Evaluation of new methods for estimating exposure to traffic-related pollution and early health effects for large population epidemiological studies

Objective: There is emerging evidence that local traffic-related pollution (TRP) has adverse health effects that are independent of regional pollution effects. Current methods to assess TRP exposure have limitations that may account for uncertainty and inconsistency in the observed traffic-related health effects. New methods are needed to assess TRP exposure in different microenvironments and to assess early biological effects of these exposures in population based studies of air pollution. I evaluated new tools that can be used to assess time and activity and also evaluated the impact on novel biological markers of exposure to TRP and biomarkers of early biological effects.;Specifically the objectives of my research were: 1) to evaluate the accuracy of a time-resolved step counter in children and the duration of consecutive zero step count minutes that indicated non-wear time periods 2) evaluate the ability of a GPS data logger to assess location of children during usual activity and 3) to assess feasibility of collecting urine samples at school and to evaluate urinary biomarkers of exposure and early effect of traffic-related air pollution. The overall goal of my research was to identify methods that could greatly improve exposure assessments of TRP by providing an integrated metric of dose that could be used to strengthen studies investigating the relationship between TRP exposure and health affects.;Methods: To evaluate these tools, I conducted two studies. In the first study, a new time-resolved step counter, the SportBrain, was evaluated for accuracy. Seventeen children walked or ran on a treadmill at 2, 3, 4 and 5 miles/hour and walked around a track while wearing the SportBrain and Digiwalker SW-701 pedometers. We compared percent error in step counts for the two pedometers relative to observer counts. A sub-sample wore an accelerometer and SportBrain pedometer during up to 5 days of usual activity. In the second study, up to five urine samples per child were collected before and after a school field trip with bus travel on a busy highway from fifteen 9-10 year olds recruited from two classrooms in a low pollution region of Los Angeles. Samples were analyzed for biomarkers of exposure (ten polycyclic aromatic hydrocarbon metabolites and 1-aminopyrene) and of effect (Clara cell protein 16 and 8-iso-PGF2alpha, a major F2-isoprostane). Four days of data from 17 children wearing GPS loggers recording every 15 seconds were evaluated for completeness by time of day during weekend and weekdays and for accuracy during nighttime at home. Percentage of possible GPS recorded points and of 5-minute intervals with at least one recorded location were examined.;Results: The SportBrain pedometer performed with acceptable accuracy at all evaluated treadmill speeds and during self-paced walking, recording steps within an average of 4% of observed step counts. During normal wear only 1% of zero count periods were less than 60 minutes. 60% of participants collected all five urine samples. There was no statistically significant difference between the pre- and post-trip measurements of any biomarker. There was a high proportion of missing GPS location data. Mean percentage of total possible 15-second interval locations recorded daily was less than 30%. Across participants, the GPS loggers recorded 1% to 47% of total possible location points on weekends and 1% to 55% on weekdays. More complete data were measured during travel to school (average 90%). During nighttime (12am-6am), on average, location was recorded for less than 25% of 5-minute intervals and accuracy was poor. Urine collection was feasible in a school setting. 60% of participants collected all urine five samples. However, there was no statistically significant difference between the pre- and post-trip measurements of any biomarker.;Conclusion: The SportBrain iStep X1 pedometer provides a valid measure of step counts in short averaging times useful for assessing patterns of physical activity in population studies and periods of non-wear. Collecting urine samples from children at school was feasible, but traffic effects were not detected after exposure in this small population sample. The large proportion of missing data, which varied by location, limits the usefulness of GPS logging instruments for population studies. They have potential utility for assessing on-road travel time and route.