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Plastic is considered one of the most practical inventions of the 20th century, providing us with a range of very practical materials. However, due to mismanaged waste the plastic pollution has become persistent in aquatic environments. As the plastic products undergo environmental weathering once released in the aquatic environment, they degrade and are fragmented into a highly heterogeneous group of particles with different sizes (i.e., from centimeter over millimeter and micrometer to nanometer scale), shapes, densities, and chemical compositions. However, due to the lack of suitable analytical methodology, knowledge on degradation and/or fragmentation of plastics to nanoplastics (NPs, 1-1000nm), especially in the aquatic environments is still largely lacking.In the framework of the MS4Plastics project, 15 different plastic materials, including a surgical face mask, different polymer pellets, rubber dust, and plastic powders as common examples of plastics expected to be present in the aquatic system were added to Milli Q water and exposed to UV-light for 120 hours to better understand plastic degradation and/or fragmentation into NPs. Finally, for detection and size determination of NPs formed after accelerated UV-driven plastic fragmentation in water, dynamic light scattering was used. For a fraction of the samples, asymmetric flow field-flow fractionation (AF4) hyphenated to multi-angle light scattering (MALS) was used as a complementary analytical technique for characterization of NPs.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101023205.

While the exact health risks associated with nanoplastics are currently the focus of intense research, there is no doubt that humans are exposed to nanoplastics and that food could be a major source of exposure. Nanoplastics are released from plastic materials and articles used during food production, processing, storage, preparation, and serving. They are also likely to enter the food chain via contaminated water, air, and soil. However, very limited exposure data for risk assessment exists so far due to the lack of suitable analytical methods. Nanoplastic detection in food poses a great analytical challenge due to the complexity of plastics and food matrices as well as the small size and expectedly low concentration of the plastic particles. Multidetector field flow fractionation has emerged as a valuable analytical technique for nanoparticle separation over the last decades, and the first studies using the technique for analyzing nanoplastics in complex matrices are emerging. In combination with online detectors and offline analysis, multidetector field flow fractionation is a powerful platform for advanced characterization of nanoplastics in food by reducing sample complexity, which otherwise hampers the full potential of most analytical techniques. The focus of this article is to present the current state of the art of multidetector field flow fractionation for nanoplastic analysis and to discuss future trends and needs aiming at the analysis of nanoplastics in food.

Development of analytical methods for the characterization (particle size determination, chemical identification, and quantification) of the low μm-range microplastics (MPs; 1–10 μm) and nanoplastics (NPs; 1 nm to 1 μm) in air – coarse (PM10

The presence of small plastic fragments in open ocean water was first noticed in the 1970’s. Throughout the last decade, the scientific interest has been renewed and has pointed out that rivers may act as sinks for land-based plastic pollution and a potential major source of marine plastic debris, thus presenting an environmental threat. As a long-term consequence, plastic fragmentation will lead to pollution release that can impose a negative impact on river, as well as marine ecosystems, especially once they enter the food webs. As a result, this is a topic of increasing concern, but research on this issue is still in its early stages with fundamental gaps in the understanding of the sources, transformation pathways, fragmentation processes, fate of the land-based plastic pollution and estimates of the riverine plastic flux in general.In order to identify the most polluting rivers and to prioritize mitigation efforts, accurate estimates of global riverine plastic emissions are required. The present work is aimed to give an overview of the morphology, size and composition of plastic debris found in the Sea Scheldt estuary (Belgium). For that purpose, in 2018, 3 sampling campaigns were performed by using an anchor netting technique with the mesh size of the nets progressively becoming smaller, reaching 5 mm at the tip of the nets. The samples originating from the Scheldt were separated into two categories based on their appearance (morphology) and size. The morphology consisted of 5 classes: fragments, foam, foil, filaments and pellets, whilst the size was divided into 6 categories: 0-2.5 cm (where 0 represents smallest size of the mesh being 5 mm); 2.5-5 cm; 5-10 cm; 10-20 cm; 20-30 cm; and larger than 30 cm. As a result, a grand total of 12,801 plastic items were collected. On average 1.6x10-3 items per m3 were found as suspended fraction of plastic debris in the Scheldt river. Foils were the most abundant with more than 88% of the samples being characterized as such, followed by fragments for 11% of the samples and filaments constituting less than 1% of the plastic debris. By using FTIR, polypropylene and polyethylene were identified as the most common polymers found with an abundance of more than 70%. This can be expected, as polypropylene and polyethylene make up for more than 50% of the plastic production in general. Finally, analysis of plastic debris by using μ-XRF spectrometry presents a good method for the identification of the mineral elements present. Ca, P, S and Si are the most abundant elements in the plastic debris, followed by Al, Fe and Ti.M.V. is a senior postdoctoral fellow of the Research Foundation – Flanders (FWO 12ZD120N).

