Analysis of carbon nanotube levels in organic matter: an inter-laboratory comparison to determine best practice.

Carbon nanotubes (CNTs) are increasingly being used in industrial applications, but their toxicological data in animals and humans are still sparse. To assess the toxicological dose-response of CNTs and to evaluate their pulmonary biopersistence, their quantification in tissues, especially lungs, is crucial. There are currently no reference methods or reference materials for low levels of CNTs in organic matter. Among existing analytical methods, few have been fully and properly validated. To remedy this, we undertook an inter-laboratory comparison on samples of freeze-dried pig lung, ground and doped with CNTs. Eight laboratories were enrolled to analyze 3 types of CNTs at 2 concentration levels each in this organic matrix. Associated with the different analysis techniques used (specific to each laboratory), sample preparation may or may not have involved prior digestion of the matrix, depending on the analysis technique and the material being analyzed. Overall, even challenging, laboratories' ability to quantify CNT levels in organic matter is demonstrated. However, CNT quantification is often overestimated. Trueness analysis identified effective methods, but systematic errors persisted for some. Choosing the assigned value proved complex. Indirect analysis methods, despite added steps, outperform direct methods. The study emphasizes the need for reference materials, enhanced precision, and organized comparisons.

Investigating environmentally persistent free radicals (EPFRs) emissions of 3D printing process.

In recent years, the emission of particles and gaseous pollutants from 3D printing has attracted much attention due to potential health risks. This study investigated the generation of environmentally persistent free radicals (EPFRs, organic free radicals stabilized on or inside particles) in total particulate matter (TPM) released during the 3D printing process. Commercially available 3D printer filaments, made of acrylonitrile-butadiene-styrene (ABS) in two different colors and metal content, ABS-blue (19.66 µg/g Cu) and ABS-black (3.69 µg/g Fe), were used for printing. We hypothesized that the metal content/composition of the filaments contributes not only to the type and number of EPFRs in TPM emissions, but also impacts the overall yield of TPM emissions. TPM emissions during printing with ABS-blue (11.28 µg/g of printed material) were higher than with ABS-black (7.29 µg/g). Electron paramagnetic resonance (EPR) spectroscopy, employed to measure EPFRs in TPM emissions of both filaments, revealed higher EPFR concentrations in ABS-blue TPM (6.23 × 1017 spins/g) than in ABS-black TPM (9.72 × 1016 spins/g). The presence of copper in the ABS-blue contributed to the formation of mostly oxygen-centered EPFR species with a g-factor of ~2.0041 and a lifetime of 98 days. The ABS-black EPFR signal had a lower g-factor of ~2.0011, reflecting the formation of superoxide radicals during the printing process, which were shown to have an "estimated tentative" lifetime of 26 days. Both radical species (EPFRs and superoxides) translate to a potential health risk through inhalation of emitted particles.

The elemental fingerprint as a potential tool for tracking the fate of real-life model nanoplastics generated from plastic consumer products in environmental systems.

Metals and metalloids are widely used in producing plastic materials as fillers and pigments, which can be used to track the environmental fate of real-life nanoplastics in environmental and biological systems. Therefore, this study investigated the metal and metalloids concentrations and fingerprint in real-life model nanoplastics generated from new plastic products (NPP) and from environmentally aged ocean plastic fragments (NPO) using single particle-inductively coupled plasma-mass spectrometry (SP-ICP-TOF-MS) and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX). The new plastic products include polypropylene straws (PPS), polyethylene terephthalate bottles (PETEB), white low-density polyethylene bags (LDPEB), and polystyrene foam shipping material (PSF). All real-life model nanoplastics contained metal and metalloids, including Si, Al, Sr, Ti, Fe, Ba, Cu, Pb, Zn, Cd, and Cr, and were depleted in rare earth elements. Nanoplastics generated from the white LDPEB were rich in Ti-bearing particles, whereas those generated from PSF were rich in Cr, Ti, and Pb. The Ti/Fe in the LDPEB nanoplastics and the Cr/Fe in the PSF nanoplastics were higher than the corresponding ratios in natural soil nanoparticles (NNPs). The Si/Al ratio in the PSF nanoplastics was higher than in the NNPs, possibly due to silica-based fillers. The elemental ratio of Si/Al, Fe/Cr, and Fe/Ni in the nanoplastics derived from ocean plastic fragments was intermediate between the nanoplastics derived from real-life plastic products and NNPs, indicating a combined contribution from pigments and fillers used in plastics and from natural sources. This study provides a method to track real-life nanoplastics in controlled laboratory studies based on nanoplastic elemental fingerprints. It expands the realm of nanoplastics that can be followed based on their metallic signatures to all kinds of nanoplastics. Additionally, this study illustrates the importance of nanoplastics as a source of metals and metal-containing nanoparticles in the environment.

