Thesis (PhD (Botany and Zoology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The use of organophosphate pesticides is still an integral part of commercial farming
activities and these substances have been implicated as a major source of environmental
contamination in South Africa. Evidence exists that many non target animals in and around
agricultural areas are at risk of being affected due to the mobile nature of pesticides and the
intermittent nature of pesticide application. The extent to which non-target animals are
affected by exposure to two organophosphates (azinphos-methyl and chlorpyrifos) was
investigated through monitoring selected biomarker responses and life cycle effects under
laboratory conditions in two selected test species. A representative species from both the
aquatic and terrestrial environment was used as these two compartments of the environment
are inevitably linked due to the mobility of pesticides from the area of application to
surrounding areas. The earthworm Eisenia fetida was used as test organism in the terrestrial
environment while the fish Oreochromis mossambicus served as representative of the aquatic
environment. Juvenile life stages of both species were subjected to standard acute toxicity
tests which showed that for both species, juvenile life stages were more sensitive to both
pesticides than adults. It was also illustrated that azinphos-methyl is more toxic than
chlorpyrifos to both species.
Both test species were also subjected to an intermittent exposure regime in order to assess the
effects of repeated pesticide application on biomarker, life-cycle and behaviour responses.
The results indicated that for similar exposure regimes, azinphos-methyl was more toxic to
E. fetida than chlorpyrifos and detrimentally affected all endpoints investigated. The present
study suggests that exposure concentration may have a more pronounced effect in inducing a
toxic response than exposure interval, irrespective of the pesticide used. In addition to this,
E. fetida was unable to avoid the presence of these pesticides in soil, even at concentrations
as high as 50% of the LC50 value, indicating that the presence of pesticides in the soil pose a
realistic threat to earthworms and other soil dwelling organisms. Biomarker responses,
morphological effects and feeding behaviour was assessed for O. mossambicus and similar to
the terrestrial toxicity experiments, there was evidence to suggest that in the case of an
intermittent exposure scenario, azinphos-methyl was more hazardous than chlorpyrifos to this
species. For the majority of endpoints that were investigated, it appeared that exposure
interval played a more important role in inducing an effect than exposure concentration. At a shorter exposure interval, the majority of endpoints showed no difference between higher and
lower exposure concentrations, while at a longer exposure interval the effects of exposure
concentration became evident. In addition, feeding behaviour was affected by pesticide
exposure in a dose-dependent manner.
The present study yielded important results that improve the understanding of biological
impacts of pesticide pollution on the environment. This can aid in optimising farming
practices such as pesticide application not only in terms of eradicating the pest organisms, but
also in terms of mitigating the environmental effects associated with large-scale pesticide use,
thereby ensuring sustained biodiversity in these areas. / AFRIKAANSE OPSOMMING: Die gebruik van organofosfaat plaagdoders is ‘n integrale deel van kommersiële landbou
aktiwiteite maar hierdie middels is ook ‘n prominente bron van omgewingsbesoedeling in
Suid-Afrika. Daar is bewys dat verskeie nie-teiken diere in en om landbouareas geaffekteer
word weens die nie-statiese aard van plaagdoders in die omgewing, sowel as die herhalende
aard van plaagdodertoediening. Die graad waartoe nie-teiken diere geaffekteer word deur die
plaagdoders azinphos-metiel en chlorpyrifos is ondersoek deur die monitering van verskeie
biomerkerresponse en lewenssiklus-effekte in geselekteerde toetsspesies binne ‘n beheerde
laboratoriumomgewing. ‘n Verteenwoordigende spesie van beide die akwatiese en die
terrestriële omgewing is gebruik aangesien hierdie twee dele van die omgewing onlosmaaklik
verbind is weens die beweging van plaagdoders vanaf die area van toediening na omringende
areas. Die erdwurm Eisenia fetida is gekies as toetsorganisme vir die terrestriële omgewing
en die varswatervis Oreochromis mossambicus het gedien as verteenwoordigende spesie vir
die akwatiese omgewing. Onvolwasse diere van beide spesies is onderwerp aan standaard
akute toksisiteitstoetse en daar is gevind dat, vir beide spesies, onvolwasse diere meer
sensitief vir die betrokke plaagdoders is as volwasse diere. Dit is ook gevind dat azinphosmetiel
giftiger is as chlorpyrifos vir beide spesies.
Beide toetsspesies is ook onderwerp aan ‘n chroniese blootstellingsregime om die effek van
herhaalde plaagdodertoediening op biomerker-, lewenssiklus- en gedragsresponse te
ondersoek. Die resultate van die herhaalde blootstelling het aangedui dat vir soortgelyke
blootstellingsregimes, azinphos-metiel giftiger is as chlorpyrifos vir E. fetida en dat beide
middels alle eindpunte wat ondersoek is, nadelig affekteer. Die huidige studie toon ook
bewyse dat blootstellingskonsentrasie ‘n meer prominente effek as blootstellingsinterval kan
hê in die teweegbringing van ‘n toksiese respons. Verder was E. fetida nie in staat om die
teenwoordigheid van die plaagdoders in grond te vermy nie, self nie by konsentrasies so hoog
as 50% van die LC50 waarde nie. Laasgenoemde resultaat dui dus aan dat die aanwesigheid
van plaagdoders in die grondomgewing ‘n realisitese bedreiging inhou vir erdwurms en ander
grondorganismes.
Soortgelyk aan die terrestriële toksisiteitseksperimente, was daar getuienis vir die verhoogde
toksisiteit van azinphos-metiel relatief tot chlorpyrifos vir O. mossambicus. Dit blyk dat blootstellingsinterval ‘n meer prominente rol as blootstellingskonsentrasie speel in die
teweegbringing van effekte vir die meerderheid van die eindpunte wat ondersoek is. In die
geval van ‘n korter blootstellingsinterval het die meerderheid van eindpunte wat ondersoek is
geen verskille getoon tussen ‘n hoër en ‘n laer konsentrasie nie, terwyl met ‘n langer
blootstellingsinterval daar ‘n aanduiding was dat blootstellingskonsentrasie ‘n meer
prominente rol gespeel het. Verder is gevind dat voedingsgedrag in O. mossambicus
geaffekteer is op ‘n konsentrasie verwante manier.
Die huidige studie toon resultate wat ‘n belangrike bydrae kan lewer tot die begrip van die
biologiese impakte van organofosfaat plaagdoders op die omgewing. Die resultate kan
gebruik word vir die optimisering van boerderypraktyke soos plaagdodertoediening, sodat
laasgenoemde effektief is vir die beheer van pes-organismes, maar ook die impakte van
grootskaalse plaagdodertoediening kan minimaliseer en sodoende die biodiversiteit binne
hierdie areas sal beskerm.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5312 |
| Date | 12 1900 |
| Creators | Jordaan, Martine Saskia |
| Contributors | Reinecke, Sophie, Brink, Danie, University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 195 p. : ill. |
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