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Hg isotopes as tracers of pollution in environments affected by artisanal- and small-scale gold mining

Posted on 2017-11-01 in Events
Nov 3, 2017

Please join us for a special graduate student seminar this Friday Nov 3 at 3:30 pm in rm 155 Geology presented by Gary Schudel, PhD candidate, U of S/TerreCreate/Universite du Quebec:

Hg isotopes as tracers of pollution in environments affected by artisanal- and small-scale gold mining

Artisanal- and small-scale gold mining (ASGM) is currently recognized as the largest anthropogenic source of mercury (Hg) to the atmosphere. Although less information is available, ASGM likely also represents one of the most significant sources of Hg to freshwater environments. Traditionally, assessments of the source and extent of Hg contamination in waterways downstream of ASGM activities relied upon spatial correlations between the locations of ASGM sites and Hg concentration data measured in environmental samples, as well as other physicochemical data. However, analytical advancements and the fact that Hg can undergo both mass-dependent (MDF; ∂xxxHg) and mass-independent isotopic fractionation (MIF; ∆xxxHg) have enabled the use of Hg isotopes as a powerful tool for tracing natural and anthropogenic Hg sources and transformations in the environment.

In this study, Hg concentrations and stable isotopes (along with other trace metal data) were examined in environmental samples from Ecuador and Peru’s shared Puyango-Tumbes River. The objective of the study was to determine the extent to which ASGM in Portovelo-Zaruma, Ecuador contributes to Hg pollution in the downstream aquatic ecosystem. Sediments up to 120 km downstream of Portovelo-Zaruma displayed isotopically heavy signatures with minimal MIF, which matched the signatures of tailings samples taken from ASGM sites even after Hg concentrations had returned to upstream levels. Given the magnitude and extend of the observed Hg, Pb, Cu, and Zn pollution, it is unlikely that rudimentary artisanal-scale gold mining (AGM) is responsible for downstream pollution. In contrast, small-scale gold mining (SGM) is characterized by its larger scale and use of cyanide leaching, which likely facilitates and enhances the release and transport of these metals into downstream waterways.