Cyanide Contamination of the Puyango-Tumbes River Caused by Artisanal Gold Mining in Portovelo-Zaruma, Ecuador
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WATER AND HEALTH (T WADE, SECTION EDITOR)
Cyanide Contamination of the Puyango-Tumbes River Caused by Artisanal Gold Mining in Portovelo-Zaruma, Ecuador Bruce G. Marshall 1 & Marcello M. Veiga 1 & Henrique A. M. da Silva 2 & Jean Remy Davée Guimarães 2
# Springer Nature Switzerland AG 2020
Abstract Purpose of Review To examine cyanide (CN-) contamination of a large river in southeastern Ecuador that has been severely impacted by the indiscriminate discharge of untreated gold processing effluents. Recent Findings Poor environmental stewardship of cyanide (CN-) use by 87 gold processing centers in Portovelo-Zaruma in southern Ecuador to leach residual gold from Hg-contaminated tailings has resulted in high CN- contamination of the PuyangoTumbes River downstream from the centers. Summary Free CN- concentrations were high in river surface waters for 50 km below the processing plants, with the highest concentration 9088 times above the CCME standard of 5 μg/L and 1136 times above the 24-h LC50 concentration of 40 μg/L free CN- for some fish species. Due to cyanidation of mercury-contaminated tailings, the formation of Hg-CN complexes is a grave concern, as these complexes have been shown to be highly bioavailable. Preliminary tests conducted in a laboratory using bioassays with Danio rerio sp. and varying concentrations of synthetic Hg(CN)2 salt have shown significant THg bioaccumulation in muscle and kidney fish tissues exposed to concentrations >0.12 mg/L. Furthermore, low MeHg results in fish tissues demonstrated little occurrence of methylation and that the bulk of the total mercury content was in the form of inorganic mercury. Although construction of a communal tailings facility (CTF) in Portovelo is a positive development to reduce riverine pollution, the requirement to truck tailings up to the CTF likely results in inadequate compliance of environmental regulations that are poorly enforced. Keywords Mercury cyanide . Gold processing centers . Artisanal miners . Tailings management
Introduction Artisanal gold mining (AGM) continues to proliferate in developing countries around the world, due to a combination of high gold prices, limited economic alternatives for rural populations, and poor institutional frameworks [1, 2]. Different from responsible small-scale gold mining, AGM constitutes operations, irrespective of the size, that use rudimentary This article is part of the Topical Collection on Water and Health * Bruce G. Marshall [email protected] 1
Norman B. Keevil Institute of Mining Engineering, University of British Columbia, 517-6350 Stores Road, Vancouver, BC V6T 1Z4, Canada
2
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil
techniques to prospect, mine, and process gold ores [3]. In particular, AGM involves the use of processing methods such as inefficient gravity concentration techniques, mercury (Hg) amalgamation, and irresponsible cyanidation of tailings that cause serious environmental impacts, including siltation in streams an
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