Effect of filter extraction solvents on the measurement of the oxidative potential of airborne PM2.5

Determination of airborne metal-containing nanoparticles in a historic mining area using single particle ICP-MS

Given limited information on airborne metal-containing NPs-a highly bioaccessible fraction of metals relevant to human exposure-in the upper Meža Valley, a historic mining area in Slovenia, this study aimed to assess their presence in PM10 air filters from the region using the spICP-MS method. The extraction procedure, refined using a certified reference material of PM10-like fine dust deposited on filters, achieved an extraction efficiency of 9.1% for Zn- and 14.0% for Pb-containing NPs after two hours of ultrasonication in 10 mM sodium pyrophosphate. The method proved effective for detecting metal-containing NPs in PM10 from mining and smelting areas, as demonstrated by a case study from the upper Meža Valley. SpICP-MS analyses identified both Zn- and Pb-containing NPs in PM10 samples, with 0.6-3.8% of Zn and 0.3-1.7% of Pb extracted as NPs. Additionally, SEM-EDS analysis confirmed the presence of Zn- and Pb-containing (nano)particles of different chemical compositions. This study is the first to report the occurrence of metal-containing NPs in PM10 from this region. Although they represent only a small fraction of total Zn and Pb in the samples, NPs are more bioaccessible and thus more relevant for assessing local population's exposure to these particles.

Exploring the Chemical Complexity and Sources of Airborne Fine Particulate Matter in East Asia by Nontarget Analysis and Multivariate Modeling

The complex and dynamic nature of airborne fine particulate matter (PM2.5) has hindered understanding of its chemical composition, sources, and toxic effects. In the first steps of a larger study, here, we aimed to elucidate relationships between source regions, ambient conditions, and the chemical composition in water extracts of PM2.5 samples (n = 85) collected over 16 months at an observatory in the Yellow Sea. In each extract, we quantified elements and major ions and profiled the complex mixtures of organic compounds by nontarget mass spectrometry. More than 50,000 nontarget features were detected, and by consensus of in silico tools, we assigned a molecular formula to 13,907 features. Oxygenated compounds were most prominent, followed by mixed nitrogenated/oxygenated compounds, organic sulfates, and sulfonates. Spectral matching enabled identification or structural annotation of 43 substances, and a workflow involving SIRIUS and MS-DIAL software enabled annotation of 74 unknown per- and polyfluoroalkyl substances with primary source regions in China and the Korean Peninsula. Multivariate modeling revealed seasonal variations in chemistry, attributable to the combination of warmer temperatures and maritime source regions in summer and to cooler temperatures and source regions of China in winter.

Impact of PM2.5 filter extraction solvent on oxidative potential and chemical analysis

Fine particulate matter (PM2.5) is hypothesized to induce oxidative stress, and has been linked to acute and chronic adverse health effects. To better understand the risks and underlying mechanisms following exposure, PM2.5 is collected onto filters but prior to toxicological analysis, particles must be removed from filters. There is no standard method for filter extraction, which creates the possibility that the methods of extraction selected can alter the chemical composition and ultimately the biological implications. In this study, comparisons were made between extraction solvents (methanol (MeOH), dichloromethane (DCM), 0.9% saline, and Milli-Q water) and the results of oxidative potential and elemental concentration analysis of PM2.5 collected across sites in Arkansas, USA. Significant differences were observed between solvents, with DCM having significantly different results compared to all other extraction solvents (p ≤ 0.001). Significant correlations between element, black carbon, and PM2.5 concentrations and oxidative potential were observed. The observed correlations were extraction solvent dependent. For example, in saline extracted samples, oxidative potential had significant negative correlations with: Ba, Cd, Ce, Co, Ga, Mn and significant positive correlations with: Cr, Ni, Th, U. While in MeOH extracted samples, significant positive correlations were only between oxidative potential and Ga, U and significant negative correlations with V. This indicates that PM2.5 samples extracted with different solvents will yield different conclusions about the causal components. This study highlights the importance of filter extraction methods in interpretation of oxidative potential results and comparisons between studies.Implications: While there is no standard method for PM2.5 filter extraction, variation of extraction methods impact analytical results. This project identifies that extraction method variation, particularly extraction solvent selection, leads to discrepancies in chemical and toxicological analysis for PM2.5 collected on the same filter. This work highlights the need for methods standardization to support accurate comparisons between PM2.5 research studies, thus providing better understanding of PM2.5 across the globe.

