James F. Ranville

Nanoparticle analysis and characterization methodologies in environmental risk assessment of engineered nanoparticles

Environmental risk assessments of engineered nanoparticles require thorough characterization of nanoparticles and their aggregates. Furthermore, quantitative analytical methods are required to determine environmental concentrations and enable both effect and exposure assessments. Many methods still need optimization and development, especially for new types of nanoparticles in water, but extensive experience can be gained from the fields of environmental chemistry of natural nanomaterials and from fundamental colloid chemistry. This review briefly describes most methods that are being exploited in nanoecotoxicology for analysis and characterization of nanomaterials. Methodological aspects are discussed in relation to the fields of nanometrology, particle size analysis and analytical chemistry. Differences in both the type of size measures (length, radius, aspect ratio, etc.), and the type of average or distributions afforded by the specific measures are compared. The strengths of single particle methods, such as electron microscopy and atomic force microscopy, with respect to imaging, shape determinations and application to particle process studies are discussed, together with their limitations in terms of counting statistics and sample preparation. Methods based on the measurement of particle populations are discussed in terms of their quantitative analyses, but the necessity of knowing their limitations in size range and concentration range is also considered. The advantage of combining complementary methods is highlighted.

Potential Scenarios for Nanomaterial Release and Subsequent alteration in the Environment

The risks associated with exposure to engineered nanomaterials (ENM) will be determined in part by the processes that control their environmental fate and transformation. These processes act not only on ENM that might be released directly into the environment, but more importantly also on ENM in consumer products and those that have been released from the product. The environmental fate and transformation are likely to differ significantly for each of these cases. The ENM released from actual direct use or from nanomaterial-containing products are much more relevant for ecotoxicological studies and risk assessment than pristine ENM. Released ENM may have a greater or lesser environmental impact than the starting materials, depending on the transformation reactions and the material. Almost nothing is known about the environmental behavior and the effects of released and transformed ENM, although these are the materials that are actually present in the environment. Further research is needed to determine whether the release and transformation processes result in a similar or more diverse set of ENM and ultimately how this affects environmental behavior. This article addresses these questions, using four hypothetical case studies that cover a wide range of ENM, their direct use or product applications, and their likely fate in the environment. Furthermore, a more definitive classification scheme for ENM should be adopted that reflects their surface condition, which is a result of both industrial and environmental processes acting on the ENM. The authors conclude that it is not possible to assess the risks associated with the use of ENM by investigating only the pristine form of the ENM, without considering alterations and transformation processes.

Determining Transport Efficiency for the Purpose of Counting and Sizing Nanoparticles via Single Particle Inductively Coupled Plasma Mass Spectrometry

Currently there are few ideal methods for the characterization of nanoparticles in complex, environmental samples, leading to significant gaps in toxicity and exposure assessments of nanomaterials. Single particle-inductively coupled plasma-mass spectrometry (spICPMS) is an emerging technique that can both size and count metal-containing nanoparticles. A major benefit of the spICPMS method is its ability to characterize nanoparticles at concentrations relevant to the environment. This paper presents a practical guide on how to count and size nanoparticles using spICPMS. Different methods are investigated for measuring transport efficiency (i.e., nebulization efficiency), an important term in the spICPMS calculations. In addition, an alternative protocol is provided for determining particle size that broadens the applicability of the technique to all types of inorganic nanoparticles. Initial comparison, using well-characterized, monodisperse silver nanoparticles, showed the importance of having an accurate transport efficiency value when determining particle number concentration and, if using the newly presented protocol, particle size. Ultimately, the goal of this paper is to provide improvements to nanometrology by further developing this technique for the characterization of metal-containing nanoparticles.

Detecting nanoparticulate silver using single‐particle inductively coupled plasma–mass spectrometry

The environmental prevalence of engineered nanomaterials, particularly nanoparticulate silver (AgNP), is expected to increase substantially. The ubiquitous use of commercial products containing AgNP may result in their release to the environment, and the potential for ecological effects is unknown. Detecting engineered nanomaterials is one of the greatest challenges in quantifying their risks. Thus, it is imperative to develop techniques capable of measuring and characterizing exposures, while dealing with the innate difficulties of nanomaterial detection in environmental samples, such as low-engineered nanomaterial concentrations, aggregation, and complex matrices. Here the authors demonstrate the use of inductively coupled plasma-mass spectrometry, operated in a single-particle counting mode (SP-ICP-MS), to detect and quantify AgNP. In the present study, two AgNP products were measured by SP-ICP-MS, including one of precisely manufactured size and shape, as well as a commercial AgNP-containing health food product. Serial dilutions, filtration, and acidification were applied to confirm that the method detected particles. Differentiation of dissolved and particulate silver (Ag) is a feature of the technique. Analysis of two wastewater samples demonstrated the applicability of SP-ICP-MS at nanograms per liter Ag concentrations. In this pilot study, AgNP was found at 100 to 200 ng/L in the presence of 50 to 500 ng/L dissolved Ag. The method provides the analytical capability to monitor Ag and other metal and metal oxide nanoparticles in fate, transport, stability, and toxicity studies using a commonly available laboratory instrument. Rapid throughput and element specificity are additional benefits of SP-ICP-MS as a measurement tool for metal and metal oxide engineered nanoparticles.

