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Inhalation toxicity of graphene and its derivatives As occupational exposure to graphene and its derivatives increases, its inhalation toxicity should continue to be investigated. Zorawar Singh, PhD Department of Zoology, Khalsa College Various studies of graphene inhalation in rats and mice have not shown it to be toxic. Several examined the effects of graphene inhalation on bronchoalveolar lavage (BAL) fluid, 3 ,5, 6 microalbumin and lactate dehy- drogenase (LDH). 5 One study evaluated the pulmo- nary effects of graphene oxide (GO) using male Sprague-Dawley rats and a single 6-hour, nose-only inhalation technique. e rats were allowed to recover for 1 day, 7 days or 14 days and a total of three groups including control (fresh air), low concentration and high concentration were compared. e exposure to GO was not found to induce any significant changes in the organ weights, body weight or food consumption during the 14 days of recovery time. Levels of microal- bumin, lactate dehydrogenase, total cell count, macro- phages, polymorphonuclear leukocytes and lympho- cytes in BAL fluid were found to be changed, however, the changes failed to reach statistical significance. erefore, only a minimal toxic response in rat lungs was found. 5 In an another study, male Wistar rats were exposed "head-nose" to atmospheres composed of different materials, including multi-wall carbon nanotubes, graphene, graphite nanoplatelets and low surface car- bon black for 6 hours per day for 5 consecutive days. Toxicity was determined after 3-week recovery. No adverse effects were observed after inhalation exposure to 10 mg/m 3 graphite nanoplatelets or relatively low, specific surface area carbon black. Increase of lavage markers indicative for inflammatory processes started at exposure concentration of 0.5 mg/m 3 for multi-wall carbon nanotubes and 10 mg/m 3 for graphene. Micro- granulomas were observed at 2.5 mg/m 3 for multi-wall carbon nanotubes and 10 mg/m 3 for graphene. 6 Graphene as nanoplatelets (GNPs), if inhaled, may pose risks to the respiratory system. In 2012, Schin- wald, et al 3 revealed the risk to the respiratory system as a consequence of unusual aerodynamic properties of graphene-based nanoplatelets that consisted of several sheets of graphene. After calculating their aerodynamic diameter, it was found that nanoplatelets up to 25 µm in diameter were respirable and would deposit beyond the ciliated airways following inhalation. The group Introduction Graphene is a single, tightly packed, layer of carbon atoms bonded together in a hexagonal lattice. 1 The two-dimensional carbon allotrope is the thinnest, light- est, strongest material discovered and the best conduc- tor of electricity and of heat at room temperature. 1 It also has unique levels of light absorption. 1 Due to its unique properties, graphene and its hybrid structures have been widely explored for advanced technological applications. In recent years, graphene has found numerous uses, particu- larly in electronics. Some believe it could eventually have almost limitless applications. 1 With new applications, occupational exposures to graphene are increasing. Its potential for toxicity in humans is still being determined. As part of these inves- tigations, the inhalation toxicity of graphene and its derivatives is being explored. Some graphene derivatives are produced as dry pow- ders, making inhalation a likely route for their human exposure. 2 Graphene in the form of nano- platelets may also pose risks to the respiratory system following inhalation. 3 In addition, graphene-based derivatives may reach the lower parts of the lungs, causing inflammatory responses. This article will look at various graphene inhalation studies, deposition methods in respiratory pathways and mucus, which is one of the human body's primary defense mechanisms against particle exposure. It should be noted that a recent study pointed out that most existing inhalation biophysical models handle nanoparticle and pulmonary surface (NP/PS) interac- tions in the liquid phase and this limitation in current in vitro methodologies makes it difficult to determine how airborne nanoparticles may deposit at the pulmonary surface and interact with it. 4 Graphene inhalation studies Table 1 shows the results of multiple studies of graphene inhalation, using different models. 20 August 2017 Inhalation