Abstract
Mining, tailings storage facilities (TSFs), dust pollution and growth in residential housing development are synonymous with the Witwatersrand, South Africa. Encroachment of housing onto land close to TSFs, i.e. areas rendered marginal because of the dust hazard and risk of structural failure, has continued unabated for decades, intensifying human exposure to windblown mineral dust. Recent research indicates that the finer milling used for modern gold extraction results in aeolian dust emanating from the TSFs which contributes to a higher proportion of inhalable particles in the source material. Air quality dispersion modelling, validated by ambient aerosol monitoring campaigns, indicates that episodic dust events generate particulate matter (PM10) and, specifically, quartz dust concentrations that are unhealthy at distances of up to 2 km downwind from TSFs. This contribution documented residential development from 1952 to 2011 (using historical aerial photographs, census data from 2001 and 2011 and ancillary information) to determine the population exposed to dust emanations from the TSFs. Using the images, land use was classified into residential areas, TSF footprints and open areas, onto which a series of 500 m buffer zone contours were superimposed. The resulting statistics were used to assess the populations exposed to dust hazard within the defined buffer zones. Overall, housing development has experienced a growth of approximately 700% since 1952 at a rate of 14% per year. Analysis of recent monitoring campaign data has confirmed multiple occurrences of quartzrich inhalable dust in residential settings at levels that exceed occupational health standards, extrapolated to values for population exposure.
Highlights
Evolution in social, economic and political landscapes often shapes population growth, migration and settlement patterns, which in turn often influence the net environmental risks to populations
The research detailed above indicates that continued human encroachment onto marginal lands poses a growing risk of human health consequences
The growth of residential housing developments on marginal land near tailings storage facilities has been appraised over a 50-year period, using historical aerial photographic images and contemporary satellite retrievals
Summary
Economic and political landscapes often shapes population growth, migration and settlement patterns, which in turn often influence the net environmental risks to populations. Tailings storage facilities (TSFs) are intertwined with built-up areas and other mine features in the Witwatersrand.[6,7] With sparse vegetation cover and the reworking of older TSFs for their residual gold content, exposure to windgenerated mineral dust presents an intermittent but persistent environmental hazard for nearby residents.[6,8] As part of evolving technology for gold extraction, the reclaimed TSF material is milled to a much finer grade (down to 30 μm, considerably smaller than the previous 70 μm diameter). This information forms a critical component of the process of evaluating net risk, and in quantitatively assessing benefitto-cost ratio of proposed mitigation strategies that depend on scarce resources, such as water, for dust mitigation
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