There's mercury in the Amazon. This scientist is tracking it down.

 While the toxic metal is naturally occurring and gold mining is not the sole source, Angel-Amaya expects that mercury levels will be higher downstream of the two mining sites—and potentially throughout the Amazon watershed. The mining in this region is artisanal and small-scale, and often uses liquid mercury to extract gold from alluvial sand. When the mercury-gold amalgam is heated, the toxin evaporates but stays in the environment. 

read more... https://www.nationalgeographic.com/environment/article/amazon-river-basin-mercury-jennifer-angel-amaya