Margarita Castillejos

Air pollution and infant mortality in Mexico City.

Historic air pollution episodes of the 1950s led to acute increases in infant mortality, and some recent epidemiologic studies suggest that infant or child mortality may still result from air pollution at current levels. To investigate the evidence for such an association, we conducted a time-series study of infant mortality in the southwestern part of Mexico City in the years 1993 to 1995 using mortality data from death registrations and air pollution measurements from a monitoring station we operated. Excess infant mortality was associated with the level of fine particles in the days before death, with the strongest association observed for the average concentration of fine particles during the period 3 to 5 days previously: a 10-microg m(-3) increase in the mean level of fine particles during these 3 days was associated with a 6.9% excess of infant deaths (95% confidence interval 2.5-11.3%). Infant mortality was also associated with the levels of nitrogen dioxide and ozone 3 to 5 days before death, but not as consistently as with particles.

Airborne Coarse Particles and Mortality

Some recent epidemiologic studies suggest a stronger effect of fine particles (PM2.5) than of coarser particulate matter. To examine the support for such a differential effect, the authors conducted a daily time-series analysis of mortality in relation to measurements of PM2.5, PM10, and PM10-2.5 in southwestern Mexico City in the years 1992–1995. A generalized linear model based on Poisson regression was used to control for weather and periodic cycles, and the average concentration of the previous five days was the index of particle exposure. The mean concentrations of PM 2.5 and PM10 were 27.4 μg m−3 and 44.6 μg m-3, respectively, and the mean concentration of PM10-2.5 was 17.2 μg m-PM10 was highly correlated with both the fine and coarse fractions, but PM 2.5 and PM 10–2.5 were rather weakly correlated with each other (correlation coefficient 0.52). All three particle size fractions were associated individually with mortality: a 10-μg m3 increase in PM10 Supported by cooperative agreements CR-820076 and CR-821762 between the U.S. Environmental Protection Agency and the University of North Carolina and Harvard University Schools of Public Health and a grant from the Mexico-U.S. Commission for Educational and Cultural Exchange. We thank Bill McDonnell, Armando Retama, Daniel Varela, and Silvia Bierswinski for contributions to the research and comments on the manuscript. Address correspondence to Dr. Dana Loomis, Department of Epidemiology, CB-7400, School of Public Health, University of North Carolina, Chapel Hill, NC 27599–7400, USA. E-mail: dana.loomis@unc.edu was associated with a 1.83% increase in total mortality (95% CI −0.01-2.96), and an equal increment in PM2.5 was associated with a 1.48% increase in deaths (95% CI 0.98-2.68%). The largest effect was observed for a 10 μg m−3 increment in PM 10-2.5; mean daily mortality increased 4.07% for each 10 μg m−3 (95% CI 2.49-5.66%). The effect of coarse particles was stronger for respiratory diseases than for total mortality, cardiovascular diseases, or other noninjury causes of death. These patterns persisted after adjustment (or O3 and NO2. When both PM2.5 and PM 10-2.5 were included simultaneously in the regression model, the effect of PMW-2.5 remained about 4% per 10 μg m−3 (95% CI 1.96-6.02%), while the effect of PM2.5 was virtually eliminated (0.18% change). These associations may be attributable to specific combustion or biogenic materials within the coarse particle mass. Understanding these relationships will require analyses of the composition of coarse particles. The findings also suggest a need to that the relative effects of coarse and fine particles on mortality should be examined in more cities with a wider variety of climates, population characteristics, and air pollutants.

