Jeffrey A. Nason

Interactions between natural organic matter and gold nanoparticles stabilized with different organic capping agents.

The adsorption of natural organic matter (NOM) to the surfaces of natural colloids and engineered nanoparticles is known to strongly influence, and in some cases control, their surface properties and aggregation behavior. As a result, the understanding of nanoparticle fate, transport, and toxicity in natural systems must include a fundamental framework for predicting such behavior. Using a suite of gold nanoparticles (AuNPs) with different capping agents, the impact of surface functionality, presence of natural organic matter, and aqueous chemical composition (pH, ionic strength, and background electrolytes) on the surface charge and colloidal stability of each AuNP type was investigated. Capping agents used in this study were as follows: anionic (citrate and tannic acid), neutral (2,2,2-[mercaptoethoxy(ethoxy)]ethanol and polyvinylpyrrolidone), and cationic (mercaptopentyl(trimethylammonium)). Each AuNP type appeared to adsorb Suwannee River Humic Acid (SRHA) as evidenced by measurable decreases in zeta potential in the presence of 5 mg C L(-1) SRHA. It was found that 5 mg C L(-1) SRHA provided a stabilizing effect at low ionic strength and in the presence of only monovalent ions while elevated concentrations of divalent cations lead to enhanced aggregation. The colloidal stability of the NPs in the absence of NOM is a function of capping agent, pH, ionic strength, and electrolyte valence. In the presence of NOM at the conditions examined in this study, the capping agent is a less important determinant of stability, and the adsorption of NOM is a controlling factor.

Influence of liberated silver from silver nanoparticles on nitrification inhibition of Nitrosomonas europaea

The ecotoxicity of silver nanoparticles (Ag-NPs) to wastewater biota, including ammonia oxidizing bacteria (AOB), is gaining increasing interest as the number of products containing Ag-NPs continues to rise exponentially and they are expected to accumulate in wastewater treatment plants. This research demonstrated that the addition order of Ag-NP and the media constituents had a profound influence on the stability of the Ag-NP suspension and the corresponding repeatability of results and sensitivity of Nitrosomonas europaea. N. europaea, a model AOB, was found to be extremely sensitive to ionic silver (Ag(+)) and two sizes of Ag-NPs (20 and 80 nm). Ag(+) exposures resulted in the highest level of toxicity with smaller Ag-NPs (20 nm) being more toxic than larger Ag-NPs (80 nm). The increased sensitivity of N. europaea to smaller Ag-NPs was caused by their higher rates of dissolved silver (dAg) release, via dissolution, due to a greater surface area to volume ratio. dAg was shown to be responsible for the vast majority of the observed Ag-NP toxicity, as determined by abiotic Ag-NP dissolution tests. For the sizes of Ag-NP studied (20 and 80 nm), there appears to be a negligible nanoparticle-specific toxicity. This was further supported by similarities in inhibition mechanisms between Ag(+) and Ag-NP, with both causing decreases in AMO activity and destabilization of the outer-membrane of N. europaea. Finally, equal concentrations of total silver were found to be tightly associated to both Ag(+) and Ag-NP-exposed cells despite Ag-NP concentrations being five times greater, by mass, than Ag(+) concentrations.

Factors Influencing Dissolved Copper Concentrations in Oregon Highway Storm Water Runoff

AbstractHighway storm water runoff represents a significant source of dissolved copper to surface waters. It is well-established that even low concentrations of dissolved copper can be toxic to many aquatic organisms. In the Pacific Northwest of the United States, recent research has focused on the effects of low-level copper exposure to salmonids listed as threatened or endangered under the Endangered Species Act (ESA). In light of these recent studies, increasingly stringent guidelines for the discharge of highway storm water runoff have been imposed as part of ESA assessments of transportation projects. Assessing factors that may affect dissolved copper concentrations in storm water provides a practical framework for predicting when and where copper toxicity could be problematic. A storm water sampling effort was performed to examine the influence of site locale, traffic density, storm hydrology, the “first-flush” effect, and water quality parameters on measured dissolved copper concentrations in highw...

Calcium Chloride in Neonatal Parenteral Nutrition Solutions with and without Added Cysteine: Compatibility Studies Using Laser and Micro-Flow Imaging Methodology.

