Demographic differences in exposure to toxic trace elements in urban South Africa during the 20th century.

Abstract

Exposure to toxic elements is a significant threat to public and individual health worldwide. Toxic elements such as heavy metals are associated with increased mortality and morbidity in both men and women and are a substantial contributor to neurological deficits and developmental delay in children. Analysis of skeletal material yields important information regarding exposure to toxic elements in a given population. This project has investigated toxic element exposure in 215 adults living in urban South Africa who died between 1960 and 1999. Exposure to toxic elements, particularly exposure to lead, has significant impacts on human health, even at very low levels. To date, little research has been conducted on human exposure to toxic elements in adult urban South Africans and a clear gap exists regarding toxic element exposure rates during the latter half of the 20th century. Among the primary aims of this research is to address this gap in knowledge and to quantify human exposure to these elements during the apartheid era. Bone element concentration was analysed by ICP-MS to determine the concentration of six elements that are toxic to humans: lead, cadmium, manganese, arsenic, antimony and vanadium. The results of this research demonstrate clear racial divisions in toxic element exposure in all but one element investigated. In the case of lead and cadmium, white males in the sampled population show significantly higher bone element concentrations than either black males or black females. It is surmised that apartheid-era separation of racial groups in regards to residence, occupation and movement within the urban landscape are partly, if not significantly, responsible for these differences in toxic element exposure. Lead exposure is strongly associated with exposure to traffic in urban Pretoria and Johannesburg, which is evident in both the limited environmental data available and the present study. Designated residential areas for white individuals were situated in and adjacent to the central business districts of both cities and are the areas associated with high traffic. Black residential areas were located on the urban periphery, often near industrial areas and mine dumps. The result is a lead exposure pattern by which white individuals in the sampled population yield double the bone lead concentration of black individuals. The wide divide in socioeconomic strata between the black and white population also factors significantly and is an additional result of apartheid policy. For arsenic and antimony, black individuals, particularly females, show significantly higher bone element concentration than white individuals. These elements are strongly associated with acid mine drainage, a form of pollution which results from mining activity. The close proximity of black residential areas to mining activities and the heavy reliance on ii contaminated surface water is likely responsible for higher exposure rates to these elements in the black population. This research has established that rates of exposure to toxic elements in urban Transvaal were moderate considering the level of industrial and mining activity in the region and the notably lax environmental regulations in place during the latter half of the 20th century. Despite this, bone element levels, particularly that of lead, cadmium and manganese are within ranges documented to cause negative impacts on human health. It is highly likely, given the bone element concentrations reported here, that these elements caused significant and negative health effects in the sampled population and were a clear threat to overall public health in urban South Africans.