Extraction of Silicon-Containing Nanoparticles from an Agricultural Soil for Analysis by Single Particle Sector Field and Time-of-Flight Inductively Coupled Plasma Mass Spectrometry.

The increased use of silica and silicon-containing nanoparticles (Si-NP) in agricultural applications has stimulated interest in determining their potential migration in the environment and their uptake by living organisms. Understanding the fate and behavior of Si-NPs will require their accurate analysis and characterization in very complex environmental matrices. In this study, we investigated Si-NP analysis in soil using single-particle ICP-MS. A magnetic sector instrument was operated at medium resolution to overcome the impact of polyatomic interferences (e.g., 14N14N and 12C16O) on 28Si determinations. Consequently, a size detection limit of 29 ± 3 nm (diameter of spherical SiO2 NP) was achieved in Milli-Q water. Si-NP were extracted from agricultural soil using several extractants, including Ca(NO3)2, Mg(NO3)2, BaCl2, NaNO3, Na4P2O7, fulvic acid (FA) and Na2H2EDTA. The best extraction efficiency was found for Na4P2O7, for which the size distribution of Si-NP in the leachates was well preserved for at least one month. On the other hand, Ca(NO3)2, Mg(NO3)2 and BaCl2 were relatively less effective and generally led to particle agglomeration. A time-of-flight ICP-MS was also used to examine the nature of the extracted Si-NP on a single-particle basis. Aluminosilicates accounted for the greatest number of extracted NP (~46%), followed by NP where Si was the only detected metal (presumably SiO2, ~30%).

Analysis of Silver Nanoparticles in Ground Beef by Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS).

The regulation and characterization of nanomaterials in foods are of great interest due to the potential risks associated with their exposure and the increasing number of applications where they are used within the food industry. One factor limiting the scientifically rigorous regulation of nanoparticles in foods is the lack of standardized procedures for the extraction of nanoparticles (NPs) from complex matrices without alteration of their physico-chemical properties. To this end, we tested and optimized two sample preparation approaches (enzymatic- and alkaline-based hydrolyses) in order to extract 40 nm of Ag NP, following their equilibration with a fatty ground beef matrix. NPs were characterized using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Fast sample processing times (<20 min) were achieved using ultrasonication to accelerate the matrix degradation. NP losses during the sample preparation were minimized by optimizing the choice of enzymes/chemicals, the use of surfactants, and the product concentration and sonication. The alkaline approach using TMAH (tetramethylammonium hydroxide) was found to have the highest recoveries (over 90%); however, processed samples were found to be less stable than the samples processed using an enzymatic digestion based upon pork pancreatin and lipase (≈60 % recovery). Low method detection limits (MDLs) of 4.8 × 106 particles g-1 with a size detection limit (SDL) of 10.9 nm were achieved for the enzymatic extraction whereas an MDL of 5.7 × 107 particles g-1 and an SDL of 10.5 nm were obtained for the alkaline hydrolysis.

Sample preparation for the analysis of nanoparticles in natural waters by single particle ICP-MS.

With the significant increase in the production and use of nanoparticles (NP), concern is increasing over their release into their environment. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is emerging as one of the best techniques for detecting the very small NP at very low concentrations in natural waters. However, there is no unified protocol for the preparation of natural water samples for SP-ICP-MS analysis. In order to minimize nebulizer blockage, filtration is often used with the expectation that 0.45 µm membranes will not remove significant quantities of 1-100 nm NP. Nonetheless, there are limited data on its effect on the concentrations or size distributions of the NP. To that end, we examined the interactions between six different membrane filters and silver (Ag) and cerium oxide (CeO2) NP in aqueous samples. For Ag NP, the highest recoveries were observed for polypropylene membranes, where 55% of the pre-filtration NP were found in rainwater and 75% were found in river waters. For CeO2 NP, recoveries for the polypropylene membrane attained 60% in rainwater and 75% in river water. Recoveries could be increased to over 80% by pre-conditioning the filtration membranes with a multi-element solution. Similar recoveries were obtained when samples were centrifuged at low centrifugal forces (≤1000×g).

Quantification and Characterization of Ti-, Ce-, and Ag-Nanoparticles in Global Surface Waters and Precipitation.

