Evidence for Adverse Reproductive Effects of Exposure to Traffic-Related Air Pollution—Are Pregnant Women at Risk?

Abstract

MS7-15 Abstract: Evaluating the influence of traffic-related air pollutants on adverse birth outcomes in Southern California, we previously reported 10% to 20% increases in risk of term low birth weight (LBW) and preterm birth in infants born to women living close to heavy traffic roadways or being exposed to high levels of ambient CO and/or PM10 during sensitive periods of gestation (third trimester). The effects observed for CO, PM10, and traffic density might be attributable to toxins sorbed to primary exhaust particles such as polycyclic aromatic hydrocarbons (PAHs). With more recent data, we mapped subject home locations at birth, estimated distance-weighted traffic density (DWTD), and, in addition, determined the number of trucks on freeways within 750 feet of each residence. Although our data for births during 1994–1996 clearly linked DWTD to these outcomes, for the later period (1997–2000), associations between DWTD and preterm birth remained only for women who lived in poorer neighborhoods (relative risk [RR] = 1.08; 95% 95% confidence interval [CI]: 1.00–1.18) or who experienced their third trimester during the fall/winter months (RR = 1.07, 95% CI: 0.99–1.16, highest compared with lowest quintile). Yet, we newly observed a 23% greater risk of preterm and LBW birth among women with ≥13,290 freeway trucks passing within 750 feet of their residence per day (odds ratio: 1.23, 95% CI: 1.06–1.43). This suggests more heavily polluting vehicles within the overall cleaner motor vehicle fleet such as trucks may now be more important for these outcomes. For ambient CO, PM10, and PM2.5, we examined whether residential distance from monitoring stations affected risk estimates because local pollutant heterogeneity may be inadequately captured by ambient stations. For women residing within 1 mile of a station, we observed larger increases in risk for adverse pregnancy outcomes with high third-trimester pregnancy CO or particle exposures than for women living at larger distances from stations. These results confirmed our suspicions that it is important to address local heterogeneity for traffic-related pollutants in Los Angeles when assessing their impact on pregnancy outcomes. Land use regression (LUR) models informed by short-term and dense monitoring for traffic pollutants (typically NOx) may present the best next step in improving exposure assessment beyond these simple traffic metrics or relying on ambient air monitoring measures alone. Residential and personal monitoring of key exhaust pollutants (ultrafine particles, PAHs, hopanes, steranes) in addition to more “traditional” exhaust markers (CO, NOx) in subsamples of women might help to further elucidate the importance of motor vehicle emissions for these outcomes.