Robert D. Willis

Release of Silver from Nanotechnology-Based Consumer Products for Children

We assessed the potential for childrens exposure to bioavailable silver during the realistic use of selected nanotechnology-based consumer products (plush toy, fabric products, breast milk storage bags, sippy cups, cleaning products, humidifiers, and humidifier accessory). We measured the release of ionic and particulate silver from products into water, orange juice, milk formula, synthetic saliva, sweat, and urine (1:50 product to liquid mass ratio); into air; and onto dermal wipes. Of the liquid media, sweat and urine yielded the highest amount of silver release, up to 38% of the silver mass in products; tap water yielded the lowest amount, ≤1.5%. Leaching from a blanket into sweat plateaued within 5 min, with less silver released after washing. Between 0.3 and 23 μg m(-2) of silver transferred from products to wipes. Aerosol concentrations were not significantly elevated during product use. Fabrics, a plush toy, and cleaning products were most likely to release silver. Silver leached mainly via dissolution and was facilitated in media with high salt concentrations. Levels of silver to which children may potentially be exposed during the normal use of these consumer products is predicted to be low, and bioavailable silver is expected to be in ionic rather than particulate form.

An environmental scoping study in the Lower Rio Grande Valley of Texas — III. Residential microenvironmental monitoring for air, house dust, and soil

A principal aspect of the 1993 Lower Rio Grande Valley Environmental Scoping Study was the analysis and interpretation of residential air, household dust, and soil pollutant concentration data for exposure assessments. Measurements included respirable particulate matter (PM2.5), volatile organic compounds (VOCs), pesticides, and polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor air. Household dust, road dust, and yard soil were analyzed for elements, pesticides, and PAHs. Nine residences were monitored for three weeks in the spring of 1993. Additional monitoring was conducted at six of the nine residences for ten days the following summer. Generally good agreement was found between outdoor residential air and same-species measurements collected concurrently at a non-residential central site in Brownsville, TX (Ellenson et al. 1997) for fine particulate matter, elements, and VOCs indicating the dominance of regional influences. PM2.5 mass and element concentrations in residential indoor and outdoor air were generally higher in the summer than in the spring. Indoor air concentrations of many species were higher than outdoor air concentrations and were attributed to household activities, ventilation of residences, and track-in of dislodged soils. Evidence of agricultural activities was noted in the occurrence of crop-related pesticides (e.g., malathion and chlorpyrifos) in indoor and outdoor air. Concentrations of common household pesticides (e.g., chlordane, chlorpyrifos, diazinon, heptachlor, and propoxur) were generally higher indoors than outdoors and were also present in house dust. Seasonal comparisons of pesticides and PAHs were also presented using matched residences in spring and summer; VOCs also may have indicated seasonal effects. VOCs (notably propane and butane isomers) and PAHs were higher indoors, presumably due to cooking-related activities.

Single-particle SEM-EDX analysis of iron-containing coarse particulate matter in an urban environment: sources and distribution of iron within Cleveland, Ohio.

The physicochemical properties of coarse-mode, iron-containing particles and their temporal and spatial distributions are poorly understood. Single-particle analysis combining X-ray elemental mapping and computer-controlled scanning electron microscopy (CCSEM-EDX) of passively collected particles was used to investigate the physicochemical properties of iron-containing particles in Cleveland, OH, in summer 2008 (Aug-Sept), summer 2009 (July-Aug), and winter 2010 (Feb-March). The most abundant classes of iron-containing particles were iron oxide fly ash, mineral dust, NaCl-containing agglomerates (likely from road salt), and Ca-S containing agglomerates (likely from slag, a byproduct of steel production, or gypsum in road salt). The mass concentrations of anthropogenic fly ash particles were highest in the Flats region (downtown) and decreased with distance away from this region. The concentrations of fly ash in the Flats region were consistent with interannual changes in steel production. These particles were observed to be highly spherical in the Flats region, but less so after transport away from downtown. This change in morphology may be attributed to atmospheric processing. Overall, this work demonstrates that the method of passive collection with single-particle analysis by electron microscopy is a powerful tool to study spatial and temporal gradients in components of coarse particles. These gradients may correlate with human health effects associated with exposure to coarse-mode particulate matter.

