An environmental liability in Peru is located in Puno, in the district of Ananea, originated by informal mining activities 90 years ago. Phytoremediation was carried out with Festuca Dolichophylla, a plant native to the area, with the assistance of ammonium thiosulfate as an accelerator. Soil samples were extracted from the areas impacted with mercury. The research used a factorial design with the following response variables: the concentration of total mercury (HgT) in soil and plant tissues, and as factors the level of ammonium thiosulfate in the soil and the time of plant growth. The soils of the Ananea-Puno district have neutral pH, elemental mercury constitutes 56% of the total amount of mercury in the soil. THg concentrations in the soil range from 44 to 53 mg/ kg, which is almost 2 times higher than the upper limit for mercury content (24 mg/kg) in extractive soils in Peru. The BA...