Particulate and ozone pollutant effects on the respiratory function of children in Southwest Mexico City

We assessed the contributions of particulate matter with aerodynamic diameters < or =10 and < or =2.5 microm (PM2.5 and PM10) and ozone (O3) to peak expiratory flow (PEF) and respiratory symptoms in 40 schoolchildren 8-11 years of age for 59 days during three periods in 1991 at a school in southwest Mexico City. We measured peak expiratory flow in the morning on the childrens arrival at school and in the afternoon before their departure from school. Separately for morning and afternoon, we normalized each childs daily measurement of peak flow by subtracting his or her mean peak flow from the daily measurement. Child-specific deviations were averaged to obtain a morning and afternoon mean deviation (APEF) for each day. Mean 24-hour O3 level was 52 parts per billion (ppb; maximum 103 ppb); mean 24-hour PM2.5 and PM10 were 30 microg/m3 (maximum 69 microg/m3) and 49 microg/m3 (maximum 87 microg/m3), respectively. We adjusted moving average and polynomial distributed lag multiple regression analyses of APEF vs pollution for minimum daily temperature, trend, and season. We examined effects of PM2.5, PM10, and O3, on deltaPEF separately and in joint models. The models indicated a role for both particles and O3 in the reduction of peak expiratory flow, with shorter lags between exposure and reduction in peak expiratory flow for O3 than for particle exposure (0-4 vs 4-7 days). The joint effect of 7 days of exposure to the interquartile range of PM2.5 (17 microg/m3) and O3 (25 ppb) predicted a 7.1% (95% confidence interval = 11.0-3.9) reduction in morning peak expiratory flow. Pollutant exposure also predicted higher rates of phlegm; colinearity between pollutants limited the potential to distinguish the relative contribution of individual pollutants. In an area with chronically high ambient O3 levels, school children responded with reduced lung function to both O3 and particulate exposures within the previous 1 to 2 weeks.

Health Benefits of Air Pollution Control

As discussed in previous chapters, the Mexico City Metropolitan Area (MCMA) has a serious air pollution problem. Searching for ways to improve air quality, the city government faces some very difficult decisions. How much improvement is feasible? Which pollutants and sources should be targeted? What strategies should the government choose? Most of these approaches will require more expenditure or impose restrictions on individuals or firms; each strategy will reduce different combinations of pollutants from different emission sources. Because the primary rationale for improved air quality is improved public health, it makes sense to try to quantify the health benefits of various air pollution control policies. The results can help policy makers allocate limited resources to the most significant problems. This chapter has three goals: to develop rough estimates of the health benefits of air pollution control in the MCMA, to determine which pollutants are likely to contribute most to these benefits, and to determine where further research may be helpful in providing more precise benefit estimates.

Do associations between airborne particles and daily mortality in Mexico City differ by measurement method, region, or modeling strategy?

We evaluated whether associations between PM10 and daily mortality in Mexico City differ by the PM10 measurement device or by regional differences in particle composition. Additionally, we reanalyzed previously collected data in light of recent insights about flaws in commonly used time series analysis techniques. We examined daily associations between mortality and four indicators of ambient PM10 using Poisson regression, controlling for temperature and time trends with cubic natural splines. Associations were calculated for five subregions corresponding to five monitoring sites and pooled for the entire metropolitan area. PM10 was measured with three methods: Tapered Element Oscillating Microbalance (TEOM), Sierra–Anderson High Volume (Hi-Vol) and Harvard Impactor (HI), the latter only at one site. In addition, predicted values of daily PM10 were developed using the Hi-Vol measurements, which were taken every sixth day, and weather, visibility and other pollutant data. We assigned deaths to the exposure from the monitor nearest to their residence. We also re-evaluated the HI PM2.5 and mortality association in southwest Mexico City, which was estimated previously using nonparametric statistical models. Slight decreases in effect estimates were observed (a 1.45% increase (95% CI: 0.09%, 2.83%) in total mortality per 10 μg/m3 increment of PM2.5 at lag 0) compared to a 1.68% change (95% CI: 0.45%, 2.93%) using the previously employed nonparametric approach. Using data pooled over all the regions, PM10 measured by the TEOM and the predicted PM10 values showed little association with mortality at any of the lags examined. The pooled estimates for Hi-Vol PM10 (using one sixth of the data) were positive across all lags examined and significant for lags 3 and 5. No consistent patterns of differing associations were seen across regions that would correspond with particle toxicity or composition. Particulate air pollution, measured with gravimetric methods, is associated with daily mortality and presents a risk to health in Mexico City. The reanalysis suggests that previous research is robust to statistical method and likely to yield the same overall conclusions about the short-term effects of airborne particles on mortality.