Health effects of ambient air pollution: do different methods for estimating exposure lead to different results?

BACKGROUND: Spatially resolved exposure models are increasingly used in epidemiology. We previously reported that, although exhibiting a moderate correlation, pregnancy nitrogen dioxide (NO2) levels estimated by the nearest air quality monitoring station (AQMS) model and a geostatistical model, showed similar associations with infant birth weight. OBJECTIVES: We extended this study by comparing a total of four exposure models, including two highly spatially resolved models: a land-use regression (LUR) model and a dispersion model. Comparisons were made in terms of predicted NO2 and particle (aerodynamic diameter<10 µm, PM10) exposure and adjusted association with birth weight. METHODS: The four exposure models were implemented in two French metropolitan areas where 1026 pregnant women were followed as part of the EDEN mother-child cohort. RESULTS: Correlations between model predictions were high (≥ 0.70), except for NO2 between the AQMS and both the LUR (r = 0.54) and dispersion models (r = 0.63). Spatial variations as estimated by the AQMS model were greater for NO2 (95%) than for PM10 (22%). The direction of effect estimates of NO2 on birth weight varied according to the exposure model, while PM10 effect estimates were more consistent across exposure models. CONCLUSIONS: For PM10, highly spatially resolved exposure model agreed with the poor spatial resolution AQMS model in terms of estimated pollutant levels and health effects. For more spatially heterogeneous pollutants like NO2, although predicted levels from spatially resolved models (all but AQMS) agreed with each other, our results suggest that some may disagree with each other as well as with the AQMS regarding the direction of the estimated health effects.

Short-term impact of atmospheric pollution on fecundability.

BACKGROUND: Epidemiologic studies have reported associations between air pollution levels and semen characteristics, which might in turn affect a couple's ability to achieve a live birth. Our aim was to characterize short-term effects of atmospheric pollutants on fecundability (the month-specific probability of pregnancy among noncontracepting couples). METHODS: For a cohort of births between 1994 and 1999 in Teplice (Czech Republic), we averaged fine particulate matter (PM2.5), carcinogenic polycyclic aromatic hydrocarbons, ozone, nitrogen dioxide (NO2), and sulfur dioxide levels estimated from a central measurement site over the 60-day period before the end of the first month of unprotected intercourse. We estimated changes in the probability of occurrence of a pregnancy during the first month of unprotected intercourse associated with exposure, using binomial regression and adjusting for maternal behaviors and time trends. RESULTS: Among the 1,916 recruited couples, 486 (25%) conceived during the first month of unprotected intercourse. Each increase of 10 µg/m in PM2.5 levels was associated with an adjusted decrease in fecundability of 22% (95% confidence interval = 6%-35%). NO2 levels were also associated with decreased fecundability. There was no evidence of adverse effects with the other pollutants considered. Biases related to pregnancy planning or temporal trends in air pollution were unlikely to explain the observed associations. CONCLUSIONS: In this polluted area, we highlighted short-term decreases in a couple's ability to conceive in association with PM2.5 and NO2 levels assessed in a central monitoring station.

Short-term impact of ambient air pollution and air temperature on blood pressure among pregnant women.

BACKGROUND: Epidemiologic studies have reported inconsistent findings for the association between air pollution levels and blood pressure (BP), which has been studied mainly in elderly subjects. Short-term air pollution effects on BP have not been investigated in pregnant women, who may constitute a vulnerable population. METHODS: Between 2002 and 2006, 1500 pregnant women from a mother-child cohort study conducted in Nancy and Poitiers, France, underwent 11,220 repeated BP measurements (average, 7.5 measurements/woman). Nitrogen dioxide (NO2), particulate matter with an aerodynamic diameter below 10 µm (PM10), and meteorologic variables were measured on an hourly basis at permanent monitoring sites. We studied changes of BP in relation to short-term variations of air pollution and temperature with mixed models adjusted for meteorologic and personal characteristics. RESULTS: A 10°C decrease in temperature led to an increase in systolic BP of 0.5% (95% confidence interval = 0.1% to 1.0%). Elevated NO2-levels 1 day, 5 days and averaged over 7 days before the BP measurement were associated with reduced systolic BP. The strongest decrease was observed for the 7-day NO2 average (-0.4% [-0.7% to -0.2%] change for an 11 µg/m³ increase in NO2). PM10 effects on systolic BP differed according to pregnancy trimester: PM10 concentration was associated with systolic BP increases during the first trimester and systolic BP decreases later in pregnancy. CONCLUSIONS: We observed short-term associations of air pollution and of temperature with BP in pregnant women. Whether such changes in BP have clinical implications remains to be investigated.

Maternal exposure to nitrogen dioxide during pregnancy and offspring birth weight: comparison of two exposure models.

BACKGROUND: Studies of the effects of air pollutants on birth weight often assess exposure with networks of permanent air quality monitoring stations (AQMSs), which have a poor spatial resolution. OBJECTIVE: We aimed to compare the exposure model based on the nearest AQMS and a temporally adjusted geostatistical (TAG) model with a finer spatial resolution, for use in pregnancy studies. METHODS: The AQMS and TAG exposure models were implemented in two areas surrounding medium-size cities in which 776 pregnant women were followed as part of the EDEN mother-child cohort. The exposure models were compared in terms of estimated nitrogen dioxide (NO2) levels and of their association with birth weight. RESULTS: The correlations between the two estimates of exposure during the first trimester of pregnancy were r = 0.67, 0.70, and 0.83 for women living within 5, 2, and 1 km of an AQMS, respectively. Exposure patterns displayed greater spatial than temporal variations. Exposure during the first trimester of pregnancy was most strongly associated with birth weight for women living < 2 km away from an AQMS: a 10-µg/m3 increase in NO2 exposure was associated with an adjusted difference in birth weight of -37 g [95% confidence interval (CI), -75 to 1 g] for the nearest-AQMS model and of -51 g (95% CI, -128 to 26 g) for the TAG model. The association was less strong (higher p-value) for women living within 5 or 1 km of an AQMS. CONCLUSIONS: The two exposure models tended to give consistent results in terms of association with birth weight, despite the moderate concordance between exposure estimates.