Particulate Oxidative Potential Research Articles

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

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

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

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

Temporal variation of oxidative potential of water soluble components of ambient PM2.5 measured by dithiothreitol (DTT) assay

The exposure to ambient fine particulate matter (PM2.5) can induce oxidative stress, contributing to global burden of diseases. The evaluation of the oxidative potential (OP) of PM2.5 is thus critical for the health risk assessment. We collected ambient PM2.5 samples in Hangzhou city, China for four consecutive quarters in the year 2017 and investigated the oxidation property of PM2.5 components by the dithiothreitol (DTT) assay. The annual mean of ambient PM2.5 mass concentrations in 2017 was 63.05 μg m−3 (median: 57.34, range: 6.67–214.33 μg m−3) with the significant seasonal variations ranking as winter > spring > summer > autumn. Secondary inorganic aerosol (SIA) species including SO42−, NO3− and NH4+ totally account for >50% of PM2.5 mass. The annual mean volume-normalized DTT activity (DTTv) showed a relatively high value of 0.62 nmol/min/m3 (median: 0.62, range: 0.11–1.66 nmol/min/m3) and DTTv of four seasons was roughly at the same level, indicating a high annual exposure level of ambient PM2.5. SIA species were correlated well with the corresponding DTTv and showed significant diurnal variations with strong or moderate correlations at day and weak correlations at night, suggesting strong secondary formation in daytime with contribution to the particulate OP. The annual mean mass-normalized DTT activity (DTTm) had a relatively low value of 6.39 pmol/min/μg (median: 5.63, range: 1.99–22.70 pmol/min/μg), indicating low intrinsic oxidative toxicity. The DTTm of four seasons ranked as autumn > winter > spring > summer, indicating seasonal variations of the DTT-active components. The PM2.5 mass concentration is more related to exposure levels than intrinsic properties of components, while OP is determined by the components rather than PM2.5 mass concentration. Our results provide an insight into reactive oxygen species-induced health risk of PM2.5 exposure and decision for subsequent emission control.

Erratum: Associations between Ambient Fine Particulate Oxidative Potential and Cardiorespiratory Emergency Department Visits.

[This corrects the article DOI: 10.1289/EHP1545.].

Associations between Ambient Fine Particulate Oxidative Potential and Cardiorespiratory Emergency Department Visits.

Background:Oxidative potential (OP) has been proposed as a measure of toxicity of ambient particulate matter (PM).Objectives:Our goal was to address an important research gap by using daily OP measurements to conduct population-level analysis of the health effects of measured ambient OP.Methods:A semi-automated dithiothreitol (DTT) analytical system was used to measure daily average OP () in water-soluble fine PM at a central monitor site in Atlanta, Georgia, over eight sampling periods (a total of 196 d) during June 2012–April 2013. Data on emergency department (ED) visits for selected cardiorespiratory outcomes were obtained for the five-county Atlanta metropolitan area. Poisson log-linear regression models controlling for temporal confounders were used to conduct time-series analyses of the relationship between daily counts of ED visits and either the 3-d moving average (lag 0–2) of or same-day . Bipollutant regression models were run to estimate the health associations of while controlling for other pollutants.Results: was measured for 196 d (, ). Lag 0–2 was associated with ED visits for respiratory disease (, 95% confidence interval (CI): 1.00, 1.05 per interquartile range increase in ), asthma (, 95% CI: 1.03, 1.22), and ischemic heart disease (, 95% CI: 1.03, 1.38). Same-day was not associated with ED visits for any outcome. Lag 0–2 remained a significant predictor of asthma and ischemic heart disease in most bipollutant models.Conclusions:Lag 0–2 was associated with ED visits for multiple cardiorespiratory outcomes, providing support for the utility of as a measure of fine particle toxicity. https://doi.org/10.1289/EHP1545

Spatial and temporal variation of particulate matter characteristics within office buildings — The OFFICAIR study

