Assessment of cadium (Cd) and lead (Pb) contamination in the soils of pre-school facilities in the City of Cape Town

Abstract

In the last two centuries, the natural state of the environment has changed significantly due to anthropogenic activities. With an estimated half-life of 15 - 1100 years for cadmium in soils, the metal remains a threat to the ecosystem. In general, most soils contain <1 mg/kg, except those contaminated from discrete sources or developed on parent materials with very high cadmium contents. Anthropogenic lead in soil has several well recognized major sources, namely, lead based paint, mining and smelting activities, manures, sewage sludge usage in agriculture and contamination from vehicle exhausts. Since lead is a heavy metal, over time it will settle down and build up in soil. The main aim of this study was to determine the degree of cadmium and lead contamination of soil, in and around selected pre-school facilities in the City of Cape Town (CCT). A number of pre-school facilities, particularly those nearby heavy traffic, were selected in the CeT. Natural soil and sand pit soil samples were collected and analysed for cadmium and lead. Low soil moisture is normally associated with high pH, as found in the present study. High pH values are in turn associated with low toxicity of metal contaminants. Most urban populations rely heavily on motor vehicles and vehicle-related pollution has been an increasing concern in recent years (before 2006). Air pollution in the CCT is trapped by inversion layers. In this study it has been found that cadmium is not a significant contaminant in the soils of pre-school facilities in the CCT. The Cape Town administration area was found to be the most contaminated with this metal. This study showed that the Cape Town administration area also had the highest lead concentrations in pre-school soils in the CCT. This can be attributed to the higher density of industry and traffic activities (study conducted pre-2006) in this area. There is a need for further research to determine the relationship between soil metal concentrations and blood metal levels, especially in children.