The township of Soweto was built some 50 years ago using locally manufactured corrugated asbestos cement sheets for roofing. The presence of asbestos in the fabric of the buildings has caused some concern. A study conducted by the NIOH showed that there was no evidence of airborne asbestos fibres in the township due to asbestos cement roofs1. However it has been demonstrated that asbestos can be liberated from asbestos cement roofs during cleaning with a high pressure water jet2. The presence of a grey, water run off line directly below some roofs in Soweto led to speculation that over the years, asbestos may be leached from the roofs. A recent study conducted at 61 households in Soweto showed that asbestos was present in the soil around all of the houses examined.
The level of contamination was found to be up to 2,000,000 asbestos fibres per gram of soil. The extent of the contamination of the soil beyond the rain water run off line was not determined. A recommendation of the study was to wet down soil around houses before performing any excavations.
A method for determining asbestos fibres in soil was developed for the study. This method involves the suspension of soil in water followed by filtration and preparation for examination using scanning electron microscopy (SEM). The scanning electron microscope allows fibres to be identified by their morphology and chemical composition using energy dispersive X-ray spectroscopy (EDS). The method to determine asbestos fibres in soil has been applied to contaminated soils around rail tracks and building sites. The method is offered as a service by the NIOH and requests for this service should be addressed to Dr J I Phillips, Head of Electron microscopy, NIOH.
Reference
1Phillips JI, Renton K, Murray J, Garton E, Tylee BE, Rees D. Asbestos in and around Soweto dwellings with asbestos cement roofs. Occup Health Southern Africa 2007;13(6):3-7.
2Phillips JI, Renton K, Badenhorst C. Potential health hazard from cleaning asbestos cement roofs: a case report. Occup Health Southern Africa 2006; 12(5):20-22.
