Fine Particulate Matter Metal Composition, Oxidative Potential, and Adverse Birth Outcomes in Los Angeles

Abstract

Background: Although many studies have linked prenatal exposure to ${\mathrm{PM}}_{2.5}$ to adverse birth outcomes, little is known about the effects of exposure to specific constituents of ${\mathrm{PM}}_{2.5}$ or mechanisms that contribute to these outcomes.

Objectives: Our objective was to investigate effects of oxidative potential and ${\mathrm{PM}}_{2.5}$ metal components from non-exhaust traffic emissions, such as brake and tire wear, on the risk of preterm birth (PTB) and term low birth weight (TLBW).

Methods: For a birth cohort of 285,614 singletons born in Los Angeles County, California, in the period 2017-2019, we estimated speciated ${\mathrm{PM}}_{2.5}$ exposures modeled from land use regression with cokriging, including brake and tire wear related metals (barium and zinc), black carbon, and three markers of oxidative potential (OP), including modeled reactive oxygen species based on measured iron and copper (ROS), OH formation (${\text{OP}}^{\text{OH}}$), and dithiothreitol (DTT) loss (${\text{OP}}^{\text{DTT}}$). Using logistic regression, we estimated odds ratios (OR) and 95% confidence intervals (CI) for PTB and TLBW with speciated ${\mathrm{PM}}_{2.5}$ exposures and ${\mathrm{PM}}_{2.5}$ mass as continuous variables scaled by their interquartile range (IQR).

Results: For both metals and oxidative potential metrics, we estimated increased risks for PTB (ORs ranging from 1.01 to 1.03) and TLBW (ORs ranging from 1.02 to 1.05) per IQR exposure increment that were robust to adjustment for ${\mathrm{PM}}_{2.5}$ mass. Associations for ${\mathrm{PM}}_{2.5}$ mass, black carbon, metal components, and oxidative potential (especially ROS and ${\text{OP}}^{\text{OH}}$) with adverse birth outcomes were stronger in Hispanic, Black, and mixed-race or Native American women.

Discussion: Our results indicate that exposure to ${\mathrm{PM}}_{2.5}$ metals from brake and tire wear and particle components that contribute to oxidative potential were associated with an increased risk of PTB and TLBW in Los Angeles County, particularly among Hispanic, Black, and mixed-race or Native American women. Thus, reduction of ${\mathrm{PM}}_{2.5}$ mass only may not be sufficient to protect the most vulnerable pregnant women and children from adverse effects due to traffic source exposures. https://doi.org/10.1289/EHP12196.