Solubility of nano‐zinc oxide in environmentally and biologically important matrices

Increasing manufacture and use of engineered nanoparticles is leading to a greater probability for release of engineered nanoparticles into the environment and exposure to organisms. In particular, zinc oxide (ZnO) is toxic, although it is unclear whether this toxicity is due to the zinc oxide nanoparticles, dissolution to Zn(2+) , or some combination thereof. The goal of this study was to determine the relative solubilities of both commercially available and in-house synthesized ZnO in matrices used for environmental fate and transport or biological toxicity studies. Dissolution of ZnO was observed in nanopure water (7.18-7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (∼5 mg/L), but much more dissolution was observed in Dulbeccos modified Eagles medium, in which the dissolved Zn concentration exceeded 34 mg/L. Moderately hard water exhibited low Zn solubility, likely because of precipitation of a Zn carbonate solid phase. Precipitation of a Zn-containing solid phase in RPMI also appeared to limit Zn solubility. Equilibrium conditions with respect to ZnO solubility were not apparent in these matrices, even after more than 1,000 h of dissolution. These results suggest that solution chemistry exerts a strong influence on ZnO dissolution and can result in limits on Zn solubility from precipitation of less soluble solid phases.

Release of TiO2 nanoparticles from sunscreens into surface waters: a one-year survey at the old Danube recreational Lake.

Monitoring data are necessary for the future production of engineered nanomaterials and the development of regulations for nanomaterials. Therefore, it is necessary to develop methods that reliably detect and quantify nanomaterials in real-world systems at expectedly low concentrations. In this work we tested several methodological approaches to detect titanium dioxide nanomaterials released from sunscreen products into the Old Danube Lake (Vienna, Austria), which is heavily used for recreational activities like bathing and water sports during the summer season. During a 12-month period suspended particulate matter (SPM) was collected from the lake and analyzed using a combination of complementary techniques. By sampling at a location approximately 50 m from the nearest bathing area and at one meter depth from the water surface, we focused on the potentially mobile fraction of the released nanoparticles. We were able to identify titanium dioxide nanoparticles stemming from sunscreens in the suspended matter of the lake using electron microscopy. Bulk analysis of SPM clearly shows an increase of Ti-containing particles during the summer season. These analyses, however, are not able to distinguish sunscreen nanoparticles from natural Ti-bearing nanoparticles. Therefore, Elemental ratios of Ti with Al, V, Ga, Y, Nb, Eu, Ho, Er, Tm, Yb, and Ta as determined by ICPMS and ICPOES, in combination with single particle ICPMS analysis were applied to establish local background values. The observed mild increase of Ti elemental ratios, compared to spring background values indicates that the residence time of released nanomaterials in the water column is rather short. Overall, the advantages and disadvantages of the methods used to detect and characterize the nanomaterials are discussed.

Silver nanoparticle characterization using single particle ICP-MS (SP-ICP-MS) and asymmetrical flow field flow fractionation ICP-MS (AF4-ICP-MS)

Methods to detect, quantify, and characterize engineered nanoparticles (ENPs) in environmental matrices are highlighted as one of the areas of highest priority research needs with respect to understanding the potential environmental risks associated with nanomaterials. More specifically, techniques are needed to determine the size and concentration of ENPs in a variety of complex matrices. Furthermore, data should be collected at environmentally and toxicologically relevant concentrations. Both single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and asymmetrical flow field flow fractionation (AF4) ICP-MS offer substantial advantages for detecting ENPs and assessing many of the above parameters in complex matrices over traditional characterization methods such as microscopy, light scattering, and filtration. In this study, we compared the ability of two emerging techniques to detect well characterized, monodisperse silver ENPs and examined their overall applicability to environmental studies specifically with respect to their: (A) size and concentration detection limits, (B) resolution and (C) multi-form elemental analysis. We find that in terms of concentration detection limit (both, on a mass basis and particle number basis) SP-ICP-MS was considerably more sensitive than AF4-ICP-MS (ng L−1vs. μg L−1, respectively), and offers the unique ability to differentiate dissolved and nanoparticulate fractions of total metal. With a variety of optimization parameters possible, AF4-ICP-MS can detect a much smaller NP size (2 nm vs. 20 nm for SP-ICP-MS), provides the possibility for greater size resolution.

