An In Situ Method for Sizing Insoluble Residues in Precipitation and Other Aqueous Samples

Wildfire Smoke Influence on Cloud Water Chemical Composition at Whiteface Mountain, New York

Wildfires significantly impact air quality and climate, including through the production of aerosols that can nucleate cloud droplets and participate in aqueous-phase reactions. Cloud water was collected during the summer months (June-September) of 2010-2017 at Whiteface Mountain, New York and examined for biomass burning influence. Cloud water samples were classified by their smoke influence based on backward air mass trajectories and satellite-detected smoke. A total of 1,338 cloud water samples collected over 485 days were classified by their probability of smoke influence, with 49% of these days categorized as having moderate to high probability of smoke influence. Carbon monoxide and ozone levels were enhanced during smoke influenced days at the summit of Whiteface Mountain. Smoke-influenced cloud water samples were characterized by enhanced concentrations of potassium, sulfate, ammonium, and total organic carbon, compared to samples lacking identified influence. Five cloud water samples were examined further for the presence of dissolved organic compounds, insoluble particles, and light-absorbing components. The five selected cloud water samples contained the biomass burning tracer levoglucosan at 0.02-0.09 μM. Samples influenced by air masses that remained aloft, above the boundary layer during transport, had lower insoluble particle concentrations, larger insoluble particle diameters, and larger oxalate:sulfate ratios, suggesting cloud processing had occurred. These findings highlight the influence that local and long-range transported smoke have on cloud water composition.

Nanoparticle Digestion Simulator Reveals pH-Dependent Aggregation in the Gastrointestinal Tract

Determining the physicochemical properties of ingested nanoparticles within the gastrointestinal tract (GIT) is critical for evaluating the impact of environmental exposure and potential for nanoparticle drug delivery. However, it is challenging to predict nanoparticle physicochemical properties at the point of intestinal absorption due to the changing chemical environments within the GIT. Herein, a dynamic nanoparticle digestion simulator (NDS) was constructed to examine nanoparticle evolution due to changing pH and salt concentrations in the stomach and upper intestine. This multicompartment, flow-through system simulates digestion by transferring gastrointestinal fluids and digestive secretions at physiologically relevant time scales and flow rates. Pronounced differences in aggregation and aggregate stability were observed with silver nanoparticles (citrate-coated) with an initial hydrodynamic diameter (D_h) of 24.6 ± 0.4 nm examined under fasted (pH 2) and fed (pH 5) gastric conditions using nanoparticle tracking analysis (NTA) for size distributions and transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM-EDX) for morphology and elemental composition. Under fasted stomach conditions, particles aggregated to D_h = 130 ± 10 nm and remained as large aggregates in the upper intestinal compartments (duodenum and jejunum) ending with D_h = 110 ± 20 nm and a smaller mode at 59 ± 8 nm. In contrast, under fed conditions, nanoparticles aggregated to 60 ± 10 nm in the stomach, then disaggregated to individual nanoparticles (26 ± 2 nm) in the intestinal compartments. The NDS provides an analytical approach for studying nanoparticle physicochemical modifications within the GIT and the impacts of intentionally and unintentionally ingested nanoparticles.

Harmful Algal Bloom Toxins in Aerosol Generated from Inland Lake Water

Harmful algal blooms (HABs) caused by cyanobacteria in freshwater environments produce toxins (e.g., microcystin) that are harmful to human and animal health. HAB frequency and intensity are increasing with greater nutrient runoff and a warming climate. Lake spray aerosol (LSA) released from freshwater lakes has been identified on lakeshores and after transport inland, including from lakes with HABs, but little is known about the potential for HAB toxins to be incorporated into LSA. In this study, freshwater samples were collected from two lakes in Michigan: Mona Lake during a severe HAB with microcystin concentrations (>200 μg/L) well above the Environmental Protection Agency (EPA) recommended "do not drink" level (1.6 μg/L) and Muskegon Lake without a HAB (<1 μg/L microcystin). Microcystin toxins were identified in freshwater, as well as aerosol particles generated in the laboratory from Mona Lake water by liquid chromatography-tandem mass spectrometry (LC-MS/MS) at atmospheric concentrations up to 50 ± 20 ng/m3. Enrichment of hydrophobic microcystin congeners (e.g., microcystin-LR) was observed in aerosol particles relative to bulk freshwater, while enrichment of hydrophilic microcystin (e.g., microcystin-RR) was lower. As HABs increase in a warming climate, understanding and quantifying the emissions of toxins into the atmosphere is crucial for evaluating the health consequences of HABs.

Protein Corona-Induced Modification of Silver Nanoparticle Aggregation in Simulated Gastric Fluid

Due to their widespread incorporation into a range of biomedical and consumer products, the ingestion of silver nanoparticles (AgNPs) is of considerable concern to human health. However, the extent to which AgNPs will be modified within the gastric compartment of the gastrointestinal tract is still poorly understood. Studies have yet to fully evaluate the extent of physicochemical changes to AgNPs in the presence of biological macromolecules, such as pepsin, the most abundant protein in the stomach, or the influence of AgNPs on protein structure and activity. Herein, AgNPs of two different sizes and surface coatings (20 and 110 nm, citrate or polyvinylpyrrolidone) were added to simulated gastric fluid (SGF) with or without porcine pepsin at three pHs (2.0, 3.5, and 5.0), representing a range of values between preprandial (fasted) and postprandial (fed) conditions. Rapid increases in diameter were observed for all AgNPs, with a greater increase in diameter in the presence of pepsin, indicating that pepsin facilitated AgNPs aggregation. AgNPs interaction with pepsin only minimally reduced the protein's proteolytic functioning capability, with the greatest inhibitory effect caused by smaller (20 nm) particles of both coatings. No changes in pepsin secondary structural elements were observed for the different AgNPs, even at high particle concentrations. This research highlights the size-dependent kinetics of nanoparticle aggregation or dissolution from interaction with biological elements such as proteins in the gastrointestinal tract. Further, these results demonstrate that, in addition to mass, knowing the chemical form and aggregation state of nanoparticles is critical when evaluating toxicological effects from nanoparticle exposure in the body.

Nanomaterial size distribution analysis via liquid nebulization coupled with ion mobility spectrometry (LN-IMS)

Ion mobility spectrometry is used for nanomaterial size distribution measurement without the need of electrospray based aerosolization.

Rapid Kinetics of Size and pH-Dependent Dissolution and Aggregation of Silver Nanoparticles in Simulated Gastric Fluid

As silver nanoparticles (AgNPs) are used in a wide array of commercial products and can enter the human body through oral exposure, it is important to understand the fundamental physical and chemical processes leading to changes in nanoparticle size under the conditions of the gastrointestinal (GI) tract. Rapid AgNP growth was observed using nanoparticle tracking analysis with 30 s resolution over a period of 17 min in simulated gastric fluid (SGF) to explore rapid kinetics as a function of pH (SGF at pH 2, 3.5, 4.5 and 5), size (20 and 110 nm AgNPs), and nanoparticle coating (citrate and PVP). Growth was observed for 20 nm AgNP at each pH, decreasing in rate with increasing pH, with the kinetics shifting from second-order to first-order. The 110 nm AgNP showed growth at ≤3.5 pH, with no growth observed at higher pH. This behavior can be explained by the generation of Ag⁺ in acidic environments, which precipitates with Cl^-, leading to particle growth and facilitating particle aggregation by decreasing their electrostatic repulsion in solution. These results highlight the need to further understand the importance of initial size, physicochemical properties, and kinetics of AgNPs after ingestion to assess potential toxicity.