Association of prenatal exposure to criteria air pollutants and traffic-related air toxics with adverse birth outcomes: A population-based cohort study in California (1990-2021).

While traffic exhaust emissions remain the largest contributor of air pollution in California, levels have declined over time. Contrarily, non-tailpipe brake and tire wear and industrial emissions have persisted and remain a major health concern. Here we studied how air pollution levels have impacted adverse birth outcomes over a period of 30 years in California. Based on birth records (1990-2021) from the California Department of Public Health, we assessed associations of gestational exposure to criteria air pollutants (PM2.5, NO2, O3) and traffic and industry-related air toxics (benzene, 1,3-butadiene, chromium, lead, nickel, zinc) with preterm birth (PTB) and low birth weight at term (TLBW). We used logistic regression to estimate odds ratios per interquartile range (IQR) increase in pollutants across four time periods (1990-1997, 1998-2005, 2006-2012, and 2013-2021). We also conducted analyses stratified by race/ethnicity and area-level socioeconomic status. The estimated effect size for PM2.5 and NO2 on PTB and TLBW declined over time, while those for nickel and zinc increased in the most recent period of 2013-2021 for PTB. We observed some of the strongest associations with adverse birth outcomes for zinc, nickel, and chromium, which may be from brake and tire-wear emissions, among Black and Hispanic mothers and low area-level SES populations. Effect estimates for air pollutants in California changed over a 30-year period with important differences by race/ethnicity and area-level SES, highlighting the success of air pollution reductions but also a need for additional interventions to mitigate remaining increases in risk from traffic and industry-related air toxics.