Engineered nanomaterials (NMs), defined as artificially made particles possessing at least one dimension within 1 – 100 nm range, have different physical and biological properties from bulk materials of the same chemistry due to their increased surface areas. Their novel properties have facilitated the prolific growth of commercial NM-incorporating products. NMs may be leached into the aquatic environment during the product life-cycle, but their ecological impacts on marine ecosystems are currently largely unknown. Therefore, this study primarily aimed to investigate the physicochemical characteristics (particle and aggregate sizes, dissolution rate) and in vivo toxicities of commonly-used metallic NMs to marine organisms under various environmental scenarios.
First, in vivo ecotoxicity screening tests, using the marine diatom Skeletonema costatum and the rotifer Brachionus sp., were conducted for nine common nano metal oxides which had been applied in various commercial products. Among them, nano zinc oxide (nZnO) and nano magnesia (nMgO) were found to be the most toxic NMs to both organisms, as they induced oxidative stress by increasing reactive oxygen species (ROS) production in the organism. The endocrine disrupting potential of nZnO was revealed by its modulation of transcriptions of the genes for retinoid X receptor (RXR) in the rotifer. Conversely, nano alumina (nAl2O3) and nano indium oxide (nIn2O3) were the least toxic NMs.
Due to its high potency, toxicity of nZnO was further evaluated using five marine organisms (i.e., microalgae Thalassiosira pseudonana and S. costatum, copepod Tigriopus japonicus, amphipod Elasmopus rapax, and medaka Oryzias melastigma). Crustaceans were generally more sensitive to nZnO. Toxicity of nZnO was mainly attributed to metal ion dissolution, although nanoparticulate effects such as aggregation and adhesion of nZnO onto the animal’s exoskeleton as well as physical disruption of cell structures could not be discounted.
Due to the fact that the dissolution of nZnO decreased from 16 mg Zn L-1 at 4°C to 1.4 mg Zn L-1 at 35°C, and Zn ion was the main contributing factor for nZnO toxicity at 25°C, it was postulated that nZnO toxicity would increase with decreasing temperature. This hypothesis was tested with S. costatum, O. melastigma and the amphipod Melita longidactyla through a factorial design experiment (i.e., 2 concentrations x 4 temperatures). In agreement with the hypothesis, the growth of S. costatum was significantly inhibited by nZnO at the lowest test temperature (15°C). However, contradictive results were observed in the two animal species. For instance, the amphipod could reduce the nZnO uptake and its toxicity by undergoing metabolic depression and dormancy at lower temperatures.
As the morphology and coating of NMs utilized in commercial products may differ from those employed in toxicity studies, T. japonicus was exposed to nZnO-containing sunscreens to assess the effects of nZnO and Zn2+ released in seawater during epidermal applications. Based on their genetic biomarker responses, the results suggested that other components in sunscreens could react synergistically or antagonistically on nZnO toxicity. Clearly, there is a need for further study of the combined effects of NMs and other common chemical contaminants to marine organisms. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/183044 |
| Date | January 2011 |
| Creators | Wong, Wing-yu., 黃詠如. |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47869410 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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