Particle Oxidative Potential Research Articles

Size-fractionated ambient particulate matter induce toxicity: Oxidative potential, cytotoxic effect and inflammatory potential

Present study highlighted the importance of examining the toxicological profile of size-segregated particulate matter (PM) bound metals (Fe, Mn, Ni, Pb, Zn, Cu, Cr, Co, Cd) at urban site of Pune city, India. The total aerosol mass was composed of 61.2% and 38% fine and coarse particles, respectively with maximum distribution observed in 4.7–2.1 μm size mode. Elemental size distributions indicated the prime association of Fe, Mn and Zn with coarse sized PM, while remaining metals were predominantly associated with fine PM. Seasonal mass and elemental distribution profile of size-resolved PM was characterized with maximum concentration found in winter season. Enrichment factor analysis revealed the contribution of anthropogenic emissions to Co and Ni in fine mode while less enriched metals, Fe and Mn were allied with crustal and natural sources. Oxidative potential of particles in terms of Dithiothreitol (DTT) loss was found to be maximum in the size range of 4.7–1.1 μm with dominant contribution of PM bound metals (Fe, Cu, Cr, Mn, Ni, Pb, and Zn). On exposure to PM samples, prominent enhancement in the expression of cytokines (especially TNFα) as compared to the control has confirmed their inflammatory nature. Incubation of A549 cells with PM suspension (75 mg/ml) caused pronounced reduction (p < 0.01) in cell viability with significant morphological changes, associated with cell death. Respiratory deposition doses of PM in head region were found to be more impacted by coarse sized particles while contribution of fine PM was dominant in alveolar and tracheobronchial region, signifying serious health risks to the exposed population. In addition to the basic knowledge of toxicity mechanisms associated with size fractionated PM, these results together with the analysis of correlation between PM bound metals and biological assays will be relevant to better characterize the potential health risks and possible future mitigation strategies.

Associations between short-term ambient PM2.5, oxidant gases and respiratory hospitalizations in children: effect modification by PM2.5 transition metals, sulfur and oxidative potential

Background and Aim: Exposure to particulate and gaseous pollutants impair the respiratory health of children. Mass-based measures of PM2.5 do not capture spatiotemporal variability in particle composition/toxicity. The aim of this study is to examine whether associations between short-term ambient PM2.5 or oxidant gases and respiratory hospitalizations in children are modified by metals or sulfur content in PM2.5, or particle oxidative potential. Methods: This is a case-crossover study of 10,500 children (0-17 years) in Canada. Daily PM2.5 mass concentration and the combined weighted oxidant capacity of NO2 and O3 (Ox) were collected. Monthly estimates of transition metals (copper, iron, nickel, manganese, zinc) and sulfur in PM2.5, and three metrics of particle oxidative potential (OPAA, OPGSH, OPDTT) were measured at each monitoring site. Conditional logistic regression models were used to estimate associations between PM2.5 or Ox and respiratory hospitalizations, above and below median metals, sulfur, and particle oxidative potential. Results: Without stratifying above and below median metals, sulfur, or particle oxidative potential, there were no associations between PM2.5 mass and respiratory hospitalizations (OR and 95% CI per 10 &amp;#x3bc;g/m3 increase in PM2.5: 1.004 [0.955, 1.056]). However, when the analyses were performed above/below median metals, sulfur, and oxidative potential, positive associations were observed when metals, sulfur and OPGSH were above the median. For example, when copper was above the median, the OR and 95% CI per 10 &amp;#x3bc;g/m3 increase in PM2.5 was 1.084 [1.007, 1.167], while the OR and 95% CI was 0.970 [0.929, 1.014] when copper was below the median. Stronger associations between Ox and respiratory hospitalizations were also observed when metals, sulfur and oxidative potential were above the median. Conclusions: Stronger associations between short-term PM2.5, oxidant gases and respiratory hospitalizations in children were observed when metals, sulfur and particle oxidative potential were elevated. Keyword: PM2.5, respiratory health, children, oxidant gases

Examination of effect modification of the relationship between PM2.5 and cardiovascular mortality by particle oxidative potential within two Canadian cities

