Oxidative Potential Of Particulate Matter Research Articles

Unveiling the optimal regression model for source apportionment of the oxidative potential of PM10

Abstract. The capacity of particulate matter (PM) to generate reactive oxygen species (ROS) in vivo leading to oxidative stress is thought to be a main pathway in the health effects of PM inhalation. Exogenous ROS from PM can be assessed by acellular oxidative potential (OP) measurements as a proxy of the induction of oxidative stress in the lungs. Here, we investigate the importance of OP apportionment methods for OP distribution by PM10 sources in different types of environments. PM10 sources derived from receptor models (e.g., EPA positive matrix factorization (EPA PMF)) are coupled with regression models expressing the associations between PM10 sources and PM10 OP measured by ascorbic acid (OPAA) and dithiothreitol assay (OPDTT). These relationships are compared for eight regression techniques: ordinary least squares, weighted least squares, positive least squares, Ridge, Lasso, generalized linear model, random forest, and multilayer perceptron. The models are evaluated on 1 year of PM10 samples and chemical analyses at each of six sites of different typologies in France to assess the possible impact of PM source variability on PM10 OP apportionment. PM10 source-specific OPDTT and OPAA and out-of-sample apportionment accuracy vary substantially by model, highlighting the importance of model selection according to the datasets. Recommendations for the selection of the most accurate model are provided, encompassing considerations such as multicollinearity and homoscedasticity.

Resolving Organic Aerosol Components Contributing to the Oxidative Potential of PM2.5 in the North China Plain

AbstractThe oxidative potential (OP) of ambient particulate matter (PM) is a common metric for estimating PM toxicity and linking PM exposure to adverse health effects. Organic aerosol (OA), a dominant fraction of ambient PM worldwide, may significantly contribute to PM toxicity. Here, we investigated the source‐based OA components contributing to the OP of PM in the urban (Beijing, summer and winter) and rural (Gucheng, winter) environments of the North China Plain (NCP). Various OA components as identified by the aerosol mass spectrometer/aerosol chemical speciation monitor (AMS/ACSM), transition metals, and black carbon were compared with the OP of PM measured by dithiothreitol assays. The results consistently demonstrate the importance of OA as a contributor to PM's OP in both urban and rural NCP environments. Higher intrinsic OP was observed in winter Beijing than in summer, possibly due to OA being predominantly from anthropogenic sources in winter. Furthermore, different OA components were found to drive the response of OP in the two environments. More‐oxidized oxygenated OA (MO‐OOA), cooking OA, and oxidized primary OA (during winter) are the OA contributors to OP in the urban environment, with a dominant contribution from MO‐OOA. In contrast, biomass burning OA (BBOA) and OOA play a major role in the OP in the rural environment, with BBOA making the largest contribution. Overall, this work highlights the significance of OA in determining PM's OP and calls for more work to reveal the sources and characteristics of OA components contributing to OP across different regions.

Oxidative potential of particulate matter and its association to respiratory health endpoints in high-altitude cities in Bolivia

Exposure to particulate matter (PM) pollution is a significant health risk, driving the search for innovative metrics that more accurately reflect the potential harm to human health. Among these, oxidative potential (OP) has emerged as a promising health-based metric, yet its application and relevance across different environments remain to be further explored. This study, set in two high-altitude Bolivian cities, aims to identify the most significant sources of PM-induced oxidation in the lungs and assess the utility of OP in assessing PM health impacts. Utilizing two distinct assays, OPDTT and OPDCFH, we measured the OP of PM samples, while also examining the associations between PM mass, OP, and black carbon (BC) concentrations with hospital visits for acute respiratory infections (ARI) and pneumonia over a range of exposure lags (0–2 weeks) using a Poisson regression model adjusted for meteorological conditions. The analysis also leveraged Positive Matrix Factorization (PMF) to link these health outcomes to specific PM sources, building on a prior source apportionment study utilizing the same dataset. Our findings highlight anthropogenic combustion, particularly from traffic and biomass burning, as the primary contributors to OP in these urban sites. Significant correlations were observed between both OPDTT and PM2.5 concentration exposure and ARI hospital visits, alongside a notable association with pneumonia cases and OPDTT levels. Furthermore, PMF analysis demonstrated a clear link between traffic-related pollution and increased hospital admissions for respiratory issues, affirming the health impact of these sources. These results underscore the potential of OPDTT as a valuable metric for assessing the health risks associated with acute PM exposure, showcasing its broader application in environmental health studies.

