Abstract
D.Phil.
The endocrine system regulates important physiological processes in an organism.
Numerous natural and synthetic chemicals are released into the environment and
can disrupt the normal functioning of the endocrine system, influencing physiological
processes even at relatively low concentrations. These chemicals are known as
endocrine disrupting chemicals (EDCs). These compounds are highly persistent in
nature due to a resistance to biodegradation, and because of their hydrophobicity.
EDCs bio-accumulate especially in the fatty tissue of aquatic and terrestrial
organisms. Developmental and reproductive disorders are potentially harmful effects
of exposure. EDC sources include agricultural and urban runoff, and industrial
effluent discharges that eventually pass through sewage- and wastewater treatment
plants. These chemicals degrade at various rates and to varying extents during
treatment processes, forming many new chemicals. Methods to predict the
occurrence of endocrine disruption include the occurrence of intersex, and changes
in spermatogenesis and secondary sexual characteristics (SSCs) of supposedly
exposed organisms. The urogenital papilla (UGP) is a SSC whose development and
morphology is hormonally controlled and may be influenced when exposed to EDCs.
The sharptooth catfish (Ciarias gariepinus) is often used in environmental toxicity
studies. Sex is determined by the external dimorphic UGP found only in males.
Intersex has been observed in this species in South African freshwater systems. A
field study was carried out in the Rietvlei (RVD) and Marais (MD) dams in the Rietvlei
Nature Reserve (RNR). MD acts as a sedimentation dam before water enters RVD,
and is theoretically more polluted. The RNR system receives effluent from various
domestic and industrial sources including agriculture, industries, informal settlements
and municipal sewage treatment plants. Four sampling surveys, two low and two
high flow, were carried out over a period of two years. Supposedly male catfish (n=97)
were collected and identified as male or possible intersex based on the UGP. Water
and sediment was collected for target EDC and endocrine disrupting metal (EDM)
analyses. Fish length and mass, and UGP length and width were measured.
Laparotomy was performed and gonads were inspected macroscopically for
alterations. A section of the gonad and the entire UGP was removed and processed
according to standard techniques for histological analysis. The gonadosomatic- (GSI),
hepatosomatic- (HSI) and UGP length (UGPLI) indices were calculated. Fish fat was
removed and analysed for target EDCs.