A high-throughput, automated technique for microplastics detection, quantification, and characterization in surface waters using laser direct infrared spectroscopy.

A high-throughput approach to detecting, quantifying, and characterizing microplastics (MPs) by shape, size, and polymer type using laser direct infrared (LDIR) spectroscopy in surface water samples is demonstrated. Three urban creeks were sampled for their MP content near Cincinnati, OH. A simple Fenton reaction was used to oxidize the surface water samples, and the water samples were filtered onto a gold-coated polyester membrane. Infrared (IR) analysis for polymer identification was conducted, with recoveries of 88.3% ± 1.2%. This method was able to quantify MPs down to a diameter of 20 µm, a size comparable to that of MPs quantified by other techniques such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. A shape-classifying algorithm was designed using the aspect ratio values of particles to categorize MPs as fibers, fibrous fragments, fragments, spherical fragments, or spheres. Cut-off values were identified from measurements of known sphere, fragment, and fibrous particles. About half of all environmental samples were classified as fragments while the other shapes accounted for the other half. A cut-off hit quality index (HQI) value of 0.7 was used to classify known and unidentified particles based on spectral matches to a reference library. Center for Marine Debris Research Polymer Kit 1.0 standards were analyzed by LDIR and compared to the given FTIR spectra by HQI, showing that LDIR obtains similar identifications as FTIR analysis. The simplicity and automation of the LDIR allows for quick, reproducible particle analysis, making LDIR attractive for high-throughput analysis of MPs.

Zinc transport and partitioning of a mine-impacted watershed: An evaluation of water and sediment quality.

Watershed systems influenced by mining waste products can persist for many years after operations are ceased, leading to negative impacts on the health of the surrounding environment. While geochemical behaviors of these trace metals have been studied extensively at the benchtop-scale, much fewer studies have looked at controls on their distributions at the watershed-level. In this study, trace metals (As, Cd, Cr, Cu, Ni, and Zn) were reported from water and stream bed sediments at eight sites between the years 2014-2018 along a watershed undergoing active remediation efforts. Zn was determined to be the only trace metal analyzed with concentrations above EPA and Kansas Department of Health guidelines for both water and sediment in the watershed, and thus was the primary focus for determining the health of the watershed system. Controls on trace metal pollution distribution over the watershed were investigated to determine where remediation efforts should be focused. Surface cover seemed to have the highest effectivity with pasture lands having a strong positive correlation to Zn concentrations. Initial remediation efforts were assessed by calculating the geoaccumulation index (Igeo) and the contamination factor (Cf-sediment) from sediments and contamination factor from water (Cf-water) after decades of chat pile removal efforts. Most of the sites showed significant reduction in metal concentration values compared to previous studies in the watershed for water and sediment, with four sites still reporting concentrations that reveal potential health risks. Results from this study will inform management and policy makers for areas to focus their remediation efforts on the Spring River Watershed as well as providing a framework for assessing pollution at a watershed scale.

Assessing the efficiency and mechanism of zinc adsorption onto biochars from poultry litter and softwood feedstocks.

The efficiency and adsorption mechanism of zinc removal was assessed in aqueous solution using four biochars from multiple biomass residues (poultry litter and three tree species). The effect of pH, kinetic effects, and isotherm fittings were investigated, as well as zinc-laden biochar using x-ray diffraction and absorption near edge structure. Sorbent load results showed softwood biochar exhibited the greatest zinc removal from both deionized (15 mgZn/L) and mining influenced river water (10 mgZn/L). The Langmuir isotherm was the best fit for the majority of the biochars. Exchangeable cations contributed most for the adsorption mechanism from the softwood biochars, while precipitation was greatest contribution for the poultry litter biochar. Overall, our results suggest that biochars from Douglas Fir trees are more efficient at removing zinc from aqueous solutions (up to 19.80 mgZn/g) compared to previously studied biochars (0.61 to 11.0 mgZn/g) and should be used for future remediation efforts.

Silver Nanoparticle Interactions with Surfactant-Based Household Surface Cleaners.