Development of analytical methods for the characterization (particle size determination, identification, and quantification) of the micro- and nanoscale plastic debris in the environment is a quickly emerging field and has gained considerable attention, not only within the scientific community, but also on the part of policy makers and the general public. In this Trends paper, the importance of developing and further improving analytical methodologies for the detection and characterization of sub-20-μm-range microplastics and especially nanoplastics is highlighted. A short overview of analytical methodologies showing considerable promise for the detection and characterization of such micro- and nanoscale plastic debris is provided, with emphasis on recent developments in mass spectrometry (MS)-based analytical methods. Novel hyphenated techniques combining the strengths of different analytical methods, such as field flow fractionation and MS-based detection, may be a way to adequately address the smallest fractions in plastic debris analysis, making such approaches worthwhile to be further explored.

The occurrence of microplastics in many, if not all environmental compartments is a matter of increasing concern and deserves proper attention. However, there is still a lack of analytical tools for straightforward monitoring of these tiny plastic particles at environmentally relevant levels in water. Inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-particle mode (SP-ICP-MS) was demonstrated to be a powerful technique for the characterization of metallic nanoparticles, but to the best of the authors' knowledge, SP-ICP-MS has not yet been evaluated for the purpose of detection of microplastics and their quantitative determination (particle number density). In this work, spherical polystyrene microspheres of 1 and 2.5 μm – to mimic microplastics coming from plastic waste – have been detected using ICP-MS. The approach developed relies on the ultra-fast monitoring of transient signals (with a dwell time of 100 μs) when using a quadrupole-based ICP-MS unit in the so-called single-event mode and registering the signal spikes produced by individual microparticles by monitoring the signal intensity at a mass-to-charge ratio (m/z) of 13 (13C+). The accuracy of the number-based concentration results (particle number densities) has been assessed by comparing the number of events detected when monitoring 13C+ to those detected when monitoring 165Ho+ for 2.5 μm lanthanide-doped polystyrene beads. Additionally, the results obtained for both polystyrene microspheres in terms of size (most frequently occurring intensity of the signal distribution) compare well with the size as determined using electron microscopy. ICP-MS operated in single-event mode thus allows information on both the size distribution and mass concentration of microplastics to be obtained. As this approach makes use of instrumentation already available in many routine labs analyzing environmental samples, it can enable these labs to analyze microplastics by using their instrument in single-event mode.

The Sea Scheldt estuary has been suggested to be a significant pathway for transfer of plastic debris to the North Sea. We have studied 12,801 plastic items that were collected in the Sea Scheldt estuary (Belgium) during 3 sampling cam-paigns (in spring, summer, and autumn) using a technique called anchor netting. The investigation results indicated that the abundance of plastic debris in the Scheldt River was on average 1.6 x 10-3 items per m3 with an average weight of 0.38 x 10-3 g per m3. Foils were the most abundant form, accounting for > 88 % of the samples, followed by fragments for 11 % of the samples and filaments, making up for < 1 % of the plastic debris. FTIR spectroscopy of 7 % of the total number of plastic debris items collected in the Sea Scheldt estuary (n = 883) revealed that polypropylene (PP), polyethylene (PE), and polystyrene (PS) originating from disposable packaging materials were the most abun-dant types of polymers. A limited number of plastic debris items (n = 100) were selected for non-destructive screening of their mineral element composition using micro-X-ray fluorescence spectrometry (mu XRF). The corresponding results revealed that S, Ca, Si, P, Al, and Fe were the predominant mineral elements. These elements originate from flame re-tardants, mineral fillers, and commonly used catalysts for plastic production. Finally, machine learning algorithms were deployed to test a new concept for forensic identification of the different plastic entities based on the most impor-tant elements present using a limited subset of PP (n = 36) and PE (n = 35) plastic entities.

