Abstract: In Youjiang River basin, 71 shallow soil samples were collected according to the network density of 10 km×3 km, and the contents of Cd and Pb were analyzed and tested. Cumulative frequency method and fractal analysis method were used to analyze and calculate their environmental geochemical baseline values, so as to assess the Cd and Pb pollution of shallow soil in this area. The results showed that, there was not much difference between the environmental geochemical baseline obtained by the two methods, among which Cd had a difference of 10.3% in upper limit of baseline, 9.4% in baseline value, Pb had a difference of 3.6% in upper limit of baseline, 6.7% in baseline value, indicating that the calculation results of the two methods were reasonable. In this study, the arithmetic average of the two methods was taken as the environmental geochemical baseline values, that was, Pb was 25.44 mg/kg, and Cd was 0.304 mg/kg. The single factor pollution assessment results of Cd showed that the light pollution, intermediate pollution and heavy pollution accounted for 67.61%, 23.94% and 5.63%, respectively, while the single factor pollution assessment of Pb showed that the light pollution, intermediate pollution and heavy pollution accounted for 53.52%, 25.35% and 11.27%, respectively. Nemerow comprehensive pollution assessment showed that light pollution, intermediate polltuion and heavy pollution accounted for 52.11%, 33.88% and 8.45%, respectively. This showed that the pollution in this area was dominated by light pollution, followed by moderate pollution, only a small number of samples were severely polluted. Moderate and severe pollution areas were mainly distributed in the southeast and northwest of the study area, and there was a moderate pollution point in the central and western regions. The geoaccumulation index of Cd and Pb of most samples was less than 1, indicating that the accumulation effect of Cd and Pb in this area was not obvious. However, the geoaccumulation index of Cd and Pb in the southeastern part of the study area and the north-central part of the study area reached the level of moderate pollution. All these indicated that the development of bauxite resources in the east area and the production activities of the thermal power plant in the middle area had a great impact on the pollution of Cd and Pb in the area.

Key words: environmental geochemical baseline, fractal analysis, pollution assessment, Cd, Pb, Youjiang River basin