| Summary: | Thesis (MSc) -- University of Stellenbosch, 2000. === ENGLISH ABSTRACT: Shrews are excellent bioindicators of environmental heavy metal pollution. This is
due to their diets and the high rate of consumption at which these small mammals consume
their prey. Shrews feed mostly on earthworms, and earthworms accumulate high levels of
heavy metals in their bodies. Biomarkers measure responses to environmental pollution in the
bodies of exposed organisms. Cellular biomarkers give an indication of responses to
pollutants at levels of pollutant exposure that are not yet lethal to the organism.
This study was prompted by concern that the number of shrews in the Stellenbosch
region was declining. For the present study, shrews (Myosorex varius and Crocidura
jlavescens) from the Stellenbosch region were sampled. The levels of Cd and Pb in their
bodies were analysed in order to ascertain whether or not these two heavy metals, which
occur in the environment as a result of various anthropogenic activities, are present in the
food chain of the shrews. In the laboratory, shrews were fed live control and metal exposed
earthworms from laboratory cultures. The earthworms had been exposed to either Cd or Pb in
these cultures over a number of generations. This was performed to determine whether the
presence of the metals in the body of the shrews, had resulted from metal accumulation from
the earthworms which were fed to the shrews. Cellular biomarkers were used to determine
the cellular response to the metals and membrane integrity and DNA integrity were
investigated. This was done by exposing the cells of the shrews and ofBALB/c mice to metal
salt solutions of Cd, Pb and Zn in vitro. Membrane integrity was tested by cell leaching
techniques viz. the LDH assay and the trypan blue assay. DNA integrity was determined by
using the comet assay as a biomarker of exposure.
The results of the study show that the shrews in the immediate Stellenbosch region are
exposed to lower levels of Cd and even lower levels of Pb than shrews from a site 16km out
of the town of Stellenbosch. The cellular responses induced by metal exposure of laboratory
mice show that the metals are indeed cytotoxic and genotoxic to the cells of small mammals.
Cd and Pb were found to be more cytotoxic than Zn, while Zn was more genotoxic than either
CqorPb. === AFRIKAANSE OPSOMMING: Skeerbekke is uitstekende bioindikatore van swaarmetaalbesoedeling in die
omgewing. Dit is as gevolg van hul dieët en die hoë koers waarteen hierdie klein soogdiere
hul prooi verorber. Skeerbekke voed meestalop erdwurms, en erdwurms akkumuleer hoë
vlakke van swaarmetale in hul liggaam. Biomerkers meet response as gevolg van
omgewingsbesoedeling in die liggame van blootgestelde organismes. Sellulêre biomerkers
gee 'n aanduiding van response op besoedelingstowwe by vlakke wat nog nie dodelik is vir
die organisme nie.
Die studie is aangespoor deur die bekommernis dat die getal van skeerbekkies in
Stellenbosch besig is om te daal. In die studie is skeerbekke (Myosorex varius en Crocidura
flavescens) van die Stellenbosch omgewing gevang en die vlakke van Cd en Pb in hul
liggame gemeet om vas te stelof die twee swaarmetale, wat in die omgewing beland as
gevolg van verskeie antropogeniese aktiwiteite, teenwoordig is in die voedselketting van die
skeerbekke. Die skeerbekke is in die laboratorium met lewende kontrole en
metaalblootgestelde erdwurms uit kulture in die laboratorium gevoer. Die erdwurms is aan
Cd en Pb oor baie generasies blootgestel in hierdie kulture. Dit is gedoen om vas te stelof die
teenwoordigheid van die metale in die liggame van die skeerbekke 'n oorsaak is van metaalakkumuleering
as gevolg van die erdwurms waarmee hulle gevoer is. Sellulêre biomerkers is
gebruik om sellulêre respons op die metale op die membraanintegriteit en DNA-integriteit vas
te stel. Dit is gedoen deur die selle van skeerbekke so wel as BALB/c muise in vitro bloot te
stel aan metaalsoutoplossings van Cd, Pb en Zn. Membraanintegriteit is getoets deur selmembraan
permeabiliteit tegnieke nl. die LDH en tripaan blou toetse. DNA-integriteit is
getoets deur die komeettoets te gebruik.
Die resultate van die studie dui daarop dat die skeerbekke van Stellenbosch aan laer
vlakke van Cd, en nóg laer vlakke van Pb blootgestel is as die skeerbekke van 'n perseel
16km buite die dorp. Die sellulêre response geïndusseer deur blootstelling aan metale by die
laboratoriummuise het aangetoon dat die metale inderdaad skadelik is vir die selmembraan en
die DNA van die selle van die muise. Cd en Pb is meer toksies vir die selmembraan as Zn,
terwyl Zn weer meer toksies is vir die DNA-integriteit as Cd en Pb.
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