Plastic fragments, weathered into or released in the form of micro- and nanoplastics, are persistent and widespread in the environment, and it is anticipated that they have negative environmental impacts. This necessitates immediate efforts for management strategies throughout the entire plastics lifecycle. This opinion paper was initiated by the EU COST Action CA20101 PRIORITY, which focuses on the need to develop an effective global networking platform dealing with research, implementation, and consolidation of ways to address the worldwide challenges associated with micro- and nanoplastics pollution in the environment., Microplastics, 1 (2), ISSN:2673-8929

In recent years, interest in using unsupported catalysts, especially Pt-based nanomaterials, has resurged in direct methanol fuel cells (DMFC). Unsupported catalysts eliminate the problems related to the corrosion of carbon catalyst supports, thus improving the long-term stability of DMFC. In addition, the design of catalyst synthesis protocols to tailor nanostructured materials with high surface area and catalytic activity improves catalyst performance.1 Consequently, we recently reported a method for the synthesis of platinum group metal (PGM, i.e., Pt, Pd, Rh) nanoparticles (NPs), using a process called Gas Diffusion Electrocrystallization (GDEx) (Fig. 1a).2 The simultaneous electrochemical reduction of CO2 and water occurs at the triple-phase boundary of uncatalyzed gas-diffusion electrodes, producing H2 and CO. Both gases, but especially H2, are reducing agents for water-soluble noble metal ions leading to the formation of small metal nanoclusters. CO can also act as a capping agent. Furthermore, the presence of CO2 stabilizes the pH, avoiding the formation of metal (hydr)oxides. In this work, we used the GDEx process to synthesize unsupported Pt NPs using polyvinyl pyrrolidone (PVP, 55000 Mw) as a stabilizer and evaluated their electrocatalytic activity for methanol oxidation. The synthesis was performed at -30 mA cm-2, using 3.0 mM Pt4+ (as H2PtCl4) as metal precursor and different concentrations of PVP (i.e., 0.0, 0.01, 0.1 and 1.0 g L-1). We chose low concentrations of stabilizer to facilitate its removal after synthesis, as clean surface catalysts are required for electrocatalytic applications. The size distribution of the Pt NPs, measured using Scanning Electron Microscopy (SEM), was 64 ± 22, 60 ± 22, 42 ± 18, and 38 ± 12 nm for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0, respectively. For comparison, the reduction of 3.0 mM Pt4+ using 1.0 g L-1 PVP with only H2 (either electrogenerated or bubbled) produced bigger and much more polydisperse particles (100 nm–1000 nm), highlighting the importance of the GDEx process and the presence of CO to synthesize small NPs using low concentrations of stabilizer. Furthermore, Transmission Electron Microscopy (TEM) images (Fig. 1b) revealed that the NPs are nanoclusters of single crystals of 2 nm–4 nm in diameter. The synthesized Pt NPs were cleaned using NaOH,3 and their electrocatalytic activity was evaluated in acidic media. The CV curves of Pt NPs in 0.5 M H2SO4 are shown in Fig. 1c. All catalysts showed hydrogen adsorption-desorption peaks from -0.2 to 0.1 VAg/AgCl. The calculated electrochemical surface area (ECSA), obtained by integrating the charge in the hydrogen adsorption-desorption region, was 7.6 ± 0.7, 14.1 ± 1.2, 33.6 ± 1.2, and 30.3 ± 1.0 m2 g-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1 and PVP 1.0 respectively. The MeOH electro-oxidation experiments were performed in 0.5 M H2SO4 containing 1.0 M MeOH, and the CV curves are shown in Fig. 1d. The forward anodic peak (If) at about 0.7 VAg/AgCl corresponds to MeOH oxidation, while the backward anodic peak (Ib) at about 0.5 VAg/AgCl corresponds to the oxidation of the incompletely oxidized carbonaceous species formed in the forward sweep. The mass activity (MA), defined by the forward peak current density per unit of catalyst loading, was 71 ± 2, 136 ± 7, 463 ± 28, and 341 ± 25 mA mg-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0 g L-1, respectively. Hence, the MA scale with the ECSA . Besides, ECSA (and hence MA) increases when the PVP concentration during synthesis increases. However, this trend is not followed for a PVP concentration of 1.0 g L-1. Even though all catalysts were cleaned using the same protocol, residual PVP might still be left on the surface of Pt NPs synthesized using 1.0 g L-1 PVP, lowering their electrocatalytic activity. Overall, the GDEx process was a useful tool for synthesizing unsupported Pt NPs using low concentrations of stabilizer and with high electrocatalytic activity. This project has received funding from the European Union's Horizon 2020 Research and Innovation program under Grant Agreements n° 730224 (PLATIRUS) and n° 958302 (PEACOC) 1. E. Antolini, J. Perez, J. Mat. Sci, 2011, 46, 4435–4457. 2. X. Dominguez-Benetton, O. Martinez-Mora, J. Fransaer, EP21165681, 2021. 3. A. Zalineeva, S. Baranton, C. Coutanceau, G. Jerkiewicz, Langmuir, 2015, 31, 1605–1609. Figure 1