Nanoparticle Size Detection Limits by Single Particle ICP-MS for 40 Elements

The quantification and characterization of natural, engineered, and incidental nano- to micro-size particles are beneficial to assessing a nanomaterials performance in manufacturing, their fate and transport in the environment, and their potential risk to human health. Single particle inductively coupled plasma mass spectrometry (spICP-MS) can sensitively quantify the amount and size distribution of metallic nanoparticles suspended in aqueous matrices. To accurately obtain the nanoparticle size distribution, it is critical to have knowledge of the size detection limit (denoted as Dmin) using spICP-MS for a wide range of elements (other than a few available assessed ones) that have been or will be synthesized into engineered nanoparticles. Herein is described a method to estimate the size detection limit using spICP-MS and then apply it to nanoparticles composed of 40 different elements. The calculated Dmin values correspond well for a few of the elements with their detectable sizes that are available in the literature. Assuming each nanoparticle sample is composed of one element, Dmin values vary substantially among the 40 elements: Ta, U, Ir, Rh, Th, Ce, and Hf showed the lowest Dmin values, ≤10 nm; Bi, W, In, Pb, Pt, Ag, Au, Tl, Pd, Y, Ru, Cd, and Sb had Dmin in the range of 11-20 nm; Dmin values of Co, Sr, Sn, Zr, Ba, Te, Mo, Ni, V, Cu, Cr, Mg, Zn, Fe, Al, Li, and Ti were located at 21-80 nm; and Se, Ca, and Si showed high Dmin values, greater than 200 nm. A range of parameters that influence the Dmin, such as instrument sensitivity, nanoparticle density, and background noise, is demonstrated. It is observed that, when the background noise is low, the instrument sensitivity and nanoparticle density dominate the Dmin significantly. Approaches for reducing the Dmin, e.g., collision cell technology (CCT) and analyte isotope selection, are also discussed. To validate the Dmin estimation approach, size distributions for three engineered nanoparticle samples were obtained using spICP-MS. The use of this methodology confirms that the observed minimum detectable sizes are consistent with the calculated Dmin values. Overall, this work identifies the elements and nanoparticles to which current spICP-MS approaches can be applied, in order to enable quantification of very small nanoparticles at low concentrations in aqueous media.

Photodegradation of roxarsone in poultry litter leachates

Arsenic compounds have been used extensively in agriculture in the US for applications ranging from cotton herbicides to animal feed supplements. Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), in particular, is used widely in poultry production to control coccidial intestinal parasites. It is excreted unchanged in the manure and introduced into the environment when litter is applied to farmland as fertilizer. Although the toxicity of roxarsone is less than that of inorganic arsenic, roxarsone can degrade, biotically and abiotically, to produce more toxic inorganic forms of arsenic, such as arsenite and arsenate. Experiments were conducted on aqueous litter leachates to test the stability of roxarsone under different conditions. Laboratory experiments have shown that arsenite can be cleaved photolytically from the roxarsone moiety at pH 4-8 and that the degradation rate increases with increasing pH. Furthermore, the rate of photodegradation increases with nitrate and natural organic matter concentration, reactants that are commonly found in poultry-litter-water leachates. Additional photochemical reactions rapidly oxidize the cleaved arsenite to arsenate. The formation of arsenate is not entirely undesirable, because it is less mobile in soil systems and less toxic than arsenite. A possible mechanism for the degradation of roxarsone in poultry litter leachates is proposed. The results suggest that poultry litter storage and field application practices could affect the degradation of roxarsone and subsequent mobilization of inorganic arsenic species.

Single particle inductively coupled plasma-mass spectrometry: a performance evaluation and method comparison in the determination of nanoparticle size.

Sizing engineered nanoparticles in simple, laboratory systems is now a robust field of science; however, application of available techniques to more complex, natural systems is hindered by numerous challenges including low nanoparticle number concentrations, polydispersity from aggregation and/or dissolution, and interference from other incidental particulates. A new emerging technique, single particle inductively coupled plasma-mass spectrometry (spICPMS), has the potential to address many of these analytical challenges when sizing inorganic nanoparticles in environmental matrices. However, to date, there is little beyond the initial feasibility studies that investigates the performance characteristics and validation of spICPMS as a nanoparticle sizing technique. This study compares sizing of four silver nanoparticle dispersions (nominal diameters of 40, 60, 80, and 100 nm) by spICPMS to four established sizing techniques: dynamic light scattering, differential centrifugal sedimentation, nanoparticle tracking analysis, and TEM. Results show that spICPMS is able to size silver nanoparticles, across different sizes and particle number concentrations, with accuracy similar to the other commercially available techniques. Furthermore, a novel approach to evaluating particle coincidence is presented. In addition, spICPMS size measurements were successfully performed on nanoparticles suspended in algal growth media at low concentrations. Overall, while further development of the technique is needed, spICPMS yields important advantages over other techniques when sizing nanoparticles in environmentally relevant media.