7 research outputs found
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 SO<sub>2</sub> in any mineral for any size fraction.
X-ray absorption near edge structure (XANES) measurements showed no
change in iron speciation [FeÂ(II) and FeÂ(III)] in any minerals following
SO<sub>2</sub> exposure. SEM-EDS measurements of SO<sub>2</sub>-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 (TiO<sub>2</sub>) 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 TiO<sub>2</sub> that is nanoscale, or the physical and chemical
properties of TiO<sub>2</sub> that
influence its human and environmental fate or toxicity. Instead of
analyzing TiO<sub>2</sub> properties in complex food or environmental
samples, we procured samples of food-grade TiO<sub>2</sub> 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-TiO<sub>2</sub> that is generally sold for catalytic applications (P25) and
widely used in toxicity studies, was analyzed for comparison. Food-grade
and P25 TiO<sub>2</sub> 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
TiO<sub>2</sub> 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 TiO<sub>2</sub> 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 TiO<sub>2</sub>. 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 TiO<sub>2</sub> suspension in deionized water ranged from
−10
to −45 mV around pH 7, and the iso-electric point for food-grade
TiO<sub>2</sub> (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 TiO<sub>2</sub>. X-ray diffraction analysis
confirmed the presence of anatase and/or rutile in the food-grade
materials, and although the presence of amorphous TiO<sub>2</sub> could
not be ruled out, it is unlikely on the basis of Raman analysis. The
food-grade TiO<sub>2</sub> was solar photoactive. Cationic dyes adsorbed
more readily to food-grade TiO<sub>2</sub> than P25, indicating very
different potentials for interaction with
organics in the environment. This research shows that food-grade TiO<sub>2</sub> contains engineered nanomaterials with properties quite different
from those of P25, which has previously been used in many ecotoxicity
studies, and because food-grade TiO<sub>2</sub> 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 TiO<sub>2</sub>
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><sub>D</sub>, 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><sub>D</sub> 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 USValue) 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