Hydrogen peroxide formation in a surrogate lung fluid by transition metals and quinones present in particulate matter

Kinetics of ascorbate and dithiothreitol oxidation by soluble copper, iron, and manganese, and 1,4-naphthoquinone: Influence of the species concentration and the type of fluid

An alternative metric to account for particulate matter (PM) composition-based toxicity is the ability of PM-species to generate reactive oxygen species (ROS) and deplete antioxidants, the so-called oxidative potential (OP). Acellular OP assays are the most used worldwide, mainly those based on ascorbic acid (AA) and dithiothreitol (DTT) depletion; OP values are calculated from AA/DTT concentration over time kinetic curves. Since a great variability in OP-DTT and OP-AA values can be found in the literature, the understanding of those factors affecting the kinetic rate of AA and DTT oxidation in the presence of PM-bound species will improve the interpretation of OP values. In this work, a kinetic study of the oxidation rate of AA and DTT driven by species usually found in PM (transition metals and naphthoquinone (NQ)) was carried out. In particular, the influence of the concentration of Cu(II), Fe(II), Fe(III), Mn(II), Mn(III), and 1,4-NQ, and the type of fluid used in the assay (phosphate buffer (PB), phosphate buffer saline (PBS) and artificial lysosomal fluid (ALF)) is analysed and discussed. The reaction orders with respect to the AA/DTT and the active compound, and the kinetic rate constants were also determined. The results show great variability in OP values among the studied species depending on the fluid used; the OP values were mostly higher in PB0.05 M, followed by PBS1x and ALF. Moreover, different species concentration-responses for OP-DTT/OP-AA were obtained. These differences were explained by the different reaction orders and kinetic rate constants obtained for each active compound in each fluid.

Effects of chemical composition of ambient PM2.5 measured in Seoul on potential health risks and generation of reactive oxygen species

This study assesses the health effects associated with the chemical species of ambient particulate matter (PM) with an aerodynamic diameter ≤2.5 μm (PM2.5) in Seoul, focusing on identifying key chemical constituents and their sources. We employed two approaches to estimate health risks: (1) evaluating carcinogenic and noncarcinogenic risks using IRIS (Integrated Risk Information System) data from the US EPA (Environmental Protection Agency), and (2) quantifying the generation of hydroxyl radicals (·OH) following exposure to PM2.5 in surrogate lung fluid (SLF). Our results show a significant impact on human health from certain elements (Cr, Ni, As, and Cd) and polycyclic aromatic hydrocarbons (PAHs) (DaeP, DahA, and BaP for carcinogenic risks; BaP and BeP for noncarcinogenic risks). Notably, Cr and BaP, which are influential in both risk assessment and ·OH generation, highlight their significant roles in human health impacts. However, other components (e.g., CPP, BaP, BghiP, BaA, CHR, PYR, FLT, Ca, Mg, and Cu), though contributors to ·OH generation, were not included in the EPA's health risk assessment, suggesting a need for a broader PM2.5 compositional analysis to more accurately determine exposure concentrations and assess inhalation risks. These components predominantly originate from anthropogenic sources, such as combustion, vehicles, and industrial activities, underscoring the significant health implications of the pollutants emitted from these sources. The study concluded that focusing solely on the mass reduction of PM2.5 may not suffice; a dual approach that reduces both mass concentration and chemical-specific health risks is imperative for effective public health protection.

Annual variation of source contributions to PM10 and oxidative potential in a mountainous area with traffic, biomass burning, cement-plant and biogenic influences

Toxicity of particulate matter (PM) depends on its sources, size and composition. We identified PM10 sources and determined their contribution to oxidative potential (OP) as a health proxy for PM exposure in an Alpine valley influenced by cement industry. PM10 filter sample chemical analysis and equivalent black carbon (eBC) were measured at an urban background site from November 2020 to November 2021. Using an optimized Positive Matrix Factorization (PMF) model, the source chemical fingerprints and contributions to PM10 were determined. The OP assessed through two assays, ascorbic acid (AA) and dithiothreitol (DTT), was attributed to the PM sources from the PMF model with a multiple linear regression (MLR) model. Ten factors were found at the site, including biomass burning (34, 40 and 38% contribution to annual PM10, OPAA and OPDDT, respectively), traffic (14, 19 and 7%), nitrate- and sulphate-rich (together: 16, 5 and 8%), aged sea salt (2, 2 and 0%) and mineral dust (10, 12 and 17%). The introduction of innovative organic tracers allowed the quantification of the PM primary and secondary biogenic fractions (together: 13, 8 and 21%). In addition, two unusual factors due to local features, a chloride-rich factor and a second mineral dust-rich factor (named the cement dust factor) were found, contributing together 10, 14 and 8%. We associate these two factors to different processes in the cement plant. Despite their rather low contribution to PM10 mass, these sources have one of the highest OPs per µg of source. The results of the study provide vital information about the influence of particular sources on PM10 and OP in complex environments and are thus useful for PM control strategies and actions.

Airborne environmentally persistent free radicals (EPFRs) in PM2.5 from combustion sources: Abundance, cytotoxicity and potential exposure risks

As an emerging atmospheric pollutant, airborne environmentally persistent free radicals (EPFRs) are formed during many combustion processes and pose various adverse health effects. In health-oriented air pollution control, it is vital to evaluate the health effects of atmospheric fine particulate matter (PM2.5) from different emission sources. In this study, various types of combustion-derived PM2.5 were collected on filters in a partial-flow dilution tunnel sampling system from three typical emission sources: coal combustion, biomass burning, and automobile exhaust. Substantial concentrations of EPFRs were determined in PM2.5 samples and associated with significant potential exposure risks. Results from in vitro cytotoxicity and oxidative potential assays suggest that EPFRs may cause substantial generation of reactive oxygen species (ROS) upon inhalation exposure to PM2.5 from anthropogenic combustion sources, especially from automobile exhaust. This study provides important evidence for the source- and concentration-dependent health effects of EPFRs in PM2.5 and motivates further assessments to advance public health-oriented PM2.5 emission control.

Concentration-dependent effects of reductive pulmonary inhalants on ultrafine particle-induced oxidative stress: Insights for health risk assessment

The impact of reductive pulmonary inhalants on ultrafine particles (UFPs)-induced pulmonary oxidative stress remains a crucial consideration, yet the concentration-dependent effects of these inhalants have remained unexplored. Here we synthesized composite UFPs simulating atmospheric UFPs, primarily composed of metals and quinones. We subjected these UFPs to varying concentrations (0-7000 μM) of two reductive pulmonary inhalants, N-acetylcysteine and salbutamol, to assess their influence on oxidative potential, measured through the dithiothreitol assay (OPDTT). Simultaneously, we analysed the soluble metal content of UFPs to uncover potential relationships between oxidative potential and metal solubility. Our results unveil a dual role played by these inhalants in shaping the OPDTT of composite UFPs. Specifically, OPDTT generally increased as inhalant concentrations rose from 0 to 300 μM. However, an intriguing reversal occurred when concentrations exceeded 500 μM, resulting in a decline in OPDTT. Relative to untreated UFPs, these inhalants induced promotion and inhibition effects within concentration ranges of 100-500 and >1000 μM, respectively. While no significant correlation emerged between OPDTT and soluble metal content as inhalant concentrations ranged from 0 to 7000 μM, noteworthy positive correlations emerged at lower inhalant concentrations (e.g., N-acetylcysteine at 0-300 μM). These findings provide insights into the potential influence of reductive pulmonary inhalants on health risks associated with UFP exposure, further underscoring the need for continued research in this critical area.

The important role of nitrate in iron and manganese dissolution and sulfate formation in fine particles at a coastal site in Northern China

Bioavailable transition trace elements, such as soluble iron (Fes) and soluble manganese (Mns) in aerosols, play a crucial role in atmospheric sulfate formation and marine ecosystems. In this study conducted during the spring of 2017 in Qingdao, a coastal city in Northern China, we applied a combined approach of multiple linear regression (MLR) incorporating the results of positive matrix factorization (PMF) to estimate the solubility of Fe and Mn from various sources. PMF analysis showed that dust was the largest contributor to total Fe (FeT) (45.5 %), followed by non-ferrous smelting (20.3 %) and secondary formation processes (17.8 %). However, secondary formation processes (33.2 %), vehicle exhaust (19.3 %) and aqueous-phase processes (19.0 %) were found to be the primary contributors to Fes. For total Mn (MnT) and Mns, dust (21.2 % ∼ 35.0 %), secondary formation processes (20.3 % ∼ 25.6 %) and industry (12.6 % ∼ 16.3 %) were identified as the dominant contributors. The solubilities of Fe and Mn varied significantly depending on their sources. Interestingly, nitrate played a more pronounced role than sulfate in facilitating the dissolution of Fe and Mn during the acid processing due to the high molar ratio of NO3-/2SO42- (1.72 ± 0.54) under the average RH of 56 % ± 15 %. This phenomenon suggested that the acid processing was primarily triggered by nitrate formation due to the low deliquescence relative humidity (DRH) of nitrate. Additionally, we discovered that the catalytic oxidation of SO2 in aerosol water was primarily driven by Fe rather than Mn, serving as a more significant pathway for sulfate formation within a pH range of 2.0 to 4.4. These findings provide valuable insights into the impact of acidification on the dissolution of Fe and Mn under conditions of moderate RH in the real ambient atmosphere with the increasing of NO3-/2SO42- molar ratio.

