Environmental significance of PAH photoproduct formation: TiO2 nanoparticle influence, altered bioavailability, and potential photochemical mechanisms.

Interactions between polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) can produce unforeseen photoproducts in the aqueous phase. Both PAHs and TiO2-NPs are well-studied and highly persistent environmental pollutants, but the consequences of PAH-TiO2-NP interactions are rarely explored. We investigated PAH photoproduct formation over time for benzo[a]pyrene (BaP), fluoranthene (FLT), and pyrene (PYR) in the presence of ultraviolet A (UVA) using a combination of analytical and computational methods including, identification of PAH photoproducts, assessment of expression profiles for gene indicators of PAH metabolism, and computational evaluation of the reaction mechanisms through which certain photoproducts might be formed. Chemical analyses identified diverse photoproducts, but all PAHs shared a primary photoproduct, 9,10-phenanthraquinone (9,10-PQ), regardless of TiO2-NP presence. The computed reaction mechanisms revealed the roles photodissociation and singlet oxygen chemistry likely play in PAH mediated photochemical processes that result in the congruent production of 9,10-PQ within this study. Our investigation of PAH photoproduct formation has provided substantial evidence of the many, diverse and congruent, photoproducts formed from physicochemically distinct PAHs and how TiO2-NPs influence bioavailability and time-related formation of PAH photoproducts.

Indoor and Personal PM2.5 Samples Differ in Chemical Composition and Alter Zebrafish Behavior Based on Primary Fuel Source.

Fine particulate matter (PM2.5) exposure has been linked to diverse human health impacts. Little is known about the potential heterogeneous impacts of PM2.5 generated from different indoor fuel sources and how exposure differs between personal and indoor environments. Therefore, we used PM2.5 collected by one stationary sampler in a kitchen and personal samplers (female and male participants), in homes (n = 24) in Kheri, India, that used either biomass or liquified petroleum gas (LPG) as primary fuel sources. PM2.5 samples (pooled by fuel type and monitor placement) were analyzed for oxidative potential and chemical composition, including elements and 125 organic compounds. Zebrafish (Danio rerio) embryos were acutely exposed to varying concentrations of PM2.5 and behavioral analyses were conducted. We found relatively high PM2.5 concentrations (5-15 times above World Health Organization daily exposure guidelines) and varied human health-related chemical composition based on fuel type and monitor placement (up to 15% carcinogenic polycyclic aromatic hydrocarbon composition). Altered biological responses, including changes to mortality, morphology, and behavior, were elicited by exposure to all sample types. These findings reveal that although LPG is generally ranked the least harmful compared to biomass fuels, chemical characteristics and biological impacts were still present, highlighting the need for further research in determining the safety of indoor fuel sources.

A comparison of fine particulate matter (PM2.5) in vivo exposure studies incorporating chemical analysis.

The complex, variable mixtures present in fine particulate matter (PM2.5) have been well established, and associations between chemical constituents and human health are expanding. In the past decade, there has been an increase in PM2.5 toxicology studies that include chemical analysis of samples. This investigation is a crucial component for identifying the causal constituents for observed adverse health effects following exposure to PM2.5. In this review, investigations of PM2.5 that used both in vivo models were explored and chemical analysis with a focus on respiratory, cardiovascular, central nervous system, reproductive, and developmental toxicity was examined to determine if chemical constituents were considered in the interpretation of the toxicity findings. Comparisons between model systems, PM2.5 characteristics, endpoints, and results were made. A vast majority of studies observed adverse effects in vivo following exposure to PM2.5. While limited, investigations that explored connections between chemical components and measured endpoints noted significant associations between biological measurements and a variety of PM2.5 constituents including elements, ions, and organic/elemental carbon, indicating the need for such analysis. Current limitations in available data, including relatively scarce statistical comparisons between collected toxicity and chemical datasets, are provided. Future progress in this field in combination with epidemiologic research examining chemical composition may support regulatory standards of PM2.5 to protect human health.

Assessing the oxidative potential of PAHs in ambient PM2.5 using the DTT consumption assay.

