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A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions.

ABSTRACT: Generation of reactive oxygen species (ROS) - including superoxide ((•)O(2) (-)), hydrogen peroxide (HOOH), and hydroxyl radical ((•)OH) - has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and (•)OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper or iron. Samples were extracted in a cell-free, phosphate-buffered saline (PBS) solution containing 50 ?M ascorbate (Asc). In our laboratory solutions we find that Cu is a potent source of both HOOH and (•)OH, with approximately 90% of the electrons that can be donated from Asc ending up in HOOH and (•)OH after 4 h. In contrast, in Fe solutions there is no measurable HOOH and only a modest production of (•)OH. Soluble Cu in the SJV PM samples is also a dominant source of HOOH and (•)OH. In both laboratory copper solutions and extracts of ambient particles we find much more production of HOOH compared to (•)OH: e.g., HOOH generation is approximately 30 - 60 times faster than (•)OH generation. The formation of HOOH and (•)OH are positively correlated, with roughly 3 % and 8 % of HOOH converted to (•)OH after 4 and 24 hr of extraction, respectively. Although the SJV PM produce much more HOOH than (•)OH, since (•)OH is a much stronger oxidant it is unclear which species might be more important for oxidant-mediated toxicity from PM inhalation.

SUBMITTER: Shen H

PROVIDER: S-EPMC3259706 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions.

Shen Huiyun H Anastasio Cort C

Atmospheric environment (Oxford, England : 1994) 20120101

Generation of reactive oxygen species (ROS) - including superoxide ((•)O(2) (-)), hydrogen peroxide (HOOH), and hydroxyl radical ((•)OH) - has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and (•)OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper ...[more]

PMID: 22267949

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Project description:BackgroundFibrous chrysotile has been the most commonly applied asbestos mineral in a range of technical applications. However, it is toxic and carcinogenic upon inhalation. The chemical reactivity of chrysotile fiber surfaces contributes to its adverse health effects by catalyzing the formation of highly reactive hydroxyl radicals (HO•) from H2O2. In this Haber-Weiss cycle, Fe on the fiber surface acts as a catalyst: Fe3+ decomposes H2O2 to reductants that reduce surface Fe3+ to Fe2+, which is back-oxidized by H2O2 (Fenton-oxidation) to yield HO•. Chrysotile contains three structural Fe species: ferrous and ferric octahedral Fe and ferric tetrahedral Fe (Fe3+tet). Also, external Fe may adsorb or precipitate onto fiber surfaces. The goal of this study was to identify the Fe species on chrysotile surfaces that catalyze H2O2 decomposition and HO• generation.ResultsWe demonstrate that at the physiological pH 7.4 Fe3+tet on chrysotile surfaces substantially contributes to H2O2 decomposition and is the key structural Fe species catalyzing HO• generation. After depleting Fe from fiber surfaces, a remnant fiber-related H2O2 decomposition mode was identified, which may involve magnetite impurities, remnant Fe or substituted redox-active transition metals other than Fe. Fe (hydr)oxide precipitates on chrysotile surfaces also contributed to H2O2 decomposition, but were per mole Fe substantially less efficient than surface Fe3+tet. Fe added to chrysotile fibers increased HO• generation only when it became incorporated and tetrahedrally coordinated into vacancy sites in the Si layer.ConclusionsOur results suggest that at the physiological pH 7.4, oxidative stress caused by chrysotile fibers largely results from radicals produced in the Haber-Weiss cycle that is catalyzed by Fe3+tet. The catalytic role of Fe3+tet in radical generation may also apply to other pathogenic silicates in which Fe3+tet is substituted, e.g. quartz, amphiboles and zeolites. However, even if these pathogenic minerals do not contain Fe, our results suggest that the mere presence of vacancy sites may pose a risk, as incorporation of external Fe into a tetrahedral coordination environment can lead to HO• generation.

Dataset Information

A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions.

Publications

A Comparison of Hydroxyl Radical and Hydrogen Peroxide Generation in Ambient Particle Extracts and Laboratory Metal Solutions.

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