Impact of antioxidants on PM2.5 oxidative potential, radical level, and cytotoxicity

Antioxidants are typically seen as agents that mitigate environmental health risks due to their ability to scavenge free radicals. However, our research presents a paradox where these molecules, particularly those within lung fluid, act as prooxidants in the presence of airborne particulate matter (PM2.5), thus enhancing PM2.5 oxidative potential (OP). In our study, we examined a range of antioxidants found in the respiratory system (e.g., vitamin C, glutathione (GSH), and N-acetylcysteine (NAC)), in plasma (vitamin A, vitamin E, and β-carotene), and in food (tert-butylhydroquinone (TBHQ)). We aimed to explore antioxidants' prooxidant and antioxidant interactions with PM2.5 and the resulting OP and cytotoxicity. We employed OH generation assays and electron paramagnetic resonance assays to assess the pro-oxidative and anti-oxidative effects of antioxidants. Additionally, we assessed cytotoxicity interaction using a Chinese hamster ovary cell cytotoxicity assay. Our findings revealed that, in the presence of PM2.5, all antioxidants except vitamin E significantly increased the PM2.5 OP by generating more OH radicals (OH generation rate: 0.16-24.67 pmol·min-1·m-3). However, it's noteworthy that these generated OH radicals were at least partially neutralized by the antioxidants themselves. Among the pro-oxidative antioxidants, vitamin A, β-carotene, and TBHQ showed the least ability to quench these radicals, consistent with their observed impact in enhancing PM2.5 cytotoxicity (PM2.5 LC50 reduced to 91.2 %, 88.8 %, and 75.1 % of PM2.5's original level, respectively). Notably, vitamin A and TBHQ-enhanced PM2.5 OP were strongly associated with the presence of metals and organic compounds, particularly with copper (Cu) contributing significantly (35 %) to TBHQ's pro-oxidative effect. Our study underscores the potential health risks associated with the interaction between antioxidants and ambient pollutants.

Endogenous Nitric Oxide Can Enhance Oxidative Stress Caused by Air Pollutants and Explain Higher Susceptibility of Individuals with Inflammatory Disorders

Air pollution causes morbidity and excess mortality. In the epithelial lining fluid of the respiratory tract, air pollutants trigger a chemical reaction sequence that causes the formation of noxious hydroxyl radicals that drive oxidative stress. For hitherto unknown reasons, individuals with pre-existing inflammatory disorders are particularly susceptible to air pollution. Through detailed multiphase chemical kinetic analysis, we show that the commonly elevated concentrations of endogenous nitric oxide in diseased individuals can increase the production of hydroxyl radicals via peroxynitrite formation. Our findings offer a molecular rationale of how adverse health effects and oxidative stress caused by air pollutants may be exacerbated by inflammatory disorders.

Emerging Health Risks of Crumb Rubber: Inhalation of Environmentally Persistent Free Radicals via Saliva During Artificial Turf Activities

Crumb rubber (CR) is a commonly used infill material in artificial turf worldwide. However, the potential health risk associated with exposure to CR containing environmentally persistent free radicals (EPFRs) remains under investigation. Herein, we observed the widespread presence of CR particles in the range of 2.8-51.4 μg/m3 and EPFRs exceeding 6 × 1015 spins/g in the ambient air surrounding artificial turf fields. Notably, the abundance of these particles tended to increase with the number of operating years of the playing fields. Furthermore, by analyzing saliva samples from 200 participants, we established for the first time that EPFR-carrying CR could be found in saliva specimens, suggesting the potential for inhaling them through the oral cavity and their exposure to the human body. After 40 min of exercise on the turf, we detected a substantial presence of EPFRs, reaching as high as (1.15 ± 1.00) × 1016 spins of EPFR per 10 mL of saliva. Moreover, the presence of EPFRs considerably increased the oxidative potential of CR, leading to the inactivation of Ca2+, redox reactions, and changes in spatial binding of the α-1,4-chain of salivary amylase to Ca2+, all of which could influence human saliva health. Our study provides insights into a new pathway of human exposure to CR with EPFRs in artificial turf infill, indicating an increased human health risk of CR exposure.

Computational and experimental assessment of health risks of fine particulate matter in Nanjing and Yangzhou, China

Fine particulate matter (PM2.5) is a major air pollutant in most cities of China, and poses great health risks to local residents. In this study, the health effects of PM2.5 in Nanjing and Yangzhou were compared using computational and experimental methods. The global exposure mortality model (GEMM), including the results of a cohort study in China, was used to estimate the disease-related risks. Premature mortality attributable to PM2.5 exposure were markedly higher in Nanjing than that in Yangzhou at comparable levels of PM2.5 (8191 95% CI, 6975-9994 vs. 6548 95% CI, 5599-8049 in 2015). However, the baseline mortality rate was on a country-level and the age distribution was on a province-level, traditional estimation method could not accurately represent the health burdens of PM2.5 on a city-level. We proposed a refined calculation method which based on the actual deaths of each city and the disease death rates. Conversely, similar concentrations of PM2.5 exposure resulted in higher actual deaths per million population in Yangzhou (1466 95% CI, 1266-1746) than that in Nanjing (1271 95% CI, 1098-1514). Health risks of PM2.5 are associated with the generation of reactive oxygen species, among which hydroxyl radial (·OH) is the most reactive one. We then collected these PM2.5 samples and quantified the induced ·OH. Consistently, average ·OH concentration in 2015 was higher in Yangzhou than that in Nanjing, again indicating that PM2.5 in Yangzhou was more toxic. The combination of computational and experimental methods demonstrated the complex relationship between health risks and PM2.5 concentrations. The refined estimation method could help us better estimate and interpret the risks caused by PM2.5 exposure on a city-level.

The complexation of atmospheric Brown carbon surrogates on the generation of hydroxyl radical from transition metals in simulated lung fluid

Atmospheric particulate matter (PM) poses great adverse effects through the production of reactive oxygen species (ROS). Various components in PM are acknowledged to induce ROS formation, while the interactions among chemicals remain to be elucidated. Here, we systematically investigate the influence of Brown carbon (BrC) surrogates (e.g., imidazoles, nitrocatechols and humic acid) on hydroxyl radical (OH) generation from transition metals (TMs) in simulated lung fluid. Present results show that BrC has an antagonism (interaction factor: 20-90 %) with Cu2+ in OH generation upon the interaction with glutathione, in which the concentrations of BrC and TMs influence the extent of antagonism. Rapid OH generation in glutathione is observed for Fe2+, while OH formation is very little for Fe3+. The compositions of antioxidants (e.g., glutathione, ascorbate, urate), resembling the upper and lower respiratory tract, respond differently to BrC and TMs (Cu2+, Fe2+ and Fe3+) in OH generation and the degree of antagonism. The complexation equilibrium constants and site numbers between Cu2+ and humic acid were further analyzed using fluorescence quenching experiments. Possible complexation products among TMs, 4-nitrocatechol and glutathione were also identified using quadropule-time-of-flight mass spectrometry. The results suggest atmospheric BrC widely participate in complexation with TMs which influence OH formation in the human lung fluid, and complexation should be considered in evaluating ROS formation mediated by ambient PM.

Iron and Copper Alter the Oxidative Potential of Secondary Organic Aerosol: Insights from Online Measurements and Model Development

The oxidative potential (OP) of particulate matter has been widely suggested as a key metric for describing atmospheric particle toxicity. Secondary organic aerosol (SOA) and redox-active transition metals, such as iron and copper, are key drivers of particle OP. However, their relative contributions to OP, as well as the influence of metal-organic interactions and particulate chemistry on OP, remains uncertain. In this work, we simultaneously deploy two novel online instruments for the first time, providing robust quantification of particle OP. We utilize online AA (OPAA) and 2,7-dichlorofluoroscein (ROSDCFH) methods to investigate the influence of Fe(II) and Cu(II) on the OP of secondary organic aerosol (SOA). In addition, we quantify the OH production (OPOH) from these particle mixtures. We observe a range of synergistic and antagonistic interactions when Fe(II) and Cu(II) are mixed with representative biogenic (β-pinene) and anthropogenic (naphthalene) SOA. A newly developed kinetic model revealed key reactions among SOA components, transition metals, and ascorbate, influencing OPAA. Model predictions agree well with OPAA measurements, highlighting metal-ascorbate and -naphthoquinone-ascorbate reactions as important drivers of OPAA. The simultaneous application of multiple OP assays and a kinetic model provides new insights into the influence of metal and SOA interactions on particle OP.