Evaluation of Computer-Controlled Scanning Electron Microscopy Applied to an Ambient Urban Aerosol Sample

Concerns about the environmental and public health effects of particulate matter (PM) have stimulated interest in analytical techniques capable of measuring the size and chemical composition of individual aerosol particles. Computer-controlled scanning electron microscopy (CCSEM) coupled with energy-dispersive X-ray analysis (EDX) allows automated analysis of particle size, chemistry, and particle classification. In combination with manual SEM and bulk analytical techniques such as X-ray fluorescence, CCSEM can be a valuable tool for characterizing individual ambient particles and determining sources of ambient PM. The goal of this study was to examine several issues related to the quality and validity of CCSEM data. These included the stability of unattended CCSEM for multihour runs, the number of particles that must be analyzed in order to yield representative results, and errors associated with CCSEM. CCSEM was applied to the analysis of a 24 h ambient particle sample collected in Baltimore, MD. The coarse-fraction sample (PM10-2.5) was collected with a dichotomous sampler on a polycarbonate filter. A total of 2819 particles in 78 randomly selected fields of view were analyzed by CCSEM during an unattended 8 h run. Particle diameter, aspect ratio, particle location, X-ray counts for 20 elements, and digital images of each particle and its field of view were stored. The average number of particles per field (N/F), average particle diameter (Dave), average mass loading per field (Mave), and average particle composition were calculated for subsets of the data and compared against results for the full data set in order to assess the stability of the CCSEM analysis over time and the number of particles needed to obtain representative results. These comparisons demonstrated excellent stability of CCSEM over the 8 h run. Physical properties (represented by N/F, Dave, and Mave) of the sample were well characterized by analyzing approximately 360 particles. Chemical properties of the sample (average elemental composition and major chemical class abundances) converged to within a few percent of their final values after analyzing about 1000 particles. However, for many purposes several hundred particles may provide adequate characterization. Convergence of minor class abundances was limited by statistical fluctuations as the number of particles populating a class became very small. Manual review of the CCSEM data identified errors associated with CCSEM due to missed particles, overlapping particles, contrast artifacts, sizing errors, and heterogeneous particles. Most errors could be corrected or eliminated during manual off-line review of the data or avoided by maintaining a proper particle loading on the filter.

Characterization of silver nanoparticles in selected consumer products and its relevance for predicting children’s potential exposures

Due to their antifungal, antibacterial, antiviral, and antimicrobial properties, silver nanoparticles (AgNPs) are used in consumer products intended for use by children or in the home. Children may be especially affected by the normal use of consumer products because of their physiological functions, developmental stage, and activities and behaviors. Despite much research to date, childrens potential exposures to AgNPs are not well characterized. Our objectives were to characterize selected consumer products containing AgNPs and to use the data to estimate a childs potential non-dietary ingestion exposure. We identified and cataloged 165 consumer products claiming to contain AgNPs that may be used by or near children or found in the home. Nineteen products (textile, liquid, plastic) were selected for further analysis. We developed a tiered analytical approach to determine silver content, form (particulate or ionic), size, morphology, agglomeration state, and composition. Silver was detected in all products except one sippy cup body. Among products in a given category, silver mass contributions were highly variable and not always uniformly distributed within products, highlighting the need to sample multiple areas of a product. Electron microscopy confirmed the presence of AgNPs. Using this data, a childs potential non-dietary ingestion exposure to AgNPs when drinking milk formula from a sippy cup is 1.53 μg Ag/kg. Additional research is needed to understand the number and types of consumer products containing silver and the concentrations of silver in these products in order to more accurately predict childrens potential aggregate and cumulative exposures to AgNPs.