In the frame of the OFFICAIR project, office buildings were investigated across Europe to assess how the office workers are exposed to different particulate matter (PM) characteristics (i.e. PM2.5 mass concentration, particulate oxidative potential (OP) based on ascorbate and reduced glutathione depletion, trace element concentration and total particle number concentration (PNC)) within the buildings. Two offices per building were investigated during the working hours (5 consecutive days; 8h per day) in two campaigns.Differences were observed for all parameters across the office buildings. Our results indicate that the monitoring of the PM2.5 mass concentration in different offices within a building might not reflect the spatial variation of the health relevant PM characteristics such as particulate OP or the concentration of certain trace elements (e.g., Cu, Fe), since larger differences were apparent within a building for these parameters compared to that obtained for the PM2.5 mass concentration in many cases. The temporal variation was larger for almost all PM characteristics (except for the concentration of Mn) than the spatial differences within the office buildings. These findings indicate that repeated or long-term monitoring campaigns are necessary to have information about the temporal variation of the PM characteristics. However, spatial variation in exposure levels within an office building may cause substantial differences in total exposure in the long term. We did not find strong associations between the investigated indoor activities such as printing or windows opening and the PNC values. This might be caused by the large number of factors affecting PNC indoors and outdoors.

Short-term associations between particle oxidative potential and daily mortality and hospital admissions in London.

Particulate matter (PM) from traffic and other sources has been associated with adverse health effects. One unifying theory is that PM, whatever its source, acts on the human body via its capacity to cause damaging oxidation reactions related to its content of pro-oxidants components. Few epidemiological studies have investigated particle oxidative potential (OP) and health. We conducted a time series analysis to assess associations between daily particle OP measures and numbers of deaths and hospital admissions for cardiovascular and respiratory diseases. During 2011 and 2012 particles with an aerodynamic diameter less than 2.5 and 10μm (PM2.5 and PM10 respectively) were collected daily on Partisol filters located at an urban background monitoring station in Central London. Particulate OP was assessed based on the capacity of the particles to oxidize ascorbate (OP(AA)) and glutathione (OP(GSH)) from a simple chemical model reflecting the antioxidant composition of human respiratory tract lining fluid. Particulate OP, expressed as % loss of antioxidant per μg of PM, was then multiplied by the daily concentrations of PM to derive the daily OP of PM mass concentrations (% loss per m(3)). Daily numbers of deaths and age- and cause-specific hospital admissions in London were obtained from national registries. Poisson regression accounting for seasonality and meteorology was used to estimate the percentage change in risk of death or admission associated with an interquartile increment in particle OP. We found little evidence for adverse associations between OP(AA) and OP(GSH) and mortality. Associations with cardiovascular admissions were generally positive in younger adults and negative in older adults with confidence intervals including 0%. For respiratory admissions there was a trend, from positive to negative associations, with increasing age although confidence intervals generally included 0%. Our study, the first to analyse daily particle OP measures and mortality and admissions in a large population over two years, found little evidence to support the hypothesis that short-term exposure to particle OP is associated with adverse health effects. Further studies with improved exposure assessment and longer time series are required to confirm or reject the role of particle OP in triggering exacerbations of disease.

Oxidative potential and chemical composition of PM2.5 in office buildings across Europe – The OFFICAIR study

In the frame of the OFFICAIR project, indoor and outdoor PM2.5 samples were collected in office buildings across Europe in two sampling campaigns (summer and winter). The ability of the particles to deplete physiologically relevant antioxidants (ascorbic acid (AA), reduced glutathione (GSH)) in a synthetic respiratory tract lining fluid, i.e., oxidative potential (OP), was assessed. Furthermore, the link between particulate OP and the concentration of the PM constituents was investigated.The mean indoor PM2.5 mass concentration values were substantially lower than the related outdoor values with a mean indoor/outdoor PM2.5 mass concentration ratio of 0.62 and 0.61 for the summer and winter campaigns respectively. The OP of PM2.5 varied markedly across Europe with the highest outdoor OPAA m−3 and OPGSH m−3 (% antioxidant depletion/m3 air) values obtained for Hungary, while PM2.5 collected in Finland exhibited the lowest values. Seasonal variation could be observed for both indoor and outdoor OPAA m−3 and OPGSH m−3 with higher mean values during winter. The indoor/outdoor OPAA m−3 and OPGSH m−3 ratios were less than one with 4 and 17 exceptions out of the 40 cases respectively. These results indicate that indoor air is generally less oxidatively challenging than outdoors. Correlation analysis revealed that trace elements play an important role in determining OP, in particular, the Cu content. Indoor air chemistry might affect OP since weaker correlations were obtained for indoor PM2.5. Our findings also suggest that office workers may be exposed to health relevant PM constituents to a different extent within the same building.

