Eric P. Vejerano

Environmentally Persistent Free Radicals (EPFRs). 1. Generation of Reactive Oxygen Species in Aqueous Solutions

Reactive oxygen species (ROS) generated by environmentally persistent free radicals (EPFRs) of 2-monochlorophenol, associated with CuO/silica particles, were detected using the chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy. Yields of hydroxyl radical ((•)OH), superoxide anion radical (O(2)(•-)), and hydrogen peroxide (H(2)O(2)) generated by EPFR-particle systems were reported. Failure to trap superoxide radicals in aqueous solvent, formed from reaction of EPFRs with molecular oxygen, results from fast transformation of the superoxide to hydrogen peroxide. However, formation of superoxide as an intermediate product in hydroxyl radical formation in aprotic solutions of dimethyl sulfoxide (DMSO) and acetonitrile (AcN) was observed. Experiments with superoxide dismutase (SOD) and catalase (CAT) confirmed formation of superoxide and hydrogen peroxide, respectively, in the presence of EPFRs. The large number of hydroxyl radicals formed per EPFR and monotonic increase of the DMPO-OH spin adduct concentration with incubation time suggest a catalytic cycle of ROS formation.

Formation and Stabilization of Combustion-Generated Environmentally Persistent Free Radicals on an Fe(III)2O3/Silica Surface

Previous studies have shown environmentally persistent free radicals (EPFRs) form when chlorine- and hydroxy-substituted benzenes chemisorb on Cu(II)O-containing surfaces under postcombustion conditions. This paper reports the formation of EPFRs on silica particles containing 5% Fe(III)(2)O(3). The EPFRs are formed by the chemisorption of substituted aromatic molecular adsorbates on the metal cation center followed by electron transfer from the adsorbate to the metal ion at temperatures from 150 to 400 °C. Depending on the nature of the adsorbate and the temperature, two organic EPFRs were formed: a phenoxyl-type radical, which has a lower g-value of 2.0024-2.0040, and a second semiquinone-type radical, with a g-value of 2.0050-2.0065. Yields of EPFRs were ∼10× lower for iron than copper; however, the half-lives of EPFRs on iron ranged from 24 to 111 h, compared to the half-lives on copper of 27 to 74 min. The higher oxidation potential of Fe(III)(2)O(3) is believed to result in greater decomposition of the adsorbate, resulting in the lower EPFR yields, but increased stabilization of the EPFR once formed, resulting in the longer half-lives.

Formation and stabilization of combustion-generated, environmentally persistent radicals on Ni(II)O supported on a silica surface.

Previous studies have indicated environmentally persistent free radicals (EPFRs) are formed when hydroxyl- and chlorine-substituted aromatics chemisorbed on Cu(II)O and Fe(III)(2)O(3) surfaces and were stabilized through their interactions with the surface metal cation. The current study reports our laboratory investigation on the formation and stabilization of EPFRs on a Ni(II)O surface. The EPFRs were produced by the chemisorption of adsorbates on the supported metal oxide surface and transfer of an electron from the adsorbate to the metal center, resulting in reduction of the metal cation. Depending on the temperature and the nature of the adsorbate, more than one type of organic radical was formed. A phenoxyl-type radical, with g-value between 2.0029 and 2.0044, and a semiquinone-type radical, with g-value from 2.0050 to as high as 2.0081, were observed. The half-lives on Ni(II)O were long and ranged from 1.5 to 5.2 days, which were similar to what were observed on Fe(III)(2)O(3). The yields of the EPFRs formed on Ni(II)O were ~8× higher than on Cu(II)O and ~50× higher than on Fe(III)(2)O(3).

Characterization of particle emissions and fate of nanomaterials during incineration

As the use of nanotechnology in consumer products continues to grow, it is inevitable that some nanomaterials will end up in the waste stream and will be incinerated. Through laboratory-scale incineration of paper and plastic wastes containing nanomaterials, we assessed their effect on emissions of particulate matter (PM) and the effect of incineration on the nanomaterials themselves. The presence of nanomaterials did not significantly influence the particle number emission factor. The PM size distribution was not affected except at very high mass loadings (10 wt%) of the nanomaterial, in which case the PM shifted toward smaller sizes; such loadings are not expected to be present in many consumer products. Metal oxide nanomaterials reduced emissions of particle-bound polycyclic aromatic hydrocarbons. Most of the nanomaterials that remained in the bottom ash retained their original size and morphology but formed large aggregates. Only small amounts of the nanomaterials (0.023–180 mg g−1 of nanomaterial) partitioned into PM, and the emission factors of nanomaterials from an incinerator equipped with an electrostatic precipitator are expected to be low. However, a sustainable disposal method for nanomaterials in the bottom ash is needed, as a majority of them partitioned into this fraction and may thus end up in landfills upon disposal of the ash.

Oxidation of c60 aerosols by atmospherically relevant levels of o3.

Atmospheric processing of carbonaceous nanoparticles (CNPs) may play an important role in determining their fate and environmental impacts. This work investigates the reaction between aerosolized C60 and atmospherically relevant mixing ratios of O3 at differing levels of humidity. Results indicate that C60 is oxidized by O3 and forms a variety of oxygen-containing functional groups on the aerosol surface, including C60O, C60O2, and C60O3. The pseudo-first-order reaction rate between C60 and O3 ranges from 9 × 10(-6) to 2 × 10(-5) s(-1). The reaction is likely to be limited to the aerosol surface. Exposure to O3 increases the oxidative stress exerted by the C60 aerosols as measured by the dichlorofluorescein acellular assay but not by the uric acid, ascorbic acid, glutathione, or dithiothreitol assays. The initial prevalence of C60O and C60O2 as intermediate products is enhanced at higher humidity, as is the surface oxygen content of the aerosols. These results show that C60 can be oxidized when exposed to O3 under ambient conditions, such as those found in environmental, laboratory, and industrial settings.