Satellite Remote Sensing for Developing Time and Space Resolved Estimates of Ambient Particulate in Cleveland, OH.

This article empirically demonstrates the use of fine resolution satellite-based aerosol optical depth (AOD) to develop time and space resolved estimates of ambient particulate matter (PM) ≤2.5 μm and ≤10 μm in aerodynamic diameters (PM2.5 and PM10, respectively). AOD was computed at three different spatial resolutions, i.e., 2 km (means 2 km × 2 km area at nadir), 5 km, and 10 km, by using the data from MODerate Resolution Imaging Spectroradiometer (MODIS), aboard the Terra and Aqua satellites. Multiresolution AOD from MODIS (AODMODIS) was compared with the in situ measurements of AOD by NASAs AErosol RObotic NETwork (AERONET) sunphotometer (AODAERONET) at Bondville, IL, to demonstrate the advantages of the fine resolution AODMODIS over the 10-km AODMODIS, especially for air quality prediction. An instrumental regression that corrects AODMODIS for meteorological conditions was used for developing a PM predictive model. The 2-km AODMODIS aggregated within 0.025° and 15-min intervals shows the best association with the in situ measurements of AODAERONET. The 2-km AODMODIS seems more promising to estimate time and space resolved estimates of ambient PM than the 10-km AODMODIS, because of better location precision and a significantly greater number of data points across geographic space and time. Utilizing the collocated AODMODIS and PM data in Cleveland, OH, a regression model was developed for predicting PM for all AODMODIS data points. Our analysis suggests that the slope of the 2-km AODMODIS (instrumented on meteorological conditions) is close to unity with the PM monitored on the ground. These results should be interpreted with caution, because the slope of AODMODIS ranges from 0.52 to 1.72 in the site-specific models. In the cross validation of the overall model, the root mean square error (RMSE) of PM10 was smaller (2.04 μg/m3 in overall model) than that of PM2.5 (2.5 μg/m3). The predicted PM in the AODMODIS data (∼2.34 million data points) was utilized to develop a systematic grid of daily PM at 5-km spatial resolution with the aid of spatiotemporal Kriging.

A review of selected engineered nanoparticles in the atmosphere: sources, transformations, and techniques for sampling and analysis.

Abstract A state-of-the-science review was undertaken to identify and assess sampling and analysis methods to detect and quantify selected nanomaterials (NMs) in the ambient atmosphere. The review is restricted to five types of NMs of interest to the Office of Research and Development Nanomaterial Research Strategy (US Environmental Protection Agency): cerium oxide, titanium dioxide, carbon nanostructures (carbon nanotubes and fullerenes), zero-valent iron, and silver nanoparticles. One purpose was determining the extent to which present-day ultrafine sampling and analysis methods may be sufficient for identifying and possibly quantifying engineered NMs (ENMs) in ambient air. Conventional sampling methods for ultrafines appear to require modifications. For cerium and titanium, background levels from natural sources make measurement of ENMs difficult to quantify. In cases where field studies have been performed, identification from bulk analysis samples have been made. Further development of methods is needed to identify these NMs, especially in specific size fractions of ambient aerosols.

Impact of Mine Waste on Airborne Respirable Particulates in Northeastern Oklahoma, United States

