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

Characterization of Polymeric Nanomaterials Using Analytical Ultracentrifugation

The characterization of nanomaterials represents a complex analytical challenge due to their dynamic nature (small size, high reactivity, and instability) and the low concentrations in the environment, often below typical analytical detection limits. Analytical ultracentrifugation (AUC) is especially useful for the characterization of small nanoparticles (1–10 nm), which are often the most problematic for the commonly used techniques such as electron microscopy or dynamic light scattering. In this study, small polymeric nanomaterials (allospheres) that are used commercially to facilitate the distribution of pesticides in agricultural fields were characterized under a number of environmentally relevant conditions. Under most of the studied conditions, the allospheres were shown to have a constant hydrodynamic diameter (<i>d</i>_H) of about 7.0 nm. Only small increases in diameter were observed, either at low pH or very high ionic strength or hardness, demonstrating their high physicochemical stability (and thus high mobility in soils). Furthermore, natural organic matter had little effect on the hydrodynamic diameters of the allospheres. The concentration of the nanoparticles was an important parameter influencing their agglomerationresults obtained using dynamic light scattering at high particle concentrations showed large agglomerate sizes and significant particle losses through sedimentation, clearly indicating the importance of characterizing the nanomaterials under environmentally relevant conditions

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 (Mg²⁺, Ca²⁺, 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

CFU values (/mL) for <i>S</i>. <i>mutans</i> isolated from biofilms that were either exposed to bare, positively charged or negatively charged SPIONs or were incubated in the absence of SPIONs.

<p>CFU values (/mL) for <i>S</i>. <i>mutans</i> isolated from biofilms that were either exposed to bare, positively charged or negatively charged SPIONs or were incubated in the absence of SPIONs.</p

Zeta potential values of the SPIONs determined before and after incubation with the biofilm.

<p>Zeta potential values of the SPIONs determined before and after incubation with the biofilm.</p

Structure of the charged SPIONs.

<p>The amine and carboxyl functional groups are attached to the silica shell on the surface of the SPIONs.</p

Thermal Degradation of Conventional and Nanoencapsulated Azoxystrobin due to Processing in Water, Spiked Strawberry, and Incurred Strawberry Models

Nanoencapsulated formulations of pesticides have been recently developed, and some products are now marketed for specific applications in agriculture. Pesticide residues present in raw agricultural products can degrade or react during food processing steps. To date, the fate of nanopesticides during food processing has not been well described. In this study, the thermal degradation of azoxystrobin (AZOX) in conventional and nanoencapsulated (Allosperse and nSiO2) formulations was first assessed in water, spiked strawberry, and incurred strawberry models. The thermal degradation followed first-order kinetics when heated at 100 °C in the water model. The thermal degradation of AZOX in nanoformulations in strawberry models (18% AZOX decrease) was comparable to or lower than in the conventional formulation (21%), possibly due to the nanocarriers protecting the active ingredient from hydrolytic degradation. Out of 32 thermal degradation products (TDPs), only two were detected in both the spiked water and strawberry models, indicating differences in the thermal degradation reactions for AZOX in these two models. Identical TDPs were detected for both conventional and nanoformulations for each specific model, except for the absence of one (TDP22) in the nSiO2 formulations. The nanoencapsulation of AZOX did not result in new TDPs in any of the matrices. Only six of the TDPs detected in water, four in spiked strawberries, and two in incurred strawberries have been previously reported in environmental studies on the metabolism of AZOX. Based on the observed TDPs, AZOX thermal degradation pathways include ether cleavage, hydrolysis, demethylation, and decarboxylation. Overall, although nanocarriers have no impact on the degradation product types, nanocarriers had a slight but significant impact on the degradation rate of pesticide active ingredients

Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg–Carbon Bond Cleavage and Metal Binding Specificity

In bacterial resistance to mercury, the organomercurial lyase (MerB) plays a key role in the detoxification pathway through its ability to cleave Hg–carbon bonds. Two cysteines (C96 and C159; <i>Escherichia coli</i> MerB numbering) and an aspartic acid (D99) have been identified as the key catalytic residues, and these three residues are conserved in all but four known MerB variants, where the aspartic acid is replaced with a serine. To understand the role of the active site serine, we characterized the structure and metal binding properties of an <i>E. coli</i> MerB mutant with a serine substituted for D99 (MerB D99S) as well as one of the native MerB variants containing a serine residue in the active site (<i>Bacillus megaterium</i> MerB2). Surprisingly, the MerB D99S protein copurified with a bound metal that was determined to be Cu­(II) from UV–vis absorption, inductively coupled plasma mass spectrometry, nuclear magnetic resonance, and electron paramagnetic resonance studies. X-ray structural studies revealed that the Cu­(II) is bound to the active site cysteine residues of MerB D99S, but that it is displaced following the addition of either an organomercurial substrate or an ionic mercury product. In contrast, the <i>B. megaterium</i> MerB2 protein does not copurify with copper, but the structure of the <i>B. megaterium</i> MerB2–Hg complex is highly similar to the structure of the MerB D99S–Hg complexes. These results demonstrate that the active site aspartic acid is crucial for both the enzymatic activity and metal binding specificity of MerB proteins and suggest a possible functional relationship between MerB and its only known structural homologue, the copper-binding protein NosL