The oxidative potential (OP) of atmospheric fine particulate matter (PM2.5) has been linked to organic content, which includes polycyclic aromatic hydrocarbons (PAHs). The OP of 135 individual PAHs (including six subclasses) was measured using the dithiolthreitol (DTT) consumption assay. The DTT assay results were used to compute the concentration of each PAH needed to consume 50% of the DTT concentration in the assay (DTT50), and the reduction potential of the PAHs (ΔGrxn). Computed reduction potential results were found to match literature reduction potential values (r2 = 0.97), while DTT50 results had no correlations with the computed ΔGrxn values (r2 < 0.1). The GINI equality index was used to assess the electron distribution across the surface of unreacted and reacted PAHs. GINI values correlated with ΔGrxn in UPAH, HPAH, and OHPAH subclasses, as well as with all 135 PAHs in this study but did not correlate with DTT50, indicating that electron dispersion is linked to thermodynamic reactions and structural differences in PAHs, but not linked to the OP of PAHs. Three ambient PM2.5 filters extracts were measured in the DTT assay, alongside mixtures of analytical standards prepared to match PAH concentrations in the filter extracts to test if the OP follows an additive model of toxicity. The additive prediction model did not accurately predict the DTT consumption in the assay for any of the prepared standard mixtures or ambient PM2.5 filter extracts, indicating a much more complex model of toxicity for the OP of PAHs in ambient PM2.5. This study combined computed molecular properties with toxicologically relevant assay results to probe the OP of anthropogenically driven portions of ambient PM2.5, and results in a better understanding of the complexity of ambient PM2.5 OP.

Time-Related Alteration of Aqueous-Phase Anthracene and Phenanthrene Photoproducts in the Presence of TiO2 Nanoparticles.

Polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) are photoactive environmental pollutants that can contaminate aquatic environments. Aqueous-phase interactions between PAHs and TiO2-NPs are of interest due to their emerging environmental relevance, particularly with the deliberate application of TiO2-NPs to remediate pollution events (e.g., oil spills). Our objective was to investigate anthracene (ANT) and phenanthrene (PHE) photoproduct formation and transformation following ultraviolet A (UVA) irradiation in the presence and absence of TiO2-NPs. ANT and PHE solutions were prepared alone or in combination with TiO2-NPs, UVA-irradiated, and either exposed to larval zebrafish or collected for chemical analyses of diverse hydroxylated PAHs (OHPAHs) and oxygenated PAHs (OPAHs). The expression profiles of genes encoding for enzymes involved in PAH metabolism showed PAH-specific and time-dependent inductions that demonstrated changes in PAH and photoproduct bioavailability in the presence of TiO2-NPs. Chemical analyses of PAH/NP solutions in the absence of zebrafish larvae identified diverse photoproducts of differing size and ring arrangements, which suggested photodissociation, recombination, and ring re-arrangements of PAHs occurred either during or following UVA irradiation. Both ANT and PHE solutions showed heightened oxidative potential following irradiation, but TiO2-NP-related increases in oxidative potential were PAH-specific. The exploitation of multiple analytical methods provided novel insights into distinct PAH photoactivity, TiO2-NP influence on photoproduct formation in a PAH-specific manner, and the significant role time plays in photochemical processes.

Advances and limitations in the determination and assessment of gunshot residue in the environment.

Gunshot residue (GSR) stemming from the discharge of firearms has been essential to advancements in the field of forensic science however the human and environmental health impacts from GSR are far less researched. GSR represents a multifaceted concern: it contains a complex mixture of inorganic and organic components and produces airborne particles with variable sizes, depositions, and fates. Herein we evaluate studies in the literature examining GSR collection, deposition, composition, environmental contamination, and potential remediation techniques within the last two decades (2000 - 2020). Throughout we reflect upon key findings and weaknesses in relation to environmental characterization of GSR and associated firearm contaminants. Research focused on techniques to analyze both inorganic and organic GSR simultaneously has begun, but requires additional effort. A vast majority of the available environmental characterization literature focuses on soil contamination at outdoor firing ranges for a select number of elements (Cu, Pb, Sb) with comparisons between ranges or at different collection distances and depths. There is limited ability for between study comparisons due to collection and analysis differences as well as a lack of background soil sampling. Notably, these studies lack direct quantification of the contribution of contaminants from GSR as well as analysis of organic compounds. Currently, there is a need for air monitoring to determine the composition, deposition, and fate of GSR, particularly in outdoor settings. This review summarizes the collection, characterization, and environmental studies related to GSR and highlights areas of research needed to establish the environmental health impacts.

Workflow for Comparison of Chemical and Biological Metrics of Filter Collected PM2.5.

