Ultrastructural Changes in Human Placental Tissues and Evidence of Particulate Matter Transport into the Umbilical Vein Following PM2.5 Exposure in Chiang Rai, Thailand

Introduction: Air pollution poses significant risks to human health. In Thailand, PM2.5 concentrations in Chiang Rai during March and April have been reported to be the highest. This study investigated PM2.5 deposition in human placental tissue and the umbilical vein following third trimester exposure. Methods: Twenty pregnant women from Mae Chan District, Chiang Rai Province, were recruited. Placental samples were obtained from ten women exposed to elevated PM2.5 levels between February and April and from ten women without exposure to high PM2.5 concentrations during pregnancy. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to evaluate tissue morphology and elemental composition. Transmission electron microscopy (TEM) was used to assess ultrastructural morphology. Results: Placental villi from PM2.5-exposed samples demonstrated surface flattening with a rough and irregular morphology. Metal-containing particles were observed adherent to the placental surface and within the umbilical vein. Elemental analysis detected Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Si, and Ti, while PM2.5 collected from air filters exhibited a comparable elemental profile, with additional trace amounts of Cl and Br. Histological and ultrastructural evaluation using transmission electron microscopy revealed abnormal syncytiotrophoblast morphology, thickening of the placental barrier, and endothelial cell abnormalities in small vessels. Discussion: The elemental composition of suspected particulate matter in the placenta and umbilical vein was similar to that identified in the PM2.5 dust analysis. These findings provide direct evidence that PM2.5 can deposit in human placental tissue and the umbilical vein, indicating potential pathways for fetal exposure.