Influence of Indium Contamination from E-waste on Cell Behaviour

Abstract

Recent trends show a massive increase in the production of electronic waste (e-waste) worldwide. These e-waste materials often contain heavy metals whose biological impact on human health and the environment is unknown. One of these contaminants is indium, which can be found in many e-waste materials such as solar panels and liquid-crystal displays (LCDs). This thesis investigates how indium affects the functionality, behaviour, morphology, and viability of live mammalian cells. Two types of cells are used in this work: human dermal fibroblast cells (GM5565) and Vero cells (CCL81) isolated from C. aethiops kidney of an African green monkey (Cercopithecus aethiops). Cell adhesion is an essential biological function for division, migration, signalling, and tissue development. Although it has been demonstrated that this cell function can be modified by using nanometer-scale surface topographic structures, it remains unknown how contaminants such as indium (III) ions might influence this specific cell behaviour. Different tissues and organs, such as skin, muscle, and cornea, consist of cells organized in specific patterns that support their function. It is, therefore, important to understand how external cues, such as engineered surfaces or chemical contaminants, can influence the organization and morphology of cells. Two different indium compounds that are commonly seen in both extracting and recycling indium are indium sulfate (In2(SO4)3) and indium chloride (InCl3). These are two of the main sources of indium that humans are regularly exposed to, and can result in potential long-term harmful effects on human health. This thesis investigates the effect of indium on mammalian cells by exposing cells to different concentrations of each of these indium compounds and measuring an array of cell function indicators such as viability, production of Reactive Oxygen Species (ROS), cell alignment, cell morphology, and focal adhesion protein expression. In this thesis, first, the influence of indium chloride on cell adhesion characteristics is investigated, and the morphology of the adherent cells and their mitochondrial reticulum is characterized on cell culture dishes and nanopatterned surfaces using fluorescence confocal microscopy and scanning electron microscopy. Results showed that exposure to indium chloride decreased cell viability, affected cell alignment, had detrimental effects on the behaviour of human fibroblasts, and adversely impacted their mitochondrial morphology. Next, the impact of indium sulfate on cell viability, production of ROS, morphology, and alignment behaviour on tantalum/silicon oxide parallel line/trench surface structures is studied. Cell morphology and orientation on the engineered surfaces are characterized using fluorescence confocal and scanning electron microscopy. Results again confirmed that average cell viability decreased, the concentration of cellular ROS increased, and cell alignment and mitochondrial morphology were adversely affected. Finally, a study on the impact of indium chloride and indium sulfate on Vero cells is presented to investigate the effect of these contaminants on cell viability, ROS production, morphology, and alignment on tantalum/silicon oxide parallel line/trench surface structures. Results showed that when Vero cells were cultured in media containing indium chloride, the cell viability decreased by ∼35% on average, ROS concentration increased, and the cell geometry and alignment were again affected. The impact of indium chloride and indium sulfate on focal adhesion proteins was also studied using the Western blotting technique. The results showed that focal adhesion kinase (FAK) expression increased with increased concentration of indium in the media, and paxillin phosphorylates, while α−actinin stayed unchanged. All of these results confirm that indium has a negative effect on both human dermal fibroblast cells (GM5565) and Vero cells (CCL81) functionality. Their viability dropped to about 65%, and the ROS production increased. The morphology of cells changed to a more compact and circular shape. The alignment of GM5565 cells on the parallel patterns decreased with an increase in indium concentration, while Vero cells’ alignment on patterns in sizes of less than 1 μm increased. It also revealed that indium solutions alter the signalling pathway in Vero cells that are involved in forming focal adhesions.