In a piece published by The Guardian, David Hill highlights the results of studies carried out by Duke Global Health Institute in the United States which seek to quantify how much local populations are exposed to mercury poisoning. Perhaps surprisingly, the data published (which is preliminary in character) suggests that mercury contamination may be more intense in areas upstream from the region’s main gold mining areas. Where mercury pollution appears most intense is on the Madre de Dios river between the towns of Boca Colorado and Boca Manu, in the buffer zone of the Manu National Park, and within the park itself. One reason for this is the impact of deforestation itself. This results in the release into the river system of mercury naturally stored in the soils of the Amazon rain forest.
https://www.theguardian.com/environment/andes-to-the-amazon/2016/nov/19/leaked-map-reveals-chronic-mercury-epidemic-in-perus-amazon