Silver nanoparticles (AgNPs) are the most widely used engineered nanomaterials in consumer products, primarily due to their antimicrobial properties. This widespread usage has resulted in concerns regarding potential adverse environmental impacts and increased probability of human exposure. As the number of AgNP consumer products grows, the likelihood of interactions with other household materials increases. AgNP products have the potential to interact with household cleaning products in laundry, dishwashers, or during general use of all-purpose surface cleaners. This study has investigated the interaction between surfactant-based surface cleaning products and AgNPs of different sizes and with different capping agents. One AgNP consumer product, two laboratory-synthesized AgNPs, and ionic silver were selected for interaction with one cationic, one anionic, and one nonionic surfactant product to simulate AgNP transformations during consumer product usage before disposal and subsequent environmental release. Changes in size, morphology, and chemical composition were detected during a 60 min exposure to surfactant-based surface cleaning products using ultraviolet-visible (UV/Vis) spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX), and dynamic light scattering (DLS). Generally, once AgNP suspensions were exposed to surfactant-based surface cleaning products, all the particles showed an initial aggregation, likely due to disruption of their capping agents. Over the 60 min exposure, cleaning agent-1 (cationic) showed more significant particle aggregates than cleaning agent-2 (anionic) and cleaning agent-3 (nonionic). In addition, UV/Vis, TEM-EDX, and DLS confirmed formation of incidental AgNPs from interaction of ionic silver with all surfactant types.

Influence of polymer additives on gas-phase emissions from 3D printer filaments.

A collection of six commercially available, 3D printer filaments were analyzed with respect to their gas-phase emissions, specifically volatile organic compounds (VOCs), during simulated fused filament fabrication (FFF). Filaments were chosen because they were advertised to contain metal particles or carbon nanotubes. During experimentation, some were found to contain other non-advertised additives that greatly influenced gas-phase emissions. Three polylactic acid (PLA) filaments containing either copper, bronze, or stainless steel particles were studied along in addition to three carbon nanotube (CNT) filaments made from PLA, acrylonitrile-butadiene-styrene (ABS), and polycarbonate (PC). The metal-additive PLA filaments were found to emit primarily lactide, acetaldehyde, and 1-chlorododecane. The presence of metal particles in the PLA is a possible cause of the increased total emissions, which were higher than any other PLA filament reported in the literature. In addition, the filament with stainless steel particles had a threefold increase in total VOCs compared to the copper and bronze particles. Two of three CNT-containing filaments emitted compounds that have not been reported before for PLA and PC. A comparison between certain emitted VOCs and their suggested maximum inhalation limits shows that printing as little as 20 g of certain filaments in a small, unventilated room can subject the user to hazardous concentrations of multiple toxic VOCs with carcinogenic properties (e.g., acetaldehyde, 1,4-dioxane, and bis(2-ethylhexyl) phthalate). The use of certain additives, whether advertised or not, should be reevaluated due to their effects on VOC emissions during 3D printing.

Isotope ratio mass spectrometry and spectroscopic techniques for microplastics characterization.

Micro- and nano-scale plastic particles in the environment result from their direct release and degradation of larger plastic debris. Relative to macro-sized plastics, these small particles are of special concern due to their potential impact on marine, freshwater, and terrestrial systems. While microplastic (MP) pollution has been widely studied in geographic regions globally, many questions remain about its origins. It is assumed that urban environments are the main contributors but systematic studies are lacking. The absence of standard methods to characterize and quantify MPs and smaller particles in environmental and biological matrices has hindered progress in understanding their geographic origins and sources, distribution, and impact. Hence, the development and standardization of methods is needed to establish the potential environmental and human health risks. In this study, we investigated stable carbon isotope ratio mass spectrometry (IRMS), attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectroscopy, and micro-Raman spectroscopy (µ-Raman) as complementary techniques for characterization of common plastics. Plastic items selected for comparative analysis included food packaging, containers, straws, and polymer pellets. The ability of IRMS to distinguish weathered samples was also investigated using the simulated weathering conditions of ultraviolet (UV) light and heat. Our IRMS results show a difference between the δ13C values for plant-derived and petroleum-based polymers. We also found differences between plastic items composed of the same polymer but from different countries, and between some recycled and nonrecycled plastics. Furthermore, increasing δ13C values were observed after exposure to UV light. The results of the three techniques, and their advantages and limitations, are discussed.