Spatiotemporal distribution of oxidative potential in PM2.5 and its key components across six Chinese cities

Increasing evidence has supported that oxidative potential (OP) serves as a crucial indicator of health risk of exposure to PM2.5 over mass concentration. However, there is a lack of comparative studies across multiple cities, particularly on a fine temporal scale. In this study, we aim to investigate daily variation of ambient PM2.5 OP through simultaneous samplings in six Chinese cities for one year. Results showed that more than 60 % of the sampling days exhibited non-zero ranking difference between volume-normalized oxidative potential (OPv) and mass concentration among the six cities. Key components contributing to OPv inculde Mn, NO3-, and K+, followed by Ca2+, Al, SO42-, Cl-, Fe, and NH4+. Based on these chemical components, we developed a stepwise multivariable linear regression model (R2: 0.71) for OPv prediction. The performance of the model is comparable to both species- and sources-based ones in the literature. These findings suggest that a relatively lower daily-averaged mass concentration of PM2.5 does not necessarily indicate a lower oxidative risk. Future studies and policy developments on health benefits should also consider OPv rather than mass concentration alone. Priority could be given to sources/species that contribute significantly to oxidative potential of ambient PM2.5. SYNOPSIS: This study highlights inclusion of oxidative potential as a complementary metric for air pollution assessment and control.

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.

Experimental factors influencing the bioaccessibility and the oxidative potential of transition metals from welding fumes

Inhalation of welding fumes (WFs) containing high levels of transition metals (Cr, Cu, Fe, Mn, Ni…) is associated with numerous health effects including oxidative stress. However, the measurements of the oxidative potential (OP) and bioaccessibility of WF transition metals depend on several physicochemical parameters and may be subject to several experimental artifacts. In this work, we investigated the influence of the experimental conditions that may affect the bioaccessibility of transition metals and their OP on stainless-steel WF extracts. WFs were produced using a generation bench and sampled on filters. The soluble fraction of the metals was analysed. Two different extraction fluids mimicking physiological pulmonary conditions were studied: phosphate buffer and Hatch's solution. Three extraction times were tested to determine the optimal time for a significant OPDTT using the dithiothreitol (DTT) method. The storage conditions of WFs after filter sampling such as duration, temperature and atmospheric conditions were investigated. The results indicate that experimental conditions can significantly affect the OPDTT and metal bioaccessibility analyses. Cr, Cu and Ni show higher solubility in Hatch's solution than in the phosphate buffer. Mn is highly sensitive to DTT and shows close solubility in the two fluids. An extraction time of 0.5 h in phosphate buffer allows a better sensitivity to OPDTT, probably by limiting complexations, interactions between metals and precipitation. Storage time and temperature can influence the physical or chemical evolution of the WFs, which can affect their OPDTT and Mn solubility. However, storage under N2(g) limits these changes. On-line measurements of OPDTT could provide an alternative to filter sampling to overcome these artifacts.

Insights the dominant contribution of biomass burning to methanol-soluble PM2.5 bounded oxidation potential based on multilayer perceptron neural network analysis in Xi'an, China

Atmospheric fine particulate matter (PM2.5) is associated with cardiorespiratory morbidity and mortality due to its ability to generate reactive oxygen species (ROS). Ambient PM2.5 samples were collected during heating and nonheating seasons in Xi'an, China, and the ROS-generation potential of PM2.5 was quantified using the dithiothreitol (DTT) assay. Additionally, positive matrix factorization combined with multilayer perceptron was employed to apportion sources contributing to the oxidation potential of PM2.5. Both the mass concentration of PM2.5 and the volume-based DTT activity (DTTv) were higher during the heating season than during the nonheating season. The primary contributors to DTTv were combustion (biomass and coal) sources during the heating season (>52 %), whereas secondary formation dominated DTT activity during the nonheating season (35.7 %). In addition, the secondary reaction process promoted the generation of intrinsic oxidation potential (OP) of sources. Among all the sources investigated (traffic source, industrial emission, mineral dust, biomass burning, secondary formation and coal combustion), the inherent oxidation potential of biomass burning was the highest, whereas that of mineral dust was the lowest. Our study indicates that anthropogenic sources, especially biomass burning, should be prioritized in PM2.5 toxicity control strategies.