Development of analytical methods for the characterization (particle size determination, chemical identification, and quantification) of the low µm-range microplastic (MPs; 1-10 µm) and nanoscale plastic (NPs; 1-1000 nm) debris in environmental matrices is a quickly emerging scientific field and has gained considerable attention, not only within the scientific community, but also on the part of policy makers and the general public. However, due to the limited sensitivity of the current state of the art monitoring techniques, detection of MPs and NPs in water is one of the biggest challenges for their monitoring, source identification and, ultimately, risk assessment.As it is evident that no single method will provide all the information required for a complete characterization of MPs and NPs in water, the present work is aimed to give an overview of different complementary analytical methodologies showing considerable promise for the particle size determination, chemical identification, and quantification of MPs and NPs [1]. In addition, results of three case studies will be included to adequately address the smallest fractions in plastic debris size determination, making such approaches worthwhile to be further explored.The first case study offers a novel method based on the use of inductively coupled plasma-mass spectrometry operated in single-event mode and relies on our previous work where for the first time ever single particle inductively coupled plasma-mass spectrometry based on carbon monitoring was successfully used for the detection, particle size characterization and particle number concentration of polystyrene MPs [2]. The second case study further explore light scattering methods, including nanoparticle tracking analysis or dynamic light scattering, for MPs and NPs particle size distribution and particle number in water. Finally, the capabilities of size exclusion chromatography in combination with online detection techniques such as UV-visible absorption spectrometry will be presented for the particle size determination of smallest fraction of NPs (1-100 nm). M.V. is a senior postdoctoral fellow of the Research Foundation – Flanders (FWO 12ZD120N). References[1] Velimirovic M., Tirez K., Voorspoels S., Vanhaecke F. (2020) Recent developments in mass spectrometry for the characterization of micro- and nanoscale plastic debris in the environment, Analytical and Bioanalytical Chemistry, 1-9.[2] Bolea-Fernandez E., Rua-Ibarz A., Velimirovic M., Tirez K., and Vanhaecke F. (2020) Detection of microplastics using inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-event mode. Journal of Analytical Atomic Spectrometry 35, 455-460.

