2003 Progress Report: Traffic Density and Human Reproductive Health

EPA Grant Number: R827352C008
Subproject: this is subproject number 008 , established and managed by the Center Director under grant R827352
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Southern California Particle Center and Supersite
Center Director: Froines, John R.
Title: Traffic Density and Human Reproductive Health
Investigators: Ritz, Beate R.
Institution: University of California - Los Angeles
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2002 through May 31, 2003
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


The overall objective of this research project is to determine whether exposure to motor vehicle-related air pollution affects the risk of low birth weight (LBW) and preterm birth in infants born to women living in Los Angeles County, CA. Residential proximity to heavy traffic roadways is being used as a surrogate measure of exposure to motor vehicle exhaust.

This is one of the research projects of the Southern California Particle Center and Supersite (SCPCS). The progress of the other projects is reported separately (see reports for R827352, R827352C001 through R827352C012, and R827352C014 through R827352C021).

Progress Summary:

In a previous study, we evaluated the relationship between distance-weighted traffic density (DWTD)—a surrogate measure of residential exposure to elevated air pollution levels in the immediate vicinity of roadways—and low weight and preterm birth for infants born during 1994-1996 to women living in Los Angeles County. We observed an approximately 10-20 percent increase in the risk of term LBW and preterm birth in infants born to women living close to heavy traffic roadways. In Year 5 of the project, we expanded our analysis to the time period 1994-2000 and incorporated available information on the number of trucks frequenting freeways in our study area.

We mapped subject home locations at birth and estimated DWTD and the number of trucks on freeways within 750 ft of each residence. The Caltrans truck data list the annual average number and percents of 2-, 3-, 4-, and 5-axle or more trucks passing a given freeway count location within a 24-hour period. We used these data to determine the total number of trucks on freeways within 750 ft of subject residences. We also estimated the number of heavy-duty diesel trucks, assuming 43 percent of the 2-axle (6 tire), 90 percent of the 3-axle, and 100 percent of the 4-axle and 5-or-more axle trucks were heavy-duty diesel. Odds ratios (ORs) for term LBW and preterm and LBW (preterm-LBW) birth, and risk ratios (RRs) for preterm birth, were estimated based on quintiles of the DWTD distribution and the 90th and 95th percentiles of the freeway truck distributions using logistic regression. We also evaluated the associations between background air pollution concentrations (as measured at monitoring stations) and the risk of these three outcomes.

Although our results for births during 1994-1996 were similar to those reported previously, we did not observe associations between DWTD and term LBW and preterm-LBW birth for 1997-2000. In addition, associations between DWTD and preterm birth for this time period were observed only for certain subgroups: women whose third trimesters fell primarily during fall/winter months (November-April) (R R = 1.07, 95% confidence interval [CI] = 0.99-1.16, comparing the highest to lowest DWTD quintile) and women living in census block groups with a fraction of children in poverty at or above the median value (RR = 1.08; 95% CI = 1.00-1.18). We observed an 11 percent increase in the risk of term LBW, a 10 percent increase in the risk of preterm-LBW birth, and a 4 percent increase in the risk of preterm birth per one ppm increase in annual average background CO (OR = 1.11, 95 % CI = 0.97-1.28; OR = 1.10, 95 % CI = 0.95-1.27; and RR = 1.04, 95 % CI = 0.97-1.12, respectively) for births during 1997-2000. We also observed a 23 percent greater risk of preterm-LBW birth for women with greater than or equal to 13,290 freeway trucks passing within 750 ft of their residence per day (95th percentile) (OR = 1.23, 95 % CI = 1.06-1.43) for births during the later time period.

The limitations associated with using DWTD as a measure of motor vehicle exhaust exposure in pregnant women were discussed previously. We noted that the DWTD model assumes motor vehicle exhaust dispersion follows a Gaussian curve centered on a given roadway with 96 percent decay occurring at 500 ft (152.4 m) and that such a curve may not adequately represent dispersion conditions because meteorologic factors such as wind direction, wind speed, and inversion layer height may be important. We did try and address this issue in this study by incorporating some simple adjustments for wind direction and wind speed into our DWTD measure. In general, we did not observe overall patterns of greater positive association estimates and clearer exposure-response patterns between DWTD and the outcomes after incorporating simple wind direction and wind speed adjustments.

In summary, a lthough residential proximity to traffic did not appear to be associated with higher risks of term LBW or preterm-LBW birth in the later time period included in this analysis (1997-2000), residential proximity to trucks on freeways did appear to be associated with greater risks of these outcomes, especially preterm-LBW, during 1997-2000. This suggests more heavily polluting vehicles within the overall cleaner motor vehicle fleet, such as trucks, may now be more important for these outcomes. Our finding of positive associations between background CO concentrations and term LBW, preterm-LBW birth, and preterm birth in 1997-2000 suggests that overall air pollution still may be harmful. We believe that a more refined exposure assessment approach is needed at this point to derive further conclusions on the associations we have seen in our studies.