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.

Seasonal and Spatial Variations of the Oxidative Properties of Ambient PM2.5 in the Po Valley, Italy, before and during COVID-19 Lockdown Restrictions

This study describes the chemical and toxicological characteristics of fine particulate matter (PM2.5) in the Po Valley, one of the largest and most polluted areas in Europe. The investigated samples were collected in the metropolitan area of Milan during the epidemic lockdown and their toxicity was evaluated by the oxidative potential (OP), measured using ascorbic acid (OPAA) and dithiothreitol (OPDTT) acellular assays. The study was also extended to PM2.5 samples collected at different sites in the Po Valley in 2019, to represent the baseline conditions in the area. Univariate correlations were applied to the whole dataset to link the OP responses with the concentrations of the major chemical markers of vehicular and biomass burning emissions. Of the two assays, OPAA was found mainly sensitive towards transition metals released from vehicular traffic, while OPDTT towards the PM carbonaceous components. The impact of the controlling lockdown restrictions on PM2.5 oxidative properties was estimated by comparing the OP values in corresponding time spans in 2020 and 2019. We found that during the full lockdown the OPAA values decreased to 80-86% with respect to the OP data in other urban sites in the area, while the OPDTT values remained nearly constant.

Polycyclic aromatic hydrocarbons and their oxygenated derivatives in urban aerosol: levels, chemical profiles, and contribution to PM2.5 oxidative potential

The concentrations of polycyclic aromatic hydrocarbons (PAHs) and quinones, a subgroup of oxygenated PAHs (oxy-PAHs), were measured in PM_2.5 samples collected during warm (May-June 2019) and cold (February-March 2020) seasons in the city of Bologna, Italy. Total PAHs concentration was nearly double in winter (6.58 ± 1.03 ng m^-3) compared with spring (3.16 ± 0.53 ng m^-3), following the trend of the PM_2.5 mass concentration. Molecular diagnostic ratios suggested that, together with traffic, biomass burning was the dominant emission source contributing to the peaks of concentration of PM_2.5 registered in the cold season. Quinone level was constant in both seasons, being 1.44 ± 0.24 ng m^-3, that may be related to the increased secondary formation during warm season, as confirmed by the higher Σoxy-PAHs/ΣPAHs ratio in spring than in winter. The oxidative potential (OP) of the PM_2.5 samples was assessed using acellular dithiothreitol (DTT) and ascorbic acid (AA) assays. The obtained responses showed a strong seasonality, with higher volume-normalized (OP_V) values in winter than in spring, i.e., OP_V^DTT: 0.32 ± 0.15 nmol min^-1 m^-3 vs. 0.08 ± 0.03 nmol min^-1 m^-3 and OP_V^AA: 0.72 ± 0.36 nmol min^-1 m^-3 vs. 0.28 ± 0.21 nmol min^-1 m^-3. Both OP_V^DTT and OP_V^AA responses were significantly associated with total PAHs, as a general descriptor of redox-active PAH derivatives, associated with co-emission from burning sources or secondary atmospheric oxidation of parent PAHs. Otherwise, only winter OP_V^DTT responses showed a significant correlation with total Ʃoxy-PAHs concentration.

Seasonal and Spatial Variations of PM10 and PM2.5 Oxidative Potential in Five Urban and Rural Sites across Lombardia Region, Italy

Oxidative potential (OP) of particulate matter (PM) is gaining strong interest as a promising health exposure metric. This study investigated OP of a large set of PM10 and PM2.5 samples collected at five urban and background sites near Milan (Italy), one of the largest and most polluted urban areas in Europe, afflicted with high particle levels. OP responses from two acellular assays, based on ascorbic acid (AA) and dithiothreitol (DTT), were combined with atmospheric detailed composition to examine any possible feature in OP with PM size fraction, spatial and seasonal variations. A general association of volume-normalized OP with PM mass was found; this association may be related to the clear seasonality observed, whereby there was higher OP activity in wintertime at all investigated sites. Univariate correlations were used to link OP with the concentrations of the major chemical markers of vehicular and biomass burning emissions. Of the two assays, AA was particularly sensitive towards transition metals in coarse particles released from vehicular traffic. The results obtained confirm that the responses from the two assays and their relationship with atmospheric pollutants are assay- and location-dependent, and that their combination is therefore helpful to singling out the PM redox-active compounds driving its oxidative properties.

