Particulate Reactive Oxygen Species Research Articles

An automated online instrument to quantify aerosol-bound reactive oxygen species (ROS) for ambient measurement and health-relevant aerosol studies

Abstract. The adverse health effects associated with ambient aerosol particles have been well documented, but it is still unclear which aerosol properties are most important for their negative health impact. Some studies suggest the oxidative effects of particle-bound reactive oxygen species (ROS) are potential major contributors to the toxicity of particles. Traditional ROS measurement techniques are labour-intensive, give poor temporal resolution and generally have significant delays between aerosol sampling and ROS analysis. However, many oxidising particle components are reactive and thus potentially short-lived. Thus, a technique to quantify particle-bound ROS online would be beneficial to quantify also the short-lived ROS components. We introduce a new portable instrument to allow online, continuous measurement of particle-bound ROS using a chemical assay of 2′7′-dichlorofluorescein (DCFH) with horseradish peroxidase (HRP), via fluorescence spectroscopy. All components of the new instrument are attached to a containing shell, resulting in a compact system capable of automated continuous field deployment over many hours or days. From laboratory measurements, the instrument was found to have a detection limit of ∼ 4 nmol [H2O2] equivalents per cubic metre (m3) air, a dynamic range up to at least ∼ 2000 nmol [H2O2] equivalents per m3 air and a time resolution of ≤ 12 min. The instrument allows for ∼ 16 h automated measurement if unattended and shows a fast response to changes in concentrations of laboratory-generated oxidised organic aerosol. The instrument was deployed at an urban site in London, and particulate ROS levels of up to 24 nmol [H2O2] equivalents per m3 air were detected with PM2.5 concentrations up to 28 µg m−3. The new and portable Online Particle-bound ROS Instrument (OPROSI) allows fast-response quantification; this is important due to the potentially short-lived nature of particle-bound ROS as well as fast-changing atmospheric conditions, especially in urban environments. The instrument design allows for automated operation and extended field operation with twice-daily presence of an operator. As well as having sensitivity suitable for ambient level measurement, the instrument is also suitable at concentrations such as those required for laboratory and chamber toxicological studies.

Particulate reactive oxygen species on total suspended particles - measurements in residences in Austin, Texas.

The biologically relevant characteristics of particulate matter (PM) in homes are important to assessing human health. The concentration of particulate reactive oxygen species (ROS) was assessed in eight homes and was found to be lower inside (mean±s.e.=1.59±0.33nmol/m3 ) than outside (2.35±0.57nmol/m3 ). Indoor particulate ROS concentrations were substantial and a major fraction of indoor particulate ROS existed on PM2.5 (58±10%), which is important from a health perspective as PM2.5 can carry ROS deep into the lungs. No obvious relationships were evident between selected building characteristics and indoor particulate ROS concentrations, but this observation would need to be verified by larger, controlled studies. Controlled experiments conducted at a test house suggest that indoor ozone and terpene concentrations substantially influence indoor particulate ROS concentrations when outdoor ozone concentrations are low, but have a weaker influence on indoor particulate ROS concentrations when outdoor ozone concentrations are high. The combination of substantial indoor concentrations and the time spent indoors suggest that further work is warranted to assess the key parameters that drive indoor particulate ROS concentrations.

Technical Note: Particulate reactive oxygen species concentrations and their association with environmental conditions in an urban, subtropical climate

Abstract. Reactions between hydrocarbons and ozone or hydroxyl radicals lead to the formation of oxidized species, including reactive oxygen species (ROS), and secondary organic aerosol (SOA) in the troposphere. ROS can be carried deep into the lungs by small aerodynamic particles where they can cause oxidative stress and cell damage. While environmental studies have focused on ROS in the gas phase and rainwater, it is also important to determine concentrations of ROS on respirable particles. Samples of PM2.5 collected over 3 h at midday on 40 days during November 2011 and September 2012 show that the particulate ROS concentration in Austin, Texas, ranged from a minimum value of 0.02 nmoles H2O2 m−3 air in December to 3.81 nmoles H2O2 m−3 air in September. Results from correlation tests and linear regression analysis on particulate ROS concentrations and environmental conditions (which included ozone and PM2.5 concentrations, temperature, relative humidity, precipitation and solar radiation) indicate that ambient particulate ROS is significantly influenced by the ambient ozone concentration, temperature and incident solar radiation. Particulate ROS concentrations measured in this study were in the range reported by other studies in the US, Taiwan and Singapore. This study is one of the first to assess seasonal variations in particulate ROS concentrations and helps explain the influence of environmental conditions on particulate ROS concentrations.

