'n Studie om die potensiaal waaroor Chrysopogon zizanioides beskik om gekontamineerde oppervlakwater te remedieer, te bepaal
Abstract
This study was motivated since metals are contributing to a decline in the quality of surface water.
During this study, the phytoremediation potential of Chrysopogon zizanioides has been evaluated
for its ability to rehabilitate Zn-contaminated surface water. The analyses that were done
throughout the study was by means of an atomic absorption spectrophotometry (AAS) to measure
the Zn concentration in the water and plant material, while light microscopy was used to determine
structural damage caused by the exposure medium.
In Article 1, the uptake and translocation of different Zn concentrations, including 0.1, 1.5, and 30
mg/L were determined in C. zizanioides within an aquatic system. It was established that C.
zizanioides have the potential to absorb the Zn from the water and it mainly accumulated within
the roots. From the translocation factor it was confirmed that a small amount of the absorbed Zn
was translocated and stored within the leaves. A saturation level of Zn in the roots reached a
constant value between exposure concentrations of 15 and 30 mg/L Zn.
Article 2 aimed to determine the degree of structural damage caused within 14 days by Zn at the
1.5 and 30 mg/L concentrations by making use of light microscopy. From the results, it was
evident that limited damage occurred in the roots as reflected by the presence of vascuolation,
after the exposure period at a Zn concentration of 1.5 mg/L. No visible damage was observed in
the leaves. In contrast to this, extensive damage was observed in the roots, as well as leaves
after the 14 days’ exposure to 30 mg/L Zn. This included the deformation of coronary structures
and cell necrosis within the leaves, as well as, an increase in visible vacuolation, deformation of
parenchyma cells and numerous air spaces in the cortex of the roots. A high tolerance towards
elevated Zn concentrations is evident in C. zizanioides, as limited damage occurred at the 1.5
mg/L exposure media, which is extremely high compared to natural Zn concentrations found in
surface waters.
The purpose of Article 3 was to determine whether accumulated Zn is released into the aquatic
environment during the decomposition of Zn exposed C. zizanioides. For this experiment, roots
exposed to 1.5, 15 and 30 mg/L Zn concentrations were allowed to decompose over a period of
four months in an aquatic environment. During this period, the Zn concentrations were determined
in the water at fixed times and before and after the decomposing period in the roots. The results
indicated that a large amount of Zn was present in the decomposition medium after only one
week, a finding that indicates that the accumulated Zn leached from the roots. During the fourmonth
period, the Zn in the decomposition medium decreased significantly after the spike in the
first week and could probably be attributed to the algae that started growing in the decomposition
medium. This was confirmed by the Zn analyses done in the algae that displayed a large
concentration of Zn. Although Zn leaches from the roots during decomposition, it has been found
that the Zn maybe adsorbed to other reactive surfaces or precipitated as a salt.
It has been concluded that C. zizanioides is a good candidate plant to employ as a
phytoremediation plant to rehabilitate Zn contaminated surface water