Influence of oxygen content of the certain types of biodiesels on particulate oxidative potential

Oxidative potential (OP) is related to the organic phase, specifically to its oxygenated organic fraction (OOA). Furthermore, the oxygen content of fuel molecules has significant influence on particulate OP. Thus, this study aimed to explore the actual dependency of the OOA and ROS to the oxygen content of the fuel. In order to reach the goal, different biodiesels blends, with various ranges of oxygen content; have been employed. The compact time of flight aerosol mass spectrometer (c-ToF AMS) enabled better identification of OOA. ROS monitored by using two assays: DTT and BPEA-nit. Despite emitting lower mass, both assays agreed that oxygen content of a biodiesel is directly correlated with its OOA, and highly related to its OP. Hence, the more oxygen included in the considered biodiesels, the higher the OP of PM emissions. This highlights the importance of taking oxygen content into account while assessing emissions from new fuel types, which is relevant from a health effects standpoint.

Oxidative Potential of Particles in Different Occupational Environments: A Pilot Study.

The oxidative potential (OP) of particulate matter has been proposed as a toxicologically relevant metric. This concept is already frequently used for hazard characterization of ambient particles but it is still seldom applied in the occupational field. The objective of this study was to assess the OP in two different types of workplaces and to investigate the relationship between the OP and the physicochemical characteristics of the collected particles. At a toll station, at the entrance of a tunnel ('Tunnel' site), and at three different mechanical yards ('Depot' sites), we assessed particle mass (PM4 and PM2.5 and size distribution), number and surface area, organic and elemental carbon, polycyclic aromatic hydrocarbon (PAH), and four quinones as well as iron and copper concentration. The OP was determined directly on filters without extraction by using the dithiothreitol assay (DTT assay-OP(DTT)). The averaged mass concentration of respirable particles (PM4) at the Tunnel site was about twice the one at the Depot sites (173±103 and 90±36 µg m(-3), respectively), whereas the OP(DTT) was practically identical for all the sites (10.6±7.2 pmol DTT min(-1) μg(-1) at the Tunnel site; 10.4±4.6 pmol DTT min(-1) μg(-1) at the Depot sites). The OP(DTT) of PM4 was mostly present on the smallest PM2.5 fraction (OP(DTT) PM2.5: 10.2±8.1 pmol DTT min(-1) μg(-1); OP(DTT) PM4: 10.5±5.8 pmol DTT min(-1) μg(-1) for all sites), suggesting the presence of redox inactive components in the PM2.5-4 fraction. Although the reactivity was similar at the Tunnel and Depot sites irrespective of the metric chosen (OP(DTT) µg(-1) or OP(DTT) m(-3)), the chemicals associated with OP(DTT) were different between the two types of workplaces. The organic carbon, quinones, and/or metal content (Fe, Cu) were strongly associated with the DTT reactivity at the Tunnel site whereas only Fe and PAH were associated (positively and negatively, respectively) with this reactivity at the Depot sites. These results demonstrate the feasibility of measuring of the OP(DTT) in occupational environments and suggest that the particulate OP(DTT) is integrative of different physicochemical properties. This parameter could be a potentially useful exposure proxy for investigating particle exposure-related oxidative stress and its consequences. Further research is needed mostly to demonstrate the association of OP(DTT) with relevant oxidative endpoints in humans exposed to particles.

Changes in chemical composition and oxidative potential of urban PM2.5 between 2010 and 2013 in Hungary

