Increased amounts of pesticide production and application of pesticides for agriculture,
plant protection and animal health has resulted in soil, water and air pollution,
consequently relating a serious risk to the environment and also to human health.
Pesticides include several groups of compounds, herbicides, insecticides, rodenticides and
fumigants consisting of several hundred individual chemicals. Herbicides are an integral
pan of modem agriculture and for industries requiring total vegetation control. Most
herbicides are soil applied and more and more concern is raised that herbicides not only
affect target organisms but also the microbial community present in soil. The ESKOM
sub-station Zeus, in Mpumalanga (South Africa) used to apply an industrial weed control
program for the eradication of vegetation, which led to the contamination of soil by
several herbicides. These herbicides consisted of Bromacil, Tebuthiuron and Ethidimuron
which are all photosynthesis inhibitors, more specifically, they disrupt the plastoquinone
protein during electron transport at photosystem I1 (PSII). In this study the effect of biostimulation
and bio-augmentation of a specific bioremediation agent (B350) as prescribed
by ESKOM, on residual herbicides, Bromacil, Tebuthiuron and Ethidimuron was
evaluated by monitoring the soil physical and chemical properties, microbial attributes,
including potential microbial activity and community structure, as well as the
physiological effect experienced by plants (Cynodoh dactylon and Zea mays). Results
from soil physical and chemical analyses were correlated with results obtained for the
functional and structural diversity of microbial communities. All results were investigated
through statistical and multivariate analysis and the most prominent soil physical and
chemical parameters that influence the biological and biochemical properties of the soil
were identified. Results obtained from this study indicated that there were no significant
difference (p < 0.05) between the treatments, with bioremediation agent, irradiated agent
and without the agent based on results obtained from soil microbial properties and plant
physiology. Before the trial started the uncontaminated soil showed an active microbial
function, characterised by dehydrogenase, urease and arylsulphatase activity, but
community structure was not very diverse. The contaminated soil, irradiated contaminated
soil and silica sand showed less enzymatic function and was characterised by
phospholipid fatty acid groups, mid-branched saturated fatty acids, terminally branched
saturated fatty acids, normal saturated fatty acids and monosaturated fatty acids which are
indicative of microorganisms that survive better in harsh environments. Three weeks after
the addition of the specific bioremediation took place, the uncontaminated soil showed an
increase in P-glucosidase activity and percentage organic carbon (%C), which could be a
result of the presence of available plant material. Furthermore, an increase in major PLFA
groups were seen, suggesting that an increase in diversity within the soil community
occurred. The contaminated soil, irradiated contaminated soil and silica sand once again
was characterised by a low microbial function and diversity, showing no improvement.
Fluorescence data clearly show a decline in PS 11 function that result in the decline of the
rate of photosynthesis, which was seen from COz gas exchange rates. Furthermore, the
decrease in photosynthetic activity after three weeks was too severe to supply additional
information about the mechanism within photosynthesis or the photoprotective
mechanisms. A detailed study was conducted in which a 3: 1 dilution of contaminated soil
with silica sand, was also monitored for changes within plant physiology. Results revealed
that inhibition of PS I1 function already takes place within a few days time and the decline
in photosynthesis is as a result of electron transport that does not supply adenosine
triphosphate (ATP) and P-nicotinamide adenine dinucleotide (NADPH) to the Calvin
cycle (or Reductive Pentose Phosphate pathway). It does not appear that rubulose-1,sbisphosphate
carboxylase-oxygenase (Rubisco) is affected within the Calvin cycle. As a
result of PS I1 function failure, reaction centres are damaged by the production of harmful
singlet oxygen and photoprotective mechanisms (xanthophyll cycle) can not be activated.
Thus, except for dealing with ineffective electron transport, additional damage is caused
to physiological functions. After six weeks a decrease in the estimated viable biomass for
all growth mediums was found. Results of the of trans- to cis- monoenoic fatty acids and
cyclopropyl fatty acids to their monoenoic precursors ratios indicated that the soil
microbial community for the contaminated growth mediums, all experienced nutritional
stress throughout this trail. The specific bioremediation agent (B350) used, seemed to
have no effect on the microbial function and community structure within soil and as agent
had no effect on the residual herbicides or the plant physiology which experienced an
extreme decline in major metabolic functions. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/107 |
| Date | January 2005 |
| Creators | De Beer, Misha |
| Publisher | North-West University |
| Source Sets | North-West University |
| Detected Language | English |
| Type | Thesis |
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