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October 19, 2017 @ 12:30 pm - 1:45 pm
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In Portovelo in southern Ecuador, 87 gold processing centers along the Puyango-Tumbes River produce an estimated 6 tonnes of gold, using a combination of mercury amalgamation and/or cyanidation. At monitoring points immediately below the processing plants, high concentrations of total arsenic, cadmium, copper, lead, cyanide and mercury were found in surface waters and bottom sediments of the Puyango-Tumbes River. The highest concentration of free cyanide was 13,560 times above the Canadian Council of Ministers of the Environment (CCME) thresholds for the protection of aquatic life, and 1695 times over the 24-hour LC50 concentration of 40 μg/L for some fish species. The highest total mercury (THg) concentrations in sediments were found within a 40-kilometre stretch down river from the processing plants, with most concentrations above the CCME guideline of 0.5 mg/kg. Data from mercury isotopic analyses support the conclusion that mercury use during gold processing in Portovelo is the source of the mercury pollution that is found 160 kilometres downstream in the Tumbes Delta in Peru.
About Dr. Marshall
Dr. Bruce Gavin Marshall is an associate researcher and postdoctoral fellow at UBC’s Norman B Keevil Institute of Mining Engineering (NBKI). After completing his PhD in Brazil, where he investigated the autotrophic energy sources and mercury contamination of fish populations in an Amazonian blackwater river, he worked as an undergraduate professor and advisor at Amazonas State University (UEA) in the Department of Environmental Management, specifically with respect to water and mineral resources. Dr. Marshall also worked at Centro Universitário do Norte (UNINORTE – Laureate International Universities) in Manaus as an undergraduate professor in different departments, including Petroleum and Gas Technology, Environmental Engineering, Industrial Production and Geography. Currently, under the supervision of Prof. Dr. Marcello Veiga at NBKI, Dr. Marshall’s post-doctoral research is investigating the bioavailability of mercury cyanide in aquatic environments, including whether this chemical complex bioaccumulates and biomagnifies in fish. Apart from research, Dr. Marshall is currently teaching two post-graduate classes at NBKI, including: Environmental Risk Assessment in Relation to Mining; and Mining and Society. Dr. Marshall was part of a large UNIDO study investigating heavy metal contamination of the Puyango-Tumbes River in Ecuador in relation to ASGM production in Portovelo-Zaruma, which found that pollution reaches 160 kilometres down river to the Tumbes Delta in Peru. Dr. Marshall has also conducted environmental risk assessments for large-scale gold mining companies in Colombia that are frequented by artisanal miners, whereby a co-existence model is promoted to ensure social, environmental and economic sustainability.