The use of multivariate statistical analysis of geochemical data for assessing the spatial distribution of soil contamination by potentially toxic elements in the Aljustrel mining area (Iberian Pyrite Belt, Portugal)

Aljustrel mine is located in SW Portugal, in the western sector of the Iberian Pyrite Belt. The Aljustrel village was developed around the exploitations of massive polymetallic sulphides that occur in the area (4 orebodies mined, 2 in exploration phase). The pyrite ore was extensively exploited from 1850 to 1993, when production was discontinued. A mining restart occurred in 2008, only during a few months. The objectives of the study were to assess the levels of soil contamination, to determine associations between the different chemical elements and their spatial distribution, as well as to identify possible sources of contamination that can explain the spatial patterns of soil pollution in the area. Principal component analysis combined with spatial interpretation successfully grouped the elements according to their sources and provided evidence about their geogenic or anthropogenic origin. From this study, it is possible to conclude that soils around Algares/Feitais tailing deposits, Estéreis and Águas Claras mine dams and S. João mine show severe contamination. The highest concentrations of As (up to 3,936 mg kg⁻¹) and certain heavy metals (up to 321.7 mg kg⁻¹ for Bi, 5,414 mg kg⁻¹ for Cu, 20,000 mg kg⁻¹ for Pb, 980.6 mg kg⁻¹ for Sb, and 22 mg kg⁻¹ Cd) were obtained near Algares area while the highest concentration of Cd (up to 61.6 mg kg⁻¹) and Zn (up to 20,000 mg kg⁻¹) were registered in samples collected in the S. João area. The highest pollution load index (>4.0) was recorded at the Algares area where the metal concentrations exceed typical soil background levels by as much as two orders of magnitude.