Toxicity of particulate matter from incineration of nanowaste

Disposal of some nanomaterial-containing waste by incineration and the subsequent formation of particulate matter (PM) along with hazardous combustion by-products are inevitable. The effect of nanomaterials on the toxicity of the PM is unknown. We assessed the oxidative potential (OP) and toxicity of PM resulting from the incineration of pure nanomaterials and of paper and plastic wastes containing Ag, NiO, TiO2, ceria, C60, Fe2O3, or CdSe/ZnS quantum dots (CdSe QD) at mass loadings ranging from 0.1 wt% to 10 wt%. We measured reactive oxygen species (ROS) using the dichlorofluorescein assay, and we also measured consumption of ascorbic acid, dithiothreitol (DTT), glutathione (GSH), or uric acid antioxidants from raw and solvent-extracted PM, denoted “cleaned PM”. We determined cytotoxicity and genotoxicity of PM to A549 human lung epithelial cells with the WST-1 cell viability and histone immunofluorescence assays, respectively. In most cases, the presence of nanomaterials in the waste did not significantly affect the OP of PM; however, PM derived from waste containing Ag, TiO2, and C60 had elevated ROS response in the GSH and DTT assays. The ratio of reduced to oxidized glutathione was significantly higher for cleaned PM compared to raw PM for almost all nanomaterials at almost all concentrations, indicating that combustion by-products adsorbed on raw PM play an important role in determining OP. The presence of nanomaterials did not significantly modify the cytotoxicity or genotoxicity of the PM. Different antioxidants used to assess OP had varying sensitivity towards organic compounds v. metals in PM. The presence of these seven nanomaterials at low concentrations in the waste stream is not expected to exacerbate the hazard posed by PM that is produced by incineration.

Toxicity of engineered nanomaterials and their transformation products following wastewater treatment on A549 human lung epithelial cells

Graphical abstract

Aerosol microdroplets exhibit a stable pH gradient

Significance Aerosols with high water content (aerosol droplets) are ubiquitous and play a significant role in atmospheric chemistry and meteorology. However, directly measuring the pH of an individual aerosol droplet remains challenging due to its inaccessibility to pH electrodes. In this study, nanometer-sized pH probes were dispersed in droplets to report pH via surface-enhanced Raman spectroscopy. The droplet core exhibits higher pH than the bulk solution, suggesting the presence of a stable pH gradient. This in situ technique extends pH characterization to confined water environments and deepens our understanding of aerosol chemistry and the air/water interface. Suspended aqueous aerosol droplets (<50 µm) are microreactors for many important atmospheric reactions. In droplets and other aquatic environments, pH is arguably the key parameter dictating chemical and biological processes. The nature of the droplet air/water interface has the potential to significantly alter droplet pH relative to bulk water. Historically, it has been challenging to measure the pH of individual droplets because of their inaccessibility to conventional pH probes. In this study, we scanned droplets containing 4-mercaptobenzoic acid–functionalized gold nanoparticle pH nanoprobes by 2D and 3D laser confocal Raman microscopy. Using surface-enhanced Raman scattering, we acquired the pH distribution inside approximately 20-µm-diameter phosphate-buffered aerosol droplets and found that the pH in the core of a droplet is higher than that of bulk solution by up to 3.6 pH units. This finding suggests the accumulation of protons at the air/water interface and is consistent with recent thermodynamic model results. The existence of this pH shift was corroborated by the observation that a catalytic reaction that occurs only under basic conditions (i.e., dimerization of 4-aminothiophenol to produce dimercaptoazobenzene) occurs within the high pH core of a droplet, but not in bulk solution. Our nanoparticle probe enables pH quantification through the cross-section of an aerosol droplet, revealing a spatial gradient that has implications for acid-base–catalyzed atmospheric chemistry.

Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants

Environmentally persistent free radicals, EPFRs, exist in significant concentration in atmospheric particulate matter (PM). EPFRs are primarily emitted from combustion and thermal processing of organic materials, in which the organic combustion byproducts interact with transition metal-containing particles to form a free radical-particle pollutant. While the existence of persistent free radicals in combustion has been known for over half-a-century, only recently that their presence in environmental matrices and health effects have started significant research, but still in its infancy. Most of the experimental studies conducted to understand the origin and nature of EPFRs have focused primarily on nanoparticles that are supported on a larger micrometer-sized particle that mimics incidental nanoparticles formed during combustion. Less is known on the extent by which EPFRs may form on engineered nanomaterials (ENMs) during combustion or thermal treatment. In this critical and timely review, we summarize important findings on EPFRs and discuss their potential to form on pristine ENMs as a new research direction. ENMs may form EPFRs that may differ in type and concentration compared to nanoparticles that are supported on larger particles. The lack of basic data and fundamental knowledge about the interaction of combustion byproducts with ENMs under high-temperature and oxidative conditions present an unknown environmental and health burden. Studying the extent of ENMs on catalyzing EPFRs is important to address the hazards of atmospheric PM fully from these emerging environmental contaminants.

Influenza Virus Infectivity Is Retained in Aerosols and Droplets Independent of Relative Humidity

In contrast to previously published reports, we have detected sustained infectivity of aerosolized influenza viruses in respiratory mucus over a wide-range of relative humidity conditions, indicating a risk of airborne transmission in a broad range of environments.