Co-Exposure of airborne microplastics and chromium: Impairment of pulmonary surfactant monolayer

Airborne microplastics (AMPs) and their interactions with heavy metals have attracted global concern, however, little is known about their combined effects in the lung environment. In this study, the adverse effects of polypropylene (PP, as representative AMPs)-chromium (Cr) co-exposure on natural pulmonary surfactant (PS) monolayer function was investigated. It was found that upon contact with PS, the desorption of Cr carried by inhaled PP-Cr increased and partially was (∼60 %) reduced to Cr(III). The phase behaviour of PS monolayer in co-exposure scenarios was PP dominated due to the insertion of particulates. Effects among the lipid components were observed that saturated phospholipids suffered the combined effects of Cr(VI) and Cr(III) that impaired its ability to regulate surface pressure, and unsaturated phospholipids were susceptible to infiltration by PP due to their lax structure, leading to a reduction in monolayer compressibility. Co-exposure also led to changes in lipid composition along with metabolic disturbances, and protein contained in PS tended to fold and destabilize. These findings provided front-line evidence of changes in air-liquid interface properties for PS upon PP-Cr co-exposure, suggest targets for the traceability of PS dysfunction, which is helpful for deeply understanding the unfavorable physicochemical effects of AMPs on lung health.