No abstract

Heavy metal toxicity in agro-ecosystems is a global problem. Recently, it has been indicated that the soils used for agriculture and the fresh produce grown on these soils in the Philippi Horticultural Area (PHA) contains heavy metals exceeding the maximum permissible concentrations thereof in South Africa. This study was therefore aimed at evaluating the concentrations of heavy metals in the soils and vegetables produced in the PHA, as well as to determine the major agronomic sources of these metals in this area. Cu, Pb, and Zn concentrations in the soils exceeded the maximum permissible concentrations of 6.6, 6.6, and 46 mg/kg, respectively. Cd, Pb, and Zn concentrations in the vegetables also exceeded the maximum permissible concentrations of 0.1, 0.5, and 40 mg/kg, respectively. The biggest agronomic contributors of these heavy metals to the soils in the PHA were found to be the farmyard manures. Knowing what the major sources of these heavy metals are, it is important to determine ways to mitigate the inputs thereof, as well as to remove existing concentrations from the soils without contaminating the groundwater resources in the area.

This study evaluated Co, Cr, Mn, Ni, Se, Sn and V status in the soils of the PHA, as well as the vegetables produced on these soils. We also determined the agronomic sources of these elements to the soils in the PHA. Farmyard manures applied as fertilizer amendments to the soils in the PHA were found to be the major agronomic sources of the metal and metalloid elements. These elements were however, retained in significantly higher concentrations in the soils compared to the concentrations found in the edible portions of the vegetable crops collected. This, in turn, resulted in these vegetables being poor sources of several of the essential mineral nutrients. It is therefore suggested that: (1) a wider variety of crops are assessed for their mineral nutrient status, (2) to find ways to increase the availability of these mineral nutrients and (3), that the possibilities of micronutrient and trace element deficiencies be assessed in the communities surrounding the PHA.