Assessing oxidative stress induction ability and oxidative potential of PM2.5 in cities in eastern and western Japan

Oxidative stress is an important cause of respiratory diseases associated with exposure to PM_2.5. Accordingly, acellular methods for assessing the oxidative potential (OP) of PM_2.5 have been evaluated extensively for use as indicators of oxidative stress in living organisms. However, OP-based assessments only reflect the physicochemical properties of particles and do not consider particle-cell interactions. Therefore, to determine the potency of OP under various PM_2.5 scenarios, oxidative stress induction ability (OSIA) assessments were performed using a cell-based method, the heme oxygenase-1 (HO-1) assay, and the findings were compared with OP measurements obtained using an acellular method, the dithiothreitol assay. For these assays, PM_2.5 filter samples were collected in two cities in Japan. To quantitatively determine the relative contribution of the quantity of metals and subtypes of organic aerosols (OA) in PM_2.5 to the OSIA and the OP, online measurements and offline chemical analysis were also performed. The findings showed a positive relationship between the OSIA and OP for water-extracted samples, confirming that the OP is generally well suited for use as an indicator of the OSIA. However, the correspondence between the two assays differed for samples with a high water-soluble (WS)-Pb content, which had a higher OSIA than would be expected from the OP of other samples. The results of reagent-solution experiments showed that the WS-Pb induced the OSIA, but not the OP, in 15-min reactions, suggesting a reason for the inconsistent relationship between the two assays across samples. Multiple linear regression analyses and reagent-solution experiments showed that WS transition metals and biomass burning OA accounted for approximately 30-40% and 50% of the total OSIA or the total OP of water-extracted PM_2.5 samples, respectively. This is the first study to evaluate the association between cellular oxidative stress assessed by the HO-1 assay and the different subtypes of OA.

Effects of endogenous and exogenous reductants in lung fluid on the bioaccessible metal concentration and oxidative potential of ultrafine particles

Health risk posed by ultrafine particles (UFPs) is potentially increased by reducing substances present in lung fluid, although knowledge of the underlying mechanisms is insufficient. Here, UFPs mainly consisting of metals and quinones were prepared. The reducing substances examined included lung endogenous and exogenous reductants. UFPs were extracted in simulated lung fluid containing reductants. Extracts were used to analyze metrics relevant to health effects, including the bioaccessible metal concentration (Me_BA) and oxidative potential (OP^DTT). The Me_BA of Mn (974.5-9896.9 μg L^-1) was higher than those of Cu (155.0-599.6 μg L^-1) and Fe (79.9-500.9 μg L^-1). Correspondingly, UFPs containing Mn had higher OP^DTT (2.07-12.0 pmol min^-1 μg^-1) than those containing Cu (2.03-7.11 pmol min^-1 μg^-1) and Fe (1.63-5.34 pmol min^-1 μg^-1). Endogenous and exogenous reductants can increase Me_BA and OP^DTT, and the increments were generally higher for composite than pure UFPs. Positive correlations between OP^DTT and Me_BA of UFPs in the presence of most reductants emphasized the importance of the bioaccessible metal fraction in UFPs for inducing oxidative stress by reactive oxygen species (ROS)-generating reactions between quinones, metals, and lung reductants. Present findings provide novel insight into the toxicity and health risks of UFPs.

Oxidative potential of heavy-metal contaminated soil reflects its ecological risk on earthworm

The ecological risk of heavy metal-contaminated soil is usually evaluated by its oxidative stress on terrestrial animals, which are vulnerable to the impact of individual differences of animals and environmental conditions. Oxidative potential (OP) is the potential of particles to induce the formation of reactive oxygen species (ROS). In this study, OP of the in situ contaminated soils collected from an industrial site (i.e., 64.5-7783 mg/kg of Cu, 54.9-397 mg/kg of Pb, 278-2085 mg/kg of Zn and 0.615-121 mg/kg of Cd) were measured as 38.0-60.1 pmol/min/mg, and the water extractable Cu, Pb, Zn, and Cd in soils have been proved to contribute 89%-98% to OP. Oxidative stress in earthworms (Eisenia fetida) caused by the industrial contaminated soils can be reflected by the biomarkers such as 8-hydroxy-2'-deoxyguanosine, metallothionein, and antioxidant enzymes, and a negative correlation presents between the comprehensive biomarker response index and the OP of soils (r = -0.979, p < 0.01). This is the first time to propose a dose-response relationship between OP and oxidative stress. Metabolomic analysis also verified that the regulation of four ROS-related metabolites (i.e., l-pipecolate, 1-methylhistidine, 5-methoxytryptamine, and xanthosine) in earthworms treated with contaminated soil were directly correlated with OP values. These results indicate that OP can be used as an indicator for ecological risk assessment of heavy metal-contaminated soil, which provides a fast, stable and easily testable chemical method.

Seasonal variation of driving factors of ambient PM2.5 oxidative potential in Shenzhen, China

Reactive oxygen species (ROS) play a central role in health effects of ambient fine particulate matter (PM_2.5). In this work, we screened for efficient and complementary oxidative potential (OP) measurements by comparing the response values of multiple chemical probes (OP^DTT, OP^OH, OP^GSH) to ambient PM_2.5 in Shenzhen, China. Combined with meteorological condition and PM_2.5 chemical composition analysis, we explored the effects of different chemical components and emission sources on the ambient PM_2.5 OP and analyzed their seasonal variations. The results show that OP_m^DTT(mass-normalized) and OP_m^GSH-SLF were highly correlated (r = 0.77). OP^DTT was mainly influenced by organic carbon, while OP^OH was highly dominated by heavy metals. The combination of OP^DTT and OP^OH provides an efficient and comprehensive measurement of OP. Temporally, the OPs were substantially higher in winter than in summer (1.4 and 4 times higher for OP_m^DTT and OP_m^OH, respectively). The long-distance transported biomass burning sources from the north dominated the OP^DTT in winter, while the ship emissions mainly influenced the summer OP. The OP_m^DTT increased sharply with the decrease of PM_2.5 mass concentration, especially when the PM_2.5 concentration was lower than 30 μg/m³. The huge differences in wind fields between the winter and summer cause considerable variations in PM_2.5 concentrations, components, and OP. Our work emphasizes the necessity of long-term, multi-method, multi-component assessment of the OP of PM_2.5.

Organic Peroxides in Aerosol: Key Reactive Intermediates for Multiphase Processes in the Atmosphere

Organic peroxides (POs) are organic molecules with one or more peroxide (-O-O-) functional groups. POs are commonly regarded as chemically labile termination products from gas-phase radical chemistry and therefore serve as temporary reservoirs for oxidative radicals (HOx and ROx) in the atmosphere. Owing to their ubiquity, active gas-particle partitioning behavior, and reactivity, POs are key reactive intermediates in atmospheric multiphase processes determining the life cycle (formation, growth, and aging), climate, and health impacts of aerosol. However, there remain substantial gaps in the origin, molecular diversity, and fate of POs due to their complex nature and dynamic behavior. Here, we summarize the current understanding on atmospheric POs, with a focus on their identification and quantification, state-of-the-art analytical developments, molecular-level formation mechanisms, multiphase chemical transformation pathways, as well as environmental and health impacts. We find that interactions with SO2 and transition metal ions are generally the fast PO transformation pathways in atmospheric liquid water, with lifetimes estimated to be minutes to hours, while hydrolysis is particularly important for α-substituted hydroperoxides. Meanwhile, photolysis and thermolysis are likely minor sinks for POs. These multiphase PO transformation pathways are distinctly different from their gas-phase fates, such as photolysis and reaction with OH radicals, which highlights the need to understand the multiphase partitioning of POs. By summarizing the current advances and remaining challenges for the investigation of POs, we propose future research priorities regarding their origin, fate, and impacts in the atmosphere.