Sources, transport, measurement and impact of nano and microplastics in urban watersheds.

The growing and pervasive presence of plastic pollution has attracted considerable interest in recent years, especially small (< 5 mm) plastic particles known as 'microplastics' (MPs). Their widespread presence may pose a threat to marine organisms globally. Most of the nano and microplastic (N&MP) pollution in marine environments is assumed to originate from land-based sources, but their sources, transport routes, and transformations are uncertain. Information on freshwater and terrestrial systems is lacking, and data on nanoplastic pollution are particularly sparse. The shortage of systematic studies of freshwater and terrestrial systems is a critical research gap because estimates of plastic release into these systems are much higher than those for oceans. As most plastic pollution originates in urban environments, studies of urban watersheds, particularly those with high population densities and industrial activities, are especially relevant with respect to source apportionment. Released plastic debris is transported in water, soil, and air. It can be exchanged between environmental compartments, adsorb toxic compounds, and ultimately be carried long distances, with potential to cause both physical and chemical harm to a multitude of species. Measurement challenges and a lack of standardized methods has slowed progress in determining the environmental prevalence and impacts of N&MPs. An overall aim of this review is to report the sources and abundances of N&MPs in urban watersheds. We focus on urban watersheds, and summarize monitoring methods and their limitations, knowing that identifying N&MPs and their urban/industrial sources is necessary to reduce their presence in all environments.

Transformation of Silver Nanoparticle Consumer Products during Simulated Usage and Disposal.

Twenty-two silver nanoparticle (AgNP) consumer products (CPs) were analyzed with respect to their silver speciation. Three CPs and three lab-synthesized particles were selected to simulate environmental fate and transport by simulating their intended usage and disposal methods. Since many of these products are meant for ingestion, we simulated their usage by exposing them to human synthetic stomach fluid followed by exposure to wastewater sludge. We found that during the products individual exposure to wastewater sludge, the conversion rate of silver to AgCl and Ag2S was affected by both the amount of silver ion present and the properties of the AgNP. The rates of conversion of metallic silver to silver sulfide was heavily dependent on the particle size for the lab-synthesized particles, with 90 nm PVP-capped particles reacting to a much lesser extent than the 15 nm PVP-capped or the citrate-capped particles. We observed similar sulfidation rates on two of the tested CPs with the 15 nm lab-synthesized particles despite containing silver nanoparticles >5 times larger, indicating the presence of other influencing factors. Pre-treatment with synthetic stomach fluid modified the rates of Ag2S formation. Due to the variable composition of CPs and the conditions they are exposed to between manufacture, sale, use, and disposal, their final composition may be somewhat unpredictable in the environment. In the present study, we have achieved a more accurate approximation of the expected interactions between silver nanoparticle-containing CPs and environmental media by utilizing real CPs and evaluating them with solid phase and aqueous phase analytical techniques.

Multivariate Calibration for Carbon Nanotubes in the Environment Using the Microwave Induced Heating Method.

The goal of the present paper is to develop chemometrics-based multivariate calibration approaches for simultaneously determining quantity of individual carbon nanotubes (CNTs) in a multicomponent environmental matrix using a microwave induced heating method. A multifactor and multilevel experiment design was used to create 4 separate calibration datasets. Each calibration dataset contained 25 orthogonal CNTs with 2 or 3 factors (CNTs: single-walled CNTs (SWCNTs)/multi-walled CNTs (MWCNTs)/carboxylated MWCNTs (MWCNT-COOH)) and 5 levels (CNTs mass). The temperature rise (ΔT) spectral information was obtained for each sample by exposing to varying microwave conditions. This study showed the potential and applicability of partial least square regression (PLS), least square-support vector machine (LS-SVM) and artificial neural networks (ANN) in predicting quantities of SWCNTs, MWCNTs and MWCNT-COOH in environmental matrices with microwave induced temperature rises data. Our results revealed that the developed LS-SVM model presented higher R2 and lower root mean square error of prediction (RMSEP) (R2 = 0.74-0.93, RMSEP =0.0251 mg to 0.0328 mg in 2-component systems and R2 = 0.64-0.95, RMSEP = 0.0243 mg to 0.0410 mg in 3-component systems), while the ANN model was only accurate in estimating mass of SWCNT and MWCNT in a 2-component mixture (R2 = 0.77-0.89, RMSEP = 0.0322 mg to 0.0503 mg). The PLS model was found not effectively interpret relationship between microwave induced temperature rises data and mass of CNTs, indicated by small R2 (0.20-0.87) and large RMSEP (0.0209 mg -0.1021 mg).

