The Impact of Particle Size, Relative Humidity, and Sulfur Dioxide on Iron Solubility in Simulated Atmospheric Marine Aerosols

Iron is a limiting nutrient in about half of the world’s oceans, and its most significant source is atmospheric deposition. To understand the pathways of iron solubilization during atmospheric transport, we exposed size segregated simulated marine aerosols to 5 ppm sulfur dioxide at arid (23 ± 1% relative humidity, RH) and marine (98 ± 1% RH) conditions. Relative iron solubility increased as the particle size decreased for goethite and hematite, while for magnetite, the relative solubility was similar for all of the fine size fractions (2.5–0.25 μm) investigated but higher than the coarse size fraction (10–2.5 μm). Goethite and hematite showed increased solubility at arid RH, but no difference (<i>p</i> > 0.05) was observed between the two humidity levels for magnetite. There was no correlation between iron solubility and exposure to SO₂ in any mineral for any size fraction. X-ray absorption near edge structure (XANES) measurements showed no change in iron speciation [Fe­(II) and Fe­(III)] in any minerals following SO₂ exposure. SEM-EDS measurements of SO₂-exposed goethite revealed small amounts of sulfur uptake on the samples; however, the incorporated sulfur did not affect iron solubility. Our results show that although sulfur is incorporated into particles via gas-phase processes, changes in iron solubility also depend on other species in the aerosol

Adsorption of <i>N</i>‑Nitrosodimethylamine Precursors by Powdered and Granular Activated Carbon

Activated carbon (AC) has been shown to remove precursors of halogenated disinfection byproducts. Granular and powdered activated carbon (GAC, PAC) were investigated for their potential to adsorb <i>N-</i>nitrosodimethylamine (NDMA) precursors from blends of river water and effluent from a wastewater treatment plant (WWTP). At bench scale, waters were exposed to lignite or bituminous AC, either as PAC in bottle point experiments or as GAC in rapid small-scale column tests (RSSCTs). NDMA formation potential (FP) was used as a surrogate for precursor removal. NDMA FP was reduced by 37, 59, and 91% with 3, 8, and 75 mg/L of one PAC, respectively, with a 4-h contact time. In RSSCTs and in full-scale GAC contactors, NDMA FP removal always exceeded that of the bulk dissolved organic carbon (DOC) and UV absorbance at 254 nm. For example, whereas DOC breakthrough exceeded 90% of its influent concentration after 10 000 bed volumes of operation in an RSSCT, NDMA FP was less than 40% of influent concentration after the same bed life of the GAC. At full or pilot scale, high NDMA FP reduction ranging from >60 to >90% was achieved across GAC contactors, dependent upon the GAC bed life and/or use of a preoxidant (chlorine or ozone). In all experiments, NDMA formation was not reduced to zero, which suggests that although some precursors are strongly sorbed, others are not. This is among the first studies to show that AC is capable of adsorbing NDMA precursors, but further research is needed to better understand NDMA precursor chemical properties (e.g., hydrophobicity, molecular size) and evaluate how best to incorporate this finding into full-scale designs and practice

Characterization of Food-Grade Titanium Dioxide: The Presence of Nanosized Particles

Titanium dioxide (TiO₂) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO₂ that is nanoscale, or the physical and chemical properties of TiO₂ that influence its human and environmental fate or toxicity. Instead of analyzing TiO₂ properties in complex food or environmental samples, we procured samples of food-grade TiO₂ obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO₂ that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO₂ are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO₂ samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO₂ aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO₂. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO₂ suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO₂ (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO₂. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO₂ could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO₂ was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO₂ than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO₂ contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO₂ is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO₂

Extraction and Quantification of Carbon Nanotubes in Biological Matrices with Application to Rat Lung Tissue