Nanoparticle (NP) emissions to the environment are increasing as a result of anthropogenic activities, prompting concerns for ecosystems and human health. In order to evaluate the risk of NPs, it is necessary to know their concentrations in various environmental compartments on regional and global scales; however, these data have remained largely elusive due to the analytical difficulties of measuring NPs in complex natural matrices. Here, we measure NP concentrations and sizes for Ti-, Ce-, and Ag-containing NPs in numerous global surface waters and precipitation samples, and we provide insights into their compositions and origins (natural or anthropogenic). The results link NP occurrences and distributions to particle type, origin, and sampling location. Based on measurements from 46 sites across 13 countries, total Ti- and Ce-NP concentrations (regardless of origin) were often found to be within 104 to 107 NP mL-1, whereas Ag NPs exhibited sporadic occurrences with low concentrations generally up to 105 NP mL-1. This generally corresponded to mass concentrations of <1 ng L-1 for Ag-NPs, <100 ng L-1 for Ce-NPs, and <10 µg L-1 for Ti-NPs, given that measured sizes were often below 15 nm for Ce- and Ag-NPs and above 30 nm for Ti-NPs. In view of current toxicological data, the observed NP levels do not yet appear to exceed toxicity thresholds for the environment or human health; however, NPs of likely anthropogenic origins appear to be already substantial in certain areas, such as urban centers. This work lays the foundation for broader experimental NP surveys, which will be critical for reliable NP risk assessments and the regulation of nano-enabled products.

Measurement of CeO2 Nanoparticles in Natural Waters Using a High Sensitivity, Single Particle ICP-MS.

As the production and use of cerium oxide nanoparticles (CeO2 NPs) increases, so does the concern of the scientific community over their release into the environment. Single particle inductively coupled plasma mass spectrometry is emerging as one of the best techniques for NP detection and quantification; however, it is often limited by high size detection limits (SDL). To that end, a high sensitivity sector field ICP-MS (SF-ICP-MS) with microsecond dwell times (50 µs) was used to lower the SDL of CeO2 NPs to below 4.0 nm. Ag and Au NPs were also analyzed for reference. SF-ICP-MS was then used to detect CeO2 NPs in a Montreal rainwater at a concentration of (2.2 ± 0.1) × 108 L-1 with a mean diameter of 10.8 ± 0.2 nm; and in a St. Lawrence River water at a concentration of ((1.6 ± 0.3) × 109 L-1) with a higher mean diameter (21.9 ± 0.8 nm). SF-ICP-MS and single particle time of flight ICP-MS on Ce and La indicated that 36% of the Ce-containing NPs detected in Montreal rainwater were engineered Ce NPs.

Lowering the Size Detection Limits of Ag and TiO2 Nanoparticles by Single Particle ICP-MS.

As the production and use of engineered nanomaterials increase, there is an urgent need to develop analytical techniques that are sufficiently sensitive to be able to measure the very small nanoparticles (NP) at very low concentrations. Although single particle ICP-MS (SP-ICP-MS) is emerging as one of the best techniques for detecting NP, it is limited by relatively high size detection limits for several NP, including many of the oxides. The use of a high sensitivity sector field ICP-MS (ICP-SF-MS), microsecond dwell times, and dry aerosol sample introduction systems were examined with the goal of lowering the size detection limits of the technique. For samples injected as a wet aerosol, size detection limits as low as 4.9 nm for Ag NP and 19.2 nm for TiO2 NP were determined. By using a dry aerosol, a significant gain in ion extraction from the plasma was obtained, which resulted in a noticeable decrease of the size detection limits to 3.5 nm for the Ag NP and 12.1 nm for the TiO2 NP. These substantial improvements were applied to the detection of TiO2 NP in sunscreen lotions, rainwaters, and swimming pool waters. Concentrations of Ti-containing NP between 27 and 193 µL-1 were found in rain samples. Similar NP concentrations were detected in public swimming pools, although much higher particle number concentrations (6046 ± 290 µL-1) were measured in a paddling pool, which was attributed to a high concentration of sunscreen lotions in a small recirculated water volume. High losses of TiO2 NP through adsorption or agglomeration resulted in recoveries ranging from 14-34%.

Quantification of ZnO nanoparticles and other Zn containing colloids in natural waters using a high sensitivity single particle ICP-MS.