Superoxide Release by Macrophages through NADPH Oxidase Activation Dominating Chemistry by Isoprene Secondary Organic Aerosols and Quinones to Cause Oxidative Damage on Membranes

Oxidative stress mediated by reactive oxygen species (ROS) is a key process for adverse aerosol health effects. Secondary organic aerosols (SOA) account for a major fraction of fine particulate matter, and their inhalation and deposition into the respiratory tract causes the formation of ROS by chemical and cellular processes, but their relative contributions are hardly quantified and their link to oxidative stress remains uncertain. Here, we quantified cellular and chemical superoxide generation by 9,10-phenanthrenequinone (PQN) and isoprene SOA using a chemiluminescence assay combined with electron paramagnetic resonance spectroscopy as well as kinetic modeling. We also applied cellular imaging techniques to study the cellular mechanism of superoxide release and oxidative damage on cell membranes. We show that PQN and isoprene SOA activate NADPH oxidase in macrophages to release massive amounts of superoxide, overwhelming the superoxide formation by aqueous chemical reactions in the epithelial lining fluid. The activation dose for PQN is 2 orders of magnitude lower than that of isoprene SOA, suggesting that quinones are more toxic. While higher exposures trigger cellular antioxidant response elements, the released ROS induce oxidative damage to the cell membrane through lipid peroxidation. Such mechanistic and quantitative understandings provide a basis for further elucidation of adverse health effects and oxidative stress by fine particulate matter.

High fraction of soluble trace metals in fine particles under heavy haze in central China

Atmospheric trace metals are a key component of particulate matter and significantly influence the atmospheric process and human health. The dissolved fraction of trace metals represents their bioavailability and exhibits high chemical activity. However, the optimum measurement method for detecting the soluble fraction of trace metals is still undetermined. The impact of variations in pollution on the soluble fraction is largely unrevealed. Therefore, in this work, a one-month field observation was conducted in Central China and different extraction solvents were used to determine the proper measurement method for the soluble fraction of trace metals and investigate the variation pattern under different pollution conditions. The findings show that solvents with acidity near that of aerosol water can better reflect the actual soluble fraction of trace metals in fine particulate matter. The soluble fraction of trace metals tends to increase with pollution level increased, demonstrating unexpectedly high health risks and chemical activity under heavy haze conditions. Our results indicate that remediation and trace metal pollution control are urgently needed.

Unveiling the pH-Dependent Yields of H2O2 and OH by Aqueous-Phase Ozonolysis of m-Cresol in the Atmosphere

Hydrogen peroxide (H₂O₂) and hydroxyl radical (OH) are important oxidants in the atmospheric aqueous phase such as cloud droplets and deliquescent aerosol particles, playing a significant role in the chemical transformation of organic and inorganic pollutants in the atmosphere. Atmospheric aqueous-phase chemistry has been considered to be a source of H₂O₂ and OH. However, our understanding of the mechanisms of their formation in atmospheric waters is still incomplete. Here, we show that the aqueous-phase reaction of dissolved ozone (O₃) with substituted phenols such as m-cresol represents an important source of H₂O₂ and OH exhibiting pH-dependent yields. Intriguingly, the formation of H₂O₂ through the ring-opening mechanism is strongly promoted under lower pH conditions (pH 2.5-3.5), while higher pH favors the ring-retaining pathways yielding OH. The rate constant of the reaction of O₃ with m-cresol increases with increasing pH. The reaction products formed during the ozonolysis of m-cresol are analyzed by an Orbitrap mass spectrometer, and reaction pathways are suggested based on the identified product compounds. This study indicates that aqueous-phase ozonolysis of phenolic compounds might be an alternative source of H₂O₂ and OH in the cloud, rain, and liquid water of aerosol particles; thus, it should be considered in future model studies.

Iron Speciation in Respirable Particulate Matter and Implications for Human Health

Particulate matter (PM) air pollution poses a major global health risk, but the role of iron (Fe) is not clearly defined because chemistry at the particle-cell interface is often not considered. Detailed spectromicroscopy characterizations of PM_2.5 samples from the San Joaquin Valley, CA identified major Fe-bearing components and estimated their relative proportions. Iron in ambient PM_2.5 was present in spatially and temporally variable mixtures, mostly as Fe(III) oxides and phyllosilicates, but with significant fractions of metallic iron (Fe(0)), Fe(II,III) oxide, and Fe(III) bonded to organic carbon. Fe(0) was present as aggregated, nm-sized particles that comprised up to ∼30% of the Fe spectral fraction. Mixtures reflect anthropogenic and geogenic particles subjected to environmental weathering, but reduced Fe in PM originates from anthropogenic sources, likely as abrasion products. Possible mechanistic pathways involving Fe(0) particles and mixtures of Fe(II) and Fe(III) surface species may generate hydrogen peroxide and oxygen-centered radical species (hydroxyl, hydroperoxyl, or superoxide) in Fenton-type reactions. From a health perspective, PM mixtures with reduced and oxidized Fe will have a disproportionate effect in cellular response after inhalation because of their tendency to shuttle electrons and produce oxidants and electrophiles that induce inflammation and oxidative stress.

The lung surfactant activity probed with molecular dynamics simulations

The surface of pulmonary alveolar subphase is covered with a mixture of lipids and proteins. This lung surfactant plays a crucial role in lung functioning. It shows a complex phase behavior which can be altered by the interaction with third molecules such as drugs or pollutants. For studying multicomponent biological systems, it is of interest to couple experimental approach with computational modelling yielding atomic-scale information. Simple two, three, or four-component model systems showed to be useful for getting more insight in the interaction between lipids, lipids and proteins or lipids and proteins with drugs and impurities. These systems were studied theoretically using molecular dynamic simulations and experimentally by means of the Langmuir technique. A better understanding of the structure and behavior of lung surfactants obtained from this research is relevant for developing new synthetic surfactants for efficient therapies, and may contribute to public health protection.

Sources of cellular oxidative potential of water-soluble fine ambient particulate matter in the Midwestern United States

We investigated the spatiotemporal distribution and sources of cellular oxidative potential (OP) in the Midwest US. Weekly samples were collected from three urban [Chicago (IL), Indianapolis (IN), and St. Louis (MO)], one rural [Bondville (IL], and one roadside site [Champaign (IL)] for a year (May 2018 to May 2019), and analyzed for water-soluble cellular OP using a macrophage reactive oxygen species (ROS) assay. Chemical composition of the samples including several carbonaceous components, inorganic ions, and water-soluble elementals, were also analyzed. The emission sources contributing to water-soluble cellular OP and PM_2.5 mass were analyzed using positive matrix factorization. The secondary organic aerosols contributed substantially (≥54%) to PM_2.5 cellular OP at urban sites, while the roadside and rural OP were dominated by road dust (54%) and agricultural activities (62%), respectively. However, none of these sources contributed substantially to the PM_2.5 mass (≤21%). Other sources contributing significantly to the PM_2.5 mass, i.e., secondary sulfate and nitrate, biomass burning and coal combustion (14-26%) contributed minimally to the cellular OP (≤13%). Such divergent profiles of the emission sources contributing to cellular OP vs. PM_2.5 mass demonstrate the need of considering more health-relevant metrics such as OP in the design of air pollution control strategies.

In Vitro Assessment Reveals the Effects of Environmentally Persistent Free Radicals on the Toxicity of Photoaged Tire Wear Particles

Tire wear particles (TWP) have been identified as one of the major sources of microplastics (MPs), and few studies have focused on their environmental behaviors and impacts. However, a thorough characteristic and toxicity assessment associated with environmentally persistent free radicals (EPFRs) on the photoaged TWP is missing. In this study, we investigated EPFRs in the process of TWP photoaging and evaluated their toxicity using in vitro bioassays. Our results showed that a total of around 1.0 × 10¹⁷ spins/g EPFRs (g-factors ranging 2.00308-2.00318) was formed on TWP with 60 days of light irradiation, which contained more than 29% of reactive EPFRs (r-EPFRs). Using macrophages as model cells for bioassays, TWP-associated EPFRs trigged endpoints, including the decrease of cell viability (27 to 45%) and the increase of oxidative stress response (46-93%) and inflammatory factor secretion. The enhancement of TWP toxicity with photoaging was confirmed to be attributed to the generated EPFRs combined with other TWP's chemical compositions (e.g., various metals and organics). Most importantly, the toxicity of photoaged TWP was closely correlated with the generated r-EPFRs, which induced reactive oxidant species (ROS) generation. This study provides direct evidence of toxicity on the photoaged TWP particles, revealing the potential contributions of EPFRs to the adverse effect on human health and highlighting the need for an improved understanding of the impacts of EPFRs on the risk assessment of TWP released into the environment.

