On-line Measurement of the Capacity of Airborne Particulate Matter to Generate Reactive Oxygen Species

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Project summary The oxidative capacity of airborne particulate matter has been correlated with the generation of oxidative stress both in-vitro and in-vivo. In recent years, epidemiological studies have associated damaged caused by cellular oxidative stress with several common diseases such as asthma, chronic obstructive pulmonary disease (COPD), Alzheimer's and other neurological diseases. Even though recent studies have identified short-term peaks in particulate matter exposures as important factors in health threat, currently available chemical and in- vitro assays to determine the oxidative capacity of ambient particles require large samples, and hence long sampling periods, typically 24 to 48 hours. Proposed is the development of an on-line monitor of the oxidative capacity of aerosols to provide on-line, time-resolved assessment of the capacity of airborne particles to generate reactive oxygen species (ROS). Our approach combines a chemical module optimized in Phase I for on-line measurement of the oxidative capacity of aerosol, and our firm's new particle growth technology to collect particles directly into small volumes of liquid. The aerosol collector uses the water condensational growth technology that allows collection of particles as small as 10 nm into concentrated water suspensions with efficiencies >90%. The oxidative potential of the collected particles will be measured using the chemical assay commonly known as the DTT (dithiothreitol) assay. Our approach efficiently collects both soluble and insoluble constituents of particulate matter directly into a small volume of water, and analyzes this sample in-field to provide immediate, time-resolved analysis. The direct collection and rapid analysis also reduces artifacts associated with long filter collection periods and extraction. The ability to characterize the oxidative potential of aerosols accurately and in a time-resolved manner will provide a more complete data set for better assessing possible adverse outcomes related to oxidative stress responses resulting from exposure to ambient particulate matter. In Phase I, we demonstrated our approach by developing a laboratory prototype that was validated in the laboratory for reproducibility and sensitivity, and that successfully ran unattended for 3 days, providing 3-hour time resolution of the ROS capacity of ambient particulate matter. In Phase II, we will make a portable, robust and fully automated system for unattended field operation. Specific aims are: i) development of a compact and more sensitive version of our Phase I chemical module; ii) integration of this chemical module with an improved version of the commercially available Liquid Spot Sampler; iii) extension of analysis capability to distinguish the contribution of metals and organics to particle oxidative capacity; iv) demonstration of the system performance under field conditions.