Linking the Exposure to Engineered Nanoparticles Released From Nano-Enabled Products to Toxicology: a Case Study of Laser Printers

Abstract

A research gap in the fields of exposure assessment and toxicology that remains unaddressed is the assimilation of experimental conditions to those of the real world human exposure. Currently, there is a lack of understanding of the properties of particles released by nano-enabled products (NEPs). Thus, we designed a multi-tiered methodology to physico-chemically, morphologically and toxicologically characterize engineered nanomaterials (ENMs) released from NEPs (i.e., toner powder). It is well established that printers emit nanoparticles during their operation; however, the physico-chemical and toxicological characterization of real world printer-emitted nanoparticles (PEPs) remains incomplete, hampering proper risk assessment efforts. For example, a number of studies estimating the potential adverse effects of PEPs used bulk toner particles as test particles rather than the actual particulate matter released by laser printers. Thus, the public health implications of exposure to PEPs remain largely unknown. For this project, a printer exposure generation system suitable for the subsequent physico-chemical, morphological, and toxicological characterization of PEPs was developed and used to assess the properties of particulate matter released from the use of commercially available laser printers. The system consists of a glovebox type environmental chamber for uninterrupted printer operation, real-time and time-integrated particle sampling instrumentation for size fractionation and sampling of PEPs and an exposure chamber for inhalation toxicological studies. Results from our extensive analysis show that laser printers emit up to 1,300,000 particles/cm3, most of which are nanoparticles. Further, we confirmed that a number of ENMs incorporated into toner formulations (e.g., silica, alumina, titania, ceria,) become airborne during printing. Both in vitro and in vivo toxicological evaluation showed PEPs are biologically reactive and may cause significant cytotoxicity, membrane integrity damage, reactive oxygen species production, pro-inflammatory cytokine release, angiogenesis, cytoskeletal and epigenetic changes as well as lung inflammation. This work highlights the importance of understanding life-cycle nano environmental health and safety implications of NEPs and assessing real world exposures and their associated toxicological properties rather than focusing on ‘‘raw’’ materials used in the synthesis of an NEP. Such analysis can be achieved for pollutants emitted by any NEP by employing the multi-tiered methodology described in this dissertation.