“…Crude oil, produced waters and drilling muds can contain a number of potentially toxic agents, including heavy metals, such as lead, cadmium, arsenic and mercury amongst others (E&P Forum/UNEP, 1997;Fakhru'l-Razi et al, 2009;Lienemann et al, 2007;Neff, 2002;Wilhelm, 1999). Poor environmental practices by the oil industry, such as the dumping of around 1 million barrels/day of produced water on soils and rivers in the study area, and recurrent oil spills have contaminated the Corrientes, Pastaza, and Tigre river basins, all tributary rivers of the Marañon river ( Figure 1) and exposed the indigenous population to metals among other contaminants (Orta-Martínez et al, 2018;Orta Martínez et al, 2007).…”