Recent advances in flue gas desulfurization gypsum processes and applications - A review.

Flue gas desulfurization gypsum (FGDG) is an industrial by-product generated during the flue gas desulfurization process in coal-fired power plants. Due to its abundance, chemical and physical properties, FGDG has been used in several beneficial applications. However, during the past decade, the rate of beneficially used FGDG has gradually decreased, while its production has drastically increased. The presence of hazardous elements such as arsenic, mercury, cadmium, lead, and selenium in FGDG has reduced its beneficial value. Nevertheless, due to the recent developments in flue gas desulfurization processes, the "modern" FGDG contains lesser amounts of these elements, thus increasing its beneficial value and appeal to be included in other products. Hence, there are novel and traditional FGDG applications in different reuse scenarios investigated recently that have been deemed to pose minimal environmental concern - these need to be better understood. This review summarizes beneficial FGDG applications that have been deemed to pose minimal environmental concern, emphasizing their principles, research gaps, and potential developments, with the aim of increasing the reuse rate of FGDG.

Material- and Site-Specific Partition Coefficients for Beneficial Use Assessments.

Partition coefficient (Kd) values available in the literature are often used in fate and transport modeling conducted as part of beneficial use risk assessments for industrial byproducts. Because element partitioning depends on soil properties as well as characteristics of the byproduct leachate, site-specific Kd values may lead to more accurate risk assessment. In this study, contamination risk to groundwater of beneficially reused byproducts was assessed using batch leaching tests on waste to energy bottom ash and coal combustion fly ash. Leachates were equilibrated with eight different soils to obtain the waste-soil-specific Kd,exp values for the metals of interest. The Kd,exp values were used as inputs in the Industrial Waste Management Evaluation Model to demonstrate the degree to which Kd estimates affect risk assessment outcomes. Measured Kd,exp values for the most part fell within the large range of Kd values reported in the literature, but IWEM results using default Kd values for some types of soils resulted in overestimated risk compared to those derived from Kd,exp values. Modeled concentration at the receptor location was much lower for some elements for those soils with high concentrations of iron and aluminum.

Correction to: Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating.

The original publication of this paper contains a mistake.

VOC Emissions and Formation Mechanisms from Carbon Nanotube Composites during 3D Printing.

A commercially available, 3D printer nanocomposite filament of carbon nanotubes (CNTs) and acrylonitrile-butadiene-styrene (ABS) was analyzed with respect to its VOC emissions during simulated fused deposition modeling (FDM) and compared with a regular ABS filament. VOC emissions were quantified and characterized under a variety of conditions to simulate the thermal degradation that takes place during FDM. Increasing the residence time and temperature resulted in significant increases in VOC emissions, and the oxygen content of the reaction gas influenced the VOC profile. In agreement with other studies, the primary emitted VOC was styrene. Multiple compounds are reported in this work for the first time as having formed during FDM, including 4-vinylcyclohexene and 2-phenyl-2-propanol. Our results show that printing 222.0 g of filament is enough to surpass the reference concentration for inhalation exposure of 1 mg/m3 according to the EPA's Integrated Risk Information System (IRIS). The presence of CNTs in the filament influenced VOC yields and product ratios through three types of surface interactions: (1) adsorption of O2 on CNTs lowers the available O2 for oxidation of primary backbone cleavage intermediates, (2) adsorption of styrene and other VOCs to CNTs leads to surface-catalyzed degradation, and (3) CNTs act as a trap for certain VOCs and prevent them from entering vapor emissions. While the presence of CNTs in the filament lowered the total VOC emission under most experimental conditions, they increased the emission of the most hazardous VOCs, such as α-methylstyrene and benzaldehyde. The present study has identified an increased risk associated with the use of CNT nanocomposites in 3D printing.

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating.

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500 °C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Dissolution of Silver Nanoparticles in Colloidal Consumer Products: Effects of Particle Size and Capping Agent.