Oxidative potential associated with reactive oxygen species of size-resolved particles: The important role of the specific sources

Oxidative potential (OP) is a predictor of particulate matter (PM) toxicity. Size-resolved PM and its components that influence OP values can be generated from several sources. However, There is little research have attempted to determine the PM toxicity generated from specific sources. This paper studied the OP characterization and reactive oxygen species (ROS) formation of particles from specific sources and their effects on human health. OP associated with ROS of size-resolved particles was analyzed by using dithiothreitol (DTT) method and electron paramagnetic resonance (EPR) spectroscopy technology. And OP and ROS deposition of specific source PM were calculated for health through the Multi-path particle deposition (MPPD) model. The results evidenced that the highest water-soluble OP (OPws) from traffic sources (OPm: 104.50 nmol min−1·ug−1; OPv: 160.15 nmol min−1·m−3) and the lowest from ocean sources (OPm: 22.25 nmol⋅min−1⋅ug−1; OPv: 54.16 nmol min−1·m−3). The OPws allocation in PM from different sources all have a unimodal pattern range from 0.4 to 3.2 μm. ROS (·OH) displayed the uniform trend as PM OPws, indicating that PM< 3.2 is the major contributor to adverse health impacts for size-resolved PM because of its enhanced oxidative activity compared with PM> 3.2. Furthermore, this study predicted the DTT consumption of PM were assigned to different components. Most DTT losses are attributed to the transition metals. For specific sources, transition metals dominates DTT losses, accounting for 38%–80% of DTT losses from different sources, followed by Hulis-C, accounting for 1%–10%. MPPD model calculates that over 66% of pulmonary DTT loss comes by PM< 3.2, and over 71% of pulmonary ROS generation from PM< 3.2. Among these sources of pollution, traffic emissions are the primary contributors to reactive oxygen species (ROS) in environmental particulate matter (PM). Therefore, emphasis should be placed on controlling traffic emissions, especially in coastal areas.

Overview of the Alaskan Layered Pollution and Chemical Analysis (ALPACA) Field Experiment.

The Alaskan Layered Pollution And Chemical Analysis (ALPACA) field experiment was a collaborative study designed to improve understanding of pollution sources and chemical processes during winter (cold climate and low-photochemical activity), to investigate indoor pollution, and to study dispersion of pollution as affected by frequent temperature inversions. A number of the research goals were motivated by questions raised by residents of Fairbanks, Alaska, where the study was held. This paper describes the measurement strategies and the conditions encountered during the January and February 2022 field experiment, and reports early examples of how the measurements addressed research goals, particularly those of interest to the residents. Outdoor air measurements showed high concentrations of particulate matter and pollutant gases including volatile organic carbon species. During pollution events, low winds and extremely stable atmospheric conditions trapped pollution below 73 m, an extremely shallow vertical scale. Tethered-balloon-based measurements intercepted plumes aloft, which were associated with power plant point sources through transport modeling. Because cold climate residents spend much of their time indoors, the study included an indoor air quality component, where measurements were made inside and outside a house to study infiltration and indoor sources. In the absence of indoor activities such as cooking and/or heating with a pellet stove, indoor particulate matter concentrations were lower than outdoors; however, cooking and pellet stove burns often caused higher indoor particulate matter concentrations than outdoors. The mass-normalized particulate matter oxidative potential, a health-relevant property measured here by the reactivity with dithiothreiol, of indoor particles varied by source, with cooking particles having less oxidative potential per mass than pellet stove particles.