Development of analytical methods for the characterization (particle size determination, identification, and quantification) of the micro- and nanoscale plastic debris in the environment is a quickly emerging field and has gained considerable attention, not only within the scientific community, but also on the part of policy makers and the general public. In this Trends paper, the importance of developing and further improving analytical methodologies for the detection and characterization of sub-20-μm-range microplastics and especially nanoplastics is highlighted. A short overview of analytical methodologies showing considerable promise for the detection and characterization of such micro- and nanoscale plastic debris is provided, with emphasis on recent developments in mass spectrometry (MS)-based analytical methods. Novel hyphenated techniques combining the strengths of different analytical methods, such as field flow fractionation and MS-based detection, may be a way to adequately address the smallest fractions in plastic debris analysis, making such approaches worthwhile to be further explored.

Humic acid-coated goethite nanoparticles (HA-GoeNPs) have been recently proposed as an effective reagent for the in situ nanoremediation of contaminated aquifers. However, the effective dosage of these particles has been studied only at laboratory scale to date. This study investigates the possibility of using HA-GoeNPs in remediation of real field sites by mimicking the injection and transport of HA-GoeNPs under realistic conditions. To this purpose, a three-dimensional (3D) transport experiment was conducted in a large-scale container representing a heterogeneous unconfined aquifer. Monitoring data, including particle size distribution, total iron (Fetot) content and turbidity measurements, revealed a good subsurface mobility of the HA-GoeNP suspension, especially within the higher permeability zones. A radius of influence of 2 m was achieved, proving that HA-GoeNPs delivery is feasible for aquifer restoration. A flow and transport model of the container was built using the numerical code Micro and Nanoparticle transport Model in 3D geometries (MNM3D) to predict the particle behavior during the experiment. The agreement between modeling and experimental results validated the capability of the model to reproduce the HA-GoeNP transport in a 3D heterogeneous aquifer. Such result confirms MNM3D as a valuable tool to support the design of field-scale applications of goethite-based nanoremediation.

The impact of a silica coating on the degradation potential of nanoscale zerovalent iron (nZVI) particles toward a mixture of chlorinated ethylenes is presented. The newly employed stabilization method for nZVI, based on silica deposition from saturated sodium silicate water glass, produces nZVI particles with a similar reactivity as non-stabilized particles. Moreover the removal rate constant kM of trichloroethylene (0.1740 L g−1 d−1 Fe0) and cis-dichloroethylene (0.1045 L g−1 d−1Fe0) was significantly improved (almost by a factor of 2) for stabilized nZVI. X-ray photoelectron spectroscopy (XPS) and Wavelength Dispersive X-ray Fluorescence (WDXRF) analyzes revealed a high durability of silica coating and the coating left at least half of nZVI surface silica free for reaction for more than 5 weeks. The silica coating did not affect the surface composition of silica coated nZVI which was confirmed by the very similar distribution of degradation products and corrosion products (Fe3O4, FeOOH) as was found for non-coated nanoparticles. An enhanced reactivity supplemented with a stable corrosion properties indicates that silica coated nZVI has potential as an efficient remediation agent toward chlorinated ethylenes.

The reactivity and apparent corrosion rate of newly produced boron-alloyed microscale zerovalent iron (mZVI) particles toward a variety of chlorinated aliphatic hydrocarbons (CAHs) were assessed in laboratory-scale batch reactors. For comparison, commercially available nanoscale zerovalent irons (nZVIs) were also included in the study. Based on mass normalized ( k M ) pseudo first-order degradation rate constants, the reactivity of boron-alloyed mZVIs appeared to be one order of magnitude lower than most reactive nZVI. However, specific surface area normalized reaction rate constants ( k SA ) were 1–2 orders of magnitude higher than for nZVIs showing that boron-alloyed mZVIs can compete with nZVIs. The high reactivity of boron-alloyed mZVIs was attributed to (1) the prevented iron surface passivation during anaerobic corrosion due to the simultaneous iron and boron dissolution kinetics preventing the formation of insoluble oxidized iron species, (2) the involvement of boron in facilitating electron transfer by inducing β-elimination followed by hydrogenation to ethane and/or (3) involvement of boron in improved particle size reduction during milling process leading to increased active surface areas of the particles. Results of this study suggest that boron-alloyed mZVIs could be an efficient alternative to nZVIs for in situ groundwater remediation of different CAHs in terms of their reactivity and apparent corrosion rate.