Synergistic and Antagonistic Effects of Aerosol Components on Its Oxidative Potential as Predictor of Particle Toxicity

Quantifying the component-specific contribution to the oxidative potential (OP) of ambient particle matter (PM) is the key information to properly representing its acute health hazards. In this study, we investigated the interactions between the major contributors to OP, i.e., transition metals and quinones, to highlight the relative effects of these species to the total OP. Several synergistic and antagonistic interactions were found that significantly change the redox properties of their binary mixtures, increasing or decreasing the values computed by a simple additive model. Such results from the standard solutions were confirmed by extending the study to atmospheric PM_2.5 samples collected in winter in the Lombardia region, a hot spot for air pollution in northern Italy. This work highlights that a solid estimation of oxidative properties of ambient PM requires an interaction-based approach accounting for the interaction effects between metals and quinones.

The oxidative and neurotoxic potentials of the ambient PM2.5 extracts: The efficient multi-solvent extraction method

The health effects of ambient air particulate matter with a diameter of ≤2.5 μm (PM_2.5) on the central nervous system are well known and the induced oxidative stress has been shown as their main neuropathologic outcome. Ambient air PM_2.5 sampling methods mostly use air sampler systems that collect PM_2.5 on filters, which is followed by a PM_2.5 extraction approach. Inefficient extraction may lead to compositional bias and unreal interpretation of the results. This study aimed to compare our proposed multi-solvent extraction (MSE) approach for PM_2.5 extraction with a conventional aqueous extraction (AqE) method using the analysis of oxidative effects and cytotoxicity in the human neuroblastoma SH-SY5Y cell line. Ambient PM_2.5 samples were collected from an urban traffic location in Tehran city, the capital of Iran, using a high-volume sampler. The developed MSE method was proved to have superior advantages over the AqE method including an increased extraction efficiency (as much as 96 against 48% for PM_ms and PM_aq, respectively), and decreased artifacts and compositional biases. Ambient PM_2.5, besides PM_ms and PM_aq were analyzed for water-soluble ions, metals, and major elements. Dithiothreitol, ascorbic acid, lipid peroxidation, and cell viability assays on SH-SY5Y cells represented the significantly higher oxidative potential for PM_ms compared to PM_aq. The increased cytotoxicity may occur because of the increased oxidative potential of PM_ms and possibly is associated with higher efficiency of the MSE over the AqE method for removal of total redox-active PM components.

A New Method for the Assessment of the Oxidative Potential of Both Water-Soluble and Insoluble PM

Water-soluble and insoluble fractions of airborne particulate matter (PM) exhibit different toxicological potentials and peculiar mechanisms of action in biological systems. However, most of the research on the oxidative potential (OP) of PM is focused exclusively on its water-soluble fraction, since experimental criticisms were encountered for detaching the whole PM (soluble and insoluble species) from field filters. However, to estimate the actual potential effects of PM on human health, it is essential to assess the OP of both its water-soluble and insoluble fractions. In this study, to estimate the total OP (TOP), an efficient method for the detachment of intact PM10 from field filters by using an electrical toothbrush was applied to 20 PM10 filters in order to obtain PM10 water suspensions to be used for the DCFH, AA and DTT oxidative potential assays (OPDCFH, OPAA and OPDTT). The contribution of the insoluble PM10 to the TOP was evaluated by comparing the TOP values to those obtained by applying the three OP assays to the water-soluble fraction of 20 equivalent PM10 filters. The OP of the insoluble fraction (IOP) was calculated as the difference between the TOP and the WSOP. Moreover, each PM10 sample was analyzed for the water-soluble and insoluble fractions of 10 elements (Al, Cr, Cs, Cu, Fe, Li, Ni, Rb, Sb, Sn) identified as primary elemental tracers of the main emission sources in the study area. A principal component analysis (PCA) was performed on the data obtained to identify the predominant sources for the determination of TOP, WSOP, and IOP. Results showed that water-soluble PM10 released by traffic, steel plant, and biomass burning is mainly responsible for the generation of the TOP as well as of the WSOP. This evidence gave strength to the reliability of the results from OP assays performed only on the water-soluble fraction of PM. Lastly, the IOPDCFH and IOPDTT were found to be principally determined by insoluble PM10 from mineral dust.