Application Of nZVI Research Articles

Green synthesis and toxicity assessment of nano zerovalent iron against chromium contaminated surface water

Parthenium hysterophorus an annual herbaceous weed is known for its vigorous growth and as a causative agent for contact dermatitis, hay fever and diarrhea in humans and systemic toxicity in livestock. However, in spite of all the problems associated with this weed, some beneficial activities also reported. The objective of this study is to evaluate the potential of Parthenium hysterophorus leaf extracts for the synthesis of nanoscale zerovalent iron (nZVI) and their chromium remediation property. Due its high toxicity and mobility, hexavalent chromium is considered to be a high priority pollutant. In addition this work was executed to carry out toxicity appraisal in a water sample collected from Puliyanthangal Lake, Tamilnadu, India using nZVI. The water samples were examined before and after the nZVI application by means of microbial cultivation tests, phospholipid fatty acid analysis (PLFA) and toxicological tests. The present experimental results revealed that Cr (VI) is considerably adsorbed on nZVI nanoparticles and it could be a cost effective method for the in situ remediation of Cr (VI). In addition, standard plate count assay showed the dose dependent decrease in the bacterial cell viability in lake water sample after the addition of nZVI.

Green synthesis and toxicity assessment of nano zerovalent iron against chromium contaminated surface water

Parthenium hysterophorus an annual herbaceous weed is known for its vigorous growth and as a causative agent for contact dermatitis, hay fever and diarrhea in humans and systemic toxicity in livestock. However, in spite of all the problems associated with this weed, some beneficial activities also reported. The objective of this study is to evaluate the potential of Parthenium hysterophorus leaf extracts for the synthesis of nanoscale zerovalent iron (nZVI) and their chromium remediation property. Due its high toxicity and mobility, hexavalent chromium is considered to be a high priority pollutant. In addition this work was executed to carry out toxicity appraisal in a water sample collected from Puliyanthangal Lake, Tamilnadu, India using nZVI. The water samples were examined before and after the nZVI application by means of microbial cultivation tests, phospholipid fatty acid analysis (PLFA) and toxicological tests. The present experimental results revealed that Cr (VI) is considerably adsorbed on nZVI nanoparticles and it could be a cost effective method for the in situ remediation of Cr (VI). In addition, standard plate count assay showed the dose dependent decrease in the bacterial cell viability in lake water sample after the addition of nZVI.

High nitrate removal by starch-stabilized Fe0 nanoparticles in aqueous solution in a controlled system.

This study was conducted to investigate biodenitrification efficiency with starch-stabilized nano zero valent iron (S-nZVI) as the additional electron donor in the presence of S2O3 in aqueous solutions, under anaerobic conditions. The main challenge for nZVI application is their tendency to agglomeration, thereby resulting in loss of reactivity that necessitates the use of stabilizers to improve their stability. In this study, S-nZVI was synthesized by chemical reduction method with starch as a stabilizer. The synthesized nanoparticles were characterized by TEM, XRD, and FTIR. Transmission electron microscopy (TEM) image shows S-nZVI has a size in the range of 5-27.5 nanometer. Temperature and S-nZVI concentration were the important factors affecting nitrate removal. Biodenitrification increased at 35°C and 500mg/L of S-nZVI, in these conditions, biodenitrification efficiency increased from 40.45 to 78.84%. Experimental results suggested that biodenitrification increased by decreasing initial nitrate concentration. In the bioreactor biodenitrification rate was 94.07% in the presence of S-nZVI. This study indicated that, Fe2+ could be used as the only electron donor or as the additional electron donor in the presence of S2O3 to increase denitrification efficiency.

Selective Nitrate Reduction to Dinitrogen by Electrocatalysis on Nanoscale Iron Encapsulated in Mesoporous Carbon.

Excessive nutrients (N and P) are among the most concerned pollutants in surface and ground waters. Herein, we report nanoscale zero-valent iron supported on ordered mesoporous carbon (nZVI@OMC) for electrocatalytic reduction of nitrate (NO3-) to nitrogen gas (N2). This material has a maximum removal capacity of 315 mg N/g Fe and nitrogen selectivity up to 74%. The Fe-C nanocomposite is prepared via a postsynthetic modification including carbon surface oxidation, in-situammonia prehydrolysis of iron precursor and hydrogen reduction. The synthesized materials have large surface areas (660-830 m2/g) and small iron nanoparticles (3-9 nm) uniformly dispersed in the carbon mesochannels. The iron loading can be adjusted in the range of 0-45%. Results demonstrate that the reaction reactivity of electrocatalysis can be fine-tuned by manipulating iron nanoparticle size, degree of crystallization, as well as porous structure. Meanwhile, the small, uniform, and stable iron nanoparticle promotes fast hydrogen generation for rapid cleavage of the N-O bond. Furthermore, this material can maintain its high performance over repetitive experimental cycles. Results suggest a new approach for fast and eco-friendly nitrate reduction and a novel nZVI application.