The utilization of silver nanoparticles (AgNPs) in consumer products has significantly increased in recent years, primarily due to their antimicrobial properties. Increased use of AgNPs has raised ecological concerns. Once released into an aquatic environment, AgNPs may undergo oxidative dissolution leading to the generation of toxic Ag+. Therefore, it is critical to investigate the ecotoxicological potential of AgNPs and determine the physicochemical parameters that control their dissolution in aquatic environments. We have investigated the dissolution trends of aqueous colloidal AgNPs in five products, marketed as dietary supplements and surface sanitizers. The dissolution trends of AgNPs in studied products were compared to the dissolution trends of AgNPs in well-characterized laboratory-synthesized nanomaterials: citrate-coated AgNPs, polyvinylpyrrolidone-coated AgNPs, and branched polyethyleneimine-coated AgNPs. The characterization of the studied AgNPs included: particle size, anion content, metal content, silver speciation, and capping agent identification. There were small differences in the dissolved masses of Ag+ between products, but we did not observe any significant differences in the dissolution trends obtained for deionized water and tap water. The decrease of the dissolved mass of Ag+ in tap water could be due to the reaction between Ag+ and Cl-, forming AgCl and affecting their dissolution. We observed a rapid initial Ag+ release and particle size decrease for all AgNP suspensions due to the desorption of Ag+ from the nanoparticles surfaces. The observed differences in dissolution trends between AgNPs in products and laboratory-synthesized AgNPs could be caused by variances in capping agent, particle size, and total AgNP surface area in suspensions.

Comparison of the efficiency of chitinous and ligneous substrates in metal and sulfate removal from mining-influenced water.

Mining-influenced water (MIW) remediation is challenging, not only due to its acidity and high metal content, but also due to its presence in remotely located mine sites with difficult surrounding environments. An alternative to common remediation technologies, is the use of sulfate-reducing bacteria (SRB) to achieve simultaneous sulfate reduction and metal removal in on-site anaerobic passive systems. In these systems, the organic carbon source (substrate) selection is critical to obtaining the desired effluent water quality and a reasonable treated volume. In this study, we evaluated the use of two different substrates: a chitinous product obtained from crushed crab shells, and a more traditional ligneous substrate. We put the substrates, both with and without water pretreatment consisting of aeration and pH adjustment, in anaerobic experimental columns. The treatment with the chitinous substrate was more effective in removing metals (Al, Cu, Fe, Cd, Mn, Zn) and sulfate for a longer period (458 days) than the ligneous substrate (78 days) before suffering Zn breakthrough. The reactors fed with pretreated water had longer operational periods and lower metals and sulfate concentrations in the effluent than those with untreated influent water. Zn was consistently removed to levels <0.3 mg/L for 513 days in the chitinous substrate columns, while levels <0.3 mg/L were maintained for only 140 days in the ligneous substrate pretreated column. The highest sulfate removal rates achieved in this study were in the range of 5-6 mol/m3/d for the chitinous substrate and 1-2 mol/m3/d for the ligneous substrate. Overall, the chitinous substrate proved to be more efficient in the removal of all the aforementioned metals and for sulfate when compared to the ligneous substrate. This could be the determinant when selecting a substrate for passive systems treating acidic MIW, particularly when Zn and Mn removal is necessary.

Characterization of engineered nanoparticles in commercially available spray disinfectant products advertised to contain colloidal silver.

Given the potential for human exposure to silver nanoparticles from spray disinfectants and dietary supplements, we characterized the silver-containing nanoparticles in 22 commercial products that advertised the use of silver or colloidal silver as the active ingredient. Characterization parameters included: total silver, fractionated silver (particulate and dissolved), primary particle size distribution, hydrodynamic diameter, particle number, and plasmon resonance absorbance. A high degree of variability between claimed and measured values for total silver was observed. Only 7 of the products showed total silver concentrations within 20% of their nominally reported values. In addition, significant variations in the relative percentages of particulate vs. soluble silver were also measured in many of these products reporting to be colloidal. Primary silver particle size distributions by transmission electron microscopy (TEM) showed two populations of particles - smaller particles (<5nm) and larger particles between 20 and 40nm. Hydrodynamic diameter measurements using nanoparticle tracking analysis (NTA) correlated well with TEM analysis for the larger particles. Z-average (Z-Avg) values measured using dynamic light scattering (DLS); however, were typically larger than both NTA or TEM particle diameters. Plasmon resonance absorbance signatures (peak absorbance at around 400nm indicative of metallic silver nanoparticles) were only noted in 4 of the 9 yellow-brown colored suspensions. Although the total silver concentrations were variable among products, ranging from 0.54mg/L to 960mg/L, silver containing nanoparticles were identified in all of the product suspensions by TEM.