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Abstract Title: Identifying Sources of Mercury in Peruvian Amazon Aquatic Systems using Mercury Stable Isotopes
Presenter Name: Krystal Nason
Company/Institution: University of Toronto
Session: Mercury in Artisanal Gold Mining
Co-Authors: Krystal Nason,Natalie Szponar,Claudia Vega,Jacqueline Gerson,Emily Bernhardt,Luis Fernandez,Monica Moreno-Brush,Bridget Bergquist

Abstract Information :

Mercury (Hg) is a toxic global pollutant that affects both humans and wildlife, especially those dependent on aquatic food webs. In many developing parts of the world, Hg is used to extract gold from sediments and ores during artisanal and small-scale gold mining (ASGM). ASGM is currently estimated to be the largest primary source of Hg to the atmosphere and to freshwaters. In the Amazon ASGM is often the source of downstream contamination in many ecosystems, but this can be complicated by other potential sources of Hg such as increased soil erosion from land-use change (e.g., deforestation) since soils are a large reservoir for Hg. Mercury stable isotope geochemistry is a particularly powerful tool for source differentiation in regions where ASGM is prevalent due to differences in the isotopic compositions of ASGM-derived Hg versus Hg from soils and erosion. For example, elevated Hg in Amap , Brazil, was consistent with mobilization of Hg from soils, whereas elevated Hg downstream of Portovelo, Ecuador, was from ASGM Hg. Understanding the source of elevated Hg in ecosystems is key to implementing effective mitigation strategies. In this study, we assessed the sources of Hg in aquatic ecosystems in Madre de Dios (MDD), Peru, a region with prevalent ASGM and local populations affected by Hg contamination. In addition to Hg use during ASGM, the ASGM in this region is also associated with deforestation and land disturbance. Aquatic sediment samples collected upstream and downstream of ASGM were analyzed for Hg and Hg isotopes along with soils in forested and deforested areas along the MDD river system. Initial results show that ASGM signatures are found near some mining areas, but that sources of Hg are more mixed farther downstream and near other mining areas. Results will be discussed in the context of locations and types of ASGM operations.

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