An Attempt to Detect Ambient Black Carbon in the Human Brain Using Mass Spectrometry Imaging

It is still controversial whether airborne ultrafine particles (UFPs) can enter the human brain by going across the blood-brain barrier (BBB) or directly through the olfactory nerve. This work established a label-free and sensitive laser desorption/ionization mass spectrometry (LDI-MS) imaging method for the identification and detection of black carbon (a typical component of PM2.5) in the human brain, with a detection limit of 4 ng/mg. To cover all possible exposure pathways, 40 human brain samples from 10 different brain locations (including duramater, choroid plexus, gyrus rectus, cerebral ventricular wall, cranium, olfactory mucosa, olfactory nerve, olfactory trigone, brain tumor tissues, and peri-tumorous normal tissues) recruited from Beijing were examined. We found that black carbon particles could be detected in only one olfactory nerve sample (<10 ng/mg) but not detected in all other samples, suggesting that the concentration of black carbon was extremely low or even absent in the human brain samples. Our results suggested that the human brain should be difficult to be invaded by ambient black carbon particles, although we still cannot exclude the possibility of other UFPs entering the human brain. More studies are needed to fully understand the neurotoxicological risks of particulate pollution.