The following case study explores engineered nanoparticles released during laser printing.
CHALLENGE: Characterize the engineered nanomaterials (ENMs) in toner formulations and study the release of the ENMs during consumer use of laser printers. Characterize their physiochemical, morphological, and toxicological properties.
SOURCE: Printers from the four most commercially available manufacturers and models using a variety of printer toner powder and paper were used during printing.
PROCESS: The printers were placed in separate chambers and used to print a single-sided monochrome document. PM2.5 was collected and weighed pre- and post-sampling to determine the collected PEPs mass and to calculate the time-averaged particle mass concentration in the chamber during printing. Detailed chemical characterization of size fractionated PEPs and toner powders, as well as the paper used during the study, were reported.
Which ENMs Should We Be Evaluating?
Electron microscopy and energy dispersive X-ray spectroscopy (EDS) analysis confirm that laser toners contain a variety of nanoscale particles that have been incorporated in their formulations to improve the functional properties of the toner. Based on current work, as well as their findings in an article recently published in Nanotoxicology entitled “Consumer Exposures to Laser Printer-Emitted Engineered Nanoparticles: A Case Study of Life-Cycle Implications from Nano-Enabled Products,” the authors ( S.V. Pirela, G.A. Sotiriou, D. Bello, M. Shafer, K.L. Bunker, V. Castranova, T. Thomas, and P.Demokritou) establish that toner manufacturing, in general, has shifted towards using nanotechnology. However, the current approach used in the nanoparticle risk assessment model focuses only on the pristine or “raw” engineered nanomaterials (ENMs). Based on this study, the physiochemical and toxicological properties of the ENMs released during realistic exposure situations, such as consumer use of the printers, should be evaluated in addition to the ENMs used in the synthesis of the toners. Consumers typically are not exposed to the pristine ENMs used in the creation of nano-enabled products (NEPs), but rather to the nanoparticles released when the product is used. Studying their release and characterizing their physiochemical, morphological and toxicological properties during use is extremely important because these printer-emitted nanoparticles (PEPs) may have potentially altered properties that are different from those of the raw ENM. In this study, the authors conducted a detailed physiochemical, morphological and toxicological characterization of the 11 toners and the resulting PEPs.
How Was the Sampling Done?
Eleven laser printers from the four most commercially available manufacturers and models were used for the study. Manufacturing dates varied but all were manufactured within the last nine years (2004–2013) and some were new. Each printer was placed in an environmental chamber and set to print a single-sided monochrome document. The PEPs were sampled using a cascade impactor, a scanning mobility particle spectrometer, a condensation particle counter, and an electrostatic precipitator. Toner powder was also collected directly from each cartridge and transferred to clean scintillation vials for subsequent chemical and morphological analysis.
How Was the Characterization Performed?
Chemical Analysis: PEPs and toner powders, as well as the paper used during the study, were characterized using:
- Inductively coupled plasma mass spectrometry (ICP-MS)
- Organic carbon/elemental carbon analysis (OC-EC)
- Fourier transform infrared spectroscopy (FTIR)
- Ion chromatography (IC) analysis for anions and cations
Morphological and Elemental Analysis: PEPs and toner powders from the six highest emitting printers were collected onto TEM copper grids using an electrostatic precipitator and characterized using:
- Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) for the morphological characterization of the particles
- Energy dispersive X-ray spectroscopy (EDS) to evaluate the chemical composition of both the toner powders and the PEPs
Were Nanoparticles Emitted?
The release of nanoparticles during the printing of the tested laser printers was confirmed with real-time monitors. The morphology and elemental composition of some of the emitted particles that were collected directly onto TEM grids was characterized by STEM. The size of the PEPs obtained from the STEM images corresponded well to the real-time particle size distributions. The elemental EDS analysis of the PEPs identified inorganic elements, including zinc, cooper, titanium, cerium, silicon, calcium, and sulfur.
Are There Health Implications?
- The presence of metal/metal oxide nanoparticles in the PEPs and the complex chemistry of particulate matter (PM), even at minute concentrations, is concerning because metals/metal oxides have the potential to trigger a toxic response in the lungs and translocate to other organs.
- There was a release of volatile organic compounds (VOCs) that have been shown to be associated with adverse changes in the pulmonary and cardiovascular system.
- The highest emitting laser printers emitted over one million particles/cm3—comparable to the high-particle exposure levels of highly polluted highways.
The thorough evaluation of the toner powder and PM emitted from the printing equipment provided ample evidence that a variety of ENMs (at least eight different types) were embedded in toner powders and are released in the air during printing.
An important contribution of this study is not only the confirmation of the release of nanoparticles into the air during the printing of laser printers, but also the detailed physicochemical and morphological characterization of both toner and released particles. The authors demonstrated that realistic exposure properties should be used in the toxicological characterization studies for printer emissions rather than the current practice of using only toner particles.