Aquatic ecotoxicity of nanomaterials in fish in vitro models: Cytotoxicity and sublethal effect screening of pristine and transformed nanoparticles.

Abstract

With the increased production and use of engineered nanoparticles (ENPs) came an increased risk of release into the aquatic environment. This has raised concerns about the unknown impact on the aquatic ecosystem. To improve our understanding of the situation we face, knowledge of nanoparticle effects on aquatic organisms needs to be extensively studied. Enquiry into a better understanding of the transformation processes these particles undergo in the environment is essential for ecotoxicological risk assessment. This thesis explores the effects of pristine ENPs on fish in vitro models. It presents results on the impact of natural organic matter (NOM) and chemical mixtures on the environmental transformation of nanoparticles ranging from metal/metal oxides to rare earth elements and plastics. Results revealed a dose-dependent reduction in cellular metabolic activity, membrane integrity and lysosomal activity after particle exposure in higher concentrations with some particles exerting more damage than others. An increase in ROS and EROD activity indicates cellular infiltration of the NPs, which leads to redox imbalances which could induce oxidative stress and cell damage. At the same time, in most particles, the presence of NOM generally reduced the intracellular ROS generation The plastic particles did not significantly affect the cytotoxicity, though the trends observed were particle size and concentration dependent. Co-exposures with high-dosed WAF significantly decreased cell viability and increased ROS generation with an additive effect, while lower concentrations were found to be protective compared to the single exposures. The combined exposure of these products was indeed found to induce complex results that cannot be attributed to a single contributor, even though WAF was found to be highly toxic. This thesis emphasizes the need for more sensitive methods and biomarkers to assess toxicity and that environmental transformation of nanoparticles and mixtures with other environmental pollutants do impact the overall toxicity of the particles. It also highlights the critical need to incorporate these factors into nanoparticle risk evaluations to better inform policy and regulation.