There is limited understanding of adverse health effect associations with chemical constituents of fine particulate matter (PM2.5) as well as the underlying mechanisms. We outlined a workflow to assess metrics, beyond concentration, using household and personal PM2.5 filter samples collected in India as a proof of concept for future large-scale studies. Oxidative potential, chemical composition (polycyclic aromatic hydrocarbons and elements), and bioactivity (developmental exposures in zebrafish) were determined. Significant differences were observed in all metrics between personal and household PM2.5 samples. This work established methods to characterize multiple metrics of PM2.5 to ultimately support the identification of more health-relevant metrics than concentration.

Neurodevelopmental toxicity assessments of alkyl phenanthrene and Dechlorane Plus co-exposure in zebrafish.

Alkyl phenanthrene (A-Phen) and Dechlorane Plus (DP) are ubiquitous environmental pollutants that widely co-exist in the environment. It has been established that both A-Phen and DP elicit neurotoxicity, but the potential interactive toxicity of these contaminants is not well-known. To determine whether a mixture of A-Phen and DP would exhibit interactive effects on neurodevelopment, we co-exposed 3-methylphenanthrene (3-MP), a representative of A-Phen, with DP. Our results illustrated that exposure to 5 or 20 µg/L 3-MP alone or in combination with 60 µg/L DP caused neurobehavioral anomalies in zebrafish. In accordance with the behavioral deficits, 3-MP alone or co-exposed with DP significantly decreased axonal growth of secondary motoneurons, altered intracellular Ca2+ homeostasis and induced cell apoptosis in the muscle of zebrafish. Additionally, 3-MP alone or co-exposed with DP significantly increased reactive oxygen species (ROS) and the mRNA levels of apoptosis-related genes. These findings indicate that 3-MP alone or co-exposed with DP induces neurobehavioral deficits through the combined effects on neuronal connectivity and muscle function. Chemical analysis revealed significant increases in 3-MP and DP bioaccumulation in zebrafish co-exposed with 3-MP and DP. Elevated bioaccumulation resulting from mixture exposure may represent a significant contribution of the synergistic effects observed in combined chemical exposure.

Assessment of Spatial Variability across Multiple Pollutants in Auckland, New Zealand.

Spatial saturation studies using source-specific chemical tracers are commonly used to examine intra-urban variation in exposures and source impacts, for epidemiology and policy purposes. Most such studies, however, has been performed in North America and Europe, with substantial regional combustion-source contributions. In contrast, Auckland, New Zealand, a large western city, is relatively isolated in the south Pacific, with minimal impact from long-range combustion sources. However, fluctuating wind patterns, complex terrain, and an adjacent major port complicate pollution patterns within the central business district (CBD). We monitored multiple pollutants (fine particulate matter (PM2.5), black carbon (BC), elemental composition, organic diesel tracers (polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes), and nitrogen dioxide (NO2)) at 12 sites across the ~5 km2 CBD during autumn 2014, to capture spatial variation in traffic, diesel, and proximity to the port. PM2.5 concentrations varied 2.5-fold and NO2 concentrations 2.9-fold across the CBD, though constituents varied more dramatically. The highest-concentration constituent was sodium (Na), a distinct non-combustion-related tracer for sea salt (µ = 197.8 ng/m3 (SD = 163.1 ng/m3)). BC, often used as a diesel-emissions tracer, varied more than five-fold across sites. Vanadium (V), higher near the ports, varied more than 40-fold across sites. Concentrations of most combustion-related constituents were higher near heavy traffic, truck, or bus activity, and near the port. Wind speed modified absolute concentrations, and wind direction modified spatial patterns in concentrations (i.e., ports impacts were more notable with winds from the northeast).

Formation of PAH Derivatives and Increased Developmental Toxicity during Steam Enhanced Extraction Remediation of Creosote Contaminated Superfund Soil.

Steam enhanced extraction (SEE) is an in situ thermal remediation technique used to remove and recover polycyclic aromatic hydrocarbons (PAHs) from contaminated soils. However, limited studies have been conducted on the formation of PAH derivatives during and after SEE of PAH contaminated soils. Creosote contaminated soil samples collected from the Wyckoff-Eagle Harbor Superfund site were remediated with laboratory scale SEE. The samples were quantified for unsubstituted PAHs and their derivatives and assessed for developmental toxicity, pre- and post-SEE. Following SEE, unsubstituted PAH concentrations decreased, while oxygenated PAH concentrations increased in soil and aqueous extracts. Differences in developmental toxicity were also measured and linked to the formation of PAH derivatives. Additive toxicity was measured when comparing unfractionated extracts to fractionated extracts in pre- and post-SEE samples. SEE is effective in removing unsubstituted PAHs from contaminated soil, but other, potentially more toxic, PAH derivatives are formed.

