original soils, frequently below the limit of quantification by flame-AAS, and was not affected by the pH of the leaching solutions. Efficient curbing of toxic post-remediation emissions as demonstrated herein is of paramount importance for recognition of EDTA-based remediation as environmentally safe.

New insights into the impact of nZVI on soil microbial biodiversity and functionality

Nanoscale zero-valent iron (nZVI) is a strong reducing agent used for in situ remediation of soil. The impacts of nZVI (5-10% w/w) on the soil microbial biodiversity and functionality of two soils (Lufa 2.2 and 2.4) were assessed. Illumina MiSeq technology was used to evaluate the structure of soil microbiomes after 21 days of exposure. Proteobacteria, Verrucomicrobia, Firmicutes and Actinobacteria were the most abundant phyla in both soils. However, the dynamics of bacterial community composition following nZVI addition differed. nZVI exposure induced pronounced shifts in the microbial composition of soil 2.4, but not in soil 2.2; an increase in Verrucomicrobia abundance was the unique common taxonomic pattern observed in both soils. The PICRUSt approach was applied to predict the functional composition of each metagenome. Environmental information processing function (membrane transport) was decreased in both nZVI-spiked soils, although soil 2.4 samples were enriched in functions involved in cellular processes and metabolism. The effects of nZVI on autochthonous bacterial communities clearly varied with the soil type assessed; changes at the phylogenetic level appeared to be more abundant than those observed at the functional level, and thus, the overall effort of the soil ecosystem might involve the maintenance of functionality following nZVI exposure.

Characterization of Iron Core⁻Gold Shell Nanoparticles for Anti-Cancer Treatments: Chemical and Structural Transformations During Storage and Use

Finding a cancer-selective drug that avoids damaging healthy cells and organs is a holy grail in medical research. In our previous studies, gold-coated iron (Fe@Au) nanoparticles showed cancer selective anti-cancer properties in vitro and in vivo but were found to gradually lose that activity with storage or "ageing." To determine the reasons for this diminished anti-cancer activity, we examined Fe@Au nanoparticles at different preparation and storage stages by means of transmission electron microscopy combined with and energy-dispersive X-ray spectroscopy, along with X-ray diffraction analysis and cell viability tests. We found that dried and reconstituted Fe@Au nanoparticles, or Fe@Au nanoparticles within cells, decompose into irregular fragments of γ-F₂O₃ and agglomerated gold clumps. These changes cause the loss of the particles' anti-cancer effects. However, we identified that the anti-cancer properties of Fe@Au nanoparticles can be well preserved under argon or, better still, liquid nitrogen storage for six months and at least one year, respectively.

The nanotechnology among US: are metal and metal oxides nanoparticles a nano or mega risk for soil microbial communities?

Metal nanoparticles and metal oxides nanoparticles (MNPs/MONPs) have been widely included in a great diversity of products and industrial applications and they are already a part of our everyday life. According to estimation studies, their production is expected to increase exponentially in the next few years. Consequently, soil has been suggested as the main sink of MNPs/MONPs once they are deliberately or accidentally released into the environment. The potential negative perturbations that may result on soil microbial communities and ecological processes are resulting in concerns. Several nano-toxicological studies of MNPs/MONPs, reported so far, have focused on aquatic organisms, animals, and soil invertebrates. However, during recent years, the studies have been oriented to understand the effects of MNPs/MONPs on microbial communities and their interaction with soil components. The studies have suggested that MNPs/MONPs are one of the most toxic type to soil biota, amongst different types of nanomaterials. This may threaten soil health and fertility, since microbial communities are known to support important biological processes and ecosystem services such as the nutrient cycling, whereby their protection against the environmental pollution is imperative. Therefore, in this review we summarize the actual knowledge available from the last five years (2013-2018) and gaps about the potential negative, positive or neutral effects produced on soil by different classes of MNPs/MONPs. A particular emphasis has been placed on the associated soil microorganisms and biological processes. Finally, perspectives about future research are discussed.

Nanotechnology for Environmental Remediation: Materials and Applications

Environmental remediation relies mainly on using various technologies (e.g., adsorption, absorption, chemical reactions, photocatalysis, and filtration) for the removal of contaminants from different environmental media (e.g., soil, water, and air). The enhanced properties and effectiveness of nanotechnology-based materials makes them particularly suitable for such processes given that they have a high surface area-to-volume ratio, which often results in higher reactivity. This review provides an overview of three main categories of nanomaterials (inorganic, carbon-based, and polymeric-based materials) used for environmental remediation. The use of these nanomaterials for the remediation of different environmental contaminants-such as heavy metals, dyes, chlorinated organic compounds, organophosphorus compounds, volatile organic compounds, and halogenated herbicides-is reviewed. Various recent examples are extensively highlighted focusing on the materials and their applications.