Indoor particulate reactive oxygen species concentrations

Despite the fact that precursors to reactive oxygen species (ROS) are prevalent indoors, the concentration of ROS inside buildings is unknown. ROS on PM2.5 was measured inside and outside twelve residential buildings and eleven institutional and retail buildings. The mean (±s.d.) concentration of ROS on PM2.5 inside homes (1.37±1.2nmoles/m3) was not significantly different from the outdoor concentration (1.41±1.0nmoles/m3). Similarly, the indoor and outdoor concentrations of ROS on PM2.5 at institutional buildings (1.16±0.38nmoles/m3 indoors and 1.68±1.3nmoles/m3 outdoors) and retail stores (1.09±0.93nmoles/m3 indoors and 1.12±1.1nmoles/m3 outdoors) were not significantly different and were comparable to those in residential buildings. The indoor concentration of particulate ROS cannot be predicted based on the measurement of other common indoor pollutants, indicating that it is important to separately assess the concentration of particulate ROS in air quality studies. Daytime indoor occupational and residential exposure to particulate ROS dominates daytime outdoor exposure to particulate ROS. These findings highlight the need for further study of ROS in indoor microenvironments.

Outdoor Sources of Residential Indoor Particulate Reactive Oxygen Species

Despite the fact that precursors to reactive oxygen species (ROS) are prevalent in homes, the concentration of ROS had not been assessed in homes till a recent study by our group. Given the significant concentrations of ROS that we found in homes as well as the evidence for adverse health effects caused by ROS, it becomes important to identify and control potential sources of indoor ROS. Controlled experiments were conducted at an unoccupied test house to help determine the influence of two potential outdoor sources of indoor ROS: outdoor particles and ozone (O3) that infiltrate into homes. One of the rooms was pressurized to isolate it from the rest of the house and sampling was conducted in three different situations: (i) particle-free, O3 laden air brought into the room using a High Efficiency Particulate Air (HEPA) filter at the room’s inlet, (ii) O3-free, particle laden air brought in using an activated carbon (AC) filter, and (iii) clean air brought in using HEPA and AC filters. The concentration of ROS on triplicate total suspended particle (TSP) samples was assessed with a fluorescent reagent. When the O3 concentration in the room was increased to 19 ppb, the ROS concentration in the room (1.50±0.38 nmoles/m3) was closer to the outdoor concentration (2.08±0.20 nmoles/m3) where O3 was at 40 ppb, than in the rest of the house (0.75±0.11 nmoles/m3) where O3 had remained at 3 ppb. When the PM2.5 concentration in the room was increased to 2.6 mg/m3, the ROS concentration in the room (2.26±0.42 nmoles/m3) was similar to the outdoor concentration (2.42±0.58 nmoles/m3) where PM2.5 concentration was at 3.1 mg/m3. In comparison, when no O3 or particles were brought into the room, the ROS concentration in the room (2.00±0.24 nmoles/m3) was substantially below the outdoor concentration (2.95±0.08 nmoles/m3). These results indicate that infiltration of outdoor particles and O3 into homes can strongly influence indoor particulate ROS concentrations.