BACKGROUND AND AIM There is evidence that particle oxidative potential modifies effects of fine particulate matter air pollution (PM2.5) on health outcomes in between-cities studies in Canada. Additionally, previous work shows that oxidative potential of PM2.5 varies considerably at the within-city spatial scale. The aim of the present study was to determine if differences in the oxidative potential of PM2.5 at the within-city spatial scale modify the relationship between PM2.5 and cardiovascular mortality. METHODS We conducted a cohort study in the Canadian Census Health and Environment Cohort, a population-based cohort based on the Canadian longform Census. We followed participants who lived in the cities of Toronto or Montreal, Canada, at least 2 years in the period 2001-2016 (approximately 12 271 100 person-years in 1 101 000 individuals, rounded for confidentiality). Annual estimates of PM2.5 exposures were assigned from satellite data calibrated with ground-based observations, and oxidative potential was measured on samples of PM2.5 taken at 234 sites across the study area. We used time-varying Cox proportional hazards models to estimate hazard ratios for the effect of PM2.5 on cardiovascular mortality within strata of PM2.5 oxidative potential. Additionally, we estimated hazard ratios for oxidative burden (the product of oxidative potential and PM2.5 exposures). RESULTS We did not find evidence that oxidative potential modifies the effect of PM2.5 on mortality from cardiovascular causes (N = approximately 6100 events). The overall relationship between PM2.5 exposures and cardiovascular mortality was not significantly different from the null, and the same was true for oxidative burden measures. CONCLUSIONS Spatial variability in PM2.5 and the oxidative potential of PM2.5 may be insufficient for OP to act as a modifier of the effect of PM2.5 on cardiovascular mortality within the cities of Toronto and Montreal. KEYWORDS : fine particulate matter, oxidative potential, outdoor air pollution, cardiovascular disease

Air Pollution and Pediatric Respiratory Hospitalizations: Effect Modification by Particle Constituents and Oxidative Potential.

Rationale: Outdoor particulate and gaseous air pollutants impair respiratory health in children, and these associations may be influenced by particle composition. Objectives: To examine whether associations between short-term variations in fine particulate air pollution, oxidant gases, and respiratory hospitalizations in children are modified by particle constituents (metals and sulfur) or oxidative potential. Methods: We conducted a case-crossover study of 10,500 children (0-17 years of age) across Canada. Daily fine particle mass concentrations and oxidant gases (nitrogen dioxide and ozone) were collected from ground monitors. Monthly estimates of fine particle constituents (metals and sulfur) and oxidative potential were also measured. Conditional logistic regression models were used to estimate associations between air pollutants and respiratory hospitalizations, above and below median values for particle constituents and oxidative potential. Measurements and Main Results: Lag-1 fine particulate matter mass concentrations were not associated with respiratory hospitalizations (odds ratio and 95% confidence interval per 10 μg/m3 increase in fine particulate matter: 1.004 [0.955-1.056]) in analyses ignoring particle constituents and oxidative potential. However, when models were examined above or below median metals, sulfur, and oxidative potential, positive associations were observed above the median. For example, the odds ratio and 95% confidence interval per 10 μg/m3 increase in fine particulate matter were 1.084 (1.007-1.167) when copper was above the median and 0.970 (0.929-1.014) when copper was below the median. Similar trends were observed for oxidant gases. Conclusions: Stronger associations were observed between outdoor fine particles, oxidant gases, and respiratory hospitalizations in children when metals, sulfur, and particle oxidative potential were elevated.

