Wildfire-sourced fine particulate matter and preterm birth risks in Brazil: A nationwide population-based cohort study.

Wildfire-specific particulate matter with diameters ≤ 2.5 µm (PM) is the key component of wildfire smoke, with potentially higher toxicity than PM from other sources. In this nationwide population-based cohort study, we included 22,163,195 births from Brazil during 20102019. Daily wildfire-specific PM was estimated through the chemical transport model. Time-varying Cox proportional hazards models were used to characterize the exposure-time-response (E-T-R) relationship between weekly wildfire-specific PM exposure and preterm birth (PTB) risks, followed by subgroup analyses. A 10 µg/m increment in wildfire-specific PM was associated with a hazard ratio of 1.047 (95 % confidence interval [CI]: 1.032-1.063) for PTB. Stronger associations between wildfire-specific PM and PTB were observed during earlier pregnancy, among female infants, and pregnant women < 18 years old, in ethnic minorities, with a length of education ≥ 11 years, from low-income or high-temperature municipalities, and residing in North/Northeast regions. An estimated 1.47 % (95 % CI: 1.01 %1.94 %) of PTBs were attributable to wildfire-specific PM in Brazil, increasing from 2010 to 2019. The PTBs attributable to wildfire-specific PM surpassed those attributed to non-wildfire PM (0.31 %, 95 CI: 0.09 %0.57 %). Wildfire emerged as a critical source contributing to the PM-linked PTBs. Prioritized fire management and emission control strategies are warranted for PTB prevention.