Advanced oxidation of orange G using phosphonic acid stabilised zerovalent iron

Orange G (OG) is an important chemical for the textile industry but also a major water contaminant. It is also a model compound representing more toxic azo dyes and degradation products. Activation of persulphate (PS) by zerovalent iron nanoparticles (nZVI) has been proposed as an effective technique to degrade OG even at neutral pH conditions. However, particle agglomeration leads to diminished reactivity and remains a crucial challenge for nZVI applications. This work evaluates the performance of three different nZVI that are each stabilised with one of three phosphonic acids, ATMP, DTPMP or HTPMP. While ATMP- and DTPMP-stabilised nZVI were practically inert to OG solution in the absence of PS, HTPMP-stabilised nZVI achieved ∼15% total carbon (TC) reduction under similar conditions. However, in the presence of PS, ATMP- and DTPMP-stabilised nZVI resulted in degradation rate constants that were double the rate constant obtained for HTPMP-stabilised nZVI under similar conditions. These results highlight the important role of both stabilisers and PS in modulating nZVI activity with potential niche application. A desirable feature of the PS-nZVI degradation mechanism is the rapid destruction of both the azo bond and benzene ring in OG, resulting in fewer, and less toxic, degradation products than have been previously reported. Significant mineralisation was recorded in longer term experiments, where 90% organic carbon reduction was achieved in 48h for the three stabilised nZVI. Hence, phosphonate-stabilised nZVI activation of PS is an effective means to achieve complete OG degradation and significant mineralisation with non-toxic major degradation product.

Development of new remediation technologies for contaminated soils based on the application of zero-valent iron nanoparticles and bioremediation with compost

Abstract This study aimed to develop new techniques for the remediation of contaminated soils based on the application of zero-valent iron nanoparticles (nZVI) and bioremediation with compost from organic wastes and a mixed technique of both. An assessment of the effectiveness of remediation in two soils contaminated with hydrocarbons and heavy metals was carried out, with the aim of looking for positive synergies by combining the two techniques, and demonstrating their viability on an industrial scale. The application of nZVI for in situ immobilization of As and Cr in two different soils (Soil I from a contaminated industrial site and Soil II, contaminated artificially) showed a decrease in the concentration of As in Soil I and Soil II, as well as a decrease in Cr concentration for Soil I and Soil II in the leachate of both soils. The addition of compost and nanoparticles under uncontrolled environmental conditions in biopiles was able to produce a decrease in the concentration of aliphatic hydrocarbons of up to 60% in the two soils. Especially, degradation and transformation of longer chains occurred. A significant reduction of ecotoxicity was observed throughout the process in the biopile of soil II, not reaching the LC50 even with 100% of the sample after the treatment, in both earthworm and seeds growth tests.

Nitrogen activation of carbon-encapsulated zero-valent iron nanoparticles and influence of the activation temperature on heavy metals removal

Nanoparticles of zero-valent iron (nZVI) represent a promising agent for environmental remediation. This is due to their core-shell structure which presents the characteristics of both metallic and oxidised iron, leading to sorption and reductive precipitation of metal ions. Nevertheless, nZVI application presents some limitations regarding their rapid oxidation and aggregation in the media which leads to the delivery of the ions after some hours (the “aging effect”). To address these issues, modifications of nZVI structure and synthesis methods have been developed in the last years. The aging problem was solved by using nZVI encapsulated inside carbon spheres (CE-nZVI), synthetized through Hydrothermal Carbonization (HTC). Results showed high heavy metals removal percentage. Furthermore, CE-nZVI were activated with nitrogen in order to increase the metallic iron content. The aim of this study was to test CE-nZVI post-treated with nitrogen at different temperatures in heavy metals removal, demonstrating that the influence of the temperature was negligible in nanoparticles removal efficiency.