Evaluation of indoor particulate matter control based on health risks and oxidative potential in a metro station

Particulate matter (PM) from different sources exhibits diverse chemical and physical characteristics, and it is an essential carrier of toxic chemicals. Ignoring PM properties is inappropriate for indoor air quality (IAQ) control in places with internal sources, such as metro stations. PM control measures aimed at health protection should be established based on PM health effects. The current PM control limit for metro stations may be insufficient for health protection. It is important to find a method that comprehensively evaluates PM features to set PM exposure limits. This study evaluated the health risks induced by chemical components and the oxidative potential of PM in the Tianjinzhan metro station. A PM control strategy was suggested based on health effect analysis. PM on the platform had notable underlying adverse health effects. An in-depth toxicology analysis was suggested to assess the high Ba and Mn concentrations in PM. The risk from Cr raised concern regarding the potential for carcinogenicity. As a potential composite index, the dithiothreitol (DTT) activity may be appropriate to evaluate the general adverse health effects caused by PM. The DTT activity of the platform was 3.3–5.4 times that of the ventilation shaft. Removing a unit mass of PM1 in the station hall would produce more health benefits than the removal of a unit mass of PM2.5. However, the DTT results indicated that control strategies on the platform should first focus on PM2.5, which would achieve the same protection effect as that when the PM1 mass concentration is decreased by the same level. A revision of the PM2.5 control limit for China metro stations was recommended to control oxidative potential on the platform.

Effets de la pollution de l'air sur les évènements cardiovasculaires en unité de soins intensifs cardiologiques

Many environmental factors influence the occurrence of cardiovascular events. Among these, air pollution is certainly the most harmful, due to its dual composition and effects. Air pollution is both particulate and gaseous, and can vary in concentration and composition according to its source and type of emission. Moreover, clinical effects are not only observed at long-term but also at short-term, following rapid deterioration in air quality.Air pollution must therefore be seen both as a risk factor for atherosclerotic disease, and as a trigger for cardiovascular events. These acute effects are essentially mediated by an increased risk of acute coronary syndromes and heart failure. The effects of air pollution on admissions for ventricular arrhythmias and arterial hypertension are also possible. The cardiotoxicity of pollution is mainly mediated by sympatho-vagal imbalance, by the initiation and amplification of an oxidative, inflammatory and pro-aggregatory cascade, and by endothelial dysfunction and activation of metalloproteinases.Although now well established, the consequences of air pollution on acute cardiovascular events require further investigation. Environmental cardiology is an emerging discipline whose current vision still fails to integrate qualitative aspects, such as the oxidative potential of particulate matter, and the joint effects of multiple environmental exposures.

Size distribution and lung-deposition of ambient particulate matter oxidative potential: A contrast between dithiothreitol and ascorbic acid assays

Particulate matter (PM) inhaled into human lungs causes oxidative stress and adverse health effects through antioxidant depletion (oxidative potential, OP). However, there is limited knowledge regarding the association between the lung-deposited dose (LDD) of PM and OP in extrathoracic (ET), tracheobronchial (TB), and pulmonary (P) regions of human lungs. Dithiothreitol (DTT) and ascorbic acid (AA) assays were employed to measure the OP of PM size fractions to investigate OP distribution in human lungs and identify the chemical drivers. Quasi-ultrafine particles (quasi-UFP, ≤0.49 μm) exhibited high OP deposition in the TB and P regions, while coarse particles (CP, ≥3.0 μm) dominated in the ET region. A plot of extrinsic (per air volume) and intrinsic (per PM mass) OP versus LDD revealed that the OP for fine and coarse particles was greatest in the ET region, whereas the OP of quasi-UFP was greatest in alveoli. The study also demonstrated that extrinsic OP and PM doses are not strongly related. The decline in OP with increasing PM dose reveals the need for further investigation of the antagonistic effects of the chemical compositions. Overall, the results presented herein help address the gap in knowledge regarding the association between the OP and LDD of ambient particles in specific regions of human lungs.

