Association between fine particulate matter and the peak expiratory flow of schoolchildren in the Brazilian subequatorial Amazon: a panel study.

BACKGROUND: Exposure to high levels of particulate matter with an aerodynamic diameter less than 2.5 µm (PM(2.5)) resulting from biomass burning is frequent in the subequatorial Amazon region. OBJECTIVE: To investigate whether or not current exposure to PM(2.5) in the Brazilian Amazon has adverse effects on the daily peak expiratory flow (PEF) of schoolchildren. METHODS: The study design consisted of a panel comprising 309 children aged 6 to 15 years from the same school. PEF was measured daily, except weekends and holidays, from August to December 2006. Each child contributed to the study up to 67 daily measurements. All together there were 19115 PEF measures. Participation rate was 90%. Daily measurements of PM(2.5), temperature, and humidity as well as passive smoking, and subject features were regarded in the statistical analysis. Various exposures of PM(2.5) were considered throughout the analysis, among them 24-hour, 12-hour, 6-hour, and 5-hour means. To account for subject responses to confounders, mixed effects models were applied. The effects were evaluated considering air pollution levels on the current day or at 1- or 2-day lags and the averages of 0-1-day lags, 1-2-day lags and 0-, 1-, and 2-day lags. RESULTS: The 24-hour PM(2.5) means ranged from 6.39 to 99.91 µg/m(3). The adjusted models for the entire group of children revealed adverse effects. For instance, for an increase of 10 µg/m(3) in PM(2.5,) the reduction in the PEF average varied between 0.26 l/min (95% Confidence Interval (CI): -0.49; -0.04) and 0.38 l/min (95% CI: -0.71; -0.04). Restricted to the subgroup of non-asthmatic children, classified as such according to the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire, there was a reduction in the PEF ranging from 0.38 l/min (95% CI: -0.63; -0.13) to 0.53 l/min (95% CI: -0.90; -0.16) for an increase of 10 µg/m(3) in PM(2.5). There was no significant effect in the asthmatic group. When stratified by time of the day children were at school, the concurrent effects of air pollution on PEF were not significant, whereas the 6-hour exposure from 0 am to 5:30 am was significant for both morning and afternoon groups. Finally, the 24-hour mean lagged effect was only significant for the afternoon group of children. For an increase of 10 µg/m(3) in PM(2.5,) there was a reduction in the PEF that ranged from 0.41 l/min (95% CI: -0.76; -0.06) to 0.49 l/min (95% CI: -0.91; -0.07). CONCLUSION: Exposure to current levels of PM(2.5) in the Brazilian Amazon was associated with reductions in the lung function of schoolchildren. The adverse effects were more consistent in non-asthmatic children and with respect to the 6-hour mean from 0 am to 5.30 am.