Amphibians are regarded as sensitive indicators of environmental change and are therefore
excellent subjects for use in ecotoxicology. The Phongolo River floodplain is South Africa’s
most diverse natural floodplain system and hosts more than 40 frog species. It is also a
malaria endemic region and is subjected to active spraying with
Dichlorodiphenyltrichloroethane (DDT) through means of indoor residual spraying over the
summer months. The upper Phongolo River runs through agricultural landscape and is
subjected to runoff from forest plantations, orchards and sugar cane plantations. In this study
residue levels of 22 different organochlorine pesticides (OCPs) were analysed in selected
amphibian species from in and around the Ndumo Nature Reserve coupled with 12 different
biomarker response assays to determine environmental exposure levels and possible sublethal
effects in amphibians from the lower Phongolo River floodplain. Seasonal change,
direct influence of anthropogenic activity and the influence of species’ aquatic preference in
habitat selection were all factors considered during this assessment. Stable Isotope
analyses were performed on 11 different food web components In order to determine the
food web structure pertaining to Xenopus muelleri (Müller's platanna). Samples were
collected during both high and low flow seasons from inside and outside Ndumo Nature
Reserve. Organochlorine pesticide bioaccumulation was analysed in whole frog samples
using a GC-μECD. Results indicated significant seasonal variation in OCP levels and
exposure composition. Significant differences between inside and outside sites were also
noted. Dichlorodiphenyltrichloroethane in its different isomer forms and their metabolites
along with the hexachlorocyclohexane (HCH) isomers was the two main contributing OCP
groups detected. Total OCP levels from all sample sets ranged between 8.71 ng/g lipid and
21,399.03 ng/g lipid. An increase in OCP accumulation was observed for X. muelleri over a
period of one year. Organochlorine pesticides are known to have neurotoxic effects causing
imbalances in Na+, K+, and Ca+ ion exchange. Hyperactivity has been reported in Rana
temporaria (European Common frog) tadpoles exposed to p,p-DDT concentrations above
110,000 ng/g lipid. Despite OCP levels measured in frogs from this study being lower than
reported toxic levels, the biomarker response assays indicated definite oxidative stress
responses correlating to OCP bioaccumulation, with other minor responses shown. Cellular
energy allocation showed a shift in the main energy source type from proteins to lipids
correlating to increased OCP bioaccumulation. A slight inhibition response was noted in the
hepato-somatic index correlating to γ-HCH bioaccumulation. Stable isotope analyses
indicated food web structure differences between inside and outside the reserve, with
outside showing less clear distinction between trophic groups and nitrogen enrichment of
primary producers. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/15824 |
| Date | January 2015 |
| Creators | Wolmarans, Nicolaas Johannes |
| Source Sets | North-West University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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