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Abstract
The free-living nematode, Caenorhabditis elegans, has been suggested as an excellent model organism in ecotoxicological studies. This dissertation examines the use of C. elegans to evaluate bioavailability and toxicity of transition metals and manufactured zinc oxide nanoparticles. A transgenic strain of C. elegans using metallothionein-II promoter to drive green fluorescence protein reporter (mtl-2::GFP) was developed and tested for its response to several transition metals (Cd, Hg, Cu, Zn, Ni, Pb and As) in aquatic medium. Bioavailability and toxicity of manufactured zinc oxide nanoparticles in C. elegans were evaluated using the endpoints lethality, behavior, reproduction, transgene expression, and element spatial distribution. Phototoxicity of zinc oxide nanoparticles was also assessed under natural sunlight illumination. A preliminary study of the potential impact of ZnO nanoparticles on Cu toxicity was also conducted. Findings from these studies suggest that the mtl-2::GFP transgenic C. elegans bioassay represents an alternative approach to quantify a surrogate of metallothionein in response to Cd, Hg, Cu, Zn exposure both easily and quickly, and it may potentially be used for quantitative or semiquantitative biomonitoring for contamination of these metals in aquatic systems. Manufactured zinc oxide nanoparticles caused similar toxicity as aqueous ZnCl2 to C. elegans, and thus internal biotransformation of nanoparticles to metal ions might have occurred. Phototoxicity of ZnO nanoparticles can occur under natural sunlight illumination, and this phototoxicity is greater and the onset of action is faster than the toxicity under ambient laboratory light. Therefore, evaluation of phototoxicity of nanoparticles with photocatalytic properties should not be neglected during ecological risk assessment. Zinc oxide nanoparticles seem to be able to impact Cu toxicity and bioavailability in C.elegans, although further study is required. All these findings demonstrate that C. elegans can serve as a good model for ecotoxicological studies, both for transition metals and manufactured nanoparticles.