Separating spatial patterns in pollution attributable to woodsmoke and other sources, during daytime and nighttime hours, in Christchurch, New Zealand.

During winter nights, woodsmoke may be a predominant source of air pollution, even in cities with many sources. Since two major earthquakes resulted in major structural damage in 2010 and 2011, reliance on woodburning for home heating has increased substantially in Christchurch, New Zealand (NZ), along with intensive construction/demolition activities. Further, because NZ is a relatively isolated western country, it offers the unique opportunity to disentangle multiple source impacts in the absence of long-range transport pollution. Finally, although many spatial saturation studies have been published, and levoglucosan is an established tracer for woodburning emissions, few studies have monitored multiple sites simultaneously for this or other organic constituents, with the ability to distinguish spatial patterns for daytime vs. nighttime hours, in complex urban settings. We captured seven-day integrated samples of PM2.5, and elemental and organic tracers of woodsmoke and diesel emissions, during "daytime" (7 a.m. - 5:30 p.m.) and "nighttime" (7 p.m. - 5:30 a.m.) hours, at nine sites across commercial and residential areas, over three weeks in early winter (May 2014). At a subset of six sites, we also sampled during hypothesized "peak" woodburning hours (7 p.m. - 12 a.m.), to differentiate emissions during "active" residential woodburning, vs. overnight smouldering. Concentrations of PM2.5 were, on average, were twice as high during nighttime than daytime [µâ€¯= 18.4 (SD = 6.13) vs. 9.21 (SD = 6.13) µg/m3], with much greater differences in woodsmoke tracers (i.e., levoglucosan [µâ€¯= 1.83 (SD = 0.82) vs. 0.34 (SD = 0.17) µg/m3], potassium) and indicators of treated- or painted-wood burning (e.g., arsenic, lead). Only nitrogen dioxide, calcium, iron, and manganese (tracers of vehicular emissions) were higher during daytime. Levoglucosan and most PAHs were higher during "active" woodburning, vs. overnight smouldering. Our time-stratified spatial saturation detected strong spatial variability throughout the study area, which distinctly differed during daytime vs. night time hours, and quantified the substantial contribution of woodsmoke to overnight spatial variation in PM2.5 across Christchurch. Daytime vs. nighttime differences were greater than those observed across sites. Traffic, especially diesel, contributed substantially to daytime NO2 and spatial gradients in non-woodsmoke constituents.

PM2.5 Filter Extraction Methods: Implications for Chemical and Toxicological Analyses.

Toxicology research into the global public health burden of fine particulate matter (PM2.5) exposures frequently requires extraction of PM2.5 from filters. A standardized method for these extractions does not exist, leading to inaccurate interlaboratory comparisons. It is largely unknown how different filter extraction methods might impact the composition and bioactivity of the resulting samples. We characterized the variation in these metrics by using equal portions of a single PM2.5 filter, with each portion undergoing a different extraction method. Significant differences were observed between extraction methods for concentrations of elements and polycyclic aromatic hydrocarbons (PAHs) for the PM2.5 tested following its preparation for biological response studies. Importantly, the chemical profiles differed from those observed when we used standard protocols for chemical characterization of the ambient sample, demonstrating that extraction can alter both chemical component amounts and species profiles of the extracts. The impact of these chemical differences on sensitive end points of zebrafish development was investigated. Significant differences in the percent incidence and timing of mortality were associated with the PM2.5 extraction method. This research highlights the importance of and rationale for considering the extraction method when interlaboratory comparisons of PM2.5 toxicology research are made.

Fine-Scale Source Apportionment Including Diesel-Related Elemental and Organic Constituents of PM2.5 across Downtown Pittsburgh.

