Vegetable farms in Cape Town: water quality and possible remediation techniques
Martin, Annamarie Guinnevere
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Heavy metal contamination tends to be a problem in inner city agricultural areas and gardens. High levels of certain heavy metals have been found in the soil and vegetables in the Cape Town Metropolitan area. The aim of this project was twofold. Firstly to ascertain whether water (ground or surface) was responsible for the heavy metal problem found in vegetables in the Philippi and Kraaifontein-Joostenbergvlakte farming areas in Cape Town; and secondly to evaluate the efficacy of two possible remediation methods, namely chelation (with EDTA) and precipitation (using phosphate), aimed at tackling the problem. In order to achieve this a water survey and greenhouse experiment were conducted. The water survey involved collecting a number of samples; both from surface dams and boreholes, from the two farming areas. Results showed minimal heavy metals in both, and therefore ruled this out as the source of the heavy metal problem. The greenhouse sand culture experiment tested the effects of the two remediation methods on the growth, development and elemental content of turnip and spinach plants treated with two cadmium and lead concentrations. In summary, Cd reduced growth more than Pb; Cd accumulated in roots and leaves, and Pb in roots. Several treatments, both metal and mitigation enhanced the chlorophyll content. The difference between the EDTA and phosphate mitigation treatments were not significant in the case of cadmium but in the case of lead, high phosphate resulted in increased growth. The large variation of results in this study, and indeed those of the available literature, indicate that the remedial treatments investigated here are not necessarily the most effective and that other treatments should be investigated to control the uptake of either cadmium or lead, as agricultural soils in future become more contaminated with either or both of these heavy metals.