An Overview of the Automated and On-Line Systems to Assess the Oxidative Potential of Particulate Matter

Recent years have seen a significant increase in the scientific literature related to various methods for analyzing oxidative potential (OP) of atmospheric particulate matter (PM). The presence of several types of PM, differing chemical and physical properties, released by both anthropogenic and natural sources, leads to numerous health issues in living organisms and represents an attractive target for air quality monitoring. Therefore, several studies have focused on developing rapid and self-operative tests, employing different target molecules to assess OP of atmospheric aerosols as well as unique approaches to overcome some of the most common laboratory-related issues in this kind of analysis. This work provides an overview of online and automated systems, as well as a broad picture of the state-of-art of the various devices and methods developed on this topic over the last two decades. Moreover, representative studies on this subject will be discussed, analyzing the advantages and drawbacks of the developed automated techniques.

Discovering oxidative potential (OP) drivers of atmospheric PM10, PM2.5, and PM1 simultaneously in North-Eastern Spain.

Ambient particulate matter (PM) is a major contributor to air pollution, leading to adverse health effects on the human population. It has been suggested that the oxidative potential (OP, as a tracer of oxidative stress) of PM is a possible determinant of its health impact. In this study, samples of PM10, PM2.5, and PM1 were collected roughly every four days from January 2018 until March 2019 at a Barcelona urban background site and Montseny rural background site in northeastern Spain. We determined the chemical composition of samples, allowing us to perform source apportionment using positive matrix factorization. The OP of PM was determined by measuring reactive oxygen species using dithiothreitol and ascorbic acid assays. Finally, to link the sources with the measured OP, both a Pearson's correlation and a multiple linear regression model were applied to the dataset. The results showed that in Barcelona, the OP of PM10 was much higher than those of PM2.5 and PM1, whereas in Montseny results for all PM sizes were in the same range, but significantly lower than in Barcelona. In Barcelona, several anthropogenic sources were the main drivers of OP in PM10 (Combustion + Road Dust + Heavy Oil + OC-rich) and PM2.5 (Road Dust + Combustion). In contrast, PM1 -associated OP was driven by Industry, with a much lower contribution to PM10 and PM2.5 mass. Meanwhile, Montseny exhibited no clear drivers for OP evolution, likely explaining the lack of a significant difference in OP between PM10, PM2.5, and PM1. Overall, this study indicates that size fraction matters for OP, as a function of the environment typology. In an urban context, OP is driven by the PM10 and PM1 size fractions, whereas only the PM1 fraction is involved in rural environments.

Impact of COVID-19 lockdown on particulate matter oxidative potential at urban backgroundversustraffic sites

During the lockdown period, the oxidative potential of PM decreased in a traffic site but not in an urban site due to sustained contributions from residential heating emissions. Random forest modelling is useful in predicting business-as-usual levels for air quality studies.

Source apportionment of oxidative potential: What we know so far

In numerous epidemiological studies, exposure to particulate matter (PM) has been associated with negative health outcomes. It has been established so far that the detrimental health effects of particles cannot be explained by a single parameter, such as particle mass, as the complexity of chemical composition and reactivity of particles are not always represented by the mass loadings. The oxidative potential (OP) of aerosol particles represents a promising indicator of their potential toxicity. To develop strategies and regulations at improving the air quality, an increasing number of studies are focused on the application of source apportionment (SA) of PM., while a limited number of SA investigations have been applied to OP. In this review previous research of SA of atmospheric PM OP and proposed guidelines for future studies are summarized. Most of the research studies were carried out in an urban area and focused on PM2.5, while few studies examined other PM fractions. It was noted that the three dominant contributors to OP were biomass burning (9-97%), secondary aerosols (6-67%), and traffic/vehicles (16-88%). The presence of other factors that contributed to the in-crease of OP to a lesser extent depended on the location and season. Further, a considerable discrepancy in the contribution of various OP vs. PM sources was discovered using SA models. Because of this, the use of SA is not equivalent when considering the mass of PM and its toxicity.