Quantitative Determination of Airborne Redox-Active Compounds Based on Heating-Induced Reduction of Gold Nanoparticles

Airborne redox-active compounds (ARC) account for a substantial fraction of atmospheric aerosols and play a vital role in chemical processes that influence global climate and human and ecological health. With the exception of the determination of total organic carbon by the expensive total organic carbon (TOC) analyzer, there is currently no easy-to-use method to quantify ARC. Here, we designed a method to detect the concentration of ARC by using the thermal-induced reduction and colorimetric behaviors of gold nanoparticles (AuNPs), in which the humic substances (HS) was used as a standard model of ARC to calculate the HS-equivalent concentration of ARC. Distinguished from the conventional complex methods, e.g., TOC analysis, the proposed approach measured localized surface plasmon resonance absorption of AuNPs and the target ARC concentration can be either directly quantified by the absorption spectrometer or qualitatively evaluated by the naked eyes. By using the absorption spectrometer, a limit of detection of 0.005 ppm by our AuNP sensor was achieved. To validate this sensing technique, aerosol samples collected from Basel (suburban), Bern (urban), and Rigi mountain (rural and high-altitude) sites in Switzerland were further investigated through the TOC combustion method. The results thereby substantiated that our plasmonic absorption-based AuNP sensor upholds a great promise for fast, cost-efficient total ARC detection and air quality assessment.

The chemical composition and toxicological effects of fine particulate matter (PM2.5) emitted from different cooking styles

The mass, chemical composition and toxicological properties of fine particulates (PM_2.5) emitted from cooking activities in three Hong Kong based restaurants and two simulated cooking experiments were characterized. Extracts from the PM_2.5 samples elicited significant biological activities [cell viability, generation of reactive oxygen species (ROS), DNA damage and inflammation effect (TNF-α)] in a dose-dependent manner. The composition of PAHs, oxygenated PAHs (OPAHs) and azaarenes (AZAs) mixtures differed between samples. The concentration ranges of the Σ30PAHs, Σ17OPAHs and Σ4AZAs and Σ7Carbonyls in the samples were 9627-23,452 pg m^-3, 503-3700 pg m^-3, 33-263 pg m^-3 and 158 - 5328 ng m^-3, respectively. Cell viability caused by extracts from the samples was positively correlated to the concentration of benzo[a]anthracene, indeno[1,2,3-cd]pyrene and 1,4-naphthoquinone in the PM_2.5 extracts. Cellular ROS production (upon exposure to extracts) was positively correlated with the concentrations of PM_2.5, decaldehyde, acridine, Σ17OPAHs and 7 individual OPAHs. TNF-α showed significant positive correlations with the concentrations of most chemical species (elemental carbon, 16 individual PAHs including benzo[a]pyrene, Σ30PAHs, SO₄^2-, Ca²⁺, Ca, Na, K, Ti, Cr, Mn, Fe, Cu and Zn). The concentrations of Al, Ti, Mn, Σ30PAHs and 8 individual PAHs including benzo[a]pyrene in the samples were positively correlated with DNA damage caused by extracts from the samples. This study demonstrates that inhalation of PM_2.5 emitted from cooking could result in adverse human health effects.

The dissolution of stone wool fibers with sugar-based binder and oil in different synthetic lung fluids

The biopersistence of fiber materials is one of the cornerstones in estimating potential risk to human health upon inhalation. To connect epidemiological and in vivo investigations with in vitro studies, reliable and robust methods of fiber biopersistence determination and understanding of fiber dissolution mechanism are required. We investigated dissolution properties of oil treated stone wool fibers with and without sugar-based binder (SBB) at 37 °C in the liquids representing macrophages intracellular conditions (pH 4.5). Conditions varied from batch to flow of different rates. Fiber morphology and surface chemistry changes caused by dissolution were monitored with scanning electron microscopy and time-of-flight secondary ion mass spectrometry mapping. Stone wool fiber dissolution rate depends on liquid composition (presence of ligands, such as citrate), pH, reaction products transport and fibers wetting properties. The dissolution rate decreases when: 1) citrate is consumed by the reaction with the released Al cations; 2) the pH increases during a reaction in poorly buffered solutions; 3) the dissolution products are accumulated; 4) fibers are not fully wetted with the fluid. Presence of SBB has no influence on dissolution rate if fiber material was wetted prior to dissolution experiment to avoid poorly wetted fiber agglomerates formation in the synthetic lung fluids.

Hydroxyl Radical Production by Air Pollutants in Epithelial Lining Fluid Governed by Interconversion and Scavenging of Reactive Oxygen Species

Air pollution is a major risk factor for human health. Chemical reactions in the epithelial lining fluid (ELF) of the human respiratory tract result in the formation of reactive oxygen species (ROS), which can lead to oxidative stress and adverse health effects. We use kinetic modeling to quantify the effects of fine particulate matter (PM2.5), ozone (O₃), and nitrogen dioxide (NO₂) on ROS formation, interconversion, and reactivity, and discuss different chemical metrics for oxidative stress, such as cumulative production of ROS and hydrogen peroxide (H₂O₂) to hydroxyl radical (OH) conversion. All three air pollutants produce ROS that accumulate in the ELF as H₂O₂, which serves as reservoir for radical species. At low PM2.5 concentrations (<10 μg m^-3), we find that less than 4% of all produced H₂O₂ is converted into highly reactive OH, while the rest is intercepted by antioxidants and enzymes that serve as ROS buffering agents. At elevated PM2.5 concentrations (>10 μg m^-3), however, Fenton chemistry overwhelms the ROS buffering effect and leads to a tipping point in H₂O₂ fate, causing a strong nonlinear increase in OH production. This shift in ROS chemistry and the enhanced OH production provide a tentative mechanistic explanation for how the inhalation of PM2.5 induces oxidative stress and adverse health effects.

Effects of reactive oxygen species generation induced by Wonju City particulate matter on mitochondrial dysfunction in human middle ear cell

Atmospheric particulate matter (PM) contains different components that can elicit varying adverse health effects in humans and animals. Studies on PM toxicity and its underlying mechanisms in the middle ear are limited, and they generally use a PM standard. However, as PM composition varies temporally and geographically, it is crucial to identify the toxic PM constituents according to season and region and investigate their associated health effects. Thus, we sought to determine whether PM induces cytotoxicity and inflammatory factor and reactive oxygen species (ROS) generation in human middle ear epithelial cells obtained from patients with otitis media. The cells were treated with both standard urban PM and PM directly captured from the atmosphere in Wonju City. The association between mitochondrial dysfunction and PM was investigated. PM exposure significantly increased COX-2 and TNF-α mRNA expression, increased ROS generation, induced inflammatory responses, and caused abnormalities in mitochondrial motility and function. Furthermore, PM induced cell apoptosis, which consequently reduced cell survival, particularly at the concentration of 100 μg/mL. Overall, our study provides new insights into the toxic effects of standard and atmospheric PM on middle ear cell line.

Simulated biological fluids - a systematic review of their biological relevance and use in relation to inhalation toxicology of particles and fibres

The use of simulated biological fluids (SBFs) is a promising in vitro technique to better understand the release mechanisms and possible in vivo behaviour of materials, including fibres, metal-containing particles and nanomaterials. Applications of SBFs in dissolution tests allow a measure of material biopersistence or, conversely, bioaccessibility that in turn can provide a useful inference of a materials biodistribution, its acute and long-term toxicity, as well as its pathogenicity. Given the wide range of SBFs reported in the literature, a review was conducted, with a focus on fluids used to replicate environments that may be encountered upon material inhalation, including extracellular and intracellular compartments. The review aims to identify when a fluid design can replicate realistic biological conditions, demonstrate operation validation, and/or provide robustness and reproducibility. The studies examined highlight simulated lung fluids (SLFs) that have been shown to suitably replicate physiological conditions, and identify specific components that play a pivotal role in dissolution mechanisms and biological activity; including organic molecules, redox-active species and chelating agents. Material dissolution was not always driven by pH, and likewise not only driven by SLF composition; specific materials and formulations correspond to specific dissolution mechanisms. It is recommended that SLF developments focus on biological predictivity and if not practical, on better biological mimicry, as such an approach ensures results are more likely to reflect in vivo behaviour regardless of the material under investigation.

Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China

Epidemiological studies have consistently linked exposure to PM_2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PM_2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PM_2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PM_2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PM_2.5, including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PM_2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM_2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PM_2.5 mass concentrations (μgm^-3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM_2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM_2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM_2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM_2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PM_2.5 and how they affect both PM_2.5 OP and the concentrations of particle-bound reactive oxygen species.