Health effects of fine particulate matter (PM2.5) may vary by composition, and the characterization of constituents may help to identify key PM2.5 sources, such as diesel, distributed across an urban area. The composition of diesel particulate matter (DPM) is complicated, and elemental and organic carbon are often used as surrogates. Examining multiple elemental and organic constituents across urban sites, however, may better capture variation in diesel-related impacts, and help to more clearly separate diesel from other sources. We designed a "super-saturation" monitoring campaign of 36 sites to capture spatial variance in PM2.5 and elemental and organic constituents across the downtown Pittsburgh core (~2.8 km²). Elemental composition was assessed via inductively-coupled plasma mass spectrometry (ICP-MS), organic and elemental carbon via thermal-optical reflectance, and organic compounds via thermal desorption gas-chromatography mass-spectrometry (TD-GCMS). Factor analysis was performed including all constituents-both stratified by, and merged across, seasons. Spatial patterning in the resultant factors was examined using land use regression (LUR) modelling to corroborate factor interpretations. We identified diesel-related factors in both seasons; for winter, we identified a five-factor solution, describing a bus and truck-related factor [black carbon (BC), fluoranthene, nitrogen dioxide (NO2), pyrene, total carbon] and a fuel oil combustion factor (nickel, vanadium). For summer, we identified a nine-factor solution, which included a bus-related factor (benzo[ghi]fluoranthene, chromium, chrysene, fluoranthene, manganese, pyrene, total carbon, total elemental carbon, zinc) and a truck-related factor (benz[a]anthracene, BC, hopanes, NO2, total PAHs, total steranes). Geographic information system (GIS)-based emissions source covariates identified via LUR modelling roughly corroborated factor interpretations.

Spatial Patterns in Rush-Hour vs. Work-Week Diesel-Related Pollution across a Downtown Core.

Despite advances in monitoring and modelling of intra-urban variation in multiple pollutants, few studies have attempted to separate spatial patterns by time of day, or incorporated organic tracers into spatial monitoring studies. Due to varying emissions sources from diesel and gasoline vehicular traffic, as well as within-day temporal variation in source mix and intensity (e.g., rush-hours vs. full-day measures), accurately assessing diesel-related air pollution within an urban core can be challenging. We allocated 24 sampling sites across downtown Pittsburgh, Pennsylvania (2.8 km²) to capture fine-scale variation in diesel-related pollutants, and to compare these patterns by sampling interval (i.e., "rush-hours" vs. "work-week" concentrations), and by season. Using geographic information system (GIS)-based methods, we allocated sampling sites to capture spatial variation in key traffic-related pollution sources (i.e., truck, bus, overall traffic densities). Programmable monitors were used to collect integrated work-week and rush-hour samples of fine particulate matter (PM2.5), black carbon (BC), trace elements, and diesel-related organics (polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes), in summer and winter 2014. Land use regression (LUR) models were created for PM2.5, BC, total elemental carbon (EC), total organic carbon (OC), elemental (Al, Ca, Fe), and organic constituents (total PAHs, total hopanes), and compared by sampling interval and season. We hypothesized higher pollution concentrations and greater spatial contrast in rush-hour, compared to full work-week samples, with variation by season and pollutant. Rush-hour sampling produced slightly higher total PM2.5 and BC concentrations in both seasons, compared to work-week sampling, but no evident difference in spatial patterns. We also found substantial spatial variability in most trace elements and organic compounds, with comparable spatial patterns using both sampling paradigms. Overall, we found higher concentrations of traffic-related trace elements and organic compounds in rush-hour samples, and higher concentrations of coal-related elements (e.g., As, Se) in work-week samples. Mean bus density was the strongest LUR predictor in most models, in both seasons, under each sampling paradigm. Within each season and constituent, the bus-related terms explained similar proportions of variance in the rush-hour and work-week samples. Rush-hour and work-week LUR models explained similar proportions of spatial variation in pollutants, suggesting that the majority of emissions may be produced during rush-hour traffic across downtown. Results suggest that rush-hour emissions may predominantly shape overall spatial variance in diesel-related pollutants.

Development of a high-throughput in vivo screening platform for particulate matter exposures.

