Papers by Imali Mudunkotuwa
Journal of Occupational and Environmental Hygiene, 2015
Titanium dioxide (TiO2) particles, including nanoparticles with diameters smaller than 100 nm, ar... more Titanium dioxide (TiO2) particles, including nanoparticles with diameters smaller than 100 nm, are used extensively in consumer products. In a 2011 current intelligence bulletin, the National Institute of Occupational Safety and Health (NIOSH) recommended methods to assess worker exposures to fine and ultrafine TiO2 particles and associated occupational exposure limits for these particles. However, there are several challenges and problems encountered with these recommended exposure assessment methods involving the accurate quantitation of titanium dioxide collected on air filters using acid digestion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, recommended digestion methods include the use of several hazardous chemicals, such as perchloric acid, which are typically unavailable in most accredited industrial hygiene laboratories. Other alternative methods that are used typically involve the use of nitric acid or combination of nitric acid and sulfuric acid, which yield very poor recoveries for titanium dioxide. Therefore, given the current state of the science, it is clear that a newer safe, reliable method is needed for exposure assessment. In this current study, a microwave-assisted acid digestion method has been specifically designed to improve the recovery of titanium in TiO2 nanoparticles for analysis using ICP-OES. The optimum digestion conditions were determined by changing several variables including the acids used, digestion time and temperature. Consequently, the optimized digestion temperature of 210°C with concentrated sulfuric and nitric acid (2:1 v/v) resulted in a recovery of >90% for TiO2. The method is expected to provide for a more accurate quantification of airborne TiO2 particles in the workplace environment.
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Langmuir, 2014
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Environmental Science: Nano, 2014
Given the increased use of iron-containing nanoparticles in a number of applications, it is impor... more Given the increased use of iron-containing nanoparticles in a number of applications, it is important to understand any effects that iron-containing nanoparticles can have on the environment and human health. Since iron concentrations are extremely low in body fluids, there is potential that iron-containing nanoparticles may influence the ability of bacteria to scavenge iron for growth, affect virulence and inhibit antimicrobial peptide (AMP) function. In this study, Pseudomonas aeruginosa (PA01) and AMPs were exposed to iron oxide nanoparticles, hematite (α-Fe2O3), of different sizes ranging from 2 to 540 nm (2 ± 1, 43 ± 6, 85 ± 25 and 540 ± 90 nm) in diameter. Here we show that the greatest effect on bacterial growth, biofilm formation, and AMP function impairment is found when exposed to the smallest particles. These results are attributed in large part to enhanced dissolution observed for the smallest particles and an increase in the amount of bioavailable iron. Furthermore, AMP function can be additionally impaired by adsorption onto nanoparticle surfaces. In particular, lysozyme readily adsorbs onto the nanoparticle surface which can lead to loss of peptide activity. Thus, this current study shows that co-exposure of nanoparticles and known pathogens can impact host innate immunity. Therefore, it is important that future studies be designed to further understand these types of impacts.
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Aerosol science and technology : the journal of the American Association for Aerosol Research, 2014
This study introduces spark discharge system (SDS) as a way to simulate welding fumes. The SDS wa... more This study introduces spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and concentration of the fume produced and the concentration of ozone (O3) and nitrogen oxides (NOX) were characterized. The number median diameter (NMD) and total number concentration (TNC) of fresh fume particles were ranged 10-23 nm and 3.1×10(7)-6×10(7) particles/cm(3), respectively. For fresh fume particles, the total mass concentration (TMC) measured gravimetrically ranged 85-760 μg/m(3). The size distribution was stable over a period of 12 h. The NMD and TNC of aged fume particles were ranged 81-154 nm and 1.5×10(6)-2.7×10(6) particles/cm(3), respectively. The composition of the aged fume particles was dominated by Fe and O with an estimated stoichiometry between that of Fe2O3 and Fe3O4. Concentrations of O3 and NOX were ranged 0.07-2.2 ppm and 1-20 ppm, respective...