A comprehensive chemical characterization and oxidative potential (OP) assessment of PM2.5 was carried out at an urban site of Budapest between June 2010 and May 2013 to investigate the seasonal variability of particulate phase air pollutants and their oxidative activity. Chemical analyses included the determination of the concentration of trace elements, major water-soluble inorganic ions and carbonaceous fractions (total carbon, water-soluble organic carbon, organic carbon, elemental carbon). The OP of PM2.5 was assessed by antioxidant depletion using a synthetic respiratory tract lining fluid containing ascorbate, reduced glutathione and urate.The mean PM2.5 mass concentration (21.0μgm−3) was just below the 25μgm−3 annual mean PM2.5 limit value set by the European Commission and showed a seasonal pattern with higher levels during winter. On average, 84% of the gravimetric mass could be reconstructed by the chemical measurements. Organic matter and secondary inorganic ions were the most dominant PM2.5 constituents contributing 40 and 29% of its mass, respectively. Changes in the yearly concentrations were not identified for the investigated compounds between 2010 and 2013. Temporal differences in both ascorbate and glutathione oxidation could be observed during the 3-year long sampling period; however, no clear seasonal trend was apparent. OP metrics were associated mainly with traffic-related trace elements; however, other PM sources (i.e., long-range transport, secondary aerosol formation) could also contribute to particulate OP in Budapest. The weak correlation between OP metrics and PM2.5 mass concentration suggests the possibility of using OP as an additional metric in epidemiology.

Increased oxidative burden associated with traffic component of ambient particulate matter at roadside and urban background schools sites in London.

As the incidence of respiratory and allergic symptoms has been reported to be increased in children attending schools in close proximity to busy roads, it was hypothesised that PM from roadside schools would display enhanced oxidative potential (OP). Two consecutive one-week air quality monitoring campaigns were conducted at seven school sampling sites, reflecting roadside and urban background in London. Chemical characteristics of size fractionated particulate matter (PM) samples were related to the capacity to drive biological oxidation reactions in a synthetic respiratory tract lining fluid. Contrary to hypothesised contrasts in particulate OP between school site types, no robust size-fractionated differences in OP were identified due high temporal variability in concentrations of PM components over the one-week sampling campaigns. For OP assessed both by ascorbate (OPAA m−3) and glutathione (OPGSH m−3) depletion, the highest OP per cubic metre of air was in the largest size fraction, PM1.9–10.2. However, when expressed per unit mass of particles OPAA µg−1 showed no significant dependence upon particle size, while OPGSH µg−1 had a tendency to increase with increasing particle size, paralleling increased concentrations of Fe, Ba and Cu. The two OP metrics were not significantly correlated with one another, suggesting that the glutathione and ascorbate depletion assays respond to different components of the particles. Ascorbate depletion per unit mass did not show the same dependence as for GSH and it is possible that other trace metals (Zn, Ni, V) or organic components which are enriched in the finer particle fractions, or the greater surface area of smaller particles, counter-balance the redox activity of Fe, Ba and Cu in the coarse particles. Further work with longer-term sampling and a larger suite of analytes is advised in order to better elucidate the determinants of oxidative potential, and to fuller explore the contrasts between site types.

The Air Pollution Exposure Laboratory (APEL) for controlled human exposure to diesel exhaust and other inhalants: characterization and comparison to existing facilities

Objective: The Air Pollution Exposure Laboratory (APEL) was designed for the controlled inhalation of human subjects to aged and diluted diesel exhaust (DE) to mimic “real-world” occupational and environmental conditions.Methods: An EPA Tier 3-compliant, 6.0 kW diesel generator is operated under discrete cyclic loads to simulate diesel on-road emissions. The engine accepts standard ultra-low sulfur diesel or a variety of alternative fuels (such as biodiesel) via a partitioned tank. A portion of raw exhaust is drawn into the primary dilution system and is diluted 9:1 with compressed air at standard temperature (20°C) and humidity (40%) levels. The exhaust is further diluted approximately 25:1 by high efficiency particulate air (HEPA)-filtered air (FA) and then aged for 4 min before entering the 4 × 6 × 7-foot exposure booth. An optional HEPA filter path immediately proximal to the booth can generate a particle-reduced (gas-enriched) exposure. In-booth particulate is read by a nephelometer to provide an instantaneous light scattering coefficient for closed-loop system control. A Scanning Mobility Particle Sizer and multi-stage impactor measures particle size distribution. Filter sampling allows determination of sessional average concentrations of size-fractionated and unfractionated particulate oxidative potential, elemental carbon, organic carbon and trace elements.Results: Approximately 300 μg/m3 PM2.5 is routinely achievable at APEL and is well characterized in terms of oxidative potential and elemental components.Conclusion: APEL efficiently creates fresh DE, appropriately aged and diluted for human experimentation at safe yet realistic concentrations. Description of exposure characteristics allows comparison to other international efforts to deepen the current evidence base regarding the health effects of DE.