Source Apportionment and Ecological Risk of Heavy Metals and Metalloids in Soils of the Zacatecas Mining District, Mexico: An Integrated Geoaccumulation and Multivariate Approach

Five centuries of silver mining have left extensive metal-bearing waste around Zacatecas City, Mexico, yet the spatial structure, severity and sources of the resulting soil contamination remain poorly quantified. We determined Cr, Co, Ni, Cu, Zn, As and Pb by ICP-MS in 40 surface soils from four peripheral areas of contrasting land use, assessed contamination with the geoaccumulation index (Igeo), pollution load index (PLI) and Håkanson ecological risk index (RI), and resolved sources by correlation, principal component analysis (PCA) and hierarchical clustering. Against Upper Continental Crust background, mean Igeo decreased as Pb (5.65) >As (5.44) >Zn (4.93) >Cu (4.46) >Ni (1.82) >Co (1.78) >Cr (1.27), classing Pb, As, Zn and Cu as extremely accumulated. The El Bote tailings area was the dominant hotspot (PLI 33; RI 6938), with up to 9 510 mg kg−1 Pb and 8 531 mg kg−1 As; all soils exceeded the NOM-147 arsenic limit. Arsenic alone contributed 67.2% of the ecological risk and lead 22.0%. PCA separated a polymetallic anthropogenic factor (Cu-Zn-As-Pb) from a lithogenic factor (Cr-Ni-Co). These findings identify a priority environmental- and public-health hazard and provide a reproducible basis for targeting remediation of legacy mine waste.