Importance of a Nanoscience Approach in the Understanding of Major Aqueous Contamination Scenarios: Case Study from a Recent Coal Ash Spill

A coal ash spill that occurred from an ash impoundment pond into the Dan River, North Carolina, provided a unique opportunity to study the significance and role of naturally occurring and incidental nanomaterials associated with contaminant distribution from a large-scale, acute aquatic contamination event. Besides traditional measurements of bulk watercolumn and sediment metal concentrations, the nanoparticle (NP) analyses are based on cross-flow ultrafiltration (CFUF) and advanced transmission electron microscopy (TEM) techniques. A drain pipe fed by coal ash impoundment seepage showed a high level of arsenic, with concentrations many times over the EPA limit. The majority of the arsenic was found sorbed to large aggregates dominated by incidental iron oxyhydroxide (ferrihydrite) NPs, while the remainder of the arsenic was truly dissolved. These ferrihydrites were probably formed in situ where Fe­(II) was leached through subsurface flowpaths into an aerobic environment, and further act as a significant contributor to the elevated As concentrations in downstream sediments after the spill. In addition, we discovered and describe a photocatalytic nano-TiO₂ phase (anatase) present in the coal ash impacted river water that was also carrying/transporting transition metals (Cu, Fe), which may also have environmental consequences

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

Transformation of Cerium Oxide Nanoparticles from a Diesel Fuel Additive during Combustion in a Diesel Engine

Nanoscale cerium oxide is used as a diesel fuel additive to reduce particulate matter emissions and increase fuel economy, but its fate in the environment has not been established. Cerium oxide released as a result of the combustion of diesel fuel containing the additive Envirox, which utilizes suspended nanoscale cerium oxide to reduce particulate matter emissions and increase fuel economy, was captured from the exhaust stream of a diesel engine and was characterized using a combination of bulk analytical techniques and high resolution transmission electron microscopy. The combustion process induced significant changes in the size and morphology of the particles; ∼15 nm aggregates consisting of 5−7 nm faceted crystals in the fuel additive became 50–300 nm, near-spherical, single crystals in the exhaust. Electron diffraction identified the original cerium oxide particles as cerium­(IV) oxide (CeO₂, standard FCC structure) with no detectable quantities of Ce­(III), whereas in the exhaust the ceria particles had additional electron diffraction reflections indicative of a CeO₂ superstructure containing ordered oxygen vacancies. The surfactant coating present on the cerium oxide particles in the additive was lost during combustion, but in roughly 30% of the observed particles in the exhaust, a new surface coating formed, approximately 2–5 nm thick. The results of this study suggest that pristine, laboratory-produced, nanoscale cerium oxide is not a good substitute for the cerium oxide released from fuel-borne catalyst applications and that future toxicity experiments and modeling will require the use/consideration of more realistic materials

Environmental Risk Implications of Metals in Sludges from Waste Water Treatment Plants: The Discovery of Vast Stores of Metal-Containing Nanoparticles

Nanoparticle (NP) assessment in sludge materials, although of growing importance in eco- and biotoxicity studies, is commonly overlooked and, at best, understudied. In the present study, sewage sludge samples from across the mega-city of Shanghai, China were investigated for the first time using a sequential extraction method coupled with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) to quantify the abundance of metal-containing NPs in the extraction fractions and transmission electron microscopy to specifically identify the nanophases present. In general, most sludges observed showed high concentrations of Cr, Cu, Cd, Ni, Zn, and Pb, exceeding the maximum permitted values in the national application standard of acid soil in China. NPs in these sludges contribute little to the volume and mass but account for about half of the total particle number. Based on electron microscopy techniques, various NPs were further identified, including Ti-, Fe-, Zn-, Sn-, and Pb-containing NPs. All NPs, ignored by traditional metal risk evaluation methods, were observed at a concentration of 10⁷ −10¹¹ particles/g within the bioavailable fraction of metals. These results indicate the underestimate or misestimation in evaluating the environmental risks of metals based on traditional sequential extraction methods. A new approach for the environmental risk assessment of metals, including NPs, is urgently needed