Pollutants from primary sources dominate the oxidative potential of water-soluble PM2.5 in Hong Kong in terms of dithiothreitol (DTT) consumption and hydroxyl radical production

Increasing scientific findings show that the adverse health effects of PM_2.5 are related not only to its mass but also PM_2.5 sources and chemical compositions. Here, we conducted a comprehensive characterization and source apportionment of oxidative potential (OP) of water-soluble PM_2.5 collected in Hong Kong for one year. Two OP indicators, namely dithiothreitol (DTT) consumption and ∙OH formation, were quantified. Six PM_2.5 sources, i.e. secondary sulfate, biomass burning, secondary organic aerosol (SOA), vehicle emissions, marine vessels, and a metal-related factor, were apportioned and identified to be DTT active. The four primary sources accounted for 83.5% of DTT activity of water-soluble PM_2.5, with the metal-related factor and marine vessels as the leading contributors. However, only three sources, i.e. metal-related factor, vehicle emissions, and SOA, showed ∙OH generation ability, with a predominant contribution of 96.2% from the two primary sources, especially the metal-related factor (84.5%). Based on the source apportionment results, we further evaluate the intrinsic OP of water-soluble PM_2.5 from each source. Marine vessels exhibited the highest intrinsic DTT activity; while metal-related factor was most effective in ∙OH generation.

Understanding how methodological aspects affect the release of trace metal(loid)s from urban dust in inhalation bioaccessibility tests

The bioaccessibility of metal(loid)s in ambient particulate matter (PM) has been recently used to represent the risk of inhalation exposure. Nevertheless, different methodological factors affect the bioaccessibility values; among these, the type and composition of surrogate biological fluids and the liquid to solid ratio have been revealed to be the most important. To better understand how these methodological aspects affect the bioaccessibility, a reference material corresponding to urban dust (SRM1648a) was contacted with synthetic biological fluids commonly used in the literature representing surrogate fluids that may interact with fine (Gamble's solutions, artificial lysosomal fluid (ALF)) and coarse particles (gastric fluid), for liquid to solid (L/S) ratios ranging from 500 to 20,000. Visual MINTEQ 3.1. was used to enhance the discussion on how the solubility of metals in the leaching solution depends on the composition of the simulated fluids and the speciation of metals. The results obtained indicate that a small change in the composition of Gamble's solution (the presence of glycine) may increase significantly the bioaccessibility at a L/S ratio of 5,000. The highest bioaccessibility of most of the studied metal(loid)s at a L/S ratio of 5,000 was found for ALF fluid. The study of the effect of the L/S ratio showed that metal(loid)s bioaccessibility in Gamble's fluid increased logarithmically with increasing L/S ratio, while it remained practically constant in ALF and gastric fluid. This different behavior is explained assuming that the leaching of metal(loid)s in Gamble's solution is solubility-controlled, while in ALF and gastric fluid is availability-controlled.

Iron Speciation in Particulate Matter (PM2.5) from Urban Los Angeles Using Spectro-microscopy Methods

The speciation, oxidation states, and relative abundance of iron (Fe) phases in PM2.5 samples from two locations in urban Los Angeles were investigated using a combination of bulk and spatially resolved, element-specific spectroscopy and microscopy methods. Synchrotron X-ray absorption spectroscopy (XAS) of bulk samples in situ (i.e., without extraction or digestion) was used to quantify the relative fractions of major Fe phases, which were corroborated by spatially resolved spectro-microscopy measurements. Ferrihydrite (amorphous Fe(III)-hydroxide) comprised the largest Fe fraction (34-52%), with hematite (α-Fe2O3; 13-23%) and magnetite (Fe3O4; 10-24%) identified as major crystalline oxide components. An Fe-bearing phyllosilicate fraction (16-23%) was fit best with a reference spectrum of a natural illite/smectite mineral, and metallic Fe(0) was a relatively small (2-6%) but easily identified component. Sizes, morphologies, oxidation state, and trace element compositions of Fe-bearing PM from electron microscopy, electron energy loss spectroscopy (EELS), and scanning transmission X-ray microscopy (STXM) revealed variable and heterogeneous mixtures of Fe species and phases, often associated with carbonaceous material with evidence of surface oxidation. Ferrihydrite (or related Fe(III) hydroxide phases) was ubiquitous in PM samples. It forms as an oxidation or surface alteration product of crystalline Fe phases, and also occurs as coatings or nanoparticles dispersed with other phases as a result of environmental dissolution and re-precipitation reactions. The prevalence of ferrihydrite (and adsorbed Fe(III) has likely been underestimated in studies of ambient PM because it is non-crystalline, non-magnetic, more soluble than crystalline phases, and found in complex mixtures. Review of potential sources of different particle types suggests that the majority of Fe-bearing PM from these urban sites originates from anthropogenic activities, primarily abrasion products from vehicle braking systems and engine emissions from combustion and/or wear. These variable mixtures have a high probability for electron transfer reactions between Fe, redox-active metals such as copper, and reactive carbon species such as quinones. Our findings suggest the need to assess biological responses of specific Fe-bearing phases both individually and in combination to unravel mechanisms of adverse health effects of particulate Fe.

Size distributions of particle-generated hydroxyl radical (·OH) in surrogate lung fluid (SLF) solution and their potential sources

Although it is known that increases in ambient particulate matter (PM) levels are associated with elevated occurrence of adverse health outcomes, the understanding of the mechanisms of PM-related health effects is limited by our knowledge of how particle size and composition are altered subsequent to inhalation through respiratory-deposited processing. Here we present a particle-generated hydroxyl radical (·OH) study of the size-resolved particles as particles are inhaled in the human respiratory tract (RT), and we show that accumulation-mode particles are significant factors (71-75%) in ·OH generation of lung-deposited particles using Multiple-Path Particle Dosimetry (MPPD) model. The ability of PM to catalyze ·OH generation is mainly related to transition metals, particularly towards the upper regions of the RT (75%), and to quinones deeper in the lung (42-46%). Identification of this generation ability induced by chemical composition has shown that four potential sources (biomass burning, incomplete combustion, mobile & industry, and mineral dust) are responsible for ·OH generation. With ·OH-forming ability after PM inhalation implicated as the first step towards revealing the subsequent toxic processes, this work draws a connection between the detailed ·OH chemistry occurring on size-resolved particles and a possible toxicological mechanism based on chemical composition and sources.

ROS-generation potential of Humic-like substances (HULIS) in ambient PM2.5 in urban Shanghai: Association with HULIS concentration and light absorbance

Ambient fine particulate matter (PM_2.5) can cause adverse health effects through the generation of reactive oxygen species (ROS) after inhalation. Humic-like substances (HULIS) are major constituents contributing to the ROS-generation potential in organic aerosols. In this study, PM_2.5 samples in urban Shanghai during autumn and winter (2018-2019) were collected. Mass-normalized ·OH generation rate in surrogate lung fluid (SLF) was used to denote the intrinsic ROS-generation potential of PM_2.5 or of the HULIS isolated from PM_2.5. In this study, ROS-generation potential of PM_2.5 decreased with increasing ambient PM_2.5 concentration due to higher percentage of inorganic components in high PM_2.5 event. Same trend was observed for the ROS-generation potential of unit mass of HULIS, which was higher when HULIS and PM_2.5 concentrations were both relatively lower. The HULIS with high ROS-generation potential but low concentration (High-ROS/Low-Conc HULIS) were likely produced by the atmospheric aqueous-phase reactions during nighttime or under high relative humidity conditions, not from biomass burning emissions or the photochemical pollution products. The association between ROS-generation potential and light absorption properties of HULIS was studied as well. The High-ROS/Low-Conc HULIS also showed stronger light absorbance than the other HULIS. Our results implied the potentially important roles that HULIS species might play in atmospheric environment and human health even when the PM_2.5 pollution is low.

Synergistic and antagonistic interactions among organic and metallic components of the ambient particulate matter (PM) for the cytotoxicity measured by Chinese hamster ovary cells

Although PM_2.5 toxicity is known to be related to its chemical composition, the effect of interactions among various particles' components on the toxicity is not well explored. To understand these interactions, especially metals and organic compounds on PM_2.5 cytotoxicity, we chose several redox-active substances known to be present in the ambient particles such as metals (Cu, Fe, and Mn) and quinones [9,10-phenanthraquinone (PQ), 1,2-naphthoquinone (1,2-NQ), 1,4-naphthoquinone (1,4-NQ), and 5-hydroxy-1,4-naphthoquinone (5,H-1,4-NQ)]. Cytotoxicity was assessed through a Chinese hamster ovary (CHO) cells assay and expressed by a median lethal concentration (LC₅₀). Two methods were employed to assess the interactions. In the first method, we tested the impact of nontoxic level of a component on the LC₅₀ of other components. In the second method, we mixed two components in different concentration ratios to expose the cells and calculated a mixture toxicity index (MTI). MTI is a composite value to quantify the nature of interactions such that the interactions are considered synergistic when MTI > 1, additive when 0 < MTI ≤ 1 and antagonistic when MTI < 0. The interactions between quinones and metals were largely synergistic by both methods. To further assess the environmental relevance of these mixtures, we extracted organic compounds termed as water-soluble Humic-like substances (HULIS) from real ambient PM samples and mixed them with individual metals. A similar pattern, as observed from the interaction of quinones and metals, was found. Moreover, the interactions became more synergistic as the relative concentration of metals with respect to water-soluble HULIS was decreased in these mixtures. With environmentally relevant mass concentration ratios of organics to metals (75-7500), the interactions were strongly synergistic (MTI = 1-115). These results indicate the importance of incorporating the interaction among various PM components for estimating the net toxicity of ambient PM_2.5.