Inductively coupled plasma mass spectrometry in single particle mode (SP-ICP-MS) is becoming a powerful tool of choice for the quantification and characterization of metallic nanoparticles (NP) at very low concentrations. Nonetheless, this technique has relatively high size detection limits for highly soluble nanoparticles (e.g. ZnO, CuO) or NP that are measured in the presence of high background concentrations of dissolved metal. In order to evaluate whether SP-ICP-MS could be used to measure a soluble NP under environmentally relevant conditions, an ion-exchange column (IEC) was coupled to a highly-sensitive sector-field ICP-MS (IEC-SP-ICP-MS) and then used to detect both spiked ZnO NP and natural Zn containing colloids in natural waters. The use of an ion exchange column, short dwell times (50 µs) and a high sensitivity instrument gave size detection limits for the measurement of ZnO NP of ca. 8.2 nm in pure water, 14.3 nm in a river water and 17.7 nm in a rainwater. IEC-SP-ICP-MS measured ca. 4.4 × 105 mL-1 zinc containing particles in a river water sample and ca. 1.0 × 105 mL-1 particles in a local rainwater.

Role of pH on indium bioaccumulation by Chlamydomonas reinhardtii.

For divalent metals, the Biotic Ligand Model (BLM) has been proven to be an effective tool to predict biological effects by taking into account speciation calculations and competitive interactions. Nonetheless, the BLM has only rarely been validated for trivalent metals (e.g. rare earth elements), and the potential competitive effects of protons has been understudied. In this paper, the short-term biouptake of indium (In), a trivalent metal that is a byproduct of zinc extraction and used in numerous applications including the semiconductor industry, was evaluated under controlled conditions. Short-term (i.e. 60 min) indium biouptake by Chlamydomonas reinhardtii was measured as a function of pH in order to verify the validity of the BLM. At a given pH, In biouptake could be well described by the Michaelis-Menten equation with conditional stability constants of KIn,pH=4.0 = 106.7 M-1, KIn,pH=5.0 = 108.6 M-1, KIn,pH=6.0 = 109.3 M-1 and maximum internalization fluxes of Jmax, pH=4.0 = 0.74 × 10-14 mol cm-2 s-1, Jmax, pH=5.0 = 1.60 × 10-14 mol cm-2 s-1, Jmax, pH=6.0 = 2.22 × 10-14 mol cm-2 s-1. Although several potential mechanisms for the role of pH were examined, the results were best explained by a competitive interaction of H+ with the In uptake sites using overall stability constants of logKIn = 9.76 M-1 and logKH = 15.66 M-1. Based on these results, pH will play a critical role in bioavailability measurements of the trivalent cations in natural waters.

Conditions affecting the release of thorium and uranium from the tailings of a niobium mine.

Determinations of the mobility of metals from tailings is a critical part of any assessment of the environmental impacts of mining activities. The leaching of thorium and uranium from the tailings of different processing stages of a niobium mine was investigated for several pH, ionic strengths and concentrations of natural organic matter (NOM). The pH of the leaching solution did not have a noticeable impact on the extraction of Th, however, for pH values below 4, increased U mobilization was observed. Similarly, only a small fraction of Th (0.05%, ≤15 µg kg-1) and U (1.22%, ≤6 µg kg-1) were mobilized from the tailings in the presence of environmentally relevant concentrations of Ca, Mg or Na. However, in the presence of 10 mg L-1 of fulvic acid, much higher concentrations of ca. 700 µg kg-1 of Th and 35 µg kg-1 of U could be extracted from the tailings. Generally, colloidal forms of Th and dissolved forms of U were mobilized from the tailings, however, in the presence of the fulvic acid, both dissolved and colloidal forms of the two actinides were observed. Single Particle ICP-MS was used to confirm the presence of Th (and U) containing colloids where significant numbers (up to 107 mL-1) of Th and U containing colloids were found, even in 0.2 µm filtered extracts. Although mass equivalent diameters in the range of 6-13 nm Th and 6-9 nm for U could be estimated (based upon the presence of an oxyhydroxide), most of the colloidal mass was attributed to larger (>200 nm) heterocomposite particles.

Practical limitations of single particle ICP-MS in the determination of nanoparticle size distributions and dissolution: case of rare earth oxides.

