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Urban atmospheric mercury contamination from artisanal mining : mapping, modeling, and mitigation Cordy, Paul David


Artisanal miners in more than 70 countries extract gold using mercury, which is often evaporated in densely populated urban areas. This work explores the behaviour of these emissions, and the potential implications for human health. Maps of urban mercury concentrations are used to evaluate the impact of mercury reduction interventions and estimate the distribution of health hazard. Atmospheric dispersion modeling is also used to corroborate inferences about the behaviour of urban mercury vapour that are derived from observations, and to simulate hazard distributions. Miners decompose the amalgams (with 50 to 60% mercury) and melt the raw gold in shops located near the centre of each town without sufficient condensers or filters. The average concentrations measured by mobile mercury vapour analyzer transects taken repeatedly over several weeks were 1.25 μgm -³ in 2010 in Segovia and 0.331 μgm -³ in Andacollo (2009). Mobile mercury measurements and atmospheric dispersion modeling both indicate that mercury emissions from gold shops, though high, dissipate rapidly in space and time. Mobile mercury mapping along streets can detect most frequent emitters with only a few weeks of mobile sampling. Observations of concentrations greater than 1 μgm -³ indicate that within the past 5 minutes amalgam was being burned within a 200 metre radius. Measurements from towers show the temporal variability of mercury concentrations, and show that large quantities of mercury are available for long-range atmospheric transport. By World Health Organization (WHO) standards, these towns are exposed to a significant health hazard, and globally, the millions of miners as well as non-miners who live in similar towns are at serious risk of neurological and renal disease. Various direct and indirect indicators of gold production and mercury reduction also show that mitigation efforts by the United Nations Industrial Organization (UNIDO) in Colombia have reduced urban airborne mercury concentrations by approximately 50% in Segovia, Antioquia, despite a 30% increase in gold production during that three year period. This is attributable to the adoption of retorts by miners and regulations banning new processing centres to the rural periphery.

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