Vegetated sites were also clearly separated between themselves, reflecting a spatial variability in terms of soil pH, metal availability, plant biomass, and microbial properties, characteristic of mine tailings (Cobb et al., 2000; Córdova et al., 2011; Ernst, 2005). This site heterogeneity explains the frequently variable response of each site to the same treatment (i.e., the lack of clear treatment-induced responses in many parameters), representing one of the main problems to quantify the remediation effectiveness of such mine tailings.