In epidemiological studies, researchers have found that maternal exposure to particulate matter pollution smaller than 2.5 µm in diameter (PM2.5) is associated with still and preterm births, as well as low birth weights. PM2.5 exposure is also associated with long-lasting health effects, including pulmonary, cardiovascular, and metabolic problems. Now, a study in rats provides a more direct link between PM2.5and these long-term problems (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1902925116). The researchers, led by Texas A&M University atmospheric chemist Renyi Zhang, exposed one group of pregnant rats to clean air and another group to air with high concentrations of ammonium sulfate particles about 50 nm in size for 18 days during their pregnancies. Mother rats exposed to the particles had more stillbirths and shorter gestational times, and their young had lower birthweights, compared with unexposed mothers. Pups of those exposed mothers had smaller lungs, brains, and other organs. At 105 days after birth, they also had more lipids in their livers and their blood glucose levels were higher—both effects related to metabolic disorders such as diabetes. Zhang says the aerosol nanoparticles used in the study are not currently regulated because they are so small they don’t show up in the measurements used by the US Environmental Protection Agency and other agencies. He says this study highlights why their health effects need further attention.