Particulate matter (PM) exposure is a public health burden with poorly understood health effect mechanisms and lacking an efficient model to compare the vast diversity of PM exposures. Zebrafish (Danio rerio) are amenable to high-throughput screening (HTS), but few studies have investigated PM toxicity in zebrafish, despite the multitude of advantages. To develop standardized exposure procedures, the urban PM standard reference material (SRM) 1649b was used to systematically determine sample preparation methods, design experimental controls, determine concentration ranges and evaluation procedures. Embryos (n = 32/treatment) were dechorionated and placed into 96-well plates containing SRM1649b (0-200 µg/mL) at 6 h post fertilization (hpf). Developmental toxicity was assessed at 24 and 120 hpf by evaluating morphological changes, embryonic/larval photomotor behavior, and mortality. Differences from blank medium and particle controls were observed for all biological responses measured. Differences due to SRM1649b concentration and preparation method were also observed. Exposure to SRM1649b from DMSO extraction was associated with changes in morphology and mortality and hypoactivity in photomotor responses compared to the DMSO control for the whole particle suspension (76, 68%) and soluble fraction (59, 54%) during the embryonic and larval stages, respectively. Changes in behavioral responses were not observed following exposure to the insoluble fraction of SRM1649b from DMSO extraction. The toxicity bias from PM preparation provided further impetus to select a single HTS exposure method. Based on the biological activity results, the soluble fraction of SRM1649b from DMSO extraction was selected and shown to have concentration dependent cyp1a/GFP expression. This rapid, sensitive and consistently scalable model is a potentially cost-effective vertebrate approach to study the toxicology of PM from diverse locations, and provides a path to identifying the toxic material(s) in these samples, and discover the mechanisms of toxicity.

Developmental and behavioral alterations in zebrafish embryonically exposed to valproic acid (VPA): An aquatic model for autism.

Autism spectrum disorder (ASD) has complex neurodevelopmental impairments and origins that are linked to both genetic and environmental factors. Hence, there is an urgency to establish animal models with ASD-like characteristics to understand the underlying mechanisms of ASD. Prenatal exposure to valproic acid (VPA) produced ASD-like symptoms in humans, rats, and recently zebrafish. The present study investigated the use of VPA exposure to generate an ASD model in zebrafish. Early life stage exposures produced ASD-like phenotypes in the developing brain development and behavioral changes in embryonic and larval zebrafish. Our findings revealed that treating zebrafish embryos with VPA starting at 8h post fertilization (hpf) resulted in significant: increase in the ASD macrocephalic phenotype; hyperactivity of embryo/larvae movement behaviors; and increases of ASD-like larval social behaviors. Further analysis showed increases in cell proliferation, the proportion of mature newborn neurons, and neural stem cell proliferation in the brain region, which may contribute to the brain overgrowth and macrocephaly observed following VPA exposure. Our study demonstrated that VPA exposure generates ASD-like phenotypes and behaviors, indicating that zebrafish is an alternative model to investigate underlying ASD mechanisms.

Association of IL-6 with PM2.5 Components: Importance of Characterizing Filter-Based PM2.5 Following Extraction.

Filter-based toxicology studies are conducted to establish the biological plausibility of the well-established health impacts associated with fine particulate matter (PM2.5) exposure. Ambient PM2.5 collected on filters is extracted into solution for toxicology applications, but frequently, characterization is nonexistent or only performed on filter-based PM2.5, without consideration of compositional differences that occur during the extraction processes. To date, the impact of making associations to measured components in ambient instead of extracted PM2.5 has not been investigated. Filter-based PM2.5 was collected at locations (n = 5) and detailed characterization of both ambient and extracted PM2.5 was performed. Alveolar macrophages (AMJ2-C11) were exposed (3, 24, and 48 h) to PM2.5 and the pro-inflammatory cytokine interleukin (IL)-6 was measured. IL-6 release differed significantly between PM2.5 collected from different locations; surprisingly, IL-6 release was highest following treatment with PM2.5 from the lowest ambient concentration location. IL-6 was negatively correlated with the sum of ambient metals analyzed, as well as with concentrations of specific constituents which have been previously associated with respiratory health effects. However, positive correlations of IL-6 with extracted concentrations indicated that the negative associations between IL-6 and ambient concentrations do not accurately represent the relationship between inflammation and PM2.5 exposure. Additionally, seven organic compounds had significant associations with IL-6 release when considering ambient concentrations, but they were not detected in the extracted solution. Basing inflammatory associations on ambient concentrations that are not necessarily representative of in vitro exposures creates misleading results; this study highlights the importance of characterizing extraction solutions to conduct accurate health impact research.

Spatial variation in diesel-related elemental and organic PM2.5 components during workweek hours across a downtown core.

