Microorganisms are increasingly used in toxicological studies to determine potential
environmental impacts of xenobiotic compounds. A multi-stage laboratory model was developed
to facilitate the examination of environmental impacts of selected pollutants on fundamental
cycling processes inherent to aquatic ecosystems, namely, the degradation of organic substances
and nitrogen transformations under aerobic conditions. A microbial association representative of
riverine ecosystems was enriched for, isolated and cultured within the model. Characterisation
of the microbial association were undertaken. Scanning electron microscopy and bright field
microscopy revealed that a diverse heterogenous community of microorganisms had established
within the model. Successional metabolic events, namely organic carbon catabolism,
ammonification of organic nitrogen and the process of nitrification were differentiated in time
and space with the microbial association integrity still being retained. The establishment of a
microbial association within the model was primarily dependent on: dilution rates, specific
growth rates and interactions between microorganisms and the prevailing environmental
conditions. Growth-rate independent populations of microorganisms established within the model
and were thought to contribute significantly to the metabolic processes within the model.
Nitrifying activity was identified as a rate-limiting process within the model.
Following separation of metabolic events, the ecotoxicological impacts of phenol and 2,4-dichlorophenol on the association were assessed. The biological oxidation of ammonia through to nitrate (nitrification) was found to be a sensitive indicator of perturbation. The model was
found to be suitable for testing both acute and chronic intoxication by pollutant compounds as
well as for biodegradation testing and the possible evaluation of ecotoxicological impacts of
wastewater treatment plants. The main disadvantages of the model arose from its operational
complexity, its empirical nature and its impracticality for screening large numbers of compounds.
A bioassay based on the inhibition of ammonium oxidation was developed in order to fulfil the
requirements for a simple and rapid test protocol for the initial screening of perturbant
compounds. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9141 |
| Date | January 1996 |
| Creators | Hunter, Charles H. |
| Contributors | Senior, Eric., Howard, John., Bailey, Ian. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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