Particulate matter (PM) is a mixture of chemicals, dust, and liquid droplets that can be emitted into the air from automobiles, power plants, construction sites, smokestacks, and fires. When people breathe contaminated air, this PM gets lodged into people’s lungs and bloodstream. This worsens pre-existing lung diseases and can even cause lung disease, heart disease, and lung cancer. PM is categorized based on the size of particles it contains. PM with particles that are up to 10 micrometers in diameter are designated PM₁₀. PM with particles that are smaller – up to 2.5 micrometers in diameter – are designated PM_2.5.

The World Health Organization estimates that over 90% of the worldwide population is exposed to PM above the recommended levels, and that air pollution results in more than seven million premature deaths worldwide each year. As with most pollutants, not all populations are exposed to air pollution like PM equally. In the US, Black, Native American, and Latinx communities bear a disproportionate amount of the health and economic burden from PM. For instance, a recent study estimated that Latinx people experience 63% more exposure to air pollution than they are responsible for creating.

In addition to impacts on the lungs and heart, there is evidence that when pregnant people are exposed to PM, there can be dire impacts on the fetus. Studies have found prenatal air pollution exposure impacts cognitive development in school-aged children. However, little is known about effects earlier in development. A new study has found that prenatal exposure to PM, especially during the last half of pregnancy, is associated with cognitive and motor development impairments at two years of age.

The study recruited 161 Latina mothers and their infants from Southern California. It used each mother’s household address and pregnancy dates to conduct mathematical modeling to estimate their exposure to PM while pregnant. Then, when infants were two years old, the researchers conducted clinical assessments to measure their cognitive and motor abilities. The study found that higher PM₁₀ exposure was associated with lower motor abilities. Using mathematical modeling, they determined that higher exposure to either type of PM during mid/late pregnancy (anywhere from the final 1-5 months before birth) was associated with lower cognitive and motor abilities.

As with any observational study, there are limitations to this study. With a relatively small sample size, it is possible that there are developmental effects of prenatal PM exposure that could not be conclusively determined in this study. The study also used location and timing information to estimate mothers’ PM exposure during pregnancy, but did not directly measure this PM exposure. Furthermore, it is unclear if the cognitive and motor deficits seen here will impact infants as they grow up.

Despite the limitations, the findings of this study are valuable. Importantly, Latinx populations are disproportionately exposed to air pollution like PM, but scientific studies rarely focus on them. Conducting a study of exclusively Latinx mothers and infants is crucial to understanding the consequences of racial inequities in exposure to pollution. While the cognitive and motor effects observed in this study may seem small, they make clear that human exposure to PM is dangerous to health and development, and that these dangers of exposure begin before birth.