Determination and application of soil heavy metal geochemical baseline in the southern region of Wushan County in the Yangtze River Basin, China

The geochemical baseline is an essential reference for distinguishing natural and anthropogenic environmental impacts. It is of great significance for evaluating the changes in chemical substance (element) content and concentration before and after human development, as well as the evolution of environmental quality. Using background values such as the "Background Values of Chinese Soil Elements" and expanding the research scale can easily lead to "over protection" or "under protection" when guiding pollution control and governance. The article takes Wushan County, Chongqing City, in the Yangtze River Basin, as an example to collect 100 surface soils and construct a heavy metal environmental geochemical baseline. Analysis shows that the average values of As, Hg, Co, Cd, Pb, Cu, Ni, Zn, and Mn in the soil of the study area are 14.06, 0.09, 19.39, 0.99, 31.01, 37.08, 47.77, 121.10, and 960.20 mg/kg, respectively; The ground accumulation index indicates that heavy metals are mainly pollution-free and lightly polluted, but Cd, Hg, Cu, Ni, Zn, and Mn have a certain proportion of moderate pollution (43, 7, 2, 3, 2, and 1 point, respectively). Hg and Ni each have 1 medium to strong pollution level soil site, while Cd has 6 strong pollution sites, 4 strong to extremely strong pollution sites, and 5 extremely strong pollution sites. Based on the cumulative frequency curve method, the geochemical baseline values of Hg, As, Co, Cd, Pb, Cu, Ni, Zn, and Mn were obtained as 0.06, 12.69, 16.47, 0.22, 30.15, 24.61, 34.54, 104.40 mg/kg, and 628.32 mg/kg, respectively. The constructed soil heavy metal environmental geochemical baseline determines the evaluation criteria for small-scale spatial areas, which can scientifically and accurately identify the current soil pollution status in the region.