Future Activities:

The goal of our Year 6 project is to evaluate whether maternal in-vehicle air pollutant exposures during commutes either in passenger cases, buses, or other means of public transportation affected the risk of LBW and preterm birth in infants born to women living in Los Angeles County between 2003-2004 during Year 6 of the project. We will use data from a nested case-control study in which we surveyed a sample of 2,500 women in Los Angeles County (1,250 women who gave birth to a low weight or preterm infant and 1,250 women whose infants were born at term weighing more than 2,500 g). This study will provide important information on time-activity patterns of pregnant women in a demographically diverse urban population and on the potential health risks of extended commuting and high in-vehicle air pollutant exposures to pregnant women.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this subproject

Supplemental Keywords:

particulate matter, PM, quinones, polycyclic aromatic hydrocarbons, PAHs, aldehydes, ketones, metals, allergic airway disease, human exposure studies, asthma, cardiovascular effects, aerosol sampling, atmospheric aerosol, environmental monitoring, environmental statistics, California, CA, acute exposure, aerosols, air pollution, air quality, air toxics, airway disease, allergen, allergic response, ambient aerosol, assessment of exposure, asthma triggers, atmospheric chemistry, bioaerosols, biological response, childhood respiratory disease, children, dosimetry, environmental hazard exposures, environmental health hazard, environmental triggers, environmentally caused disease, epidemiology, exposure assessment, health effects, home, household, human exposure, human health effects, indoor air quality, inhaled particles, lead, outdoor air, particle concentrator, particle transport, particulate exposure, particulates, sensitive populations, toxicology, toxics,, RFA, Scientific Discipline, Air, Geographic Area, HUMAN HEALTH, particulate matter, Environmental Chemistry, Health Risk Assessment, Air Pollutants, State, mobile sources, Environmental Monitoring, Health Effects, engine exhaust, ambient aerosol, asthma, motor vehicle emissions, epidemiology, human health effects, quinones, automotive emissions, particulate emissions, automobiles, automotive exhaust, air pollution, children, PAH, human exposure, PM characteristics, California (CA), allergens, indoor air quality, aerosols, atmospheric chemistry

Relevant Websites:

http://www.scpcs.ucla.edu/exit EPA

Progress and Final Reports:

Original Abstract
  • 1999
  • 2000
  • 2001 Progress Report
  • 2002 Progress Report
  • 2004 Progress Report
  • Final Report

  • Main Center Abstract and Reports:

    R827352    Southern California Particle Center and Supersite

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827352C001 The Chemical Toxicology of Particulate Matter
    R827352C002 Pro-inflammatory and the Pro-oxidative Effects of Diesel Exhaust Particulate in Vivo and in Vitro
    R827352C003 Measurement of the “Effective” Surface Area of Ultrafine and Accumulation Mode PM (Pilot Project)
    R827352C004 Effect of Exposure to Freeways with Heavy Diesel Traffic and Gasoline Traffic on Asthma Mouse Model
    R827352C005 Effects of Exposure to Fine and Ultrafine Concentrated Ambient Particles near a Heavily Trafficked Freeway in Geriatric Rats (Pilot Project)
    R827352C006 Relationship Between Ultrafine Particle Size Distribution and Distance From Highways
    R827352C007 Exposure to Vehicular Pollutants and Respiratory Health
    R827352C008 Traffic Density and Human Reproductive Health
    R827352C009 The Role of Quinones, Aldehydes, Polycyclic Aromatic Hydrocarbons, and other Atmospheric Transformation Products on Chronic Health Effects in Children
    R827352C010 Novel Method for Measurement of Acrolein in Aerosols
    R827352C011 Off-Line Sampling of Exhaled Nitric Oxide in Respiratory Health Surveys
    R827352C012 Controlled Human Exposure Studies with Concentrated PM
    R827352C013 Particle Size Distributions of Polycyclic Aromatic Hydrocarbons in the LAB
    R827352C014 Physical and Chemical Characteristics of PM in the LAB (Source Receptor Study)
    R827352C015 Exposure Assessment and Airshed Modeling Applications in Support of SCPC and CHS Projects
    R827352C016 Particle Dosimetry
    R827352C017 Conduct Research and Monitoring That Contributes to a Better Understanding of the Measurement, Sources, Size Distribution, Chemical Composition, Physical State, Spatial and Temporal Variability, and Health Effects of Suspended PM in the Los Angeles Basin (LAB)