Detection of Ambient Black Carbon in Conjunctival Sac Washed Fluid Reveals the Ocular Exposure Risks of Particulate Pollution

Ambient ultrafine particles have been identified in the human body, raising serious concerns about the systemic health risks of air particulate pollution. While eyes constantly and directly contact airborne particulate matter, the associated ocular surface health risks are often overlooked. Here, we developed a laser desorption/ionization mass spectrometry imaging method to identify and detect ambient black carbon particles, a typical component of PM_2.5, in conjunctival sac washed fluid samples. We have detected black carbon particles in 24 of 55 samples (selected from 656 patients), with concentrations ranging from 0.31 to 5.1 μg/mL (mean value of 0.95 μg/mL). The presence of black carbon particles at the ocular surface was influenced by daily life habits. Moreover, it is associated with some ocular indices and dry eye disease, indicating potential ocular health risks. As this is the first report about the high-frequency presence of black carbon at the human ocular surface, our findings not only demonstrate black carbon as a potential marker of airborne particulates on the ocular surface but also provide evidence for a neglected but important aspect of health impacts associated with PM_2.5 exposure.