Background Previous studies of compatibility of calcium chloride (CaCl2) and phosphates have not included particle counts in the range specified by the United States Pharmacopeia. Micro-flow imaging techniques have been shown to be comparable to light obscuration when determining particle count and size in pharmaceutical solutions. Objective The purpose of this study was to do compatibility testing for parenteral nutrition (PN) solutions containing CaCl2 using dynamic light scattering and micro-flow imaging techniques. Methods Solutions containing TrophAmine (Braun Medical Inc, Irvine, CA), CaCl2, and sodium phosphate (NaPhos) were compounded with and without cysteine. All solutions contained standard additives to neonatal PN solutions including dextrose, trace metals, and electrolytes. Control solutions contained no calcium or phosphate. Solutions were analyzed for particle size and particle count. Means of Z-average particle size and particle counts of controls were determined. Study solutions were compared to controls and United States Pharmacopeia (USP) Chapter 788 guidelines. The maximum amount of Phos that was compatible in solutions that contained at least 10 mmol/L of Ca in 2.5% amino acids (AA) was determined. Compatibility of these solutions was verified by performing analyses of 5 repeats of these solutions. Microscopic analyses of the repeats were also performed. Results Amounts of CaCl2 and NaPhos that were compatible in solutions containing 1.5%, 2%, 2.5%, and 3% AA were determined. The maximum amount of NaPhos that could be added to TrophAmine solutions of > = 2.5% AA containing at least 10 mmol/L of CaCl2 was 7.5 mmol/L. Adding 50 mg/dL of cysteine increased the amount of NaPhos that could be added to solutions containing 10 mmol/L of CaCl2 to 10 mmol/L. Conclusion Calcium chloride can be added to neonatal PN solutions containing NaPhos in concentrations that can potentially provide an intravenous intake of adequate amounts of calcium and phosphorus.

Modeling Particle-Size Distribution Dynamics during Precipitative Softening

A population balance model was developed to simulate simultaneous precipitation and flocculation during precipitative softening. Rate coefficients for nucleation, crystal growth, and flocculation were extracted from experimental particle-size distribution (PSD) data based on changes in the total number and total volume of particles. Three models of flocculation were evaluated: rectilinear, curvilinear, and an empirical size-independent model. Model simulations were compared with experimental PSD data to test which model was most appropriate. The curvilinear precipitative flocculation model was superior when seeded precipitation occurred at moderate mixing intensities ( G=50–100  s−1 ) . However, the curvilinear model overpredicts the formation of very large particles and requires values of the collision efficiency greater than 1.0, suggesting a more complicated dependence of the PSD dynamics on mixing intensity and saturation ratio than presently included in the model. At higher mixing intensities ( G=300...

Effects of surface coating character and interactions with natural organic matter on the colloidal stability of gold nanoparticles

Aggregation is one of the dominant processes controlling the environmental fate of engineered nanomaterials (ENMs) in aquatic systems. Engineered coatings and coronas obtained through interactions with natural organic matter (NOM) and other macromolecules are known to play a significant role in controlling these processes. However, our ability to predict environmental fate on the basis of nanoparticle properties and the properties of the surrounding medium is still developing. To better understand the interplay between ENM surface coatings and their interaction with NOM, the aggregation of gold nanoparticles (AuNPs) with four different surface coatings—polyethylene glycol of varying molecular weight (PEG-AuNPs), carboxylated PEG-AuNPs (PEG-COOH-AuNPs), aminated PEG-AuNPs (PEG-amine-AuNPs), and branched polyethylenimine (bPEI-AuNPs)—was investigated as a function of pH, ionic strength and the presence of a model organic matter (Suwannee River NOM, SRNOM). Time-resolved dynamic light scattering and electrophoretic mobility titrations were used to investigate how changes in the solution chemistry affect the ability of the different AuNPs to resist aggregation. Under the conditions investigated, the PEG-AuNPs and PEG-COOH-AuNPs remained stable across a range of conditions and in the presence of SRNOM due to steric and/or electrosteric stabilization. In contrast, the PEG-amine-AuNPs and bPEI-AuNPs were destabilized in the presence of SRNOM at circumneutral pH. It is hypothesized that aggregation of these AuNP types occurs via adsorption and interparticle bridging that is strongly dependent on pH and the concentration of SRNOM. At mass ratios of NOM to ENMs expected in natural systems, all the AuNP types investigated here are expected to be stable with respect to homoaggregation in the presence of SRNOM. These findings provide a foundation to investigate more complex systems where competing interactions between NOM, ENMs and natural colloids are expected to control ENM environmental fate.

Gold core-labeled TiO2 nanoparticles for tracking behavior in complex matrices: synthesis, characterization, and demonstration

Titanium dioxide nanoparticles (TiO2 NPs) are increasingly entering natural systems due to their widespread production and use. It is critical that TiO2 NP behavior is studied in real-world systems, but experimental work is complicated by the high levels of background titanium present in every environmental compartment. To assist in distinguishing between engineered NPs and background titanium, labeled particles with gold nanoparticle cores and TiO2 shells (Au@TiO2 NPs) were developed and the properties and behavior compared to unlabeled TiO2 NPs. Both particle types had primary particle diameters of approximately 200 nm and were stable in solutions at ionic strengths up to 500 mM due to a polyvinylpyrrolidone surface coating. To demonstrate utility, the Au@TiO2 NPs were used in several spike-and-recovery experiments in complex matrices such as activated sludge and a river water–sunscreen mixture. Au@TiO2 NPs were accurately quantified at using instrumental neutron activation analysis and inductively coupled plasma optical emission spectrometry.