Abstract
This study looked at the trends, variations and correlations between the metal concentration indicating toxicant exposure and the biochemical responses of Clarias gariepinus to the exposure. Metals are bio-accumulative and persistent contaminants, which have attracted worldwide attention due to their pollution of aquatic ecosystems. Metals can be essential to the functioning of organisms and non-essential or toxic to organisms however, even the essential metals become toxic when occurring at high concentrations. Metals enter aquatic systems via natural and/or anthropogenic sources where they will then either be absorbed into the sediment or accumulate within aquatic organisms. Metals, unlike organic pollutants, do not naturally decompose and when converted by organisms into organic complexes become toxic. Fish are often the apex predators within their aquatic ecosystems and therefore can accumulate high concentrations of metals. The potential human health risk of metal accumulation within fish of commercial benefit makes the determination of metals within these organisms important.
Biomarkers are biochemical or cellular modifications brought on by the exposure of organisms to toxicants and the response of the organism to the toxicant. Biomarkers are showing promise as early warning signals of the degradation of environmental condition. Acetylcholinesterase and metallothioneins are exposure biomarkers, which indicate that organisms have been exposed to pesticides and metals respectively. Biomarkers of effect indicate the response of an organism to a single or multitude of stressors and includes; superoxide dismutase, catalase, reduced glutathione, malondialdehyde and protein carbonyls.
The Nyl River system is South Africa’s largest transient floodplain wetland and is a Limpopo River tributary with Ramsar status. Donkerpoort Dam (upstream), Moorddrift Dam and Glen Alpine Dam (downstream) are impoundments along the Nyl river system. The area was experiencing drought conditions during both sampling seasons (May/September 2017 and January/February 2018). In-situ water parameters (pH, temperature and electrical conductivity) were recorded, and water samples were collected. The water samples underwent standardised nutrient tests including; chloride, cellular oxygen demand, sulphate, ammonium, phosphate, total nitrogen, nitrate and nitrite. Water samples were also analysed to determine the concentrations of the following metals; aluminium, cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, vanadium and zinc.
Sediment samples were collected using polyethylene jars and frozen before further analysis. Sediment was oven-dried and freeze-dried to allow for further analysis including; particle size, organic content and metal determination by standardised protocols. Gill nets were deployed during daylight hours and checked every two hours to remove Clarias gariepinus caught. The collected organisms were killed according to prescribed standards and dissected for the removal of gill, liver and muscle tissues. Samples for biomarker analysis (gill, liver and muscle tissue) were stored in Henriksson’s Stabilising Buffer and flash frozen in liquid nitrogen...
M.Sc. (Zoology)