Black carbon is detectable in association with small extracellular vesicles in fetal circulation.

Prenatal exposure to ambient air pollution, particularly black carbon (BC), has been linked to adverse pregnancy outcomes and life-long neurodevelopmental disorders. Yet the mechanism by which inhaled nanoparticles cross the placenta and reach fetal tissues is unclear. Here we show that black carbon (BC) is detectable in association with small extracellular vesicles (sEVs) in fetal circulation and in tissue-enriched sEV subsets. Using label-free two-photon microscopy, we visualised BC associated with individual sEVs isolated from cord-blood plasma of 20 mother-infant pairs. BC-sEV association occurred in 27 % of total cord-blood sEVs, 54 % of placental alkaline-phosphatase-positive (PLAP+) placental vesicles and 68 % of fetal-brain-derived (Contactin-2+) vesicles. Among BC-positive fetal-brain sEVs, >90 % of the vesicle fluorescence co-localised with BC, demonstrating extensive pollutant loading. These findings provide evidence that BC can be detected in association with sEV-enriched preparations in fetal circulation, consistent with a possible role for sEV-associated carriage following transplacental particle transfer, though the dominant transport mechanism remains unestablished.