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.