Capturing intra-urban variation in diesel-related pollution exposures remains a challenge, given its complex chemical mix, and relatively few well-characterized ambient-air tracers for the multiple diesel sources in densely-populated urban areas. To capture fine-scale spatial resolution (50×50m grid cells) in diesel-related pollution, we used geographic information systems (GIS) to systematically allocate 36 sampling sites across downtown Pittsburgh, PA, USA (2.8km2), cross-stratifying to disentangle source impacts (i.e., truck density, bus route frequency, total traffic density). For buses, outbound and inbound trips per week were summed by route and a kernel density was calculated across sites. Programmable monitors collected fine particulate matter (PM2.5) samples specific to workweek hours (Monday-Friday, 7 am-7 pm), summer and winter 2013. Integrated filters were analyzed for black carbon (BC), elemental carbon (EC), organic carbon (OC), elemental constituents, and diesel-related organic compounds [i.e., polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes]. To our knowledge, no studies have collected this suite of pollutants with such high sampling density, with the ability to capture spatial patterns during specific hours of interest. We hypothesized that we would find substantial spatial variation for each pollutant and significant associations with key sources (e.g. diesel and gasoline vehicles), with higher concentrations near the center of this small downtown core. Using a forward stepwise approach, we developed seasonal land use regression (LUR) models for PM2.5, BC, total EC, OC, PAHs, hopanes, steranes, aluminum (Al), calcium (Ca), and iron (Fe). Within this small domain, greater concentration differences were observed in most pollutants across sites, on average, than between seasons. Higher PM2.5 and BC concentrations were found in the downtown core compared to the boundaries. PAHs, hopanes, and steranes displayed different spatial patterning across the study area by constituent. Most LUR models suggested a strong influence of bus-related emissions on pollution gradients. Buses were more dominant predictors compared to truck and vehicular traffic for several pollutants. Overall, we found substantial variation in diesel-related concentrations in a very small downtown area, which varied across elemental and organic components.

Spatial variation in inversion-focused vs 24-h integrated samples of PM2.5 and black carbon across Pittsburgh, PA.

A growing literature explores intra-urban variation in pollution concentrations. Few studies, however, have examined spatial variation during "peak" hours of the day (e.g., rush hours, inversion conditions), which may have strong bearing for source identification and epidemiological analyses. We aimed to capture "peak" spatial variation across a region of complex terrain, legacy industry, and frequent atmospheric inversions. We hypothesized stronger spatial contrast in concentrations during hours prone to atmospheric inversions and heavy traffic, and designed a 2-year monitoring campaign to capture spatial variation in fine particles (PM2.5) and black carbon (BC). Inversion-focused integrated monitoring (0600-1100 hours) was performed during year 1 (2011-2012) and compared with 1-week 24-h integrated results from year 2 (2012-2013). To allocate sampling sites, we explored spatial distributions in key sources (i.e., traffic, industry) and potential modifiers (i.e., elevation) in geographic information systems (GIS), and allocated 37 sites for spatial and source variability across the metropolitan domain (~388 km(2)). Land use regression (LUR) models were developed and compared by pollutant, season, and sampling method. As expected, we found stronger spatial contrasts in PM2.5 and BC using inversion-focused sampling, suggesting greater differences in peak exposures across urban areas than is captured by most integrated saturation campaigns. Temporal variability, commercial and industrial land use, PM2.5 emissions, and elevation were significant predictors, but did not more strongly predict concentrations during peak hours.

Characterization of ambient and extracted PM2.5 collected on filters for toxicology applications.

Research on the health effects of fine particulate matter (PM2.5) frequently disregards the differences in particle composition between that measured on an ambient filter versus that measured in the corresponding extraction solution used for toxicological testing. This study presents a novel method for characterizing the differences, in metallic and organic species, between the ambient samples and the corresponding extracted solutions through characterization of extracted PM2.5 suspended on filters. Removal efficiency was found to be 98.0 ± 1.4% when measured using pre- and post-removal filter weights, however, this efficiency was significantly reduced to 80.2 ± 0.8% when measured based on particle mass in the extraction solution. Furthermore, only 47.2 ± 22.3% of metals and 24.8 ± 14.5% of organics measured on the ambient filter were found in the extraction solution. Individual metallic and organic components were extracted with varying efficiency, with many organics being lost entirely during extraction. Finally, extraction efficiencies of specific PM2.5 components were inversely correlated with total mass. This study details a method to assess compositional alterations resulting from extraction of PM2.5 from filters, emphasizing the need for standardized procedures that maintain compositional integrity of ambient samples for use in toxicology studies of PM2.5.