Prenatal exposure to PM2.5 components and fetal growth: identifying critical gestational weeks and key toxic components in a Chinese birth cohort.

BACKGROUND: Current evidence remains inconclusive regarding the developmental toxicity of specific fine particulate matter (PM2.5) components during critical fetal growth periods, particularly concerning key toxic components and exposure windows. METHODS: This prospective birth cohort included 2680 mother-newborn pairs with 9339 growth ultrasound measurements [abdominal circumference, head circumference (HC), femur length (FL), estimated fetal weight (EFW)] in Guangzhou, China, from 2017 to 2020. Weekly exposures to PM2.5 components-black carbon (BC), organic matter (OM), nitrate (NO3-), sulfate (SO42-), and ammonium (NH4+)-were quantified by using the Tracking Air Pollution in China database (TAP) real-time air-pollutant-exposure model. Distributed lag models with generalized estimating equations were employed to identify critical exposure windows and machine-learning approaches were used to assess constituent mixture effects and identify dominant toxic components. RESULTS: FL, HC, and EFW demonstrated component-specific vulnerability. FL reduction at gestational Weeks 12-15 was most strongly associated with BC exposure, followed by OM and SO42-; HC deficits in Weeks 5-12 and 22-24 were predominantly linked to NO3- exposure; EFW reductions during Weeks 6-8 were most sensitive to NO3- exposure. BC and NO3- were identified as the most impactful constituents. CONCLUSION: Our findings identify gestational Weeks 12-15 for BC exposure and Weeks 5-12 and 22-24 for NO3- exposure as critical vulnerable windows for adverse fetal development associated with PM2.5 components. These results support the need for further research into component-specific air-quality guidelines targeting sensitive gestational periods.