Comprehensive Assessment of Short-Lived ROS and HO in Laser Printer Emissions: Assessing the Relative Contribution of Metal Oxides and Organic Constituents

Inhalation exposure to nanoparticles from toner-based laser printer and photocopier emissions (LPEs) induces airway inflammation and systemic oxidative stress, cytotoxicity, and genotoxicity (such as DNA damage). Recent evidence from human and in vitro studies suggests a strong role for oxidative stress caused by free radicals, such as reactive oxygen species (ROS), in the toxicity of laser printer emissions. However, the amount of ROS generated from laser printer nanoparticle emissions and the relative contribution of various fractions (vapors, organics, metals, and metal oxides) have not been investigated to-date. In this study, we aim to quantify short-lived ROS and HO laser printer emissions, as well as the relative contribution of various fractions of LPEs in ROS generation. An aerosol chamber with HEPA filtered air was used to generate LPE emissions from one representative printer. In separate experiments, size fractionated LPEs were collected on filters (particles) or impingers (particles and vapors). The nanoscale fraction of LPEs (PM) was further separated into the organic fraction and inorganic (transition metals/metal oxides) following a sequence of extraction with solvents and centrifugation. The short-lived ROS and HO generated from each fraction were quantified with an acellular Trolox-based liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS) method recently developed in our lab. The particulate fraction of LPEs PM generated 2.68 times more total ROS (sum of short-lived ROS and HO) than the vapor fraction. In tested LPEs, transition metal oxides, which constituted 3% by mass, produced 69× and 202× times more short-lived ROS and HO, respectively, on a mass basis, than the organic fraction. Furthermore, fresh PM generated 282× and 32× times more short-lived ROS and HO, respectively, than aged and processed PM. We conclude that transition metal oxides, albeit a minor constituent of the LPE PM emissions, are the species responsible for the majority of acellular ROS in this printer. A larger range of printers should be tested in the future. Because transition metal oxides in toners originate primarily from engineering nanomaterials (ENMs) in printer toner powder, reformulation of toner powders to contain less of these ROS active metals is recommended.