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  1. Free, publicly-accessible full text available December 1, 2024
  2. Home dust samples were collected from the surface of heating, ventilation, and air conditioning (HVAC) filters from eleven homes at different locations in Columbia, South Carolina, USA. Bulk metal concentrations in the dusts were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Size-based elemental distributions in the <450 nm particles were determined by asymmetrical flow-field flow fractionation (AF4) coupled to ICP-MS. The bulk Ti/Nb ratios are generally higher (up to 5609) than the natural background ratios ( e.g. , 320), indicating contamination of home dusts with TiO 2 -engineered particles. Size-based Ti/Nb ratios in the <450 nm fraction are similar to the natural background ratio, indicating a natural origin of Ti-bearing particles in this size fraction, and subsequently that anthropogenic Ti-bearing particles (TiO 2 ) are associated with particles >450 nm either due to aggregation or to their release as large particles. The concentrations of TiO 2 -engineered particles were estimated by mass balance calculations using total Ti concentrations and increases in Ti/Nb ratios above the natural background ratio. They vary between 0 and 13 300 mg TiO 2 kg −1 . The upper crustal-normalized rare earth element pattern indicates a positive La and Ce anomaly. The size of the cerium and lanthanum anomalies varies from 0.8 to 1.6 and 0.7 to 3.95, respectively, indicating contamination of several home dusts with Ce and La. The concentrations of bulk anthropogenic Ce and La were estimated based on mass balance calculations and anomaly size and varied between 0 and 5.7 ± 2.2 mg Ce kg −1 and 0 and 21.1 ± 7.4 mg La kg −1 , respectively. Size-based Ce/La ratios in the <450 nm fraction are lower than the natural background ratio, indicating contamination of this size fraction with nanosized La-bearing particles. Anthropogenic Ti and La concentrations in home dust are attributed to releases from paint during home renovation. This implies that exposure of construction workers to Ti- and La-bearing particles during home renovation may potentially pose human health risks. 
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    Free, publicly-accessible full text available May 18, 2024
  3. Wildfires are increasing in size, frequency, and intensity, releasing increased amounts of contaminants, including magnetic particles, into the surrounding environment. The aim of this paper is to develop a sensing method for the detection and quantification of magnetic particles (MPs) in fire ash and fire runoff using a compact Time-Domain Nuclear Magnetic Resonance (TD-NMR) system. The system is made up of custom NMR electronics with a compact and rugged permanent magnet array designed to enable future deployment as an in situ sensor. A signal-to-noise ratio of 25 dB was measured for a single scan, and sufficient data can be acquired in one minute. A linear relationship with an R 2 value of 0.9699 was established between transverse relaxation rates and MP concentrations in ash samples. This was validated by testing known dilutions of pure magnetite particles and showing that they fit within the same linear curve. The developed approach was then applied to detect MPs in surface water, where changes in the relaxation rates as high as 400% were observed before and after a wildfire event. MPs were removed from the surface water using a magnetic particle separator to confirm that observed changes were solely due to the presence of MPs. The compact NMR system can be used as a simple and rapid approach to track and quantify the concentrations of magnetic particles released from fire ashes and also from other sources such as discharges from coal ash and other combustion ashes. 
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    Free, publicly-accessible full text available May 10, 2024
  4. Urban runoff is a significant source of pollutants, including incidental and engineered nanoparticles, to receiving surface waters. The aim of this study is to investigate the impact of urbanization on the concentrations of TiO 2 engineered particles in urban surface waters. The study area boundaries are limited to the Lower Saluda and Nicholas Creek-Broad River from upstream, and outlet of upper Congaree River in Columbia, South Carolina, United States from downstream. This sampling area captures a significant footprint of the urban area of the city of Columbia. Water samples were collected daily from four sites during two rain events. All samples were analyzed for total metal concentrations following acid digestion and for particle number concentration and elemental composition using single particle-inductively coupled plasma-time of flight-mass spectrometry (SP-ICP-TOF-MS). The Ti/Nb ratios in the Broad and Congaree River samples are generally higher than those of natural background ratios, indicating contamination of these two rivers with anthropogenic Ti-bearing particles. Clustering of multi-metal nanoparticles (mmNPs) demonstrated that Ti-bearing particles are distributed mainly among three clusters, FeTiMn, AlSiFe, and TiMnFe, which are typical of naturally occurring iron oxide, clay, and titanium oxide particles, indicating the absence of significant number of anthropogenic multi-element Ti-bearing particles. Thus, anthropogenic Ti-bearing particles are attributed to single-metal particles; that is pure TiO 2 particles. The total concentration of anthropogenic TiO 2 in the rivers was determined by mass balance calculation using bulk titanium concentration and increases in Ti/Nb above the natural background ratio. The concentration of anthropogenic TiO 2 increases following the order 0 to 24 μg L −1 in the Lower Saluda River <0 to 663 μg L −1 in the Broad River <43 to 1051 μg L −1 in Congaree River at Cayce <58 to 5050 μg L −1 in the Congaree River at Columbia. The concentration of anthropogenic TiO 2 increases with increases in urban runoff. The source of anthropogenic TiO 2 is attributed to diffuse urban runoff. This study demonstrates that diffuse urban runoff results in high concentrations of TiO 2 particles in urban surface waters during and following rainfall events which may pose increased risks to aquatic organisms during these episodic events. 
