In the Amazon, gold mining is a thriving business, pushing deep into the rainforest and indigenous lands. Small-scale operations set up primarily illicitly and operated in the shadows use mercury, a substance with neurotoxic properties, for gold extraction. Now, a team of researchers examined if trees native to the Peruvian Amazon could be used as biomonitors for gold mining activities. By examining mercury concentrations in tree rings, they concluded that some species could bear witness to illegal mining activities.