Supplementary Information
8. Coffee plantations
Coffee production in Kenya has fallen by more than 50 per cent due to the conversion of coffee plantations to real estate developments (Nyambura-Mwaura 2010).
The population density of Kiambu was 194 people per square kilometre in 1969, a figure that is estimated to have grown to 638 in 2011 – fuelling pressure on the land. Recently, coffee production has started to be replaced by real estate development, and the few coffee farms that remain have responded by increasing management intensification in order to maintain their productivity.
Source: Jalamillo et al. 2013
http://live.worldbank.org/harnessing-urbanization-for-growth-and-shared- prosperity-in-africa
9. Mining
Mining waste management challenges. In Africa approximately 80 million tonnes of mining waste is dumped each year (Lloyd 2002).
Environmental impacts of gold-mine tailings on the Witwatersrand, South Africa
Numerous old gold sand and slimes dumps on the Witwatersrand have been reprocessed since the 1980s for residual gold extraction using cyanide. There are numerous technologies available by which many cyanide species may be decomposed. However, at most gold mines in South Africa, cyanide is simply discharged with the effluent and tailings on the assumption that it will decompose within a relatively short period of time. The distribution and fate of cyanide in the environment upon release from the tailings dumps depends on its physical-chemical speciation. A study was carried out to assess the characteristics of cyanide in the superficial deposits of a reprocessed gold tailings dump in the two years after slurry re-deposition by the cycloning method, and the implications for its potential release and redistribution during the hydraulic re-working and re- deposition of old tailing slurries. Sampling was done in 2006
and 2007 on a third-generation gold slimes dam to assess the impact of tailings acidification immediately after deposition on cyanide release over that period. The total concentrations of cyanide observed were higher than could be accounted for by the most recent processing event, suggesting that residual cyanide from the historical processing had persisted in the tailings since the original deposition – a period of 30– 80 years, depending on the tailings facility. The re-working of the old slurries in the new facility resulted in a fairly rapid decline in pH of the superficial drying layer of the facility after deposition ceased. Elevated concentrations of total cyanide and weak acid dissociable cyanide were obtained for 2006. The concentrations of free cyanide, cyanates and thiocyanates were higher for 2007 than for 2006, and conversely the concentrations of metal cyanide complexes were higher in 2006 than 2007. These findings indicate that metal cyanide species in the superficial layers of the tailings rapidly degraded post-deposition as a result, primarily, of a decrease in pH.
Gold mining with mercury in Ghana Artisanal gold mining using mercury is on the increase in the Pra River basin in Ghana. Even though mercury levels determined in water, soil and sediments are below WHO safe guideline values, the current state of affairs poses a serious environmental threat. The majority of those engaged in gold mining are unaware of the dangers posed by the use of mercury in mining operations. Once mercury is exposed to atmospheric, aquatic and terrestrial influence, it may undergo transformation, eventually becoming Methyl-mercury. This is the most toxic form of the metal. Methyl-mercury is easily incorporated in living organisms and accumulates in the food chain. Consequently, fish and other aquatic species are contaminated, also endangering populations consuming the fish. In addition, mercury entering the environment is transported downstream of river systems, probably reaching the coastal region in the Gulf of Guinea. A legal instrument that governs artisanal mining could lead to a transformation of the sector into a regulated industry, and minimize the impact on the environment.
Source: Fourie et al. 2008; Donkor 2006 147
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