Abstract Atmospheric dispersion of particles from mine waste is potentially an important route of human exposure to metals in communities close to active and abandoned mining areas. This study assessed sources of mass and metal concentrations in two size fractions of respirable particles using positive matrix factorization (U.S. Environmental Protection Agency [EPA] PMF 3.0). Weekly integrated samples of particulate matter (PM) 10 µm in aerodynamic diameter or less (PM10) and fine PM (PM2.5, or PM <2.5 µm in aerodynamic diameter) were collected at three monitoring sites, varying distances (0.5–20 km) from mine waste piles, for 58 consecutive weeks in a former lead (Pb) and zinc (Zn) mining region. Mean mass concentrations varied significantly across sites for coarse PM (PM10–PM2.5) but not PM2.5 particles. Concentrations of Pb and Zn significantly decreased with increasing distance from the mine waste piles in PM10–PM2.5 (P < 0.0001) and PM2.5 (P < 0.0005) fractions. Source apportionment analyses deduced five sources contributing to PM2.5 (mobile source combustion, secondary sulfates, mine waste, crustal/soil, and a source rich in calcium [Ca]) and three sources for the coarse fraction (mine waste, crustal/soil, and a Ca-rich source). In the PM2.5 fraction, mine waste contributed 1–6% of the overall mass, 40% of Pb, and 63% of Zn. Mine waste impacts were more apparent in the PM10–PM2.5 fraction and contributed 4–39% of total mass, 88% of Pb, and 97% of Zn. Percent contribution of mine waste varied significantly across sites (P < 0.0001) for both size fractions, with highest contributions in the site closest to the mine waste piles. Seasonality, wind direction, and concentrations of the Ca-rich source were also associated with levels of ambient aerosols from the mine waste source. Scanning electron microscopy results indicated that the PMF-identified mine waste source is mainly composed of Zn-Pb agglomerates on crustal particles in the PM10–PM2.5 fraction. In conclusion, the differential impacts of mine waste on respirable particles by size fraction and location should be considered in future exposure evaluations.

Near-Road Modeling and Measurement of Cerium-Containing Particles Generated by Nanoparticle Diesel Fuel Additive Use

Cerium oxide nanoparticles (nCe) are used as a fuel-borne catalyst in diesel engines to reduce particulate emissions, yet the environmental and human health impacts of the exhaust particles are not well understood. To bridge the gap between emission measurements and ambient impacts, size-resolved measurements of particle composition and mass concentration have been performed in Newcastle-upon-Tyne, United Kingdom, where buses have used an nCe additive since 2005. These observations show that the noncrustal cerium fraction thought to be associated with the use of nCe has a mass concentration ∼ 0.3 ng m(-3) with a size distribution peaking at 100-320 nm in aerodynamic diameter. Simulations with a near-roadway multicomponent sectional aerosol dynamic model predict that the use of nCe additives increases the number concentration of nuclei mode particles (<50 nm in diameter) while decreasing the total mass concentration. The near-road model predicts a downwind mass size distribution of cerium-containing particles peaking at 150 nm in aerodynamic diameter, a value similar to that measured for noncrustal cerium in Newcastle. This work shows that both the emission and atmospheric transformation of cerium-containing particles needs to be taken into account by regional modelers, exposure scientists, and policymakers when determining potential environmental and human health impacts.

Chemical Characterization of Outdoor and Subway Fine (PM2.5–1.0) and Coarse (PM10–2.5) Particulate Matter in Seoul (Korea) by Computer-Controlled Scanning Electron Microscopy (CCSEM)

Outdoor and indoor (subway) samples were collected by passive sampling in urban Seoul (Korea) and analyzed with computer-controlled scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (CCSEM-EDX). Soil/road dust particles accounted for 42%–60% (by weight) of fine particulate matter larger than 1 µm (PM2.5–1.0) in outdoor samples and 18% of PM2.5–1.0 in subway samples. Iron-containing particles accounted for only 3%–6% in outdoor samples but 69% in subway samples. Qualitatively similar results were found for coarse particulate matter (PM10–2.5) with soil/road dust particles dominating outdoor samples (66%–83%) and iron-containing particles contributing most to subway PM10–2.5 (44%). As expected, soil/road dust particles comprised a greater mass fraction of PM10–2.5 than PM2.5–1.0. Also as expected, the mass fraction of iron-containing particles was substantially less in PM10–2.5 than in PM2.5–1.0. Results of this study are consistent with known emission sources in the area and with previous studies, which showed high concentrations of iron-containing particles in the subway compared to outdoor sites. Thus, passive sampling with CCSEM-EDX offers an inexpensive means to assess PM2.5–1.0 and PM10-2.5 simultaneously and by composition at multiple locations.