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Wildfire smoke in womb
A new study in Frontiers in Environmental Health found that wildfire smoke has become an increasingly important source of prenatal air pollution in the United States between 2003 and 2019, even as overall exposure to fine particulate matter declined.
“average daily prenatal exposure to PM₂.₅ from all sources fell by approximately 34%”
Researchers analyzed approximately 64.5 million pregnancies across 2,842 counties in 48 states and estimated how exposure to PM₂.₅ during pregnancy varied by location and demographics.
They reported that average daily prenatal exposure to PM₂.₅ from all sources fell by approximately 34%, but when wildfire-related pollution was excluded the decrease was larger, at about 37%.
The study also found wildfire smoke’s share of total prenatal PM₂.₅ exposure more than doubled during the 17-year period, rising from approximately 3.7% in 2003 to 8.2% in 2019.
By the end of the study period, around 65% of prenatal PM₂.₅ exceedance days could be attributed to wildfire smoke, using 35 micrograms per cubic meter as the threshold for unhealthy daily particle pollution levels.
Who bears the burden
The research described wildfire smoke as eroding part of the public health gains achieved during pregnancy from reduced emissions due to human activities, with the burden rising as wildfire activity increased.
Euronews said the study found that “about 65 percent of days when air pollution exceeded safe levels for pregnancy were attributable to wildfire smoke,” and it cited the authors’ warning that wildfire activity “systematically undermines the air quality gains achieved during pregnancy.”
Inside Climate News quoted senior author Michel Boudreaux saying, “We were looking at infants that were born and what their exposure was like during the prenatal period.”
The study’s highest wildfire-related exposures were recorded among low-income communities, rural populations, American Indian and Alaska Native communities, and areas facing shortages of maternity-care services.
In the northwestern United States, the study reported wildfire contributions to prenatal PM₂.₅ rose from 5.1% to 13.3%, and across western states the proportion increased from roughly 3.7% to 9.7%.
Health stakes and next steps
The study linked prenatal exposure to PM₂.₅ to outcomes such as low birth weight and preterm birth, while also noting that particles generated by fires may be more harmful because wildfire smoke contains a complex mixture of combustion products.
“PM₂.₅ refers to airborne particles with a diameter of 2.5 micrometers or smaller”
Bioengineer.org reported that PM₂.₅ refers to airborne particles with a diameter of 2.5 micrometers or smaller, and it said these particles can penetrate deep into the lungs and enter the bloodstream.
Inside Climate News warned that increasing wildfire activity is “systematically offsetting prenatal air quality gains” from reducing emissions from vehicles, refineries, factories and other human sources.
Ilona Jaspers, an inhalation toxicologist and professor of pediatrics at the University of North Carolina, Chapel Hill, said the study “confirm[s] and expand[s] the well-established finding that ambient PM2.5 in the United States is increasingly wildfire-dominated.”
The researchers emphasized that the findings do not diminish the value of air-quality regulations, but they suggest wildfire smoke is becoming a major obstacle to continued progress as climate conditions contribute to hotter, drier landscapes and longer fire seasons.