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP

In this study, an intra-laboratory assessment was carried out to establish the effectiveness of a method for the detection of TiO2 engineered nanoparticles (ENPs) present in sunscreen containing nano-scale TiO2 and a higher nanometer-range (approx. 200-500 nm) Ti02, as well as iron oxide particles. Three replicate measurements were performed on five separate days to generate the measurement uncertainties associated with the quantitative asymmetrical flow field-flow fractionation (AF4) measurement of the hydrodynamic radius r(h, mode1) (MALS), rh,,odei (ICP-MS), r(h, mode2) (ICP-MS), and calculated mass-based particle size distribution (d(10), d(50), d(90)). The validation study demonstrates that the analysis of TiO2 ENPs present in sunscreen by AF4 separation-multi detection produces quantitative data (mass-based particle size distribution) after applying the sample preparation method developed within the NanoDefine project with uncertainties based on the precision (u(IP)) of 3.9-8.8%. This method can, therefore, be considered as the method with a good precision. Finally, the bias data shows that the trueness of the method (u(t) = 5.5-52%) can only be taken as a proxy due to the lack of a sunscreen standard containing certified TiO2 ENPs.

The release of fine zerovalent iron (ZVI) particles in the environment after being introduced for in-situ treatment of compounds like chlorinated aliphatic hydrocarbons (CAHs) may raise questions toward environmental safety, especially for nanoscale materials. Classical single-species ecotoxicity tests do focus on aerobic conditions and are only relevant for the scenario when ZVI-particles reach surface water. Herein, we present an alternative approach where a CAH-degrading mixed bacterial culture was used as test-organisms relevant for the anaerobic subsurface. The impact of different ZVI particles on the bacterial culture was evaluated mainly by quantifying ATP, a reporter molecule giving a general indication of the microbial activity. These lab-scale batch tests were performed in liquid medium, without protecting and buffering aquifer material, as such representing worst-case scenario. The activity of the bacterial culture was negatively influenced by nanoscale zerovalent iron at doses as low as 0.05 g L−1. On the other hand, concentrations up to 2 g L−1 of several different types of microscale zerovalent iron (mZVI) particles stimulated the activity. However, very high doses of 15–30 g L−1 of mZVI showed an inhibiting effect on the bacterial community. Negative effects of ZVIs were confirmed by H2 accumulation in the batch reactors and the absence of lactate consumption. Observed inhibition also corresponded to a pH increase above 7.5, explicable by ZVI corrosion that was found to be dose-dependent. The obtained results suggest that low doses of mZVIs will not show severe inhibition effects on the microbial community once used for in-situ treatment of CAHs.

International audience; Milled zerovalent iron (milled ZVI) particles have been recognized as a promising agent for groundwater remediation because of (1) their high reactivity with chlorinated aliphatic hydrocarbons, organochlorine pesticides, organic dyes, and a number of inorganic contaminants, and (2) a possible greater persistance than the more extensively investigated nanoscale zerovalent iron. We have used laboratory-scale batch degradation experiments to investigate the effect that hydrogeochemical conditions have on the corrosion of milled ZVI and on its ability to degrade trichloroethene (TCE). The observed pseudo first-order degradation rate constants indicated that the degradation of TCE by milled ZVI is affected by groundwater chemistry. The apparent corrosion rates of milled ZVI particles were of the same order of magnitude for hydrogeochemical conditions representative for two contaminated field sites (133–140 mmol kg− 1 day− 1, indicating a milled ZVI life-time of 128–135 days). Sulfate enhances milled ZVI reactivity by removing passivating iron oxides and hydroxides from the Fe0 surface, thus increasing the number of reactive sites available. The organic matter content of 1.69% in the aquifer material tends to suppress the formation of iron corrosion precipitates. Results from scanning electron microscopy, X-ray diffraction, and iron K-edge X-ray adsorption spectroscopy suggest that the corrosion mechanisms involve the partial dissolution of particles followed by the formation and surface precipitation of magnetite and/or maghemite. Numerical corrosion modeling revealed that fitting iron corrosion rates and hydrogen inhibitory terms to hydrogen and pH measurements in batch reactors can reduce the life-time of milled ZVI particles by a factor of 1.2 to 1.7.

