Ecotoxicity of engineered nanomaterials and the pathway of toxic effects in an environmental model, Caenorhabditis elegans

Abstract

This thesis examined the adverse effects of engineered nanomaterials (NMs) and their potential mechanisms of toxicity. The research focussed on the toxicity of NMs and their dissolved ions, as well as bulk particles (larger size), if applicable, in the nematode, Caenorhabditis elegans. The physicochemical properties of chosen NMs were characterised using various techniques. The toxicity of NMs regarding their ability to kill nematodes was concentration-dependent. The dissolved ions of each type of NM were be the most toxic form. On the other hand, the mortality of nematodes was not observed when they were exposed to CuO NMs and bulk particles, which led to the decision to discontinue their study. The toxicity of AgNMs regarding the inhibition of reproduction was also in a concentration-dependent manner. Moreover, the concentrations inducing a decrease in the number of progeny were lower than those used in the mortality test, which suggested reproduction to be a more sensitive endpoint. The induction of oxidative stress, which was investigated by determination of reactive oxygen species (ROS) and related enzymes, was studied when nematodes were exposed to all silver substances. Nevertheless, there were differences observed across the different strains of nematodes. The initiation of apoptosis was examined by visualisation and determination of apoptotic proteins. However, induction of apoptosis was not observed in the testing conditions used in this thesis. The studies of transcriptome and proteome of nematodes treated with spherical AgNM, JRCNM03002a (previously NM300K) revealed that genes and proteins involved in ribosome and protein synthesis were mostly affected by the exposure to JRCNM03002a. However, time of exposure had an impact on the pathways of toxicity. The expression of genes and proteins in the pathways of oxidative stress were altered significantly within 30 minutes of exposure, while these pathways were not involved in 24 hours of exposure. In conclusion, engineered NMs, especially AgNMs, can trigger adverse effects in C. elegans. Although it was proven that the pathway of oxidative stress was related to the observed toxicity, the initiation of apoptosis was not established in the conditions used in this study.