Extraction of carbon nanotubes (CNTs) from biological matrices such as rat lung tissue is integral to developing a quantification method for evaluating the environmental and human health exposure and toxicity of CNTs. The ability of various chemical treatment methods, including Solvable (2.5% sodium hydroxide/surfactant mixture), ammonium hydroxide, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, and proteinase K, to extract CNTs from rat lung tissue was evaluated. CNTs were quantified using programmed thermal analysis (PTA). Two CNTs were used to represent the lower (500 °C) and upper (800 °C) PTA limit of CNT thermal stability. The recovery efficiency of each of the eight chemical reagents evaluated was found to depend on the ability to (1) minimize oxidation of CNTs, (2) remove interfering background carbon from the rat lung tissue, and (3) separate the solid-phase CNTs from the liquid-phase dissolved tissue <i>via</i> centrifugation. A two-step extraction method using Solvable and proteinase K emerged as the optimal approach, enabling a recovery of 98 ± 15% of a 2.9 ± 0.19 μg CNT loading that was spiked into whole rat lungs. Due to its high yield and applicability to low organ burdens of nanomaterials, this extraction method is particularly well suited for <i>in vivo</i> studies to quantify clearance rates and retained CNTs in lungs and other organs

Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide

U.S. sewage sludges were analyzed for 58 regulated and nonregulated elements by ICP-MS and electron microscopy to explore opportunities for removal and recovery. Sludge/water distribution coefficients (<i>K</i>_D, L/kg dry weight) spanned 5 orders of magnitude, indicating significant metal accumulation in biosolids. Rare-earth elements and minor metals (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) detected in sludges showed enrichment factors (EFs) near unity, suggesting dust or soils as likely dominant sources. In contrast, most platinum group elements (i.e., Ru, Rh, Pd, Pt) showed high EF and <i>K</i>_D values, indicating anthropogenic sources. Numerous metallic and metal oxide colloids (<100–500 nm diameter) were detected; the morphology of abundant aggregates of primary particles measuring <100 nm provided clues to their origin. For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually. A model incorporating a parameter (<i>K</i>_D × EF ×$Value) to capture the <i>relative potential for economic value from biosolids</i> revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge

Ozone in the Desert Southwest of the United States: A Synthesis of Past Work and Steps Ahead

A region often neglected in the grander scale of general atmospheric chemistry studies and model evaluation for gas-phase chemistry is the desert southwest of the U.S. Despite regulatory progress, challenges in meeting the National Ambient Air Quality Standard for ozone motivate a re-examination of the unique meteorological conditions, interactions between the desert, agricultural, and built environmental landscapes, emissions across natural and anthropogenic sources, and regional transport of precursors that govern ozone formation in the desert Southwest. Arizona includes multiple nonattainment counties with a unique situation in terms of its environment (e.g., vegetation, meteorology, fire prone areas), complex terrain, urban growth, transport vulnerability, and limited knowledge base. Here we summarize past works investigating the ozone over Arizona, including 61 peer-reviewed publications found since the first one in 1996, and determine significant knowledge gaps to guide future research with the aim of improving regulatory policy. A more in-depth focus is placed here on Maricopa County, which includes the Phoenix Metropolitan area, where significant population growth in recent decades coupled with the extreme high temperatures and surrounding complex terrain creates a poorly understood airshed in terms of ozone chemistry, thereby complicating regulatory decisions. We suggest paths forward, including improved monitoring, assessment, and modeling tools for the region, better leveraging of archived data, and engagement with the public, government, and policy. This Review is highly relevant as well to other semiarid and arid regions, which represent the most common land type globally, warranting more attention

Potential Environmental Impacts and Antimicrobial Efficacy of Silver- and Nanosilver-Containing Textiles

For textiles containing nanosilver, we assessed benefit (antimicrobial efficacy) in parallel with potential to release nanosilver (impact) during multiple life cycle stages. The silver loading and method of silver attachment to the textile highly influenced the silver release during washing. Multiple sequential simulated household washing experiments for fabric swatches in deionized water with or without detergent showed a range of silver release. The toxicity of washing experiment supernatants to zebrafish (Danio rerio) embryos was negligible, with the exception of the very highest Ag releases (∼1 mg/L Ag). In fact, toxicity tests indicated that residual detergent exhibited greater adverse response than the released silver. Although washing the fabrics did release silver, it did not affect their antimicrobial efficacy, as demonstrated by >99.9% inhibition of E. coli growth on the textiles, even for textiles that retained as little as 2 μg/g Ag after washing. This suggests that very little nanosilver is required to control bacterial growth in textiles. Visible light irradiation of the fabrics reduced the extent of Ag release for textiles during subsequent washings. End-of-life experiments using simulated landfill conditions showed that silver remaining on the textile is likely to continue leaching from textiles after disposal in a landfill