Abstract
Abstract. Epidemiological studies have shown a correlation between exposure to ambient particulate matter (PM) and adverse health effects. One proposed mechanism of PM-mediated health effects is the generation of reactive oxygen species (ROS) – e.g., superoxide (•O2−), hydrogen peroxide (HOOH), and hydroxyl radical (•OH) – followed by oxidative stress. There are very few quantitative, specific measures of individual ROS generated from PM, but this information would help to more quantitatively address the link between ROS and the health effects of PM. To address this gap, we quantified the generation of HOOH by PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California during summer and winter from 2006 to 2009. HOOH was quantified by HPLC after extracting the PM in a cell-free, phosphate-buffered saline (PBS) solution with or without 50 μM ascorbate (Asc). Our results show that the urban PM generally generates much more HOOH than the rural PM but that there is no apparent seasonal difference in HOOH generation. In nearly all of the samples the addition of a physiologically relevant concentration of Asc greatly enhances HOOH formation, but a few of the coarse PM samples were able to generate a considerable amount of HOOH in the absence of added Asc, indicating the presence of unknown reductants. Normalized by air volume, the fine PM (PM2.5) generally makes more HOOH than the corresponding coarse PM (PMcf, i.e., 2.5 to 10 μm), primarily because the mass concentration of PM2.5 is much higher than that of PMcf. However, normalized by PM mass, the coarse PM typically generates more HOOH than the fine PM. The amount of HOOH produced by SJV PM is reduced on average by (78 ± 15)% when the transition metal chelator desferoxamine (DSF) is added to the extraction solution, indicating that transition metals play a dominant role in HOOH generation. By measuring calibration curves of HOOH generation from copper, and quantifying copper concentrations in our particle extracts, we find that PBS-soluble copper is primarily responsible for HOOH production by the Fresno PM. Extrapolating our results to expected concentrations of PM-derived HOOH in human lung lining fluid suggests that typical daily PM exposures in the San Joaquin Valley are unlikely to cause HOOH-mediated acute health effects, but that very high PM events might lead to cytotoxic levels of pulmonary HOOH.
Highlights
Ambient particulate matter (PM) can have adverse health effects at relatively low concentrations (Shy, 1979; Ware et al, 1981), with epidemiological studies showing robust correlations between PM exposure and adverse health effects such as human pulmonary and cardiovascular morbidity and mortality (Pope et al, 1995, 2004; Dockery et al, 1993; Pekkanen et al, 2002; Pope and Dockery, 2006)
Examples of HOOH generation from fine and coarse San Joaquin Valley particle samples extracted in a surrogate lung fluid containing ascorbate: FRSU06 = Fresno summer 2006, WESU07
We have quantified the formation of HOOH in cell-free aqueous extracts of particulate matter from an urban and rural site in the San Joaquin Valley (SJV) of California
Summary
Ambient particulate matter (PM) can have adverse health effects at relatively low concentrations (Shy, 1979; Ware et al, 1981), with epidemiological studies showing robust correlations between PM exposure and adverse health effects such as human pulmonary and cardiovascular morbidity and mortality (Pope et al, 1995, 2004; Dockery et al, 1993; Pekkanen et al, 2002; Pope and Dockery, 2006). While the pathways involved in this relationship remain to be clarified, one proposed mechanism is PM-mediated generation of reactive oxygen species (ROS), which causes oxidative stress and cell damage (Li et al, 2008; Valavanidis et al, 2008; Gonzalez-Flecha, 2004; Donaldson et al, 2003). The major ROS species include superoxide (O−2 ), hydrogen peroxide (HOOH), and hydroxyl radical (OH). These species can be formed by transition metals (M) in the presence of reductant (e.g., ascorbate) via reactions such as Published by Copernicus Publications on behalf of the European Geosciences Union. H. Shen et al.: Hydrogen peroxide from San Joaquin Valley particles
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