Development and testing of an online method to measure ambient fine particulate reactive oxygen species (ROS) based on the 2',7'-dichlorofluorescin (DCFH) assay

Abstract. An online, semi-continuous instrument to measure fine particle (PM2.5) reactive oxygen species (ROS) was developed based on the fluorescent probe 2'7'-dichlorofluorescin (DCFH). Parameters that influence probe response were first characterized to develop an optimal method for use in a field instrument. The online method used a mist chamber scrubber to collect total (gas plus particle) ROS components (ROSt) alternating with gas phase ROS (ROSg) by means of an inline filter. Particle phase ROS (ROSp) was determined by the difference between ROSt and ROSg. The instrument was deployed in urban Atlanta, Georgia, USA, and at a rural site during various seasons. Concentrations from the online instrument generally agreed well with those from an intensive filter measurement of ROSp. Concentrations of the ROSp measurements made with this instrument were lower than reported in other studies, often below the instrument's average limit of detection (0.15 nmol H2O2 equivalents m−3). Mean ROSp concentrations were 0.26 nmol H2O2 equivalents m−3 at the Atlanta urban sites compared to 0.14 nmol H2O2 equivalents m−3 at the rural site.

Characterization of Wintertime Reactive Oxygen Species Concentrations in Flushing, New York

One of the main hypotheses for the species causing the observed health effects of ambient particulate matter is peroxides and other reactive oxygen species (ROS). However, there is currently very little data available on the concentrations of particle-bound ROS or their behavior in different physical locations and seasons. The concentrations of particle-bound ROS were determined for various size fractions of the aerosol, ranging from 10 nm to 18 μ m, in Flushing, New York during the period of January and early February 2004. Sampling was carried out at 3-hour intervals using a MOUDI™ cascade impactor. The collected particles were treated with the non-fluorescent probe dichlorofluorescin (DCFH) that fluoresces when oxidized by the presence of ROS. The measured fluorescent intensities were converted into equivalent hydrogen peroxide concentrations, which were used as indicators of ROS reactivity, by calibrations using H 2 O 2 standards. Diurnal profiles of the ROS concentrations were obtained. Correlations of the particulate ROS concentrations with the intensity of photochemical reaction, estimated secondary organic carbon (SOC) and gas phase OH and HO 2 radical concentrations were explored. The intensity of photochemical reactions and gas phase radical concentrations were found to be moderate factors affecting particulate ROS concentrations. The concentrations of ROS were found to be higher in the submicron size particles of the ambient aerosol.

Formation of Secondary Organic Aerosols and Reactive Oxygen Species from Diluted Motorcycle Exhaust

Oxidation of reactive organic gases (ROG) in ambient air produces low-volatility compounds that may condense to form secondary organic aerosols (SOA). Reactive oxygen species (ROS) are also produced in the photochemical reactions involving ROG. In the urban atmosphere, the precursors of SOA and ROS primarily come from vehicular emissions. This study aims at investigating the SOA and ROS formation potentials of diluted motorcycle exhaust under UV irradiation. Exhaust samples were obtained from a 124-cc motorcycle engine under idling conditions. Emissions from the tailpipe were directly collected in a Tedlar bag and diluted with filtered air by a ratio of 5. A filter cassette placed upstream of the bag removed particles in the exhaust while the sample was being collected. The sample in the bag was then irradiated by UV light and the number size distribution of aerosol particles was measured at various time intervals using a scanning mobility particle sizer. The concentrations of gaseous and particulate reactive oxygen species were also determined at intervals. Under continuous UV irradiation, the particle number concentration in the bag peaked at 2-3 h, while the gaseous ROS concentration peaked at 5-7 h. The peak concentration of gaseous ROS was about one order of magnitude higher than the initial value in the diluted motorcycle exhaust. From the difference between gaseous and total ROS concentrations, it was estimated that about 9.6% (by mole number) of the total ROS was in the particulate phase. The results suggest that diluted motorcycle exhaust has a high potential to form ROS and SOA under UV irradiation.

Ambient Particulate Matter Exhibits Direct Inhibitory Effects on Oxidative Stress Enzymes

A primary mechanistic hypothesis by which ambient air particles have a significant negative impact on human health is via the induction of pulmonary inflammatory responses mediated through the generation of reactive oxygen species (ROS). Development of a biosensor for the assessment of particulate ROS activity would be a significant advance in air pollution monitoring. The objective of this study was to evaluate whether air particulates interact directly with protective enzymes involved in oxidative stress responses. We performed enzyme activity assays on four enzymes involved in oxidative stress responses (Cu/Zn superoxide dismutase, Mn superoxide dismutase, glutathione peroxidase, and glutathione reductase) in the presence of particles of varying toxicities and found distinctive inhibition patterns. On the basis of these findings, we suggest a strategy for an enzyme bioassay that could be used to assess the potential of particles to generate ROS-induced responses.

