An improved method for sampling and analytical measurement of aerosol platinum in ambient air and workplace environments.

In this study we critically examined with both field and laboratory experiments key components of extant methods for measurement of aerosol soluble platinum in ambient air and workplace environments. Our goal was to develop an improved method for soluble platinum measurement that could be readily implemented in the field and laboratory using readily available modern analytical tools, and in parallel provide insight into factors influencing the robustness of specific aspects of measurement methods for soluble platinum. Experiments addressed sampler type, filter media and pre-cleaning, extraction solvent and volume, extraction time & energy and materials composition, with the objective of optimizing each specific component and promulgating strategies for improving signal/noise and precision. We used basic clean-room protocols and applied ICPMS tools to address these objectives. We document a method that provides for measurement of soluble platinum at the 0.02 ng/m3 level (8-h sample at 2 L/min). Of the four samplers evaluated (IOM, closed-face cassette, and two parallel particle impactors), the IOM exhibited the best precision. The three filter substrates evaluated (Teflon, MCE, PVC) performed similarly in most challenges, however, overall, we conclude that MCE media is the most robust collection substrate for soluble platinum measurements. To achieve the lowest detection levels, it is critical to pre-clean the filter substrates. The use of a 0.07 M HCl extractant (in preference to a water extractant) is recommended - platinum recoveries, particularly from real-world samples, are higher and more consistent with the HCl extractant. The outcomes of the extraction kinetics experiments suggest that an extraction time of 60 min may improve the method performance with 0.07 M HCl but degrade the performance with water, in comparison with a 30-min extraction period. The use of sonication in preference to a table-top shaker is recommended for energy input during extraction.

Chemical speciation of vanadium in particulate matter emitted from diesel vehicles and urban atmospheric aerosols.

We report on the development and application of an integrated set of analytical tools that enable accurate measurement of total, extractable, and, importantly, the oxidation state of vanadium in sub-milligram masses of environmental aerosols and solids. Through rigorous control of blanks, application of magnetic-sector-ICPMS, and miniaturization of the extraction/separation methods we have substantially improved upon published quantification limits. The study focused on the application of these methods to particulate matter (PM) emissions from diesel vehicles, both in baseline configuration without after-treatment and also equipped with advanced PM and NO(x) emission controls. Particle size-resolved vanadium speciation data were obtained from dynamometer samples containing total vanadium pools of only 0.2-2 ng and provide some of the first measurements of the oxidation state of vanadium in diesel vehicle PM emissions. The emission rates and the measured fraction of V(V) in PM from diesel engines running without exhaust after-treatment were both low (2-3 ng/mile and 13-16%, respectively). The V(IV) species was measured as the dominant vanadium species in diesel PM emissions. A significantly greater fraction of V(V) (76%) was measured in PM from the engine fitted with a prototype vanadium-based selective catalytic reductors (V-SCR) retrofit. The emission rate of V(V) determined for the V-SCR equipped vehicle (103 ng/mile) was 40-fold greater than that from the baseline vehicle. A clear contrast between the PM size-distributions of V(V) and V(IV) emissions was apparent, with the V(V) distribution characterized by a major single mode in the ultrafine (<0.25 µm) size range and the V(IV) size distribution either flat or with a small maxima in the accumulation mode (0.5-2 µm). The V(V) content of the V-SCR PM (6.6 µg/g) was 400-fold greater than that in PM from baseline (0.016 µg/g) vehicles, and among the highest of all environmental samples examined. Synchrotron based V 1s XANES spectroscopy of vanadium-containing fine-particle PM from the V-SCR identified V(2)O(5) as the dominant vanadium species.

Characterization of the elemental composition of newborn blood spots using sector-field inductively coupled plasma-mass spectrometry.

We developed extraction and analysis protocols for element detection in neonatal blood spots (NBSs) using sector-field inductively coupled plasma-mass spectrometry (SF-ICP-MS). A 5% (v/v) nitric acid element extraction protocol was optimized and used to simultaneously measure 28 elements in NBS card filter paper and 150 NBSs. NBS element concentrations were corrected for filter paper background contributions estimated from measurements in samples obtained from either unspotted or spotted NBS cards. A lower 95% uncertainty limit (UL) that accounted for ICP-MS method, filter paper element concentration, and element recovery uncertainties was calculated by standard methods for each individual's NBS element concentration. Filter paper median element levels were highly variable within and between lots for most elements. After accounting for measurement uncertainties, 11 elements (Ca, Cs, Cu, Fe, K, Mg, Na, P, Rb, S, and Zn) had lower 95% ULs>0 ng/spot with estimated concentrations ranging from 0.05 to >50,000 ng/spot in ≥50% of NBS samples in both correction methods. In a NBS sample minority, Li, Cd, Cs, Cr, Ni, Mo, and Pb had estimated concentrations ≥20-fold higher than the respective median level. Taking measurement uncertainties into account, this assay could be used for semiquantitative newborn blood element measurement and for the detection of individuals exposed to supraphysiologic levels of some trace elements. Adequate control of filter paper element contributions remains the primary obstacle to fully quantitative element measurement in newborn blood using NBSs.