Critical evaluation of the use of different nanoscale zero-valent iron particles for the treatment of effluent water from a small biological wastewater treatment plant

Nanoremediation procedures are usually designed so that only one contaminant or similar class of contaminants is being considered. In the present work, a holistic approach was applied towards processes which simultaneously occur after the treatment of real effluent water from a small biological wastewater treatment plant (SBWTP) with different nanoscale zero-valent iron (nZVI) particles. Three different types of nZVI particles were tested: in-house nZVI, commercially available Nanofer STAR and Nanofer25 slurry, which differ in reactivity and their methods of synthesis. In order to optimise the conditions for the efficient removal of selected elements, nitrogen species, and pathogenic bacteria (Coliform bacteria, Escherichia coli, Intestinal Enterococci and Clostridium perfringens), effluent water samples were treated with different iron loads from each of the investigated nZVI at various mixing and settling times.The results demonstrated that in-house nZVI, which is the most reactive of the nanoparticles tested, most effectively removed metals and inactivated pathogenic bacteria. However, the application of in-house nZVI is restricted, as it contaminates the remediated water with B, which originated from the reagents used in its synthesis. To a certain extent, all of the investigated types of nZVI reduced nitrates and nitrites to ammonium cations. The additional formation of ammonium nitrogen was the result of the interactions of the nZVI with the organic nitrogen present in the effluent water. At an optimised iron load, mixing time, and settling time, the most efficient removal of elements and disinfection of pathogens was achieved when Nanofer25 slurry was applied.

Comparing different commercial zero valent iron nanoparticles to immobilize As and Hg in brownfield soil.

Nanoscale zero valent iron (nZVI) particles obtained by different methods differ in their structure, which lead to different reactivity, and therefore a likely difference in the remediation efficiency. The present study compares the effectiveness of three commercial ZVI nanoparticles to immobilize As and Hg in two soils (A and B) collected from a brownfield highly contaminated by mining and metallurgy activities. Scarce data are available on the effectiveness of nZVI for Hg immobilization in soil. Two commercial nZVI slurries from Toda (RNIP and RNIP-D) and one from Nano Iron (25S) were used at different doses (1, 5 and 10%). The metal(loid) availability and mobility was evaluated with the TCLP test and Tessier extraction procedure. The influence of nZVI application on As and Hg speciation was also evaluated as well as its impact on soil pH, electrical conductivity and soil phytotoxicity to vetch germination. The three commercial nZVI particles significantly reduced As and Hg availability in the two soils studied, which led to a decrease in soil phytotoxicity. At the dose of 5% of nZVI a decrease of exchangeable-As higher than 70% was observed for both soils, whereas in the case of Hg, a higher dose of nZVI (10%) was necessary to achieve reductions of exchangeable-Hg between 63 and 90% depending on the type of nZVI and soil. No impact on soil pH and electrical conductivity was observed. The effectiveness of metal(loid) immobilization depended on type of nZVI, soil properties and metal(loid) characteristics. Nanoparticles from Nano Iron showed better results for As immobilization whereas RNIP nanoparticles were more effective for Hg. Overall, 25S at the dose of 5% resulted more effective than RNIP nanoparticles for the reduction of exchangeable-As (in the range of 6-14%), whereas RNIP and RNIP-D were 10 and 13% more effective, respectively, for the reduction of exchangeable-Hg at the dose of 10% in soil B. Thus, nZVI can be used for the remediation of highly As and Hg polluted soils, although previous experiments at lab scale are necessary to determine the most viable type of nZVI and its dose.

Viability of a nanoremediation process in single or multi-metal(loid) contaminated soils

The effectiveness of single- and multi-metal(loid) immobilization of As, Cd, Cr, Pb and Zn using different doses of nanoscale zero-valent iron (nZVI) was evaluated and compared in two different soils, a calcareous and an acidic one. The effectiveness of nZVI to immobilize metal(loid)s in soil strongly depended on the metal characteristics, soil properties, dose of nZVI and presence of other metal(loid)s. In the case of single contamination, this nanoremediation strategy was effective for all of the metal(loid)s studied except for Cd. When comparing the two soils, anionic metal(loid)s (As and Cr) were more easily retained in acidic soil, whereas cationic metal(loid)s (Cd, Pb and Zn), were immobilized more in calcareous soil. In multi-metal(loid) contaminated soils, the presence of several metal(loid)s affected their immobilization, which was probably due to the competitive phenomenon between metal(loid) ions, which can reduce their sorption or produce synergistic effects. At 10% of nZVI, As, Cr and Pb availability decreased more than 82%, for Zn it ranged between 31 and 75% and for Cd between 13 and 42%. Thus, the application of nZVI can be a useful strategy to immobilize As, Cr, Pb and Zn in calcareous or acidic soils in both single- or multi-metal(loid) contamination conditions.