Effects of N-acetylcysteine on oxidative stress and inflammation reactions in a rat model of allergic rhinitis after PM2.5 exposure

Particulate matter 2.5 (PM_2.5) exposure can increase the prevalence of allergic rhinitis (AR), the mechanism underlying which may include oxidative stress and inflammatory response. As a ROS quenching agent, N-acetylcysteine (NAC) can attenuate the accumulation of inflammatory cells and hyper-responsiveness in animal asthma models. To explore the effect of NAC on the oxidative stress and inflammatory reactions in AR rats exposed to PM_2.5, we analyzed the components of PM_2.5 and examined the nasal symptoms, redox level in nasal mucosa, Th1/Th2-related serum cytokines, nasal mucosal histopathology and ultrastructure in AR rat models with NAC intervention after PM_2.5 exposure. The results showed that the high concentrations of metal cations and PAHs in PM_2.5 could aggravate Th2-dominant allergic inflammation in AR model and cause redox imbalance, accompanied by nasal epithelial cell stripping and eosinophil infiltration, while NAC intervention could alleviate the clinical symptoms of AR model after PM_2.5 exposure, correct the redox imbalance, reduce the Th2 cytokines, reduce eosinophil infiltration, and promote the moderate regeneration of epithelial cells. The mechanism of NAC reversing PM_2.5-mediated action may be related to its anti-oxidant and anti-inflammatory effects, which may provide some new insights for the prevention of AR exacerbated by exposure to PM_2.5.

Aqueous-Phase Decomposition of Isoprene Hydroxy Hydroperoxide and Hydroxyl Radical Formation by Fenton-like Reactions with Iron Ions

Isoprene hydroxy hydroperoxides (ISOPOOH) formed by the photooxidation of isoprene under low-NO conditions play an important role in the formation and evolution of secondary organic aerosols, yet multiphase processes of ISOPOOH are poorly understood. By applying electron paramagnetic resonance spectroscopy, we observe that ISOPOOH undergoes aqueous-phase decomposition upon interacting with Fe(II) ions to form OH and organic radicals at room temperature. To reproduce the measured dependence of OH formation on the Fe concentrations by kinetic modeling, we postulate that Fe(II) ions react with ISOPOOH via Fenton-like reactions to form OH radicals with a rate constant of 7.3 × 10^-18 cm³ s^-1. At low concentrations, oxalate forms monocomplexes with Fe(II) ions, which can promote OH formation by ISOPOOH. However, at high concentrations, oxalate scavenges OH radicals, thereby lowering aqueous OH concentrations. These findings provide new insight for the atmospheric fate of ISOPOOH and reactive oxygen species generation in the aqueous phase.

Risk evaluation of environmentally persistent free radicals in airborne particulate matter and influence of atmospheric factors

Environmentally persistent free radicals (EPFRs) was considered unrecognized composition of air pollutants and might help explain the long-standing medical mystery of why non-smokers develop tobacco-related diseases like lung cancer. EPFRs in airborne fine particulate matter (PM_2.5) can induce oxidative and DNA damage when inhaled. We assessed the inhalation risk of EPFRs in PM_2.5 and factors influencing this risk in Beijing as a large city with frequent haze events. The average concentration of EPFRs in PM_2.5 was 6.00 × 10¹⁷ spins/m³ in spring, autumn, and winter; lower concentrations were recorded in the summer. To estimate the daily inhalation risk of EPFRs in PM_2.5, we used the equivalent EPFRs in cigarette tar. The average daily inhalation exposure of EPFRs in PM_2.5 was estimated to be the equivalent of 33.1 cigarette tar EPFRs per day (range: 0.53-226.9) during both haze and non-haze days. The major factors influencing EPFR concentrations in the atmosphere were precipitation and humidity, which reduced airborne concentrations. Levels of PM_2.5 and carbon monoxide were positively correlated with EPFR concentrations. The health risks of inhaling airborne EPFRs could be significant and should be recognized and quantified.

Cytotoxic Free Radicals on Air-Borne Soot Particles Generated by Burning Wood or Low-Maturity Coals

The traditional cook stove is a major contributor to combustion-derived soot particles, which contain various chemical species that may cause a significant impact to human health and ecosystems. However, properties and toxicity associated with environmentally persistent free radicals (EPFRs) in such emissions are not well known. This paper investigated the characteristics and cytotoxicity of soot-associated EPFRs discharged from Chinese household stoves. Our results showed that the concentrations of EPFRs were related to fuel types, and they were higher in wood-burning soot (8.9-10.5 × 10¹⁶ spins/g) than in coal-burning soot (3.9-9.7 × 10¹⁶ spins/g). Meanwhile, EPFR concentrations in soot decreased with an increase of coal maturity. The soot EPFRs, especially reactive fractions, readily induced the generation of reactive oxygen species (ROS). Potential health effects of soot EPFRs were also examined using normal human bronchial epithelial cell line 16HBE as a model. Soot particles were internalized by 16HBE cells inducing cytotoxicity. The main toxicity inducers were identified to be reactive EPFR species, which generated ROS inside human cells. Our findings provided valuable insights into potential contributions of soot EPFRs associated with different types of fuel to health problems. This information will support regulations to end or limit current stove usage in numerous households.

Interaction of industrial smelting soot particles with pulmonary surfactant: Pulmonary toxicity of heavy metal-rich particles

Inhalable particles can influence the interfacial behavior of pulmonary surfactant (PS) resulting in various pulmonary diseases. However, the effects of actually airborne particles on the interfacial behavior of PS and its role in the alteration for soluble metal fraction in particles are entirely unexplored. Herein, we investigated the interaction of PS extracted from porcine lungs with smelting soot fine particles as a model of inhaled heavy metal-rich particles. Our results showed that the phase behavior and foamability of PS were obviously altered in the presence of smelting soot fine particles. In addition, the soluble heavy metals in smelting soot fine particles notably increased in the presence of PS as compared to that of saline solution. Further experiments conducted by adding PS's major components (dipalmitoylphosphatidylcholine, DPPC; bovine serum albumin, BSA) demonstrated that comparison of DPPC, adsorbed BSA is beneficial for the dissolution of heavy metals in smelting soot fine particles. Dynamic light scattering experiments verified that the well dispersion of smelting soot fine particles in the presence of BSA may be responsible for the higher solubility of heavy metals. These findings indicate that PS's interfacial behavior change and PS-enhanced solubilization release of metal components may increase the potentially pulmonary risk in the exposure of airborne fine particles enriched with heavy metals.

A scoping study of component-specific toxicity of mercury in urban road dusts from three international locations

This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

TRPC6-dependent Ca2+ signaling mediates airway inflammation in response to oxidative stress via ERK pathway

Ozone (O₃) plays an extremely important role in airway inflammation by generating reactive oxygen species (ROS) including hydrogen peroxide, then promoting redox actions and causing oxidative stress. Evidences indicate that TRPC6 (canonical transient receptor potential channel 6) is a redox-regulated Ca²⁺ permeable nonselective cation channel, but its role in the setting of oxidative stress-related airway inflammation remains unknown. Here, we found that both TRPC6^-/- mice and mice pretreated with SAR7334, a potent TRPC6 inhibitor, were protected from O₃-induced airway inflammatory responses. In vitro, both knockdown of TRPC6 expression with shRNA and TRPC6 blockage markedly attenuated the release of cytokines IL-6 and IL-8 induced by O₃ or H₂O₂ in 16HBE cells (human bronchial epithelial cell line). Treatment with O₃ or H₂O₂ enhanced TRPC6 protein expression in vivo and vitro. We also observed that TRPC6-dependent increase of intracellular Ca²⁺ concentration ([Ca²⁺]_i) was triggered by H₂O₂, which consisted of the release from intracellular calcium store and the influx of extracellular Ca²⁺ and could be further strengthened by 6-h O₃ exposure in both 16HBE cells and HBEpiCs (primary human bronchial epithelial cells). Moreover, we confirmed that the activation of MAPK signals (ERK1/2, p38, JNK) was required for the inflammatory response induced by O₃ or H₂O₂ while only the phosphorylation of ERK pathway was diminished in the TRPC6-knockdown situation. These results demonstrate that oxidative stress regulates TRPC6-mediated Ca²⁺ cascade, which leads to the activation of ERK pathway and inflammation and could become a potential target to treat oxidative stress-associated airway inflammatory diseases.

