Superoxide, a reduced form of dioxygen is produced in natural waters from abiotic thermal processes such as iron(II) oxygenation photochemically, and biologically in natural waters. Superoxide is highly redox-active due to the presence of an unpaired electron and plays an important role in the geochemical cycling of trace metals and degradation of organic pollutants in natural waters. It also has a significant effect on the physiology of aquatic microorganisms and has been implicated in the growth of toxic microalga in coastal areas of Japan, Australia and Canada. The generation of superoxide by both biotic and photochemical pathways is described in this thesis and attention given to selected reactions of superoxide in simulated natural waters. Particular attention in this work has been given to the interaction of superoxide and iron and the impact of this interaction on iron availability to Chattonella marina, a red-tide phytoplankton frequently associated with fish-mortalities in Australia and Japan. Superoxide production from both phototchemical and biological sources is measured using a highly sensitive chemiluminescence technique and the effect of superoxide production on iron transformation under various environmental conditions is investigated by employing spectrophotometric techniques with high sensitivity and temporal resolution. The intermediacy of superoxide in iron acquisition mechanism by C. marina is also investigated using a radioisotope labeling technique. Our experimental results show that superoxide in natural waters is produced via reduction of dioxygen. The reduction of dioxygen takes place by transfer of electrons by the photo-excited quinone moieties present in natural organic matter or by reductases located on the outer cell membrane of organisms' surface. The experimental results suggest that the fate of iron in marine waters is closely related to the superoxidedioxygen redox couple. Superoxide can reduce a wide range of organically complexed iron(III) species to the more soluble iron(II) redox state, thus affecting its bioavailability. A simple kinetic model for redox-cycling of iron in the presence of superoxide is developed. In addition, by coupling the model for redox-cycling of iron with the forms of iron acquired by C. marina, a generalized mathematical model for iron acquisition is presented which satisfactorily describes all results obtained.
| Identifer | oai:union.ndltd.org:ADTP/215512 |
| Date | January 2007 |
| Creators | Garg, Shikha, Civil & Environmental Engineering, Faculty of Engineering, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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