Status of heavy metals contamination in the topsoil of major Oasis cities in Northwest China.

Oasis farmland and cities are vital for production and life in arid areas. However, heavy metal contamination in these cities has intensified with economic development, harming residents' health, the environment, and agriculture. The current state of contamination in oasis cities remains unclear due to a lack of research data. This study investigates the features of heavy metal contamination and its affecting elements in various oasis cities, specifically focusing on Urumqi, Korla, Aksu, and Hotan City in northwest China, which exhibit diverse economic scales and industrial structures. The Nemero index, geoaccumulation index, ecological risk index, health risk index, principal component analysis, positive matrix factorization, etc., were used to analyze the distribution characteristics, risk levels, and sources of six heavy metals (Ni, Cu, Zn, As, Cd, and Pb) in the surface soil. The results show that: (1) The degree of contamination, ranging from high risk to low, is as follows: Urumqi > Korla > Aksu > Hotan. The urban economic scale most significantly influences the degree of heavy metal contamination in soil and is closely related to the local industrial structure. Industry activities lead to more severe contamination. (2) The degree of Cd contamination is relatively high in the four cities, mainly affected by human activities such as industrial production and transportation. The overall heavy metal contamination risk in Urumqi is higher than in other oasis cities, and there is some carcinogenic risk for children. (3) The sources of heavy metal pollutants in the surface soil of different oasis vary. The main source of heavy metals in Urumqi and Aksu is the industrial source, accounting for 41.28% and 56.15%, respectively. In Korla and Hotan, natural environmental sources dominate, accounting for 66.66% and 73.49% respectively. This study provides a foundation for analyzing heavy metal sources and pollution prevention and control in major oases of an arid region.