Spatial variations in PM2.5 oxidative potential in Toronto and Montreal, Canada

BACKGROUND AND AIM: Particulate matter air pollution is a recognized threat to human health. Recently, measures of particulate air pollution have been developed that incorporate information on the effects that particles may have inside the human respiratory tract. Among these is particle oxidative potential (OP), which is a measure of the ability of PM to cause oxidative reactions. OP can be quantified using assays that measure the ability of PM to deplete antioxidants in a synthetic respiratory tract lining fluid model. An alternative approach considers the ability of particles to generate reactive oxygen species (ROS) in the respiratory tract, as estimated using a mathematical model and concentrations of transition metals. The aim of our study was to develop land-use regression models to characterize the spatial distribution of ROS-generating capacity of PM2.5 and two measures of OP. METHODS: We conducted large-scale spatial monitoring campaigns across Montreal and Toronto, Canada and developed land use regression models to predict the spatial distribution of ROS-generating capacity of PM2.5 and the ability of PM2.5 extracts to deplete the antioxidants ascorbate (OPAA) and glutathione (OPGSH). RESULTS:In Montreal, the best models explained 54% of variation in ROS, 45% in OPAA and 31% in OPGSH. In Toronto, models explained 63% of variation in ROS, 77% in OPAA, and 44% in OPGSH. Variables that were identified as predictors across multiple models included distance to PM2.5 and NOX emitting facilities, total traffic counts, and distance to highways. CONCLUSIONS:These results contribute to existing knowledge of within-city spatial variations in particle oxidative potential using an unprecedented number of sensors. Exposure surfaces generated by these models can be applied in future studies of the health impact of PM2.5. Future work could clarify the sources of the most harmful components of PM2.5 to human health to aid in targeted reductions of emissions. KEYWORDS: particulate matter, oxidative potential, land use regression

The Oxidative Potential of Fine Particulate Matter and Metabolic Perturbations in Plasma and Saliva

BACKGROUND AND AIM: Exposure assessment and health impact evaluation of particulate matter (PM) mixtures remain very challenging. Fine particle oxidative potential (FPMOP) has been considered as a key health-relevant particulate parameter. We measured FPMOP exposures in a recent panel study and corresponding metabolic perturbations to evaluate its potential epidemiologic value and examine molecular mechanisms underlying PM-related health impacts. METHODS: We recruited 54 participants from two dormitories in Atlanta, GA near and far from a congested highway. Indoor or outdoor FPMOP levels at the dormitories were measured using dithiothreitol (DTT) assay. Plasma and saliva samples were collected from participants at four time points during 12 weeks. Liquid chromatography coupled with high-resolution mass spectrometry was used to profile the participants’ metabolome. We used mixed effect models to examine associations between metabolic features and FPMOP, controlling for potential confounders including age, gender, race, and body mass index. Significant metabolic features meeting false positive discovery rate at 20% were used for pathway enrichment analysis and metabolite annotation. RESULTS:The 96h-mean water soluble FPMOP levels at the near and far dormitories prior to biosample collection were 26.3 and 22.9 nmol/min/μg, respectively. In total, we extracted 20,766 metabolic features from plasma samples and 29,013 from saliva samples. Purine metabolism, N-glycan biosynthesis, and beta-alanine metabolism were most strongly associated with 5 or more FPMOP-related measurements in plasma, while vitamin E metabolism, leukotriene metabolism, and glycosphingolipid metabolism were found associated with FPMOP in saliva. We confirmed 6 metabolites directly associated with FPMOP measurements including hypoxanthine, histidine, pyruvate, (s)-lactate/glyceraldehyde, azelaic acid, and petroselinic acid/elaidic acid/oleate, which were implications of perturbations in amino acid, carbohydrate, nucleotide and lipid metabolism. CONCLUSIONS:We identified metabolites and pathways perturbations in plasma and saliva following by higher FPMOP exposure in panel-based setting. Perturbations in amino acid, carbohydrate, nucleotide and lipid metabolism may elicit PM-related health impacts. KEYWORDS: Fine Particle Oxidative Potential, Metabolomics, Air Pollution, Dithiothreitol Assay

Identification of Toxicity Parameters Associated with Combustion Produced Soot Surface Chemistry and Particle Structure by in Vitro Assays.

Air pollution has become the world’s single biggest environmental health risk of the past decade, causing millions of yearly deaths worldwide. One of the dominant air pollutants is fine particulate matter (PM2.5), which is a product of combustion. Exposure to PM2.5 has been associated with decreased lung function, impaired immunity, and exacerbations of lung disease. Accumulating evidence suggests that many of the adverse health effects of PM2.5 exposure are associated with lung inflammation and oxidative stress. While the physical structure and surface chemistry of PM2.5 are surrogate measures of particle oxidative potential, little is known about their contributions to negative health effects. In this study, we used functionalized carbon black particles as surrogates for atmospherically aged combustion-formed soot to assess the effects of PM2.5 surface chemistry in lung cells. We exposed the BEAS-2B lung epithelial cell line to different soot at a range of concentrations and assessed cell viability, inflammation, and oxidative stress. Our results indicate that exposure to soot with varying particle surface composition results in differential cell viability rates, the expression of pro-inflammatory and oxidative stress genes, and protein carbonylation. We conclude that particle surface chemistry, specifically oxygen content, in soot modulates lung cell inflammatory and oxidative stress responses.

