Distribution characteristics and ecological risk assessment of heavy metals in soil of Lhasa City

In order to study the pollution and spatial distribution characteristics of soil heavy metals in Lhasa, the contents of 8 heavy metals in 20 surface soil samples in the main urban area were analyzed and determined. And the Nemerow comprehensive pollution index and potential ecological hazard index were used to evaluate the environmental quality and ecology risk. The research results showed that the average values of Cu, Zn, Cr, Ni, Pb, Cd, As, and Hg in the soil are 0.92, 1.02, 0.85, 0.83, 0.73, 0.83, 1.28, and 0.8 times of the Lhasa background values, All of them meet the grade Ⅱ standard of National Soil Environmental Quality Standard (GB 15618-1995), among which Zn and As have a higher rate of exceeding the standard, 45% and 95% respectively. From the spatial distribution map of heavy metals, the distribution of elements presents a certain pattern, which mostly presents a dot pattern. Among them, Ni was evenly distributed, and other elements have high value areas. The accumulation status of heavy metals in the study area was similar to the track of human activities. Except for the single pollution index of Zn and As, which was slight pollution, all other elements are non-pollution. The average value of Nemerow comprehensive pollution index was 1.24, which belongs to slight pollution; The mean value of RI was 85.96, which was low ecological hazard, and Hg and Cd were the main risk factors. The accumulation of Cu, Zn, Pb, and Cd were mainly from natural sources, partly affected by transportation activities; the accumulation of As were mainly due to the high natural background value; the accumulation of Hg was affected by both natural sources and industrial sources; the accumulation of Ni and Cr were controlled by natural factors.