Metals, PAHs and oxidative potential of size-segregated particulate matter and inhalational carcinogenic risk of cooking at a typical university canteen in Shanghai, China

Cooking is an important source of indoor emissions, and exposure to cooking emissions can instigate adverse health effects. Oxidative potential (OP) is a good indicator for assessing health risk, but studies detecting the OP of cooking emissions are rare. In this paper, size-segregated samples were collected at four sites in the canteen to study the chemical characteristics and OP of particulate matter (PM) emitted from cooking. The four sites were set to study the effects of different cooking styles and kitchen types. The results showed that the concentrations of most metals, water-soluble ions, PAHs, and OP at four sites followed the trend: deep-frying > stir-frying > second floor hall > first floor hall. And the concentration at the fine fraction (PM0.056-3.2) was much higher than that at coarse fraction (PM3.2-18). The PM OP at four sites were 1.1642 nmol m−3·min−1, 1.2088 nmol m−3·min−1, 0.8589 nmol m−3·min−1 and 0.9507 nmol m−3·min−1, respectively. The correlation between OP and other components showed that Zn (|r| = 0.444) and DBA (|r| = 0.507) were moderately related to OP, which suggested that heavy metals and PAHs might be contributed to PM OP. The carcinogenic risk assessments of heavy metals and PAHs showed that, there might be an increasing of potential carcinogenic risk if exposure to cooking environment for lifetime. Our results were firstly helpful for PM characteristics researches on cooking emissions, and also significant to public health protection, especially for people who usually cook.

Impact of COVID-19 Lockdown on Oxidative Potential of Particulate Matter: Case of Athens (Greece).

This work evaluates the aerosol oxidative potential (OP) and its changes from modified air pollution emissions during the COVID-19 lockdown period in 2020, with the intent of elucidating the contribution of aerosol sources and related components to aerosol OP. For this, daily particulate matter (PM) samples at an urban background site were collected and analyzed with a chemical (acellular) assay based on Dithiothreitol (DTT) during the COVID-19 restriction period in Athens (Greece). The obtained time-series of OP, PM2.5, organic matter (OM) and SO42− of the pre-, post- and lockdown periods were also compared to the data of the same time periods during the years 2017–2019. Even though all traffic-related emissions have been significantly reduced during the lockdown period (by 30%), there is no reduction in water-soluble OP, organics and sulfate concentrations of aerosol during 2020. The results reveal that the decrease in traffic was not sufficient to drive any measurable change on OP, suggesting that other sources—such as biomass burning and secondary aerosol from long-range transport, which remained unchanged during the COVID lockdown—are the main contributors to OP in Athens, Greece.

Simple and efficient method to detach intact PM10 from field filters: Elements recovery assessment

Toxicity of the soluble fraction of particulate matter (PM) has been extensively evaluated, but it has also been demonstrated that insoluble aerosol species can considerably contribute to toxicological potential of PM. However, most of the procedures regarding the assessment of toxicological effects of the whole PM (soluble and insoluble species) requires targeted treatments of the sampled filters, such as the employment of organic solvents, or the application of ultrasounds. Both methods can introduce a bias in the toxicological assessment, altering PM oxidative potential and biological outcomes. In this study, we applied a non-invasive, simple and efficient method for the detachment of intact PM10 from field filters by using an electrical toothbrush, which allows obtaining a PM10 water-suspension to be used for PM toxicity assessment. The efficiency of this method was evaluated by comparing the elemental content (As, Ba, Bi, Ca, Co, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sn, Sr, Ti, Tl, U and W) obtained by brushing the filters to that measured by applying a conventional procedure to PM samples (n. 20 pairs of equivalent PM10 filters). Soluble and insoluble fractions were separately analyzed, in order to discriminate the recovery due to partial solubilization of sample from that due to detachment of insoluble particles. The high recovery percentage of elements, the very-high linear correlation coefficients and the low relative percentage differences with respect to a conventional procedure for elemental analysis of PM10 confirmed the efficiency of the toothbrush method.