Oxidative potential of particles at a research house: Influencing factors and comparison with outdoor particles

The oxidative potential (OP) of particles can be represented by the ability of particles to generate hydroxyl radicals in an aqueous solution which can be measured with electron paramagnetic resonance (EPR) spectrometry. The oxidative potential of particles may be a more health-relevant metric than other physicochemical properties of particles. While OPEPR has been measured in several outdoor locations, it remains largely unstudied in indoor environments. Total suspended particle samples were collected at an unoccupied research house in eighteen four-day sampling events. The OPEPR of indoor particles was found to be 59% ± 30% of the OPEPR of outdoor particles on a sampling volume basis during normal indoor conditions in eight sampling events. However, OPEPR per particle mass was 3.5 ± 0.62 times higher indoors than outdoors, indicating that reactions taking place indoors likely increase OPEPR of indoor particles. In ten sampling events, indoor temperature, relative humidity (RH), air change rate (λ), and cooking activities were varied. OPEPR of indoor particles was found to be significantly influenced (in order of importance) by indoor RH, λ, and temperature. OPEPR of indoor particles was higher than OPEPR for outdoor particles when indoor RH and λ were increased. The presence of cooking activities did not appear to consistently increase OPEPR of indoor particles.

Maternal exposure to air pollutants and birth weight in Tehran, Iran.

Air pollution can cause various health outcomes, especially in susceptible groups including pregnant women. Low birth weight (LBW) is among the adverse birth outcomes and is one of the main causes of infant mortality. The aim of this study was to assess the association between air pollutants and LBW in Tehran, Iran. In this case-control study, 2144 babies born in three hospitals of Tehran (Iran) during 2011 to 2012 whose mothers were the residents of this city in last 5years were considered. Of these, 468 infants with birth weight < 2500g and 1676 with birth weight ≥ 2500g were regarded as case and control groups, respectively. Gestational age was also considered for definition of cases (small for gestational age (SGA)) and controls (appropriate for gestational age). Land use regression models were used to assess exposure to particulate matter ≤10μm in aerodynamic diameter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2) and volatile organic compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene (BTEX), and total BTEX) during pregnancy. Logistic regression model was applied to assess the association between air pollutants and LBW. The concentrations of air pollutants were very high but similar in cases and controls. After adjustment for potential confounding variables, no statistically significant association was observed between air pollutants and LBW. The adjusted odds ratios (95% confidence interval) for PM10, SO2, and benzene were 0.999 (0.994-1.005), 0.998 (0.993-1.003), and 0.980 (0.901-1.067), respectively. No association was found between LBW and air pollutants. Further studies with more rigorous designs and access to more comprehensive information are suggested to assess the effect of other air pollutants, such as CO, O3, PM2.5, ultrafine particles, and oxidative potential of particles on birth outcomes.

Size-resolved particle oxidative potential in the office, laboratory, and home: Evidence for the importance of water-soluble transition metals

Particulate matter (PM) oxidative potential (OP) is an emerging health metric, but studies examining the OP of indoor PM are rare. This paper focuses on the relationships between respiratory exposure to OP and PM water-soluble composition in indoor environments. Size-resolved PM samples were collected between November 2015 and June 2016 from an office, home (including bedroom, living room, and storeroom), and laboratory using a MOUDI sampler. Particles from each source were segregated into eleven size bins, and the water-soluble metal content and dithiothreitol (DTT) loss rate were measured in each PM extract. The water-soluble OP (OPws) of indoor PM was highest in the office and lowest in the home, varying by factors of up to 1.2; these variations were attributed to differences in occupation density, occupant activity, and ventilation. In addition, the particulate Cu, Mn, and Fe concentrations were closely correlated with OPws in indoor particles; the transition metals may have acted as catalysts during oxidation processes, inducing ·OH formation through the concomitant consumption of DTT. The OPws particle size distributions featured single modes with peaks between 0.18 and 3.2 μm across all indoor sites, reflecting the dominant contribution of PM3.2 to total PM levels and the enhanced oxidative activity of the PM3.2 compared to PM>3.2. Lung-deposition model calculations indicated that PM3.2 dominated the pulmonary deposition of the OPws (>75%) due to both the high levels of metals content and the high deposition efficiency in the alveolar region. Therefore, because OPws has been directly linked to various health effects, special attention should be given to PM3.2.