Enhanced methods for assessment of the trace element composition of Iron Age bone.

Modern, ultra-trace, analytical methods, coupled with magnetic sector ICP-MS (HR-ICP-MS), were applied to the determination of a large suite of major and trace elements in Iron Age bones. The high sensitivity and un-paralleled signal-to-noise characteristics of HR-ICP-MS enabled the accurate measurement of Ag, Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, La, Li, Mg, Mn, Ni, P, Pb, Pt, Rb, Sr, U, V, and Zn in small bone sections (<75 mg). Critically, the HR-ICP-MS effectively addressed molecular interferences, which would likely have compromised data generated with quadrupole-based ICP-MS instruments. Contamination and diagenetic alteration of ancient bone are grave concerns, which if not properly addressed, may result in serious misinterpretation of data from bone archives. Analytical procedures and several chemical and statistical methods (Principal Components Analysis - PCA) were studied to assess their utility in identifying and correcting bone contamination and diagenetic alteration. Uncertainties in bone (femur) sampling were characterized for each element and longitudinal variation was found to be the dominant source of sampling variability. However the longitudinal variation in most trace elements levels was relatively modest, ranging between 9 and 17% RSD. Bone surface contamination was evaluated using sequential acid leaching. Calcium-normalized metal levels in brief, timed, dilute nitric acid leaches were compared with similarly normalized interior core metal levels to assess the degree of surface enrichment. A select group of metals (Mn, Co, Ni, Ag, Cd, and Pt) were observed to be enriched by up to a factor of 10 in the bone surface, indicating that that these elements may have a higher contamination component. However, the results of sequential acid leaching experiments indicated that the single acid leaching step was effective in removing most surface-enriched contaminants. While the leaching protocol was effective in removing contaminants associated with the bone surface, there remained potentially significant residual levels of soil-sourced contaminant tracers within the leached bone. To address this issue a mathematical procedure, based on metal/aluminum ratios, was developed to correct-for the soil-contaminant metal pools. Soil correction fractions for the primary anthropogenically mobilized metals evaluated were greatest for Pb (13.6%) followed by As (4.4%), Ag (3.9%), and Cd (0.94%). Although median soil corrections were typically low, many samples did require a much larger correction, thus both bone cleaning and soil corrections may be necessary to realize accurate endogenous bone elemental data. The results of the PCA analysis were remarkably consistent with outcomes from the chemical and elemental ratio protocols evaluated in the study, and suggest that loadings on certain factors will be helpful in screening for soil-biased samples and in identifying diagenetically altered bone. Application of these contamination evaluation and correction tools was made possible by the high-quality, multi-element, datasets produced by HR-ICP-MS. Large variations in bone core concentrations between the 80 Iron Age specimens examined were observed for all the primary trace elements and in many of the supporting elements, even after correction for major contaminant components.

An algal probe for copper speciation in marine waters: laboratory method development.

Laboratory-based algal assays were developed to explore the bioavailability of copper to the marine alga Thalassiosira weissflogii. A calibration strategy was developed that avoided use of the synthetic ligand ethylenediaminetetraacetic acid (EDTA) in the Aquil growth medium, thereby allowing ambient metal speciation. In a comparison of T. weissflogii cells grown in Aquil medium with EDTA to medium containing no added copper, zinc, and less than 0.003 nM of EDTA, no significant growth differences were observed after 8 d, indicating adequate stored nutrients. A 30-h assay was selected as the optimal time frame after examination of data from concentration-response experiments. Using 65Cu stable isotope additions, parameters examined included growth, chlorophyll a, copper uptake, phytochelatin production, and dissolved organic carbon excretion. The T. weissflogii specific growth rates decreased from 1.36 d(-1)( at pCu (i.e., the negative logarithmic concentration of free Cu) = 8.8 to 0.56 d(-1) at pCu = 7.8, whereas intercellular copper concentrations increased from 13.6 to 70.1 fg/cell, respectively. Calculated values of the copper concentration that caused a 50% reduction in algal growth of pCu = 7.7 and copper per algal mass of 625 microg/g were established. Using an algal assay based on EDTA-free culture medium, along with trace-metal clean techniques, the effect of copper on T. weissflogii and the speciation of copper in marine waters can be studied.