The applicability of single particle ICP-MS (SP-ICP-MS) for the analysis of nanoparticle size distributions and the determination of particle numbers was evaluated using the rare earth oxide, La2O3, as a model particle. The composition of the storage containers, as well as the ICP-MS sample introduction system were found to significantly impact SP-ICP-MS analysis. While La2O3 nanoparticles (La2O3 NP) did not appear to interact strongly with sample containers, adsorptive losses of La3+(over 24h) were substantial (>72%) for fluorinated ethylene propylene bottles as opposed to polypropylene (<10%). Furthermore, each part of the sample introduction system (nebulizers made of perfluoroalkoxy alkane (PFA) or glass, PFA capillary tubing, and polyvinyl chloride (PVC) peristaltic pump tubing) contributed to La3+ adsorptive losses. On the other hand, the presence of natural organic matter in the nanoparticle suspensions led to a decreased adsorptive loss in both the sample containers and the introduction system, suggesting that SP-ICP-MS may nonetheless be appropriate for NP analysis in environmental matrices. Coupling of an ion-exchange resin to the SP-ICP-MS led to more accurate determinations of the La2O3 NP size distributions.

Separation, detection and characterization of nanomaterials in municipal wastewaters using hydrodynamic chromatography coupled to ICPMS and single particle ICPMS.

Engineered nanoparticles (ENP) are increasingly being incorporated into consumer products and reaching the environment at a growing rate. Unfortunately, few analytical techniques are available that allow the detection of ENP in complex environmental matrices. The major limitations with existing techniques are their relatively high detection limits and their inability to distinguish ENP from other chemical forms (e.g. ions, dissolved) or from natural colloids. Of the matrices that are considered to be a priority for method development, ENP are predicted to be found at relatively high concentrations in wastewaters and wastewater biosolids. In this paper, we demonstrate the capability of hydrodynamic chromatography (HDC) coupled to inductively coupled plasma mass spectrometry (ICPMS), in its classical and single particle modes (SP ICPMS), to identify ENP in wastewater influents and effluents. The paper first focuses on the detection of standard silver nanoparticles (Ag NP) and their mixtures, showing that significant dissolution of the Ag NP was likely to occur. For the Ag NP, detection limits of 0.03 µg L(-1) were found for the HDC ICPMS whereas 0.1 µg L(-1) was determined for the HDC SP ICPMS (based on results for the 80 nm Ag NP). In the second part of the paper, HDC ICPMS and HDC SP ICPMS were performed on some unspiked natural samples (wastewaters, river water). While nanosilver was below detection limits, it was possible to identify some (likely natural) Cu nanoparticles using the developed separation technology.

Detection and Characterization of ZnO Nanoparticles in Surface and Waste Waters Using Single Particle ICPMS.

The increasing production of ZnO nanoparticles (nZnO) makes their analysis and characterization extremely important from an ecological risk perspective, especially at the low concentrations at which they are expected to be found in natural waters. Single particle ICPMS (SP-ICPMS) is one of the few techniques available to detect and characterize nanoparticles at environmentally relevant concentrations. Unfortunately, at the very low particle concentrations where SP-ICPMS is performed, significant dissolution of the nZnO generally increases background levels of dissolved Zn to the point where measurements are not generally possible. By hyphenating SP-ICPMS with an ion-exchange resin, it was possible to characterize and quantify nZnO in order to gain insight into the nature of the nZnO in natural waters. Spiked and unspiked water samples were analyzed using a SP-ICPMS that was coupled to a column containing a strong metal binding resin (Chelex 100). In addition to the detection of ZnO nanoparticles and the determination of a size distribution in natural waters, it was possible to partition the dissolved Zn among free and/or labile and strongly bound Zn fractions. In two natural waters, a high proportion (ca. 93-100%) of dissolved Zn was measured, and the residual ZnO particles were mainly composed of small agglomerates (average sizes ranging from 133.6 to 172.4 nm in the surface water and from 167.6 to 216.4 nm in the wastewater effluent). Small numbers of small nanoparticles were also detected in nonspiked waters.

The effects of different coatings on zinc oxide nanoparticles and their influence on dissolution and bioaccumulation by the green alga, C. reinhardtii.

