Brian J. Majestic

Elemental and iron isotopic composition of aerosols collected in a parking structure

The trace metal contents and iron isotope composition of size-resolved aerosols were determined in a parking structure in Tempe, AZ, USA. Particulate matter (PM)<2.5 microm in diameter (the fine fraction) and PM>2.5 microm were collected. Several air toxics (e.g., arsenic, cadmium, and antimony) were enriched above the crustal average, implicating automobiles as an important source. Extremely high levels of fine copper (up to 1000 ng m(-3)) were also observed in the parking garage, likely from brake wear. The iron isotope composition of the aerosols were found to be +0.15+/-0.03 per thousand and +0.18+/-0.03 per thousand for the PM<2.5 microm and PM>2.5 microm fractions, respectively. The similarity of isotope composition indicates a common source for each size fraction. To better understand the source of iron in the parking garage, the elemental composition in four brake pads (two semi-metallic and two ceramic), two tire tread samples, and two waste oil samples were determined. Striking differences in the metallic and ceramic brake pads were observed. The ceramic brake pads contained 10-20% copper by mass, while the metallic brake pads contained about 70% iron, with very little copper. Both waste oil samples contained significant amounts of calcium, phosphorous, and zinc, consistent with the composition of some engine oil additives. Differences in iron isotope composition were observed between the source materials; most notably between the tire tread (average=+0.02 per thousand) and the ceramic brake linings (average=+0.65 per thousand). Differences in isotopic composition were also observed between the metallic (average=+0.18 per thousand) and ceramic brake pads, implying that iron isotope composition may be used to resolve these sources. The iron isotope composition of the metallic brake pads was found to be identical to the aerosols, implying that brake dust is the dominant source of iron in a parking garage.

Trace metal analysis of atmospheric particulate matter: A comparison of personal and ambient

This study compared the size-resolved trace metal concentrations from a standard ambient sampler to those of three commercial personal samplers. Trace metals data from each personal sampler were al...

Methods for the Detection and Characterization of Silica Colloids by Microsecond spICP-MS

The rapid development of nanotechnology has led to concerns over their environmental risk. Current analytical techniques are underdeveloped and lack the sensitivity and specificity to characterize these materials in complex environmental and biological matrices. To this end, single particle ICP-MS (spICP-MS) has been developed in the past decade, with the capability to detect and characterize nanomaterials at environmentally relevant concentrations in complex environmental and biological matrices. However, some nanomaterials are composed of elements inherently difficult to quantify by quadrupole ICP-MS due to abundant molecular interferences, such as dinitrogen ions interfering with the detection of silicon. Three approaches aimed at reducing the contribution of these background molecular interferences in the analysis of (28)Si are explored in an attempt to detect and characterize silica colloids. Helium collision cell gases and reactive ammonia gas are investigated for their conventional use in reducing the signal generated from the dinitrogen interference and background silicon ions leaching from glass components of the instrumentation. A new approach brought on by the advent of microsecond dwell times in single particle ICP-MS allows for the detection and characterization of silica colloids without the need for these cell gases, as at shorter dwell times the proportion of signal attributed to a nanoparticle event is greater relative to the constant dinitrogen signal. It is demonstrated that the accurate detection and characterization of these materials will be reliant on achieving a balance between reducing the contribution of the background interference, while still registering the maximum amount of signal generated by the particle event.

Respirable antimony and other trace-elements inside and outside an elementary school in Flagstaff, AZ, USA

Because people spend almost 90% of their time indoors, ambient air monitors may severely underestimate actual exposure to atmospheric particulate matter (PM). Therefore, it becomes increasingly important to better understand the microenvironments where people are spending their time. For preadolescent children, the best estimates of exposure may be inside of their school. In this study, 11 size fractions of PM were collected inside and outside of an elementary school in Flagstaff, AZ, USA. In particles<1 μm (PM1), the total mass indoors was similar to the mass outdoors (indoor:outdoor, I:O, ratio=0.92 ± 0.16). In the PM1-10 fraction, however, the mass concentration inside the school was highly elevated relative to outside the school (I:O ratios=13 ± 3). Mass concentrations of 27 elements were analyzed by ICP-MS. For all metals except for antimony (Sb), the PM1 and PM1-10 I:O ratios are found to be similar to the overall PM mass (near 1 and 13, respectively). In addition, indoor and outdoor particle size distributions reveal a crustal character for every element except Cu, Zn, Pb, and Sb. Therefore, we hypothesize that most of the PM mass inside the school is a result of transport from outside the school followed by resuspension from floors and clothing. In the PM1 fraction, the indoor mass of Sb was 86 times greater than the outdoor mass and had an air concentration of 17 ngm(-3) - greater than many urban areas around the world. Cu:Sb ratios and size distribution functions suggest that the excess source of PM1 indoor Sb results from the suspension of embedded Sb (used as a flame retardant) in the carpeting. This is the first study to observe elevated submicron Sb in schools and further studies are required to determine if this is a widespread health risk.

