Abstract
M.Sc.
Biomarkers are responses in living organisms that signify exposure to harmful
substances. The use of biomarkers enables researchers to detect toxicity at
suborganismal level. It can thus be used as an early warning of chronic pollution.
This project employs biomarkers in preliminary field research to assess aquatic
ecosystem health. The indigenous freshwater fish Oreochromis mossambicus and
Labeo umbratus are used as test organisms. Mature fish are collected at polluted
and unpolluted sites. Blood, brain- and liver tissue is removed and analysed.
Laboratory evaluation involves the exposure of juvenile Oreochromis
mossambicus to a variety of toxic chemicals in a static system to determine
biomarker responses.
The biomarkers investigated include acetylcholinesterase, which is inhibited by
organophosphate and carbamate pesticides and pyruvate kinase, which is a ratelimiting
enzyme of glycolysis. Lactate dehydrogenase is used as biomarker for
muscle tissue damage and glucose-6-phosphate dehydrogenase is a key
regulatory enzyme of the pentose-phosphate shunt. Osmotic anion and cation
concentrations are measured to determine stress on the regulation of water- and
osmotic balance. Although results from the field study is variable, some biomarkers show potential to
be included in a suite of biomarkers for biomonitoring, together with other
biological, physical and chemical measures. Applying techniques to assess a
suite of biomarkers in key organisms, produces a more accurate reflection of
ecosystem health. Exposure studies with juvenile fish produced extremely
variable and unreliable results. Many repetitions of each exposure will be
necessary to determine significant deviations in biomarker responses from the
normal range.