Interaction of tio2 and cuo nanoparticles with natural organic matter and their response to living systems

Abstract

Technology has always been ahead of toxicology, as the environmental and health issues take the center stage only after the technology/products are released into the market. In the past few years, studies pertaining to the adverse effects of nanomaterials (NMs) have increased exponentially. Even though the understanding of how these nanomaterials affect our environment and human health are limited

currently, newer applications are being explored in traditional and novel areas of fabric treatments, filtration systems, dental materials, surface disinfectants, diesel and fuel additives, hazardous chemical neutralizers, automotive components, electronics, scientific instruments, sports equipment, flat panel displays, drug delivery systems, and pharmaceutics. One of the most salient examples in this regard is the widespread deployment of titanium dioxide nanoparticles (TiO2 NPs) and copper oxide nanoparticles (CuO NPs) across a range of consumer goods. These NPs have genuinely begun to proliferate in our daily lives and environment. Given that waste is generated at every stage of the consumer-product cycle (from production to disposal), many items with TiO2 NPs and CuO NPs are likely to end up being discarded into bodies of water. Crucial ramifications of these occurrences are a matter of concern and have been of great interest to the scientific and regulatory community. A system level wholesome understanding will be required to leverage the beneficial aspects of nanotechnology and development of sustainable nanomaterials Many studies have been reported and are also currently being pursued to address the toxicity of nanomaterials, however these studies are usually carried out in purely laboratory environment or in the individual silos of single natural substance that can affect the toxicity of nanomaterials. While these studies do tell us about the mechanism of toxicity and the interaction between the nanoparticles and the individual substance of interest, it does not simulate the actual complexities of the environment. At the same time, it is very difficult to include all the complexities of the naturally occurring environment as the effect of individual substances towards the toxic or beneficial consequences cannot be differentiated. Thus, in order to make the study relevant to actual environment, the present study investigated the biological and ecological fate and toxicity of TiO2 NPs and CuO NPs in cellular and aquatic environment. These studies include the interaction of two abiotic factors (Humic acid [HA] and clay) on the two most popular NPs (TiO2 NPs and CuO NPs). The physiochemical properties were characterized via stability, pH, agglomeration and Derjaguin–Landau Verwey–Overbeek (DLVO) studies in the relevant media. At first we studied the response of nanoparticles in presence and absence of abiotic factors at the cellular level and then compared their effect on the development of zebrafish fish embryos, to understand higher organism level behavior. The effect of HA and clay minerals on the stability and aggregation of TiO2 NPs and CuO NPs in presence of fish embryo media at different pH was determined. The rational to perform these experiments was to understand the behavior and availabilities of these particles to fishes in different water bodies. Also, the DLVO theory was used to understand the inter-particle interaction. Hydrodynamic sizes of NPs suspended in various media and different pH were measured and the interaction energy was calculated to quantify the aggregation behavior of TiO2 NPs, CuO NPs in presence of natural organic matter (NOM). Based on the observations made in laboratory scale microcosm, our study suggests that at cellular level, TiO2 NPs and CuO NPs induce DNA double strands breaks and arrest cell cycle in G2/M and S phase via ATM/ATR pathways respectively. In aqueous environment, CuO NPs were more stable than TiO2 NPs in presence of NOM. However, the toxic potential was 4 to 5 fold higher in zebrafish embryos exposed to bare CuO NPs than TiO2 NPs that was directly related to stability of NPs. The presence of HA and clay interfered with the interaction of both CuO NPs and TiO2 NPs with zebrafish embryos and both NPs showed least toxicity in presence of a combination of HA and clay. The dorsoventral axis formation and neural network development was interrupted by bare NPs however, in presence of NOM the functioning of development genes were restored. Thus, HA and clay can act as naturally existing non-hazardous agents to remove nanoparticles contamination from water bodies regardless of their different mechanism of action. Further in-depth studies are required to understand the mechanism by which the combination of HA and clay is reducing the toxicity of NMs through reduced bioavailability or transport or internalization or a combination of all. This thesis discusses the vital role of biotic and abiotic factors in aqueous environment, interaction of abiotic factors with TiO2 NPs and CuO NPs at different pH and combined effect of abiotic factors and nanomaterials (NMs) on early developing zebrafish embryos.