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The Analyst, 2014
Given the importance of nanoparticle surface composition in nanotoxicology, analytical tools that... more Given the importance of nanoparticle surface composition in nanotoxicology, analytical tools that can probe nanoparticle surfaces in aqueous media are crucial but remain limited. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is a technique capable of in situ characterization of the liquid-solid interface to probe surface adsorption on nanoparticle surfaces in environmentally and biologically relevant media. Furthermore, given that the interfacial region in these media is dynamic, ATR-FTIR spectroscopy facilitates monitoring these dynamics by interrogating a layer of immobilized nanoparticles coated on the ATR element while changing the overlying aqueous phase. The molecular information acquired from this technique allows for the determination of the adsorption mode, including conformational and structural changes of the coordinating ligand, and can directly measure ligand displacement reactions. Furthermore, in some cases, ATR-FTIR spectroscopy can be used as a quantitative surface analytical tool. In this article, we briefly review the fundamentals of the technique and then provide several examples of using ATR-FTIR spectroscopy to probe nanoparticle surfaces in general with respect to: (i) the adsorption of different environmentally and biologically relevant coordinating ligands; (ii) competitive ligand adsorption and; (iii) the determination of kinetic and thermodynamic parameters. We have also investigated surface adsorption of TiO2 nanoparticles in different biological media typically used for toxicity studies and show that the surface composition of TiO2 nanoparticles depends to a large extent on the composition of the medium due to surface adsorption. This result has important implications for the interpretation of toxicity data as well as inter-comparisons between toxicity studies.
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Nanotechnology, 2013
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Langmuir, 2012
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Langmuir, 2011
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Journal of the American Chemical Society, 2010
Citric acid plays an important role as a stabilizer in several nanomaterial syntheses and is a co... more Citric acid plays an important role as a stabilizer in several nanomaterial syntheses and is a common organic acid found in nature. Here, the adsorption of citric acid onto TiO(2) anatase nanoparticles with a particle diameter of ca. 4 nm is investigated at circumneutral and acidic pHs. This study focuses on both the details of the surface chemistry of citric acid on TiO(2), including measurements of surface coverage and speciation, and its impact on nanoparticle behavior. Using macroscopic and molecular-based probes, citric acid adsorption and nanoparticle interactions are measured with quantitative solution phase adsorption measurements, attenuated total reflection-FTIR spectroscopy, dynamic light scattering techniques, and zeta-potential measurements as a function of solution pH. The results show that surface coverage is a function of pH and decreases with increasing pH. Surface speciation differs from the bulk solution and is time dependent. After equilibration, the fully deprotonated citrate ion is present on the surface regardless of the highly acidic solution pH indicating pK(a) values of surface adsorbed species are lower than those in solution. Nanoparticle interactions are also probed through measurements of aggregation and the data show that these interactions are complex and depend on the detailed interplay between bulk solution pH and surface chemistry.
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Journal of Environmental Monitoring, 2011
Metal and metal oxide nanomaterials are found in many consumer products for use in a wide range o... more Metal and metal oxide nanomaterials are found in many consumer products for use in a wide range of applications including catalysis, sensors and contaminant remediation. Because of the extensive use of metal-based nanomaterials, there are concerns that these materials have the potential to get into the environment sometime during production, distribution, use and/or disposal. In particular, there exists the potential that they will make their way into water systems, e.g. drinking water systems, ground water systems, estuaries and lakes. In this review, some of the uncertainties in understanding nanoparticle behavior, which is often due to a lack of fundamental knowledge of the surface structure and surface energetics for very small particles, are discussed. Although classical models may provide guidance for understanding dissolution and aggregation of nanoparticles in water, it is the detailed surface structure and surface chemistry that are needed to accurately describe the surface free energy, a large component of the total free energy, in order to fully understand these processes. Without this information, it is difficult to develop a conceptual framework for understanding the fate, transport and potential toxicity of nanomaterials. Needed research areas to fill this void are discussed.
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Environmental Science & Technology, 2012
Copper nanomaterials are being used in a large number of commercial products because these materi... more Copper nanomaterials are being used in a large number of commercial products because these materials exhibit unique optical, magnetic, and electronic properties. Metallic copper nanoparticles, which often have a thin surface oxide layer, can age in the ambient environment and become even more oxidized over time. These aged nanoparticles will then have different properties compared to the original nanoparticles. In this study, we have characterized three different types of copper-based nanoparticle (NP) samples designated as Cu(new) NPs, Cu(aged) NPs, and CuO NPs that differ in the level of oxidation. The solution phase behavior of these three copper-based nanoparticle samples is investigated as a function of pH and in the presence and absence of two common, complexing organic acids, citric and oxalic acid. The behavior of these three copper-based NP types shows interesting differences. In particular, Cu(aged) NPs exhibit unique chemistry including oxide phases that form and surface adsorption properties. Overall, the current study provides some insights into the impacts of nanoparticle aging and how the physicochemical characteristics and reactivity of nanomaterials can change upon aging.
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Environmental Health Perspectives, 2013
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Environ. Sci.: Nano, 2015
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Papers by Imali Mudunkotuwa