Reactive Oxygen Species in Incense Smoke

ABSTRACTThe objective of this study is to determine the concentration of reactive oxygen species (ROS) generated from burning incense in an experimental chamber with a volume of 288 liters and a continuous supply of filtered air at 15 1/min. A Micro-Environmental Monitor (MEM) collected PM1 and PM2.5 from the incense smoke on 37-mm polycarbonate membrane filters. The ROS in particles were extracted using dichiorofluorescin-horseradish peroxidase (DCFH2-HRP) reagent. Additionally, two parallel sampling trains, each consisting of a filter cassette and 3 impingers connected in series, were employed to simultaneously collect ROS in particles and in gas phase. Each impinger contained 10 ml of the DCFH2-HRP reagent for absorbing ROS in gas phase. The samples obtained by filter cassette were treated as the MEM samples. Subsequently, the extracts and impinger samples were incubated at 37°C for 15 min and the fluorescence intensity of resulting dichlorofluorescein (DCF) was determined. Fluorescence intensity data were converted to equivalent H2O2 concentrations using calibration curves obtained from fluorescence measurement of standard DCF solutions. For samples collected 1 hr after one joss stick of black lignaloes was lit in the experimental chamber, the mean ROS concentrations in PM1 and PM2.5 were 15.60 ± 1.00 and 13.50 ± 1.30 nmol H2O2/mg of particles, respectively. In contrast, the mean ROS concentrations in PM1 and PM2.5 sampled from an apartment (free of incense smoke, cooking fumes, and cigarette smoke) were 6.54 ± 1.00 and 4.06 ± 2.04 nmol H2O2/mg, respectively. When one joss stick of black lignaloes was burned for 1 hr in the experimental chamber, the mean ROS concentration was 0.94 ± 0.06 nmol H2O2/l of air in gas phase and 1.06 ± 0.05 nmol H2O2/I in particles. The finding could have important health implications because particulate ROS in inhaled air could easily reach the alveolar region.

Reactive Oxygen Species in Incense Smoke

The objective of this study is to determine the concentration of reactive oxygen species (ROS) generated from burning incense in an experimental chamber with a volume of 288 liters and a continuous supply of filtered air at 15 1/min. A Micro-Environmental Monitor (MEM) collected PM1 and PM2.5 from the incense smoke on 37-mm polycarbonate membrane filters. The ROS in particles were extracted using dichiorofluorescin-horseradish peroxidase (DCFH2-HRP) reagent. Additionally, two parallel sampling trains, each consisting of a filter cassette and 3 impingers connected in series, were employed to simultaneously collect ROS in particles and in gas phase. Each impinger contained 10 ml of the DCFH2-HRP reagent for absorbing ROS in gas phase. The samples obtained by filter cassette were treated as the MEM samples. Subsequently, the extracts and impinger samples were incubated at 37°C for 15 min and the fluorescence intensity of resulting dichlorofluorescein (DCF) was determined. Fluorescence intensity data were converted to equivalent H2O2 concentrations using calibration curves obtained from fluorescence measurement of standard DCF solutions. For samples collected 1 hr after one joss stick of black lignaloes was lit in the experimental chamber, the mean ROS concentrations in PM1 and PM2.5 were 15.60 ± 1.00 and 13.50 ± 1.30 nmol H2O2/mg of particles, respectively. In contrast, the mean ROS concentrations in PM1 and PM2.5 sampled from an apartment (free of incense smoke, cooking fumes, and cigarette smoke) were 6.54 ± 1.00 and 4.06 ± 2.04 nmol H2O2/mg, respectively. When one joss stick of black lignaloes was burned for 1 hr in the experimental chamber, the mean ROS concentration was 0.94 ± 0.06 nmol H2O2/l of air in gas phase and 1.06 ± 0.05 nmol H2O2/I in particles. The finding could have important health implications because particulate ROS in inhaled air could easily reach the alveolar region.