ICMGP - Conference Presentation

Abstract Information :

Artisanal and small-scale gold mining (ASGM) is the largest anthropogenic source of mercury (Hg) to the environment. In and around ASGM, elevated Hg concentrations can have mixed origins: anthropogenic from the Hg:Au amalgamation process, and natural from the perturbation and erosion of Hg-rich natural surface soils. In the Madre de Dios (MDD) River basin, in the southeastern Peruvian Amazon, higher Hg concentrations have been reported in areas downstream of ASGM activities in comparison with upstream areas. However, the origin of Hg and the influence of river hydrodynamics on its environmental fate in these affected areas is still unclear. This study re-examines the spatial distribution, transport and sources of Hg in a 240-km stretch of the MDD river and its tributaries Colorado and Inambari, which drain the largest ASGM sites in this region, using water flow patterns, sediment transport (wash load) and mercury isotope measurements. In agreement with previous reports, significantly higher Hg concentrations were found in suspended matter (SM) compared to bottom sediments. Also, higher SM-Hg concentrations were found in sites downstream from ASGM relative to upstream sites. Along the main course of the MDD river, the sediment load significantly increased after the confluence with the Colorado. The Inambari river did not contribute with a significant sediment load input. Nevertheless, the highest SM-Hg concentrations were found in the Inambari river, making this the primary contributor of Hg to the MDD river system. This is the first study to combine Hg data with water flow, sediment load and hydrodynamic measurements to understand the behavior and dispersion of Hg in Amazonian rivers. Hg isotope analyses are underway to provide insight into Hg sources and dynamics in ASGM-affected areas in the Amazonian ecosystem and ease the implementation of mitigation measurement and risk management.