Assessment of Particle Oxidative Potential as an Air Pollution Exposure Metric: A Systematic Review

Ambient particulate air pollution is linked to numerous acute and chronic health outcomes. The standard approach to measuring particulate exposure has been to estimate particle mass concentration. New measures account for oxidative potential, the ability of particles to cause oxidative stress in the body. There has been no systematic comparison of particulate air pollution exposure assessment methods between those that incorporate oxidative potential and those that do not. The aim of this review is to determine if associations between particulate air pollution exposure and health outcomes are stronger when oxidative potential is used as the exposure metric, in comparison to particle mass concentration. The databases Medline and Embase were searched from inception to 28 March 2018 for studies that reported an association between particulate air pollution exposure and a health outcome in a human population, and in which exposure was measured by both particle mass concentration and oxidative potential. Study quality was assessed using a US National Toxicology Program instrument. We identified 18 publications meeting the selection criteria. The most common oxidative potential assay was antioxidant depletion in synthetic respiratory tract lining fluid, used in 12 articles. The rate of consumption of dithiothreitol was also frequently used as an oxidative potential assay and appeared in 5 studies. The dithiothreitol assay most consistently produced stronger effect estimates, as 10/14 endpoints showed higher point estimates of associations compared to particle mass concentration estimates. Other assays showed mixed results. To date there is no consistent evidence that oxidative potential is more strongly associated with health outcomes than particle mass concentrations; however, these assays do have the advantage of not treating all particles as equally harmful and further work should explore which specific assays are most relevant to evaluating air pollution health risks.

Reactive Oxidative Species and Speciated Particulate Light-Duty Engine Emissions from Diesel and Biodiesel Fuel Blends

It is well established that particulate matter (PM) continues to be a major air pollutant challenge for human health globally, and vehicle exhaust PM emissions have been linked to many adverse health effects. However, the relative toxicity of biodiesel emissions compared to petroleum diesel remains unclear. Given the legislated mandates to increase biodiesel fuel use in response to energy security and climate concerns, in this study we examined the relationships between biodiesel fuel blend, exhaust particle oxidative potential (OP), and PM composition. Mechanistically, there is a growing consensus that the formation of reactive oxygen species (ROS) due to PM exposure leads to subsequent oxidative stress and inflammation at the cellular level. Here, dithiothreitol (DTT) assays were performed on impinger samples of PM obtained from light-duty diesel engine transient cycle emission tests with two biodiesel feedstocks, soybean (SOY) and waste vegetable oil (WVO), blended with ultralow sulfur petrodiesel at f...

Highly Acidic Ambient Particles, Soluble Metals, and Oxidative Potential: A Link between Sulfate and Aerosol Toxicity.

Soluble transition metals in particulate matter (PM) can generate reactive oxygen species in vivo by redox cycling, leading to oxidative stress and adverse health effects. Most metals, such as those from roadway traffic, are emitted in an insoluble form, but must be soluble for redox cycling. Here we present the mechanism of metals dissolution by highly acidic sulfate aerosol and the effect on particle oxidative potential (OP) through analysis of size distributions. Size-segregated ambient PM were collected from a road-side and representative urban site in Atlanta, GA. Elemental and organic carbon, ions, total and water-soluble metals, and water-soluble OP were measured. Particle pH was determined with a thermodynamic model using measured ionic species. Sulfate was spatially uniform and found mainly in the fine mode, whereas total metals and mineral dust cations were highest at the road-side site and in the coarse mode, resulting in a fine mode pH < 2 and near neutral coarse mode. Soluble metals and OP peaked at the intersection of these modes demonstrating that sulfate plays a key role in producing highly acidic fine aerosols capable of dissolving primary transition metals that contribute to aerosol OP. Sulfate-driven metals dissolution may account for sulfate-health associations reported in past studies.