Application of nanoscale zero valent iron and iron powder during sludge anaerobic digestion: Impact on methane yield and pharmaceutical and personal care products degradation

Lab scale and single stage high solid anaerobic digestion of sewage sludge spiked with freshly synthesized nanoscale zero valent iron (nZVI) and commercial iron powder (IP) under mesophilic condition (37±1°C) was performed. The effects of both additives on methane yield, and pharmaceutical and personal care product (PPCP) removal were investigated. Results showed that methane yield was increased by 25.2% and 40.8% in the presence of nZVI (0.1%) and IP (1.6%), respectively. Removal efficiencies of chemical oxygen demand were 54.4% and 66.2% in the presence of nZVI and IP, respectively, which were higher compared to the control group (44.6%). In addition, most PPCPs could be partly or completely removed during the anaerobic digestion process. The application of nZVI and IP showed positive impact on the removal of chlorinated PPCPs (p<0.05), but did not show significant impact on other PPCPs (p>0.05). Our finding suggests that the application of nZVI and IP in anaerobic digestion could be a promising way to enhance methane yield but had less improvement on PPCP degradation.

Metal(loid)s behaviour in soils amended with nano zero-valent iron as a function of pH and time

Nano zero-valent iron (nZVI) is currently investigated as a stabilising amendment for contaminated soils. The effect of pH (4–8) and time (48 and 192 h) on the behaviour of nZVI-treated Pb-Zn and As-contaminated soil samples was assessed. Additionally, soil leachates were subsequently used to study the direct interaction between soil solution components and nZVI particles in terms of mineralogical changes and contaminant retention. A typical U-shaped leaching trend as a function of pH was observed for Cd, Pb and Zn, while As was released predominantly under alkaline conditions. Oxidising conditions prevailed, so pH was the key controlling parameter rather than redox conditions. Generally, longer contact time resulted in increased soluble concentrations of metal(loid)s. However, the stabilisation effect of nZVI was only observed after the direct soil leachate-nZVI interactions, showing enhanced redox and sorption processes for the studied metals. A significant decrease of dissolved As concentrations was observed for both experimental soils, but with different efficiencies depending on neutralisation capacity, organic matter content or solid fractionation of As related to the origin of the soils. Scorodite (FeAsO4·2H2O) was predicted as a potential solubility-controlling mineral phase for As. Sorption of metal(loid)s onto secondary Fe- and Al-(oxyhydr)oxides (predicted to precipitate at pH > 5) represents an important scavenger mechanism. Moreover, transmission electron microscopy confirmed the retention of Zn and Pb under near-neutral and alkaline conditions by newly formed Fe oxides or aluminosilicates. This study shows that the efficiency of nZVI application strongly depends not only on soil pH-Eh conditions and contaminant type, but also on the presence of organic matter and other compounds such as Al/Fe/Mn oxyhydroxides and clay minerals.

A review of the environmental implications of in situ remediation by nanoscale zero valent iron (nZVI): Behavior, transport and impacts on microbial communities

The increasing use of strategies incorporating nanoscale zero valent iron (nZVI) for soil and groundwater in situ remediation is raising some concerns regarding the potential adverse effects nZVI could have on indigenous microbial communities and ecosystem functioning. This review provides an overview of the current literature pertaining to the impacts of nZVI applications on microbial communities. Toxicity studies suggest that cell membrane disruption and oxidative stress through the generation of Fe2+ and reactive oxygen species by nZVI are the main mechanisms contributing to nZVI cytotoxicity. In addition, nZVI has been shown to substantially alter the taxonomic and functional composition of indigenous microbial communities. However, because the physico-chemical conditions encountered in situ highly modulate nZVI toxicity, a better understanding of the environmental factors affecting nZVI toxicity and transport in the environment is of primary importance in evaluating the ecological consequences that could result from a more extensive use of nZVI.