Development and characterization of a gold nanoparticles glassy carbon modified electrode for dithiotreitol (DTT) detection suitable to be applied for determination of atmospheric particulate oxidative potential

A gold nanostructured electrochemical sensor based on modified GC electrode for thiols' detection is described and characterized. This sensor is a suitable device for the measurement of the oxidative potential (OP) of the atmospheric particulate matter (PM), considered a global indicator of adverse health effects of PM, as an alternative to the classic spectrophotometric methods. The operating principle is the determination of the OP, through the measurement of the consumption of DTT content. The DTT-based chemical reactivity is indeed a quantitative acellular probe for assessment of the capacity of the atmospheric PM to catalyze reactive oxygen species generation which contributes to the induction of oxidative stress in living organisms and in turn to the outcome of adverse health effects. To make the sensors, glassy carbon electrodes, traditional (GC) and screen printed (SPE) electrodes, have been electrochemically modified with well-shaped rounded gold nanoparticles (AuNPs) by using a deposition method that allows obtaining a stable and efficient modified surface in a very simple and reproducible modality. The chemical and morphological characterization of the nano-hybrid material has been performed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy coupled with electron dispersive spectroscopy analysis (SEM/EDS). The electrochemical properties have been evaluated by cyclic voltammetry (CV) and chrono-amperometry (CA) in phosphate buffer at neutral pH as requested in DTT assay for OP measurements. The electroanalytical performances of the sensor in DTT detection are strongly encouraging showing low LODs (0.750 μM and 1.5 μM), high sensitivity (0.0622 μA cm−2 μM−1 and 0.0281 μA cm−2 μM−1), wide linear and dynamic ranges extending over 2-4 orders of magnitude and high selectivity. FIA preliminary results obtained on measuring the DTT rate consumption in six PM aqueous extracts samples showed a good correlation with measurements obtained in parallel on the same set of samples by using the classic spectrophotometric method based on the Ellman's reactive use. These results confirm the high selectivity of the method and its suitability for application to be applied in PM oxidative potential measurements.

The Oxidative Potential of Fine Particulate Matter and Biological Perturbations in Human Plasma and Saliva Metabolome.

Particulate oxidative potential may comprise a key health-relevant parameter of particulate matter (PM) toxicity. To identify biological perturbations associated with particulate oxidative potential and examine the underlying molecular mechanisms, we recruited 54 participants from two dormitories near and far from a congested highway in Atlanta, GA. Fine particulate matter oxidative potential ("FPMOP") levels at the dormitories were measured using dithiothreitol assay. Plasma and saliva samples were collected from participants four times for longitudinal high-resolution metabolic profiling. We conducted metabolome-wide association studies to identify metabolic signals with FPMOP. Leukotriene metabolism and galactose metabolism were top pathways associated with ≥5 FPMOP-related indicators in plasma, while vitamin E metabolism and leukotriene metabolism were found associated with most FPMOP indicators in saliva. We observed different patterns of perturbed pathways significantly associated with water-soluble and -insoluble FPMOPs, respectively. We confirmed five metabolites directly associated with FPMOP, including hypoxanthine, histidine, pyruvate, lactate/glyceraldehyde, and azelaic acid, which were implications of perturbations in acute inflammation, nucleic acid damage and repair, and energy perturbation. The unique metabolic signals were specific to FPMOP, but not PM mass, providing initial indication that FPMOP might constitute a more sensitive, health-relevant measure for elucidating etiologies related to PM2.5 exposures.

The oxidative potential of particulate matter (PM) in different regions around the world and its relation to air pollution sources.

