Investigation and Assessment of Heavy Metals in Soils of the Taipingdong Gold Tailings Reservoir, Southwestern Guizhou

To reveal the concentrations and pollution characteristics of heavy metals in soils prior to the construction of the Taipingdong gold tailings reservoir, we systematically collected 137 soil samples. The concentrations of eight risk control elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in agricultural land, seven associated elements (Co, Mo, Sb, Sn, Tl, W, and Au), as well as pH values, were determined. The results indicate that the sources of soil heavy metals in the study area present a composite model of "two sets of stratigraphic backgrounds, one epoch of mineralization anomaly, and local anthropogenic superimposition". Specifically, the Yelang and Jialingjiang formations lay the foundation for the regional high backgrounds of Co-Ni-Cu-Cr and Tl-Pb-Cd-W-Zn, respectively. The Au-As-Mo-Sb assemblage, distributed along faults and drainage systems, indicates the superimposed influence of deep gold mineralization and historical mining activities. Sn is controlled by a stable sedimentary background; and localized high anomalies of Hg reflect potential deep gold mineralization. Single-factor pollution assessments reveal that Pb and Zn are generally clean, Cr and Ni predominantly exhibit slight pollution, and Cu and Cd pollution is prominent, with moderate pollution accounting for 5.11% and 10.95%, respectively. As and Hg are generally clean but exhibit localized severe pollution. Comprehensive evaluation indicates that 93.43% of the sample sites in the entire area are subject to composite pollution, with 58.39% slightly polluted, 35.04% moderately polluted, and 3.65% heavily polluted. Given its wide pollution range, high exceedance rate, and high bioavailability, Cd should be prioritized as a priority control pollutant. Furthermore, the high-risk As areas distributed along fault zones and drainage systems urgently require source interception and safe utilization interventions.