Factors affecting the presence of dissolved glutathione in estuarine waters.

We investigated factors influencing the presence of the thiol glutathione (GSH) in estuarine waters. Our study addressed thiol phase-association, the biological release from algal cultures, and the role of copper in both thiol release and preservation. Our measurements in three diverse estuaries in the continental United States (San Diego Bay, Cape Fear Estuary, and Norfolk Estuary) show that dissolved GSH, present at sub-nanomolar levels, is preferentially partitioned into the ultra-filtrate fraction (<1 kDa) in comparison with dissolved organic carbon (DOC). Concentrations of GSH generally increased with increases in total copper (Cu)levels, although large variability was observed among estuaries. In 30-h exposure experiments, release of dissolved GSH from the diatom Thalassiosira weissflogii into organic ligand-free experimental media was a strong function of added Cu concentration. The released GSH increased from about 0.02 to 0.27 fmol/cell as Cu was increased from the background level (0.5 nM) to 310 nM in the modified Aquil media. However, excretion of GSH was lower (up to 0.13 fmol/cell) when cells were grown in surface waters of San Diego Bay, despite much higher total Cu concentrations. Experiments conducted in-situ in San Diego Bay water indicated that high concentrations of added Cu destabilized GSH, while both Mn(II) and natural colloids promoted GSH stability. In contrast, laboratory experiments in synthetic media indicated that moderate levels of added Cu enhanced GSH stability.

Physical and kinetic speciation of copper and zinc in three geochemically contrasting marine estuaries.

The physical and kinetic speciation of Cu and Zn in three impacted marine estuaries was examined. Contrasts in sources of metal-binding ligands, solution chemistry, and hydrologic forcing between and withinthethree study systems (Cape Fear River Estuary, North Carolina; Norfolk-Hampton Roads-Elizabeth River, Virginia; San Diego Bay, California) were exploited to enhance our understanding of Cu and Zn speciation. Trace metal-optimized tangential-flow ultrafiltration at 1 kDa nominal molecular weight limit (NMWL) was used to fractionate <0.4 microm species into colloidal and "dissolved" pools. Colloidal species of dissolved organic matter (DOM) and copper were significant and often the dominant pools in each of the three study systems. Characteristic colloidal fractions of both DOM and Cu ranged from near 70% of <0.4 microm concentrations in Cape Fear to 50% in San Diego Bay. Colloidal Cu and DOM were strongly coupled, and variability in observed <0.4 microm Cu concentrations was closely related to the concentrations of colloidal-associated metal. Colloidal fractions were much smaller for Zn than that of Cu; ranging from 10-30% in Cape Fear to less than 5% in San Diego Bay, and no relationship to DOM was observed. Kinetic separations on Chelex resin revealed the presence of large nonlabile pools of Cu in each of the study systems, with the highest fractions (70-100%) in Cape Fear and Norfolk and lowest (30-50%) in San Diego Bay. A close relationship was observed between colloidal and nonlabile Cu species, implying slow reactivity of colloidal-bound Cu. The fraction of filterable Zn labile to Chelex averaged 97%, 85%, and 60% in San Diego, Norfolk, and Cape Fear, respectively. Anthropogenic Zn appeared almost exclusively in the <1 kDa fraction, while anthropogenic Cu was distributed between dissolved and colloidal pools. Copper particle-partition coefficients (Kd) followed the trend: San Diego >> Norfolk > Cape Fear and were inversely correlated with DOC concentrations. Colloid-based partition coefficients were significantly greater, in many cases an order of magnitude greater, than particle-based partition coefficients. The partitioning data suggest the presence of metal-enriched bacterial-derived exudates and/or discrete metal phases in colloidal-sized particles in impacted regions of these estuaries. The strong relationships observed between Cu and DOC indicate that Cu partitioning behavior over a range of estuarine environments may be modeled effectively with a limited set of coefficients. Our measurements of metal lability and size distribution imply that the fraction of <0.4 microm Zn that is likely to be bioavailable is greater than that for Cu, especially in impacted regions of the study systems.