Oxygenated and Nitrated Polycyclic Aromatic Hydrocarbons in Ambient Air-Levels, Phase Partitioning, Mass Size Distributions, and Inhalation Bioaccessibility

Among the nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are some of the most hazardous substances to public health, mainly because of their carcinogenicity and oxidative potential. Despite these concerns, the concentrations and fate of NPAHs and OPAHs in the atmospheric environment are largely unknown. Ambient air concentrations of 18 NPAHs, 5 quinones, and 5 other OPAHs were determined at two urban and one regional background sites in central Europe. At one of the urban sites, the total (gas and particulate) concentrations of Σ10OPAHs were 10.0 ± 9.2 ng/m3 in winter and 3.5 ± 1.6 ng/m3 in summer. The gradient to the regional background site exceeded 1 order of magnitude. Σ18NPAH concentrations were typically 1 order of magnitude lower than OPAHs. Among OPAHs, 9-fluorenone and (9,10)-anthraquinone were the most abundant species, accompanied by benzanthrone in winter. (9,10)-Anthraquinone represented two-thirds of quinones. We found that a large fraction of the target substance particulate mass was carried by submicrometer particles. The derived inhalation bioaccessibility in the PM10 size fraction is found to be ≈5% of the total ambient concentration of OPAHs and up to ≈2% for NPAHs. For 9-fluorenone and (9,10)-anthraquinone, up to 86 and 18%, respectively, were found at the rural site. Our results indicate that water solubility could function as a limiting factor for bioaccessibility of inhaled particulate NPAHs and OPAHs, without considerable effect of surfactant lipids and proteins in the lung lining fluid.

Enzymatic, Non-enzymatatic Antioxidant Levels and Heat Shock Protein Expression as Indicators of Metal Induced Toxicity and Reproductive Modulation in Female Indian Major Carp Cirrhinus cirrhosus

Effects of zinc (Zn) and lead (Pb) exposure on oxidative biomarkers and heat shock protein (HSP) expression, and their possible relation to ovarian steroidogenesis in fish were investigated. Female Cirrhinus cirrhosus were exposed to 1/10th of LC₅₀ of metals for 30 days, and kept for another 30 days without metal exposure. Metal concentrations, antioxidants, HSPs, 17β-estradiol and steroidogenic enzymes were analysed in brain and ovary after 15 and 30 days of exposure and a 15 and 30 day recovery period. Activities of enzymatic and non-enzymatic antioxidants showed duration dependent variation in both exposure and recovery period. HSP70 and HSP90 expressions increased following metal exposure, with the expression being higher in brain than ovary. 17β-Estradiol, steroidogenic enzymes decreased significantly (p < 0.05) after metal exposure. The present study suggests that metals have differential and tissue specific influence on oxidative status and manipulate ovarian steroidogenesis probably through the modulation of HSPs.

Effect of metal-organic interactions on the oxidative potential of mixtures of atmospheric humic-like substances and copper/manganese as investigated by the dithiothreitol assay

Excessive generation of reactive oxygen species (ROS) and the corresponding oxidative stress has been recognized as one important cause for the adverse health effects associated with exposure to ambient particulate matter (PM). Transition metals and humic-like substances (HULIS) in PM have been separately demonstrated to contribute to the oxidative potential (OP) of PM, however, only few studies investigated the impact of their interactions on the measured OP and the effect is little understood. HULIS is an abundant fraction of water-soluble organic material in PM and serves to represent real-world PM organics. In this study, we applied a cell-free dithiothreitol (DTT) assay to quantify the OP, termed as OP_DTT, by two representative transition metals (i.e., copper (Cu) and manganese (Mn)), HULIS, and mixtures of HULIS and metals in concentration levels relevant to those in human lung fluid resulting from PM inhalation. The organic-metal mixture effect was found to be metal-specific and concentration-specific, covering the possibility spectrum from being synergistic, additive to antagonistic. HULIS was observed to suppress OP_DTT up to 10-20% by Cu at a concentration of 0.08 μM while had no discernable effect at 0.5 μM Cu. On the contrary, obvious enhancement of OP_DTT was recorded in the mixtures of HULIS and Mn (e.g. up to ~2 times at 2.5 μM of Mn) while no mixture effects could be discerned at 0.5 μM Mn. Our work demonstrates the need for considering the metal-organic interactions and the complexity when evaluating the total OP of their mixtures, such as ambient PM samples. Further work in metal-PM organics interactions should be conducted using methods capable of measuring specific oxidants, in addition to the ability to deplete the reducing agent (i.e., DTT), in order to acquire a deeper mechanistic insight into the interactions.

Seasonal Variations and Chemical Predictors of Oxidative Potential (OP) of Particulate Matter (PM), for Seven Urban French Sites

Epidemiological studies suggest that the main part of chronic effects from air pollution is likely to be linked with particulate matter (PM). Oxidative potential (OP) of PM is gaining strong interest as a promising health exposure metric. This study combined atmospheric detailed composition results obtained for seven different urban background environments over France to examine any possible common feature in OP seasonal variations obtained using two assays (acid ascorbic (AA) and dithiothreitol (DTT)) along a large set of samples ( N > 700 ). A remarkable homogeneity in annual cycles was observed with a higher OP activity in wintertime at all investigated sites. Univariate correlations were used to link the concentrations of some major chemical components of PM and their OP. Four PM components were identified as OP predictors: OC, EC, monosaccharides and Cu. These species are notably emitted by road transport and biomass burning, targeting main sources probably responsible for the measured OP activity. The results obtained confirm that the relationship between OP and atmospheric pollutants is assay- and location-dependent and, thus, the strong need for a standardized test, or set of tests, for further regulation purposes.

Culturability, metabolic activity and composition of ambient bacterial aerosols in a surrogate lung fluid

Interactions of particulate matter (PM) and respiratory tract play a crucial role in PM-related respiratory diseases. The majority of the work focuses on the oxidative stress induced by reactions between PM-borne redox-active components and lung lining fluid (LLF). The effects of PM-borne biological components are largely unknown. Of all PM-borne biologicals, bacteria, as living microorganisms, are closely related with inflammatory immune responses. However, its inhalation risk is usually determined without considering the respiratory physiological conditions. In this study, a surrogate lung fluid (SLF) with four typical antioxidants was applied to characterize the ambient bacteria, including concentrations of total bacteria/viable bacteria/culturable bacteria, metabolic activity, bacteria-derived endotoxin, as well as the community structure. Comparing to those determined by SLF, we find that use of PBS leads to an underestimation of the bacterial culturability and metabolic activity. No effect was seen regarding the number of total bacteria and viable bacteria (with intact membrane). Population structure change was seen for bacteria cultured from SLF-collected samples, when compared to that from PBS. Spore-forming bacteria, e.g., genus Bacillus, were found to be easily recovered with SLF. This implies that use of PBS could underestimate the bacteria inhalation risk, especially those bacterial endospores. Our work highlights the necessity to consider the respiratory airway environment when evaluating microbial inhalation risk.

Oxidative Potential of Particulate Matter and Generation of Reactive Oxygen Species in Epithelial Lining Fluid

Reactive oxygen species (ROS) play a central role in adverse health effects of atmospheric particulate matter (PM). Respiratory deposition can lead to the formation of ROS in the epithelial lining fluid due to redox reactions of PM components with lung antioxidants. As direct quantification of ROS is challenging, PM oxidative potential is more commonly measured using antioxidant surrogates including dithiothreitol and ascorbic acid, assuming that the decay of surrogates corresponds to ROS formation. However, this assumption has not yet been validated and the lack of ROS quantification in the respiratory tract causes major limitations in evaluating PM impacts on oxidative stress. By combining field measurements of size-segregated chemical composition, a human respiratory tract model, and kinetic modeling, we quantified production rates and concentrations of different types of ROS in different regions of the epithelial lining fluid by considering particle-size-dependent respiratory deposition. The extrathoracic region is found to have higher ROS concentrations compared to the bronchial and alveolar regions. Although H₂O₂ and O₂^- production is governed by Fe and Cu ions, OH radicals are mainly generated by organic compounds and Fenton-like reactions of metal ions. In winter when affected by biomass burning, model comparisons suggest that humic-like substances (HULIS) contribute to ROS formation substantially. We found that PM oxidative potential is a good indicator of the chemical production of H₂O₂ and O₂^- but does not represent OH generation. These results provide rationale and limitations of the use of oxidative potential as an indicator of PM toxicity in epidemiological and toxicological studies.