Occupational exposure to nanoparticles at commercial photocopy centers

•Copiers emit very high levels of nanoparticles; with bursts up to 700X background.•Complex chemistry includes several airborne engineered nanoparticles.•This occupational and public exposure hazard warrants equipment controls/redesign. Photocopiers emit high levels of nanoparticles (PM0.1). To-date little is known of physicochemical composition of PM0.1 in real workplace settings. Here we perform a comprehensive physicochemical and morphological characterization of PM0.1 and raw materials (toners and paper) at eight commercial photocopy centers that use color and monochrome photocopiers over the course of a full week. We document high PM0.1 exposures with complex composition and several ENM in toners and PM0.1. Daily geometric mean PM0.1 concentrations ranged from 3700 to 34000 particles/cubic-centimeter (particles/cm3) (GSD 1.4–3.3), up to 12 times greater than background, with transient peaks >1.4 million particles/cm3. PM0.1 contained 6–63% organic carbon,