A nanoremediation strategy for the recovery of an As-polluted soil

The present study investigates the impact of the nanoremediation treatment on soil recovery as evaluated by the development of barley plants. Highly As-polluted brownfield soil was treated with nanoscale zero-valent iron (nZVI) commercial suspension at two doses (1% and 10%). Barley plants were cultivated in treated and untreated soils in a growth chamber, and the As, Fe, and nutrients uptake were determined. The efficacy of As immobilization was evaluated according to the toxicity characteristics leaching procedure (TCLP) as well as using a sequential extraction procedure. The application of nZVI reduced the amount of As in the more available fractions and increased the amount of As in the residual fraction. The best immobilization results were obtained for the highest dose of nZVI (10%). In turn, the lower availability of As in nZVI-treated soils, particularly at the dose of 10%, stimulated the development of the barley plants and decreased the As uptake. Neither an important increase of available Fe nor negative impact on soil physico-chemical and biological properties were observed. Thus, our results show that the use of nZVI could be an adequate strategy to recover the land use in As polluted soils.

NZVI injection into variably saturated soils: Field and modeling study

Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI field-scale mobility. In this study, a field test was combined with numerical modeling to examine nZVI reactivity along with transport properties in variably saturated soils. The field test consisted of 142L of carboxymethyle cellulose (CMC) stabilized monometallic nZVI synthesized onsite and injected into a variably saturated zone. Periodic groundwater samples were collected from the injection well, as well as, from two monitoring wells to analyze for chlorinated solvents and other geochemistry indicators. This study showed that CMC stabilized monometallic nZVI was able to decrease tricholorethene (TCE) concentrations in groundwater by more than 99% from the historical TCE concentrations. A three dimensional, three phase, finite difference numerical simulator, (CompSim) was used to further investigate nZVI and polymer transport at the variably saturated site. The model was able to accurately predict the field observed head data without parameter fitting. In addition, the numerical simulator estimated the mass of nZVI delivered to the saturated and unsaturated zones and distinguished the nZVI phase (i.e. aqueous or attached). The simulation results showed that the injected slurry migrated radially outward from the injection well, and therefore nZVI transport was governed by injection velocity and viscosity of the injected solution. A suite of sensitivity analyses was performed to investigate the impact of different injection scenarios (e.g. different volume and injection rate) on nZVI migration. Simulation results showed that injection of a higher nZVI volume delivered more iron particles at a given distance; however, the travel distance was not proportional to the increase in volume. Moreover, simulation results showed that using a 1D transport equation to simulate nZVI migration in the subsurface may overestimate the travel distance. This is because the 1D transport equation assumes a constant velocity while pore water velocity radially decreases from the well during injection. This study suggests that on-site synthesized nZVI particles are mobile in the subsurface and that a numerical simulator can be a valuable tool for optimal design of nZVI field applications.

Evaluation of the stability of a nanoremediation strategy using barley plants

This study evaluated the effectiveness of nZVI in reducing the availability of Cd, Cr or Zn in polluted soils. The influence of this nanoremediation process on the development of barley plants as well as its impact on soil properties and the stability of the metal immobilization afterwards were also evaluated in a greenhouse experiment. The application of nZVI reduced the availability of these metals in the soil, but the effectiveness of the immobilization and its stability depended on the metal chemical characteristics. Cadmium distribution in soil fractions showed an important change after the barley crop, favoring the immobilization of Cd in RS fraction for both nZVI-treated and untreated soils. The Cr immobilization was stable over the time studied and the doses of Cr were lethal for the barley plants. In contrast, the decrease of Cr availability reached after the nZVI treatment induced a reduction of soil phytotoxicity and an improvement in the development of the plants, which were able to complete their growing period. The Zn immobilization with nZVI was stable over time, but its effectiveness was moderate, and the growth of barley plants was poorer than that observed in the cases of Cd and Cr. Thus the best results of metal immobilization with nZVI were obtained for Cr-polluted soils. There was no overall increase of Fe in barley plants from nZVI-treated soils. In relation to the soil, no negative effects on its physico-chemical properties were observed after the time exposure with nZVI. Taking into account these results we can conclude that the use of nZVI is a promising remediation strategy, and its effectiveness would be conditioned to the soil properties and the bioavailable metal concentration.

