Heavy metal contamination in a school vegetable garden in Johannesburg

Background. Feeding schemes based on school garden produce have been proposed as an effective solution to food insecurity and hunger among learners in South Africa. However, few studies have looked at the potential contamination of school food gardens when situated near mine tailing dams. Objectives. The aim of the study was to evaluate the potential heavy metal contamination in a school vegetable garden in Johannesburg. Methods. Twenty soil samples were collected from the study school and a comparison school. Surface and deep (~10 cm beneath the surface) soil samples were analysed using X-ray fluorescence for levels of arsenic, chromium, copper, lead and zinc. Thirteen vegetables samples were collected from the school garden, and compared with six samples from a national retailer and four obtained from a private organic garden. The heavy metal concentrations of the vegetable samples were analysed in the laboratories of the South African Agricultural Research Council. Results. High levels of arsenic were found in the school soil samples, and elevated concentrations of lead and mercury in the school vegetables. Calculation of the estimated daily intake for a child of 30 kg, however, indicated that levels of lead, mercury and arsenic in vegetables were within acceptable limits. However, the levels of lead in the vegetable samples were high across all three sites. Conclusion. Further investigation and research should be undertaken to assess the source/s and extent of public exposure to heavy metals in vegetables in South Africa.