'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