Characterization and benefits of selenium uptake by an Astragalus hyperaccumulator and a non-accumulator

Background and AimsWe characterized the relationship between soil and leaf concentrations of selenium in a hyperaccumulator and a non-accumulator to test the hypothesis that hyperaccumulators take up selenium while non-accumulators exclude it. We examined plant performance metrics and the ability of selenium to protect against herbivory by spider mites.MethodsKnown hyperaccumulator and non-accumulator species within the genus Astragalus were grown under a range of selenium concentrations and measured for tissue selenium, extent of herbivory, and vigor.ResultsBoth hyperaccumulators and non-accumulators either failed to meet even the lenient threshold or exceeded even the strict threshold for hyperaccumulation depending on soil concentration. Both had decreased herbivory with increasing leaf selenium, and both grew larger at higher levels of selenium regardless of herbivory, despite a negative impact of higher relative uptake.ConclusionsThe relationships between selenium dosage and tissue concentrations matched only some model predictions. Under these conditions, the bioconcentration factor was a better delimiter between species than the absolute tissue concentration. We provide evidence that despite the apparent cost of uptake, selenium can enhance the growth of hyperaccumulators even when herbivory is not a significant factor. We propose the term “elemental stimulation” for this phenomenon.

Metal concentrations and soluble iron speciation in fine particulate matter from light rail activity in the Denver-Metropolitan area

Fine particulate matter samples (PM2.5) were collected from three locations around the Denver–Metropolitan area to study the impacts of the ground–level light rail on airborne metal concentrations. Size–segregated PM was collected on board the trains, at the side of the tracks, and at a background location in downtown Denver. Results from this study showed highest crustal enrichment factors of metals in samples collected on board the train, despite lower concentrations of total PM2.5. Metals commonly found in steel such as Fe, Cr, Mn, and Ni, all exhibited elevated concentrations relating to train activity over the background site. Iron in the PM2.5 at track–side and on board the trains was above the background by a factor of 1.89 and 1.54, respectively. For Mn, the ratios were 1.34 for the track–side and 0.94 for the on board samples. Cr and Ni exhibited higher ratios over the background only in samples collected on board the trains at 1.59 (Cr) and 1.26 (Ni). Soluble metals were measured with Ni (53–71%), Cu (52–81%), and Zn (30–81%) exhibiting the highest solubilities across the different sites. Soluble Fe ranged from 8–15% for the total measured Fe, indicating a non–crustal source of Fe. Soluble Fe was also characterized as Fe(II) and Fe(III) with 87–90% of the soluble Fe being Fe(II), similar to results from studies in Los Angeles, CA and East St. Louis, IL but higher than in Atlanta, GA and Waukesha, WI.

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 worlds 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 (p > 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.

Phytoremediation of cadmium and lead-polluted watersheds

Abandoned hard rock mines and the resulting acid mine drainage (AMD) are a source of vast, environmental degradation that are toxic threats to plants, animals, and humans. Cadmium (Cd) and lead (Pb) are metal contaminants often found in AMD. In our mine outwash water samples, Cd and Pb concentrations were 300 and 40 times greater than EPA Aquatic Life Use water quality standards, respectively. We tested the phytoremediation characteristics, accumulation and tolerance of Cd and Pb contamination, for annual aboveground biomass harvest of three montane willows native to the Rocky Mountains: Salix drummondiana, S. monticola, and S. planifolia. We found S. monticola best suited for Pb remediation based on greater growth and tolerance in response to the low Pb treatment compared to the high Pb treatment. Salix monticola stems also contained higher Pb concentrations in control treatment compared to S. planifolia. We found S. planifolia and S. drummondiana best suited for Cd remediation. Salix drummondiana accumulated higher concentrations of Cd in stems than both S. monticola and S. planifolia. Salix planifolia accumulated nearly 2.5 times greater concentrations of Cd in stems in control treatment than did S. drummondiana. Salix planifolia also contained more total Cd in stems than did S. monticola in Cd treatments. Based on our results, S. drummondiana and S. planifolia could aid in reduction of Cd in watersheds, and S. monticola is better suited than is S. planifolia for aboveground accumulation and tolerance of Pb pollution.

Mycofactocin Biosynthesis Proceeds through 3-Amino-5-[(p-hydroxyphenyl)methyl]-4,4-dimethyl-2-pyrrolidinone (AHDP); Direct Observation of MftE Specificity toward MftA*

The structure of the ribosomally synthesized and post-translationally modified peptide product mycofactocin is unknown. Recently, the first step in mycofactocin biosynthesis was shown to be catalyzed by MftC in two S-adenosylmethionine-dependent steps. In the first step, MftC catalyzes the oxidative decarboxylation of the MftA peptide to produce the styrene-containing intermediate MftA**, followed by a subsequent C-C bond formation to yield the lactam-containing MftA*. Here, we demonstrate the subsequent biosynthetic step catalyzed by MftE is specific for MftA*. The hydrolysis of MftA* leads to the formation of MftA(1-28) and 3-amino-5-[( p-hydroxyphenyl)methyl]-4,4-dimethyl-2-pyrrolidinone (AHDP). The hydrolysis reaction is Fe2+-dependent, and addition of the metal to the reaction mixture leads to a kobs of ∼0.2 min-1. Lastly, we validate the structure of AHDP by 1H, 13C, and COSY nuclear magnetic resonance techniques as well as mass spectrometry.