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  5. The increase in fires at the wildland–urban interface has raised concerns about the potential environmental impact of ash remaining after burning. Here, we examined the concentrations and speciation of iron-bearing nanoparticles in wildland–urban interface ash. Total iron concentrations in ash varied between 4 and 66 mg g −1 . Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy of bulk ash samples was used to quantify the relative abundance of major Fe phases, which were corroborated by transmission electron microscopy measurements. Maghemite (γ-(Fe 3+ ) 2 O 3 ) and magnetite (γ-Fe 2+ (Fe 3+ ) 2 O 4 ) were detected in most ashes and accounted for 0–90 and 0–81% of the spectral weight, respectively. Ferrihydrite (amorphous Fe( iii )–hydroxide, (Fe 3+ ) 5 HO 8 ·4H 2 O), goethite (α-Fe 3+ OOH), and hematite (α-Fe 3+ 2 O 3 ) were identified less frequently in ashes than maghemite and magnetite and accounted for 0–65, 0–54, and 0–50% of spectral weight, respectively. Other iron phases identified in ashes include wüstite (Fe 2+ O), zerovalent iron, FeS, FeCl 2 , FeCl 3 , FeSO 4 , Fe 2 (SO 4 ) 3 , and Fe(NO 3 ) 3 . Our findings demonstrate the impact of fires at the wildland–urban interface on iron speciation; that is, fires can convert iron oxides ( e.g. , maghemite, hematite, and goethite) to reduced iron phases such as magnetite, wüstite, and zerovalent iron. Magnetite concentrations ( e.g. , up to 25 mg g −1 ) decreased from black to gray to white ashes. Based on transmission electron microscopy (TEM) analyses, most of the magnetite nanoparticles were less than 500 nm in size, although larger particles were identified. Magnetite nanoparticles have been linked to neurodegenerative diseases as well as climate change. This study provides important information for understanding the potential environmental impacts of fires at the wildland–urban interface, which are currently poorly understood. 
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  6. Road dust particles including nanoparticles (NPs), with heterogeneous composition, are significant carriers of metals/metalloids and can be further transported into the atmosphere or surface runoff. However, their elemental composition remains poorly defined. In this study, seven road dust samples were collected from different areas in Shanghai, China and were analyzed for total metal concentrations, particle elemental composition and ratios, morphology, composition, and crystalline phases. Overall, the road dust particles were characterized by high concentrations of Fe, Ti, Al, Cr, Ci, V Ni, Cu, Zn, Sn, and Sb, which varied among the samples. Four potential sources of metals were identified using PCA analysis including natural sources, exhaust and non-exhaust emissions, and vehicle electronics. The bulk elemental ratios of Ti/Nb, Ti/Al, Ti/Fe, Pb/Nb, Sn/Nb and W/Nb in the road dust samples were higher than the corresponding reference ratios indicating that the road dust was contaminated with Ti, Pb, Sn, and W. Anthropogenic Ti, Pb, Sn and W were estimated by mass balance calculation and varied between 0.25 and 1.48 × 10 6 μg kg −1 , 0.19 and 1.21 × 10 5 μg kg −1 , 0.98 and 4.22 × 10 4 μg kg −1 , and 0.12 and 1.01 × 10 4 μg kg −1 , respectively. The number concentration of NPs was determined by SP-ICP-TOF-MS and was 0.66–3.3 × 10 10 particles per g for Ti-containing NPs, 0.23–1.51 × 10 10 particles per g for Pb-containing NPs, 0.28–3.10 × 10 9 particles per g for Sn-containing NPs, and 1.34–9.38 × 10 8 particles per g for W-containing NPs, respectively. TEM analysis further confirmed the occurrence of both natural and anthropogenic Ti- and W-containing NPs and the contamination of Pb- and Sn-containing NPs in Shanghai road dust. These NPs could originate from the non-exhaust emission of vehicles and coal combustion. Overall, this study provides a reliable comprehensive approach for the characterization of road dust particles and new insights into the nature of Ti-, Pb-, Sn-, and W-containing particles in dust samples. 
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