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 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.

Oxidative potential and chemical speciation of size-resolved particulate matter (PM) at near-freeway and urban background sites in the greater Beirut area

To assess particle oxidative potential in the greater Beirut area, size-resolved PM10–2.5, PM2.5–0.25 and PM0.25 samples were collected at near-freeway and urban background sites. Metals and trace elements, including Mn, Cr, Cu, Ba, Mo and Sb, displayed increased levels and crustal enrichment factors at the roadway, indicating their vehicular origin. These elements in addition to Co, V, Ni and Zn were mostly distributed in PM2.5–0.25 and PM0.25 at both sites, with moderate-to-high water-solubility (>30%). The presence of these metals, mainly air toxics, in small size ranges constitutes an added health risk. Of particular concern are elements with strong correlations (R≥0.70) with reactive oxygen species (ROS)-activity, measured by a cellular assay. In PM10–2.5, road dust component Mn and soil-related element Co were highly correlated with ROS-activity. In PM2.5–0.25, vehicular abrasion element Cu and soil-derived component Co were highly associated with ROS-activity. In PM0.25, V and Ni, originating from fuel oil combustion, strongly correlated with ROS formation. ROS-activity displayed a particle-size dependency, with lowest activity associated with PM10–2.5. On a per air volume basis, size-resolved ROS-activity was 1.5–2.8 times greater at the roadside than background location, indicating that exposure to redox-active species may be greatest near the freeway. Size-fractionated PM intrinsic activity (i.e. PM mass-normalized) was comparable at both sites, possibly suggesting a similarity in the sources of ROS-active species. Relative to other urban settings, while the intrinsic redox activity of PM10–2.5 in Beirut is comparable to that measured at an urban site in Los Angeles (LA), its PM0.25-induced ROS-activity is ~2.3-fold greater. Moreover, the intrinsic ROS-activity of ambient PM2.5 in Beirut is comparable to that reported in Milan-Italy, but 3.1-times PM2.5 activity in the heavily-polluted Lahore-Pakistan. Lastly, findings suggest a dominant role of transition metals in generating ROS compared to organic carbon in the LA area.

Concentration and oxidative potential of on-road particle emissions and their relationship with traffic composition: Relevance to exposure assessment

Particles emitted by vehicles are known to cause detrimental health effects, with their size and oxidative potential among the main factors responsible. Therefore, understanding the relationship between traffic composition and both the physical characteristics and oxidative potential of particles is critical. To contribute to the limited knowledge base in this area, we investigated this relationship in a 4.5 km road tunnel in Brisbane, Australia.On-road concentrations of ultrafine particles (<100 nm, UFPs), fine particles (PM2.5), CO, CO2 and particle associated reactive oxygen species (ROS) were measured using vehicle-based mobile sampling. UFPs were measured using a condensation particle counter and PM2.5 with a DustTrak aerosol photometer. A new profluorescent nitroxide probe, BPEAnit, was used to determine ROS levels. Comparative measurements were also performed on an above-ground road to assess the role of emission dilution on the parameters measured.The profile of UFP and PM2.5 concentration with distance through the tunnel was determined, and demonstrated relationships with both road gradient and tunnel ventilation. ROS levels in the tunnel were found to be high compared to an open road with similar traffic characteristics, which was attributed to the substantial difference in estimated emission dilution ratios on the two roadways. Principal component analysis (PCA) revealed that the levels of pollutants and ROS were generally better correlated with total traffic count, rather than the traffic composition (i.e. diesel and gasoline-powered vehicles).A possible reason for the lack of correlation with HDV, which has previously been shown to be strongly associated with UFPs especially, was the low absolute numbers encountered during the sampling. This may have made their contribution to in-tunnel pollution largely indistinguishable from the total vehicle volume. For ROS, the stronger association observed with HDV and gasoline vehicles when combined (total traffic count) compared to when considered individually may signal a role for the interaction of their emissions as a determinant of on-road ROS in this pilot study. If further validated, this should not be overlooked in studies of on- or near-road particle exposure and its potential health effects.