Nanoparticle exposures from nano-enabled toner-based printing equipment and human health: state of science and future research needs

Abstract

Toner formulations used by laser printers (LP) and photocopiers (PC), collectively called “toner-based printing equipment” (TPE), are nano-enabled products (NEP) because they contain several engineered nanomaterials (ENM) that improve toner performance. It has been shown that during consumer use (printing), these ENM are released in the air, together with other semi volatile organic nanoparticles, and newly formed gaseous co-pollutants such as volatile organic compounds (VOC). The aim of this review is to detail and analyze physico-chemical and morphological (PCM), as well as the toxicological properties of particulate matter (PM) emissions from TPE. The review covers evolution of science since the early 2000, when this printing technology first became a subject of public interest, as well as the lagging regulatory framework around it. Important studies that have significantly changed our understanding of these exposures are also highlighted. The review continues with a critical appraisal of the most up-to-date cellular, animal and human toxicological evidence on the potential adverse human health effects of PM emitted from TPE. We highlight several limitations of existing studies, including: (i) use of high and often unrealistic doses in vitro or in vivo; (ii) unrealistically high dose rates in intratracheal instillation studies; (iii) improper use of toners as surrogate for emitted nanoparticles; (iv) lack of or inadequate PCM characterization of exposures; and (v) lack of dosimetry considerations in in vitro studies. Presently, there is compelling evidence that the PM01 from TPE are biologically active and capable of inducing oxidative stress in vitro and in vivo, respiratory tract inflammation in vivo (in rats) and in humans, several endpoints of cellular injury in monocultures and co-cultures, including moderate epigenetic modifications in vitro. In humans, limited epidemiological studies report typically 2-3 times higher prevalence of chronic cough, wheezing, nasal blockage, excessive sputum production, breathing difficulties, and shortness of breath, in copier operators relative to controls. Such symptoms can be exacerbated during chronic exposures, and in individuals susceptible to inhaled pollutants. Thus respiratory, immunological, cardiovascular, and other disorders may be developed following such exposures; however, further toxicological and larger scale molecular epidemiological studies must be done to fully understand the mechanism of action of these TPE emitted nanoparticles. Major research gaps have also been identified. Among them, a methodical risk assessment based on “real world” exposures rather than on the toner particles alone needs to be performed to provide the much-needed data to establish regulatory guidelines protective of individuals exposed to TPE emissions at both the occupational and consumer level. Industry-wide molecular epidemiology as well as mechanistic animal and human studies are also urgently needed.

Synergistic effects of engineered nanoparticles and organics released from laser printers using nano-enabled toners: potential health implications from exposures to the emitted organic aerosol

“…A number of studies have focused on the exposure characterization of emissions from laser printers (14). Early on, it was documented that an increase in particle number concentrations of up to 3.8×10 4 particles/cm 3 with a count median diameter varying from 40–76 nm in an office during printing, which suggests the majority of measured particles have sizes less than 100 nm (PM 0.1 ) (15–17).…”

“…As far as the evaluation of potential toxicity of the PEPs, evidence continues to grow in the published domain as summarized in a review paper (14) and includes both in vitro and in vivo toxicological studies as well as human health studies. In our previous studies, it was found that human small airway epithelial cells, microvascular endothelial cells, macrophages, and lymphoblasts showed substantial changes in cell viability, production of reactive oxygen species, release of inflammatory cytokines and modifications to the DNA methylation machinery (18–20).…”

Review of the characteristics and possible health effects of particles emitted from laser printing devices

“…This notion, however, seems to be based on an incorrect interpretation of the work of Wensing et al30 Theegarten and colleagues were made aware that the cited work of Wensing et al30 does not contain any references or conclusions whatsoever to carbon nanoparticles in laser printer emissions 71. The aforementioned study by Pirela et al21 offers a comprehensive overview. A total of 54 studies were evaluated, of which 32 concerned emissions and 22 addressed toxicological effects from categories (b) and (c).…”

Integrated Transcriptomics, Metabolomics, and Lipidomics Profiling in Rat Lung, Blood, and Serum for Assessment of Laser Printer-Emitted Nanoparticle Inhalation Exposure-Induced Disease Risks

“…The rate at which production of new ENPs and incorporation into NEPs occurred has far exceeded our ability to test all ENPs and LCPM released over the NEP life cycle using in vivo animal studies. This study will focus on a specific real-world LCPM: laser printer-emitted particles (PEPs) generated from nano-enabled toners which has been studied extensively by the authors and others over the last decade [18,19]. In US alone, 23 million printers are produced annually, and over 160,000 workers are employed in copier centers [20][21][22][23][24][25][26][27][28].…”