In this study, we investigated the impact of urban emission sources on the chemical composition of ambient particulate matter (PM) as well as the associated oxidative potential. We collected six sets of PM samples in five urban location sites around the world over long time periods varying from weeks to months, intentionally selected for their PM to be dominated by unique emission sources: (1) PM2.5 produced mainly by traffic emissions in central Los Angeles, United States (US); (2) PM2.5 dominated by biomass burning in Milan, Italy; (3) PM2.5 formed by secondary photochemical reactions thus dominated by secondary aerosols in Athens, Greece; (4) PM10 emitted by refinery and dust resuspension in Riyadh, Saudi Arabia (SA); (5) PM10 generated by dust storms in Riyadh, SA, and (6) PM2.5 produced mainly by industrial and traffic emissions in Beirut, Lebanon. The PM samples were chemically analyzed and their oxidative potential were quantified by employing the dithiothreitol (DTT) assay. Our results revealed that the Milan samples were rich in water soluble organic carbon (WSOC) and PAHs, even exceeding the levels measured on Los Angeles (LA) freeways. The PM in Athens was characterized by high concentrations of inorganic ions, specifically sulfate which was the highest of all PM samples. The ambient PM in LA was impacted by the traffic-emitted primary organic and elemental carbon. Furthermore, the contribution of metals and elements per mass of PM in Riyadh and Beirut samples were more pronounced relative to other sampling areas. The highest intrinsic PM redox activity was observed for PM with the highest WSOC fraction, including Milan (biomass burning) and Athens (secondary organic aerosols, SOA). PM in areas characterized by high metal emissions including dust events, refinery and industry, such as Riyadh and Beirut, had the lowest oxidative potential as assessed by the DTT assay. The results of this study illustrate the impact of major emission sources in urban areas on the redox activity and oxidative potential of ambient PM, providing useful information for developing efficient air pollution control and mitigation policies in polluted areas around the globe.

Precipitation of aqueous transition metals in particulate matter during the dithiothreitol (DTT) oxidative potential assay.

Transition metals in particulate matter (PM) are hypothesized to have enhanced toxicity based on their oxidative potential (OP). The acellular dithiothreitol (DTT) assay is widely used to measure the OP of PM and its chemical components. In our prior study, we showed that the DTT assay (pH 7.4, 0.1 M phosphate buffer, 37 °C) provides favorable thermodynamic conditions for precipitation of multiple metals present in PM. This study utilizes multiple techniques to characterize the precipitation of aqueous metals present at low concentrations in the DTT assay. Metal precipitation was identified using laser particle light scattering analysis, direct chemical measurement of aqueous metal removal, and microscopic imaging. Experiments were run with aqueous metals from individual metal salts and a well-characterized urban PM standard (NIST SRM-1648a, Urban Particulate Matter). Our results demonstrated rapid precipitation of metals in the DTT assay. Metal precipitation was independent of DTT but dependent on metal concentration. Metal removal in the chemically complex urban PM samples exceeded the thermodynamic predictions and removal seen in single metal salt experiments, suggesting co-precipitation and/or adsorption may have occurred. These results have broad implications for other acellular assays that study PM metals using phosphate buffer, and subsequently, the PM toxicity inferred from these assays.

Oxidative potential of solvent-extractable organic matter of ambient total suspended particulate in Bangkok, Thailand.

Oxidative stress is a key mechanism by which ambient particulate matter induces adverse health effects. Most studies have focused on the oxidative potential (OP) of water-soluble constituents, while there has been limited work on the OP of solvent-extractable organic matter (EOM OP). In this study, the EOM OP of ambient total suspended particulate (TSP) from Bangkok, Thailand, was determined using the dithiothreitol (DTT) assay. Positive matrix factorization (PMF), combined with chemical analysis of molecular markers, was employed to apportion the contributions of various emission sources to EOM OP. The volume-normalized OP initially increased with organic carbon (OC) concentration and plateaued gradually, while the mass-normalized OP fitted well with OC concentration using a power function. Fossil fuel combustion (62%) and plastic waste burning (23%) were the major contributors to EOM OP, while biomass burning demonstrated only a limited contribution. EOM OP correlated well with each group of polycyclic aromatic hydrocarbons (PAHs), suggesting that secondary formation of quinones associated with fossil fuel combustion and plastic waste burning could be an important pathway of TSP toxicity. This study underscores the importance of considering different emission sources when evaluating potential health impacts and the implementation of air pollution regulations.