Combined abiotic and biotic in-situ reduction of hexavalent chromium in groundwater using nZVI and whey: A remedial pilot test

The paper describes a pilot remediation test combining two Cr(VI) geofixation methods – chemical reduction by nanoscale zero-valent iron (nZVI) and subsequent biotic reduction supported by whey. Combination of the methods exploited the advantages of both – a rapid decrease in Cr(VI) concentrations by nZVI, which prevented further spreading of the contamination and facilitated subsequent use of the cheaper biological method. Successive application of whey as an organic substrate to promote biotic reduction of Cr(VI) after application of nZVI resulted in a further and long-term decrease in the Cr(VI) contents in the groundwater. The effect of biotic reduction was observed even in a monitoring well located at a distance of 22m from the substrate injection wells after 10 months. The results indicated a reciprocal effect of both the phases – nZVI oxidized to Fe(III) during the abiotic phase was microbially reduced back to Fe(II) and acted as a reducing agent for Cr(VI) even when the microbial density was already low due to the consumed substrate. Community analysis with pyrosequencing of the 16S rRNA genes further confirmed partial recycling of nZVI in the form of Fe(II), where the results showed that the Cr(VI) reducing process was mediated mainly by iron-reducing and sulfate-reducing bacteria.

Residual impact of aged nZVI on heavy metal-polluted soils

In the present study, the residual toxicity and impact of aged nZVI after a leaching experiment on heavy metal (Pb, Zn) polluted soils was evaluated. No negative effects on physico-chemical soil properties were observed after aged nZVI exposure. The application of nZVI to soil produced a significant increase in Fe availability. The impact on soil biodiversity was assessed by fluorescence in situ hybridization (FISH). A significant effect of nZVI application on microbial structure has been recorded in the Pb-polluted soil nZVI-treated. Soil bacteria molecular response, evaluated by RT-qPCR using exposure biomarkers (pykA, katB) showed a decrease in the cellular activity (pykA) due to enhanced intracellular oxidative stress (katB). Moreover, ecotoxicological standardised test on Caenorhabditis elegans (C. elegans) showed a decrease in the growth endpoint in the Pb-polluted soil, and particularly in the nZVI-treated. A different pattern has been observed in Zn-polluted soils: no changes in soil biodiversity, an increase in biological activity and a significant decrease of Zn toxicity on C. elegans growth were observed after aged nZVI exposure. The results reported indicated that the pollutant and its nZVI interaction should be considered to design soil nanoremediation strategies to immobilise heavy metals.

The Application of Nano-Sized Zero-Valent Iron for In Situ Remediation of Chlorinated Ethylenes in Groundwater: A Field Case Study.

In this paper, the authors present the pilot in situ application of nano zero-valent iron (nZVI) for effective remediation of groundwater in an industrial area contaminated by chlorinated ethylenes (CEs), which create a significant group of global environmental contaminants. This work covers the entire 1-year remediation process, including systematic laboratory tests and field application techniques for nZVI. The application was carried out in the area of a metal fabrication industrial facility in the Czech Republic. Contamination of CEs in this area is a consequence of old ecological loads. The entire remediation process contained the following steps: monitoring of the area, selection of the most relevant hot spot, selection of the most appropriate application borehole, systematic laboratory tests, application of nZVI, and postapplication monitoring. Ten kilograms of nZVI were applied as a water suspension into the selected borehole. Significant decreases in concentrations of selected contaminants were observed in the first month after application. The reaction in the borehole was completed within approximately 5 to 6 months after the application and during this period almost 50% elimination of contamination was achieved.

Potential environmental implications of nanoscale zero-valent iron particles for environmental remediation.

ObjectivesNanoscale zero-valent iron (nZVI) particles are widely used in the field of various environmental contaminant remediation. Although the potential benefits of nZVI are considerable, there is a distinct need to identify any potential risks after environmental exposure. In this respect, we review recent studies on the environmental applications and implications of nZVI, highlighting research gaps and suggesting future research directions.MethodsEnvironmental application of nZVI is briefly summarized, focusing on its unique properties. Ecotoxicity of nZVI is reviewed according to type of organism, including bacteria, terrestrial organisms, and aquatic organisms. The environmental fate and transport of nZVI are also summarized with regards to exposure scenarios. Finally, the current limitations of risk determination are thoroughly provided.ResultsThe ecotoxicity of nZVI depends on the composition, concentration, size and surface properties of the nanoparticles and the experimental method used, including the species investigated. In addition, the environmental fate and transport of nZVI appear to be complex and depend on the exposure duration and the exposure conditions. To date, field-scale data are limited and only short-term studies using simple exposure methods have been conducted.ConclusionsIn this regard, the primary focus of future study should be on 1) the development of an appropriate and valid testing method of the environmental fate and ecotoxicity of reactive nanoparticles used in environmental applications and 2) assessing their potential environmental risks using in situ field scale applications.