Contamination Characteristics, Source Apportionment, and Risk Assessment of Heavy Metals in Soil from a Legacy Open Dumpsite on the Qinghai–Xizang Plateau

The Qinghai–Xizang (Formerly Tibet) Plateau, known as the Roof of the World, is an important ecological security barrier for Asia and globally; its natural environment is fragile and challenging to repair after destruction. Prior to the 21st century, waste management in China primarily relied on unregulated direct dumping. To investigate the environmental impacts of open dumpsites in high-altitude regions, this study focused on a representative dumpsite in the northern Xizang region. The aim was to characterize the occurrence and distribution patterns of heavy metals (HMs) in its surrounding soil, conduct source apportionment, and perform comprehensive risk assessment. The results showed low levels of mercury (Hg) and excessive levels of all other HMs. In addition, all HMs had the highest content in the residual fraction and the lowest content in the weak-acid fraction, which is less bioavailable. The Absolute Principal Component Score–Multiple Linear Regression (APCS-MLR) and Positive Matrix Factorization (PMF) results showed that the dumpsite contributed the most to cadmium (Cd); agricultural sources contributed the most to zinc (Zn); Hg mainly came from atmospheric transport and traffic sources; Pb was mainly derived from traffic and natural sources; and copper (Cu), nickel (Ni), chromium (Cr), and arsenic (As) mainly came from the dumpsite and natural sources. In addition, this research found that this dumpsite poses a relatively high HM risk to human health; oral and respiratory routes are the main non-carcinogenic routes, As and Cr contribute more to the adult and child groups, and As contributes the most to carcinogenic risk. The calculation results of the pollution assessment method indicate that the pollution of the natural environment from this dumpsite is at a low level, and immediate remediation measures are urgently needed to achieve site decontamination.