Abstract
M.Sc. (Zoology)
The Lower Phongolo Region has undergone extensive development and has had
increases in agriculture, industry, tourism and tribal settlements. Previous studies have
shown concern over ongoing pressures on the system, thus indicating the need to update
existing information for ongoing management. The aims of the study are: 1) to study the
accumulation and the effect of organochlorine pesticides on the physiology of O.
mossambicus and C. gariepinus within the Lower Phongolo River and floodplain; and 2) to
confirm that O. mossambicus and C. gariepinus are effective bio-indicators of pollution. It
is hypothesized that pesticide usage within the Lower Phongolo Region has adverse
effects on the biomarker responses observed within the target species.
The selected biomarkers were used to assess the possible impact on physiological
functioning included biomarkers of exposure (acetylcholine esterase, cytochrome P450
and metallothioneins); biomarkers of effect (catalase, lipid peroxidation (malondialdehyde),
protein carbonyls, superoxide dismutase and glutathione); and changes in the energy
reserves (cellular energy allocation). Verified protocols were utilised for all biomarker
analysis. Organochlorine pesticides (OCPs) were analysed in Japan through standard
procedures by means of ICP-GS. The samples were screened for the presence of
hexachlorobenzene; heptachlor; nonachlors; α-, β-, γ- and δ-hexachlorocyclohexane
isomers; DDT congeners; chlordanes, aldrin and endrin.
The biomarker responses reflected that the environmental stress and bioaccumulation
levels were the highest during April 2013 (high-flow period) when contaminated runoff,
which is influenced by upstream activities, enters the river. The trends observed within the
Usutu River indicated responses to environmental stress resulting from possible upstream
contamination and cross-border anthropogenic influences. The OCP accumulation in fish
tissues highlighted biomagnification as a root cause of high OCP levels observed within O.
mossambicus. The high ΣDDT (626 ng·g-1 lipid) and DDE (301 ng·g-1 lipid) levels
observed in C. gariepinus were attributed to its benthopelagic nature and its large amount
of mesenteric fat which allowed successful DDT storage and accumulation. The higher
DDE versus DDT presence in the Nyamithi Pan observed in November 2012 (80% DDE:
15% DDT) indicated historical influence rather than effects resulting from recent usage.
The results obtained within target species do reflect possible impacts caused by
environmental factors, metal and pesticide presence. However, the current
bioaccumulation levels and the resultant biomarker responses do not reflect any high risk
to the target species and thus signifies that the water quality of the region is still in a
relatively good condition. The high DDT levels were of most concern and require further
investigation to establish the possible effects on other aquatic organisms and resultant
impacts on humans. The pesticide levels and the established impacts affecting the target
species within the Lower Phongolo region indicate the importance of continuous
monitoring and the need for the development of effective management strategies by local
conservation authorities.