Determining the environmental risk of nanoparticles (NPs) requires an in-depth understanding of the NP core, the particle surface coatings and the interactions of the two with environmental matrices. Non-coated ZnO NPs (nZnO) are known to release ionic Zn, contributing directly to the toxicity of these particles. On the other hand, relatively less data are available for particles that have coatings designed to increase particle stability. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Zn salt or nZnO with different stabilizers: (i) bare nZnO, (ii) polyacrylic acid-stabilized, nZnO-PAA, or a (iii) sodium hexametaphosphate-stabilized, nZnO-HMP. Multiple techniques were used to quantify particle agglomeration and dissolution. The dissolution of the NPs depended on the stabilizer, with the largest dissolution obtained for the bare nZnO (near total dissolution), followed by the nZnO-PAA. When exposed to the bare and PAA-stabilized nZnOs, bioaccumulation was largely accounted for by free Zn. On the other hand, the bioaccumulation of nZnO-HMP was greater than could be attributed to the release of free Zn from the particles. The increased Zn bioaccumulation was hypothesized to have resulted from the biological stimulation of C. reinhardtii due to phosphate from the particle coating.

Improvements to single particle ICPMS by the online coupling of ion exchange resins.

Single particle ICPMS (SP-ICPMS) is becoming a very promising technique for nanoparticle detection and characterization, especially at very low concentrations (~10(-12)-10(-10) M). Nonetheless, the ability of the technique to detect smaller nanoparticles is presently limited by the setting of threshold values for the discrimination of nanoparticles from the dissolved metal background. In this study, a new approach to attaining lower particle size detection limits has been developed by the online coupling of an ion exchange column (IEC) with SP-ICPMS (IEC-SP-ICPMS). The IEC effectively removes the continuous signal of dissolved metal, allowing for both lower detection limits and an improved resolution of solutions containing multiple particles. The feasibility and the efficiency of this coupling were investigated using silver nanoparticles in the presence of various concentrations of Ag(+) and other major ions (Mg(2+), Ca(2+), Na(+), K(+), and Cl(-)). The online elimination of the dissolved metal made data processing simpler and more accurate. Following the addition of 1 to 4 µg L(-1) of Ag(+) spikes, symmetric particle size distributions were obtained using IEC-SP-ICPMS, whereas the use of SP-ICPMS alone led to asymmetric distributions, especially for nanoparticle sizes below 60 nm. Although this proof of principle study focused on nanosilver, the technique should be particularly useful for any of the metal based nanoparticles with high solubilities.

Multimethod quantification of Ag+ release from nanosilver.

There is a significant interest in determining the effects of nanomaterials on the environment and human health. Part or all of the toxicity attributed to silver nanoparticles (nAg) may be due to the release of free silver (Ag(+)). Therefore, it is necessary to have techniques that will allow the precise determination of free Ag(+) within suspensions of nAg particles. Among the different methods used for the determination of free metals in natural waters, the ion-exchange technique (IET), has promise to both distinguish Ag(+) from nAg and to attain the low detection limits required for the analysis of natural samples. In this paper, IET. centrifugal ultrafiltration and single particle inductively coupled plasma mass spectrometry (SP ICP-MS) were used to determine very low concentrations of free or dissolved Ag in commercial suspensions of nAg. Dilution of the silver nanoparticles played an important role in the measured Ag(+) concentrations. The relative release of Ag(+) from nAg increased as samples were increasingly diluted, implying that it is critical to determine Ag(+) concentrations under the precise conditions used for determinations of toxicological or environmental fate.

ÉquiNanos: innovative team for nanoparticle risk management.

Interactions between nanoparticles (NP), humans and the environment are not fully understood yet. Moreover, frameworks aiming at protecting human health have not been adapted to NP but are nonetheless applied to NP-related activities. Consequently, business organizations currently have to deal with NP-related risks despite the lack of a proven effective method of risk-management. To respond to these concerns and fulfill the needs of populations and industries, ÉquiNanos was created as a largely interdisciplinary provincial research team in Canada. ÉquiNanos consists of eight platforms with different areas of action, from adaptive decision-aid tool to public and legal governance, while including biological monitoring. ÉquiNanos resources aim at responding to the concerns of the Quebec nanotechnology industry and public health authorities. Our mandate is to understand the impact of NP on human health in order to protect the population against all potential risks emerging from these high-priority and rapidly expanding innovative technologies. FROM THE CLINICAL EDITOR: In this paper by Canadian authors an important framework is discussed with the goal of acquiring more detailed information and establishing an infrastructure to evaluate the interaction between nanoparticles and living organisms, with the ultimate goal of safety and risk management of the rapidly growing fields of nanotechnology-based biological applications.