The affinity between nanoscale zerovalent iron (nano-ZVI) and mineral surfaces hinders its mobility, and hence its delivery into contaminated aquifers. We have tested the hypothesis that the attachment of poly(acrylic acid)-coated nano-ZVI (PAA-nano-ZVI) to mineral surfaces could be limited by coating such surfaces with sodium (Na) humate prior to PAA-nano-ZVI injection. Na humate was expected to form a coating over favorable sites for PAA-nano-ZVI attachment and hence reduce the affinity of PAA-nano-ZVI for the collector surfaces through electrosteric repulsion between the two interpenetrating charged polymers. Column experiments demonstrated that a low concentration (10 mg/L) Na humate solution in synthetic water significantly improved the mobility of PAA-nano-ZVI within a standard sand medium. This effect was, however, reduced in more heterogeneous natural collector media from contaminated sites, as not an adequate amount of the collector sites favorable for PAA-nano-ZVI attachment within these media appear to have been screened by the Na humate. Na humate did not interact with the surfaces of acid-washed glass beads or standard Ottawa sand, which presented less surface heterogeneity. Important factors influencing the effectiveness of Na humate application in improving PAA-nano-ZVI mobility include the solution chemistry, the Na humate concentration, and the collector properties.

Submicron-scale milled zerovalent iron (milled ZVI) particles produced by grinding macroscopic raw materials could provide a cost-effective alternative to nanoscale zerovalent iron (nZVI) particles for in situ degradation of chlorinated aliphatic hydrocarbons in groundwater. However, the aggregation and settling of bare milled ZVI particles from suspension presents a significant obstacle to their in situ application for groundwater remediation. In our investigations we reduced the rapid aggregation and settling rate of bare milled ZVI particles from suspension by stabilization with a "green" agar agar polymer. The transport potential of stabilized milled ZVI particle suspensions in a diverse array of natural heterogeneous porous media was evaluated in a series of well-controlled laboratory column experiments. The impact of agar agar on trichloroethene (TCE) removal by milled ZVI particles was assessed in laboratory-scale batch reactors. The use of agar agar significantly enhanced the transport of milled ZVI particles in all of the investigated porous media. Reactivity tests showed that the agar agar-stabilized milled ZVI particles were reactive towards TCE, but that their reactivity was an order of magnitude less than that of bare, non-stabilized milled ZVI particles. Our results suggest that milled ZVI particles could be used as an alternative to nZVI particles as their potential for emplacement into contaminated zone, their reactivity, and expected longevity are beneficial for in situ groundwater remediation.

The injection of microscale zerovalent iron (mZVI) particles for groundwater remediation has received much interest in recent years. However, to date, monitoring of mZVI particle injection is based on chemical analysis of groundwater and soil samples and thus might be limited in its spatiotemporal resolution. To overcome this deficiency, in this study, we investigate the application of complex electrical conductivity imaging, a geophysical method, to monitor the high-pressure injection of mZVI in a field-scale application. The resulting electrical images revealed an increase in the induced electrical polarization (∼20%), upon delivery of ZVI into the targeted area, due to the accumulation of metallic surfaces at which the polarization takes place. Furthermore, larger changes (>50%) occurred in shallow sediments, a few meters away from the injection, suggesting the migration of particles through preferential flowpaths. Correlation of the electrical response and geochemical data, in particular the analysis of recovered cores from drilling after the injection, confirmed the migration of particles (and stabilizing solution) to shallow areas through fractures formed during the injection. Hence, our results demonstrate the suitability of the complex conductivity imaging method to monitor the transport of mZVI during subsurface amendment in quasi real-time.