Zinc oxide nanoparticles (ZnO-NPs) are increasingly used in sunscreens, biosensors, food additives, pigments, rubber manufacture, and electronic materials. With the wide application of ZnO-NPs, concern has been raised about its unintentional health and environmental impacts. This study investigates the toxic effects of ZnO-NPs in human lung cells. In order to assess toxicity, human lung epithelial cells (L-132) were exposed to dispersion of 50？nm ZnO-NPs at concentrations of 5, 25, 50, and 100？μg/mL for 24？h. The toxicity was evaluated by observing changes in cell morphology, cell viability, oxidative stress parameters, DNA damage analysis, and gene expression. Exposure to 50？nm ZnO-NPs at concentrations between 5 and 100？μg/mL decreased cell viability in a concentration-dependent manner. Morphological examination revealed cell shrinkage, nuclear condensation, and formation of apoptotic bodies. The oxidative stress parameters revealed significant depletion of GSH level and increase in ROS levels suggesting generation of oxidative stress. ZnO-NPs exposure caused DNA fragmentation demonstrating apoptotic type of cell death. ZnO-NPs increased the expression of metallothionein gene, which is considered as a biomarker in metal-induced toxicity. To summarize, ZnO-NPs cause toxicity in human lung cells possibly through oxidative stress-induced apoptosis. 1. Introduction Over the past decade the ability to engineer and produce materials at the nano- or near-atomic scale has triggered rapid product development due to their new interesting properties that were not previously seen at scales above the micrometer. Industrial applications using nanoparticles have resulted in an almost exponentially growing demand for nanosized materials. Due to increasing use of nanoparticles in variety of consumer goods, humans are constantly exposed to such nanomaterials besides exposure at production sites [1–5]. Unintended exposure to nanomaterials may occur via inhalation, dermal exposure, or gastrointestinal tract absorption and may pose a great risk [6, 7]. Despite their wide application, little is known about their effect on human health and environment. Zinc oxide (ZnO) is among the most commonly utilized group of nanomaterials and has wide-ranging applications [8]. As a well-known photocatalyst, ZnO has received much attention in the degradation and complete mineralization of environmental pollutants [9, 10]. ZnO nanoparticles (ZnO-NPs) are used in industrial products including cosmetics, paints, and medical materials. ZnO-NPs have external uses as antibacterial agents in
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